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DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2185–2189 2185 Macrocyclic selenoether complexes of nickel(II). Synthesis and properties of [NiX2([16]aneSe4)] ([16]aneSe4 5 1,5,9,13-tetraselenacyclohexadecane, X 5 Cl, Br or I) and [NiX2(MeSeCH2CH2- SeMe)2]* Maxwell K. Davies, William Levason and Gillian Reid Department of Chemistry, University of Southampton, Southampton, UK SO17 1BJ Reaction of NiX2 (X = Cl, Br or I) with [16]aneSe4 (1,5,9,13-tetraselenacyclohexadecane) under anhydrous conditions in n-butanol yielded trans-[NiX2([16]aneSe4)]. Similar reactions using MeSeCH2CH2SeMe produced trans-[NiX2(MeSeCH2CH2SeMe)2]. The complexes have been characterised by IR and UV/VIS spectroscopy and magnetic measurements.The crystal structure of [NiCl2(MeSeCH2CH2SeMe)2] showed an octahedral nickel centre co-ordinated to trans chlorines [2.370(2)–2.376(2) Å] with the diselenoethers present as chelating ligands in the DL conformation [2.522(1)–2.5623(8) Å].Structural data on the very poorly soluble [16]aneSe4 complexes were obtained via nickel K-edge EXAFS (extended X-ray absorption fine structure), and the results compared with related complexes. A ligand field analysis of the UV/VIS spectra of [NiX2([16]aneSe4)] and of the tetrathioether analogues [NiX2([16]aneS4)] ([16]aneS4 = 1,5,9,13-tetrathiacyclohexadecane) showed that the ligand fields produced by 16-membered ring macrocycles [Dq(xy)] lie in the order N4 > S4 > Se4, with MeSeCH2CH2SeMe aVording a stronger field that [16]aneSe4 due to the smaller chelate ring size.Acyclic thio- or seleno-ether ligands are usually classed as soft donors which typically form complexes with metal carbonyls or with soft metals such as the platinum group halides, but which have little aYnity for harder 3d metals in normal oxidation states.1,2 In contrast, macrocyclic thioethers are able to form stable complexes with most transition metals.3 The synthesis 4 of macrocyclic selenoethers including [16]aneSe4 opens up the possibility of similarly enhanced M]Se binding, and we have reported complexes with a variety of platinum metal centres, viz.[M([16]aneSe4)]21 (M = Pd or Pt),5 [PtX2([16]aneSe4)]21 (X = Cl or Br),6 [MX2([16]aneSe4)]1 (M = Rh or Ir),7 [RuX2- ([16]aneSe4)]n1 (n=0 or 1), and [MX(PPh3)([16]aneSe4)]1 (M = Ru or Os).8 Complexes of CuI and CuII have been obtained,9 but other 3d examples are limited to [CoX2([16]- aneSe4)]17 and [CrX2([16]aneSe4)]110 both of which benefit from the kinetically inert metal centres.Here we report the first examples of complexes of [16]aneSe4 with the hard labile 3d ion nickel(II), along with attempts to prepare acyclic diselenoether analogues. Results and Discussion Nickel(II) complexes The reaction of anhydrous nickel(II) halides with [16]aneSe4 in dry n-butanol gave pale green (X = Cl or Br) or brown (X = I) paramagnetic (m ca. 3 mB) complexes [NiX2([16]aneSe4)]. The complexes are insoluble in chlorocarbons or MeNO2, very poorly soluble in MeCN and decomposed by dmso.They dissolve slightly in strong mineral acids (below). Dry samples Se Se Se Se [16]aneSe4 S S S S [16]aneS4 * Non-SI units employed: mB ª 9.27 × 10224 J T21, eV ª 1.60 × 10219 J. can be handled briefly in air, although hydrolysis occurs on prolonged exposure to moisture. The corresponding [NiX2([16]- aneS4)] ([16]aneS4 = 1,5,9,13-tetrathiacyclohexadecane) were made similarly for comparison.The [NiCl2([16]aneS4)] complex has been made previously by Schröder and co-workers 11 who converted it into [Ni2(m-Cl)2([16]aneS4)2][BF4]2 by reaction with NaBF4 in MeNO2, but did not characterise the monomer. Attempts to prepare nickel(II) complexes with acyclic diselenoethers had limited success. Under anhydrous conditions, 2,5- diselenahexane (MeSeCH2CH2SeMe) aVorded green [NiX2- (MeSeCH2CH2SeMe)2] (X = Cl or Br) or orange [NiI2(MeSe- CH2CH2SeMe)2].12 In contrast, attempts to isolate complexes with MeSe(CH2)3SeMe, C6H4(SeMe)2-o or PhSeCH2CH2SePh failed, showing that the additional stability conferred by alkyl substituents at Se and five-membered chelate rings are needed to permit isolation of the nickel(II) complexes. The [NiX2- (MeSeCH2CH2SeMe)2] complexes are hydrolysed rapidly in air and decomposed by donor solvents.The assignment of trans octahedral geometries to [NiX2([16]aneS4)], [NiX2([16]- aneSe4)] and [NiX2(MeSeCH2CH2SeMe)2] follows from their paramagnetism (m ca. 3 mB) and their UV/VIS spectra (Table 1), and this was confirmed for [NiCl2(MeSeCH2CH2SeMe)2] by a single-crystal X-ray study (below). The UV/VIS spectrum of a high spin d8 ion in Oh symmetry is expected to show three bands in order of increasing energy, 3A2g æÆ 3T2g, 3A2g æÆ 3T1g(F) and 3A2g æÆ 3T1g(P). In tetragonal symmetry (D4h) the ground state becomes 3B1g, and the excited states split (3T2g æÆ 3Eg, 3B2g; 3T1g æÆ 3A2g, 3Eg).15 Weak spin-forbidden transitions to singlet states are sometimes seen to low energy of the first spin-allowed band.For our complexes only the first spin-allowed transition is clearly split (Table 1), but the information is suYcient to allow the normal ligand field analysis 13,15 to obtain the in-plane [Dq(xy)] and out-ofplane [Dq(z)] ligand fields and the tetragonality parameter (Dt). The individual numerical values from such an analysis are not of high precision, but the trends are usually reliable.Comparison of the Dq(xy) values in Table 1 with those of the analogous tetraazamacrocycle [16]aneN4 (1,5,9,13-tetraazacyclohexadecane), 13 shows that the ligand field strength increases in the order [16]aneSe4 < [16]aneS4 < [16]aneN4 for2186 J. Chem. Soc., Dalton Trans., 1998, Pages 2185–2189 Table 1 Selected UV/VIS spectroscopic data a Complex [NiCl2([16]aneSe4)] [NiBr2([16]aneSe4)] [NiI2([16]aneSe4] [NiCl2([16]aneS4)] [NiBr2([16]aneS4)] [NiI2([16]aneS4)] [NiCl2(MeSeCH2CH2SeMe)2] [NiBr2(MeSeCH2CH2SeMe)2] [NiI2(MeSeCH2CH2SeMe)2] [NiCl2([16]aneN4)] b [NiBr2([16]aneN4)] b [NiCl2([14]aneS4)] c [NiBr2([14]aneS4)] c 3B1g æÆ 1Eg 7267 7240 7235 7290 7270 7210 7260 7250 7230 3B1g æÆ 3Eg 8405 8240 7700 8530 8330 7875 8690 8450 7900 3B1g æÆ 3B2g 9390 9010 8065 7930 9345 8620 (sh) 9590 9400 8710 3B1g æÆ 3A2g,3Eg 14 710 14 620 14 900 15 340 15 450 12 800 (sh), 15 500 14 710 14 245 14 300 3B1g æÆ 3A2g,3Eg 26 300 25 000 (sh) 22 420 25 000 (sh) – 21 300 (br) 23 530 25 000 (sh) ca. 24 000 Dq(xy) 940 900 807 973 935 862 960 940 870 1116 1128 1110 1099 Dq(z) 740 745 735 733 713 710 780 750 710 440 335 723 687 Dt 113 88 42 176 150 120 102 108 23 496 582 285 302 a DiVuse reflectance spectra (cm21), samples diluted with BaSO4, assignments based upon tetragonally distorted nickel geometry (D4h symmetry). b Data from ref. 13 using mull spectra. c Calculated from the diVuse reflectance spectral data in ref. 14. the 16-membered ring macrocycles, whilst the Dq(xy) is slightly greater for 2,5-diselenahexane compared to [16]aneSe4, re- flecting the eVects of chelate ring size. Previous studies of 14- membered ring aza- and thia-macrocycles and of open-chain tetrathioethers show similar trends in Dq(xy) with chelate ring size.13,14,16 Thus we conclude that selenium ligands exert a smaller ligand field than the sulfur analogues towards hard 3d metal ions. The poor solubility of [NiX2([16]aneSe4)] in organic solvents hindered attempts to study their redox chemistry.The complexes dissolve with diYculty in concentrated acids (HClO4, H2SO4 or HNO3) with the formation of unstable pink or purple solutions which decompose quite rapidly (a few minutes in HNO3 solution, several hours in 70% HClO4). The possibility that these solutions contained d7 nickel(III) was eliminated when they were found to be ESR silent. Oxidation would be expected to lead to low-spin d7, since for NiIII the high spin æÆ low spin crossover occurs with weak ligand fields—even [NiF6]32 is low spin,17 and thus in six-co-ordination the moderate field generated in [NiX2([16]aneSe4)]1 should cause spin pairing.Similar unstable pink solutions were formed in anhydrous trifluoroacetic acid (tfa), which is more suited as a solvent to both UV/ VIS spectroscopy and electrochemical studies than the other mineral acids. In fact cyclic voltammetry of these solutions showed only completely irreversible oxidations at highly positive potentials, and it is unclear whether these reflect metal based oxidations or oxidation of displaced halide ions.The UV/ VIS spectra of the iodo complexes are ill defined, but in tfa solution [NiX2([16]aneSe4)] (X = Cl or Br) have Emax ca. 17 800 and ca. 20 400 cm21, inconsistent with Oh or square-planar d8 centres, but not unreasonable for a high-spin five-co-ordinate (Se4X) species.15,18 The complexes [NiX2(MeSeCH2CH2SeMe)2] (X = Cl or Br) also gave pink solutions in tfa, but [NiX2- ([16]aneS4)] (X = Cl or Br) gave green solutions with very weak d]d bands (ca. 10 000 and 16 000 cm21) suggesting the Oh geometry is retained in solution, whilst [NiI2([16]aneS4)] decomposed immediately in tfa. The instability of these pink solutions has prevented a more definite characterisation, but it seems clear that nickel(III) complexes are not formed, contrasting with the generation of tetragonal low-spin d7 in [Ni([9]aneS3)2]3119 and [NiX2(diphosphine)2]1.20 Unstable lowspin [NiX2{C6H4(EMe2)(SeMe)-o}2]1 (E = P or As) are known,21 but here the Group 15 donors will produce much greater ligand fields stabilising the low-spin d7 state.The [NiX2([16]aneSe4)] did not react with TlPF6 or NaBF4 under reflux in MeNO2 suspension probably reflecting their very poor solubility in this medium {contrast [NiX2([16]aneS4)] which gave blue [Ni2- (m-Cl)2([16]aneS4)2]21}.11 Crystal structure of [NiCl2(MeSeCH2CH2SeMe)2] Pale green crystals were obtained from the reaction mixture.The structure solution revealed two independent centrosymmetric molecules (Fig. 1) with no chemically significant diVerences in their dimensions. Selected bond lengths and angles are given in Table 2. The nickel is in a tetragonal six-co-ordinate environment composed of two chelating diselenoethers and two mutually trans chlorides, with the selenoether ligands in the DL form. The Ni]Cl distances 2.370(2)–2.376(2) Å are typical of high-spin NiII–Cl bonds and may be compared with those in dichlorobis(1,5-dithiacyclooctane)nickel [2,358(2) Å] 22 or [NiCl2([16]aneN4)] [ 2.428(1), 2.535(1) Å].23 The Ni]Se distances of 2.522(1)–2.5623(8) Å are typically 0.05–0.1 Å longer than the Ni]S bonds in nickel(II) thioethers,3,11,18,19 consistent with the diVerences in radii of Se vs.S. EXAFS Studies The insolubility of [NiX2([16]aneSe4)] in most solvents precluded growth of crystals suitable for an X-ray study, so we used the combination of UV/VIS spectroscopy to define the metal centre symmetry, and metal K-edge EXAFS (extended X-ray absorption fine structure) data to obtain first coordination sphere bond lengths.A similar approach has been used successfully to study nickel-(II), (III) and -(IV) diphosphine and diarsine complexes,24 and platinum-(II) and -(IV) tetrathioether macrocycles,25 and the general methodology follows that used previously (summarised in the Experimental section).Data were also collected on [NiX2(MeSeCH2CH2SeMe)2], and since we have the single-crystal X-ray data on the chloride (above) this complex provides an excellent model upon which to check the EXAFS data quality and treatment. As can be seen Fig. 1 View of the structure of one of the molecules of trans- [NiCl2(MeSeCH2CH2SeMe)2] with the numbering scheme adopted. Ellipsoids are drawn at the 40% probability level and atoms marked * are related by a crystallographic centre of symmetry.The other molecule is essentially indistinguishableJ. Chem. Soc., Dalton Trans., 1998, Pages 2185–2189 2187 for this complex by comparing the data in Tables 2 and 3, the agreement in d(Ni]Cl) and d(Ni]Se) is satisfactory within the usual precision of EXAFS determined first shell distances (±0.02–0.03 Å). For the chloro- and iodo-complexes the EXAFS data were modelled to two shells of four Se and two halides, and refined straightforwardly to the parameters in Table 3.For the bromo-complexes, in view of the similar backscattering of Br and Se, the data were fitted to models comprising 4Se 1 2Br, 6Se, and then 6Br. The two-shell fits were statistically better, resulting in significant 26 reductions in R factors and fit indices, and with no unacceptably large correlations. Thus we conclude that the two-shell fit is appropriate in this case also, consistent with the conclusions from UV/VIS spectroscopy. A typical example of the background-subtracted EXAFS data and the resulting Fourier transform are shown in Fig. 2. Comparison of the bond lengths in Table 3 show that d(Ni]X) is marginally greater in the complexes of [16]aneSe4 than in those of MeSeCH2CH2SeMe, but the variations in d(Ni]Se) are irregular. X-Ray crystallographic studies 23 on a range of azamacrocycle complexes of NiII have identified an inverse correlation between d(Ni]X) and d(Ni]N), although changes in bond lengths between complexes are small.In the present case of the selenium ligands the small number of examples available makes more detailed discussion impossible. Nonetheless the structural data confirm the pseudo-octahedral geometries inferred spectroscopically. Experimental Infrared spectra were measured as CsI discs or as Nujol mulls between CsI plates using a Perkin-Elmer 983 spectrometer over the range 200–4000 cm21, UV/VIS spectra by diVuse reflectance Table 2 Selected bond lengths (Å) and angles for trans-[NiCl2- (MeSeCH2CH2SeMe)2] Se(1)]Ni(1) Se(1)]C(2) Se(2)]C(3) Se(3)]Ni(2) Se(3)]C(6) Se(4)]C(7) Ni(1)]Cl(1) Ni(2)]Cl(2) C(2)]C(3) Ni(1)]Se(1)]C(1) C(1)]Se(1)]C(2) Ni(1)]Se(2)]C(4) Ni(2)]Se(3)]C(5) C(5)]Se(3)]C(6) Ni(2)]Se(4)]C(8) Se(1)]Ni(1)]Cl(1*) Se(2)]Ni(1)]Cl(1*) Se(3)]Ni(2)]Se(4) Se(3)]Ni(2)]Cl(2) Se(1)]C(2)]C(3) Se(3)]C(6)]C(7) 2.5581(9) 1.949(9) 1.951(9) 2.522(1) 1.933(9) 1.942(9) 2.370(2) 2.376(2) 1.50(1) 110.0(3) 96.9(4) 107.2(3) 111.2(3) 97.4(4) 110.0(3) 95.34(5) 84.35(6) 90.15(3) 96.73(5) 114.1(6) 114.7(6) Se(1)]C(1) Se(2)]Ni(1) Se(2)]C(4) Se(3)]C(5) Se(4)]Ni(2) Se(4)]C(8) Ni(1)]Cl(1) Ni(2)]Cl(2) C(6)]C(7) Ni(1)]Se(1)]C(2) Ni(1)]Se(2)]C(3) C(3)]Se(2)]C(4) Ni(2)]Se(3)]C(6) Ni(2)]Se(4)]C(7) C(7)]Se(4)]C(8) Se(1)]Ni(1)]Se(2) Se(1)]Ni(1)]Cl(1) Se(1)]Ni(1)]Se(2*) Se(4)]Ni(2)]Cl(2) Se(2)]C(3)]C(2) Se(4)]C(7)]C(6) 1.941(9) 2.5536(9) 1.944(9) 1.946(9) 2.5623(8) 1.966(9) 2.370(2) 2.376(2) 1.51(1) 96.9(3) 98.4(3) 97.5(4) 97.2(3) 97.5(3) 97.8(4) 89.55(3) 84.66(5) 90.45(3) 84.69(6) 113.5(6) 113.5(6) using samples diluted with BaSO4 using a Perkin-Elmer Lambda 19 spectrophotometer.Magnetic measurements used a Johnson Matthey balance. The EXAFS measurements were made at the Daresbury Synchrotron Radiation Source, operating at 2.0 GeV with typical currents of 200 mA. Nickel K-edge data were collected on station 7.1 using a silicon(111) order-sorting monochromator, with harmonic rejection achieved by stepping oV the peak of the rocking curve by 50% of full height level.Data were collected in transmission mode from either neat samples, or samples diluted with boron nitride as appropriate, and mounted between Sellotape in 1 mm aluminium holders. The compounds [16]aneSe4 and MeSeCH2CH2SeMe were prepared by the literature procedures.2,27 Synthesis The products were assumed to be air and moisture sensitive and prepared using Schlenk equipment. Samples were manipulated in a glove-box (<10 ppm water) using standard air sensitive Fig. 2 The background subtracted nickel K-edge EXAFS data (a) and the corresponding Fourier transform (b) for trans-[NiCl2- ([16]aneSe4)] (solid line, experimental; dashed line, calculated data) Table 3 The nickel K-edge EXAFS data a for nickel(II) selenoether compounds Complex [NiCl2([16]aneSe4)] [NiBr2([16]aneSe4)] [NiI2([16]aneSe4)] [NiCl2(MeSeCH2CH2SeMe)2] [NiBr2(MeSeCH2CH2SeMe)2] [NiI2(MeSeCH2CH2SeMe)2] d(Ni]Se) b/Å 2.600(3) 2.584(6) 2.506(2) 2.531(4) 2.574(5) 2.541(3) 2s2 c/Å2 0.0187(5) 0.0206(10) 0.0129(2) 0.0169(6) 0.0097(6) 0.0164(5) d(Ni]X)b/Å 2.393(4) 2.507(3) 2.781(5) 2.349(5) 2.446(6) 2.739(7) 2s2 c/Å2 0.0085(6) 0.0094(4) 0.0175(07) 0.0074(7) 0.0072(8) 0.0182(13) Rd 17.2 21.8 25.2 26.0 17.6 26.9 Fit index e 2.3 3.0 4.1 4.6 3.5 7.2 a Data were recorded in transmission mode on station 7.1, using powdered samples diluted with BN where appropriate.AFAC = 0.80 for all refinements. b Standard deviations in parentheses.Note that the systematic errors in bond distances arising from data collection and analysis procedures are ±0.02–0.03 Å for well defined co-ordination shells. c Debye–Waller factor. d Defined as [Ú(cT 2 cE)k3dk/ÚcEk3dk] × 100%. e Defined as Si[(cT 2 cE)ki 3]2.2188 J. Chem. Soc., Dalton Trans., 1998, Pages 2185–2189 techniques. Solvents were dried using conventional methods and distilled under dinitrogen. Nickel(II) iodide was prepared in situ by the reaction of Ni(NO3)2?6H2O with 2 equivalents of KI in n-butanol or nitromethane, the precipitated KNO3 being removed by filtration.[NiCl2([16]aneSe4)]. The compound [16]aneSe4 (0.100 g, 2.1 × 1024 mol) was added to a stirring solution of NiCl2 (0.027 g, 2.1 × 1024 mol) in n-butanol (10 cm3) under an atmosphere of dinitrogen. The resulting mixture was heated at 60 8C for ca. 45 min yielding a pale green precipitate. This solid was isolated by filtration, rinsed with diethyl ether and dried in vacuo. Yield 0.1 g, 78% (Found: C, 23.5; H, 4.1.Calc. for C12H24Cl2NiSe4: C, 23.5; H, 3.9%). n& /cm21 (Ni]Cl) 249. m 3.02 ± 0.01 mB. [NiBr2([16]aneSe4)]. This was prepared similarly from [16]- aneSe4 (0.100 g, 2.1 × 1024 mol) and NiBr2 (0.046 g, 2.1 × 1024 mol) in n-butanol (10 cm3). Yield 0.116 g, 79% (Found: C, 20.2; H, 3.6. Calc. for C12H24Br2NiSe4: C, 20.5; H, 3.4%). m 3.07 mB. [NiI2([16]aneSe4)]. The compound [16]aneSe4 (0.100 g, 2.1 × 1024 mol) was added to a stirring solution of NiI2 (2.1 × 1024 mol, prepared as described above) in n-butanol (10 cm3) under an atmosphere of dinitrogen.The resulting mixture was heated at 60 8C for ca. 45 min yielding a orange-brown precipitate. This solid was isolated by filtration, rinsed with diethyl ether and dried in vacuo. Yield 0.122 g, 73% (Found: C, 17.8; H, 2.9. Calc. for C12H24I2NiSe4: C, 18.1; H, 3.0%). m 3.10 mB. [NiCl2(MeSeCH2CH2SeMe)2]. To a solution of NiCl2 (0.052 g, 4 × 1024 mol) in n-butanol (10 cm3) was added a solution of MeSeCH2CH2SeMe (0.17 g, 8 × 1024 mol) in n-butanol (2 cm3) via a syringe.The resulting pale green solution was heated at 60 8C for ca. 1 h under an atmosphere of dinitrogen, filtered (Celite) and reduced in vacuo to ca. 6 cm3. This solution was then stored in a freezer (218 8C) yielding lime green blocks of [NiCl2(MeSeCH2CH2SeMe)2]. The crystalline product was isolated by filtration, rinsed with diethyl ether and dried in vacuo.Yield 0.117 g, 52% (Found: C, 17.3; H, 3.7. Calc. for C8H20Cl2NiSe4: C, 17.1; H, 3.6%). n& /cm21 (Ni]Cl) 260. [NiBr2(MeSeCH2CH2SeMe)2]. To a solution of NiBr2 (0.087 g, 4 × 1024 mol) in n-butanol (10 cm3) was added a solution of MeSeCH2CH2SeMe (0.17 g, 8 × 1024 mol) in n-butanol (2 cm3) via a syringe. Work-up as above yielded a lime green solid. Yield 0.196 g, 75% (Found: C, 14.8; H, 3.1. Calc. for C12H24Br2NiSe4: C, 14.8; H, 3.1%). [NiI2(MeSeCH2CH2SeMe)2]. Prepared as above from a solution of NiI2 (4 × 1024 mol) in n-butanol (10 cm3) and a solution of MeSeCH2CH2SeMe (0.17 g, 8 × 1024 mol) in n-butanol (2 cm3) as an orange-brown precipitate.Yield 0.217 g, 68% (Found: C, 12.7; H, 2.8. Calc. for C12H24I2NiSe4: C, 12.9; H, 2.7%). [NiCl2([16]aneS4)]. To a solution of NiCl2 (0.026 g, 2.0 × 1024 mol) in nitromethane (10 cm3) was added a solution of [16]aneS4 (0.061 g, 2.0 × 1024 mol) in dichloromethane (3 cm3) via a syringe. The reaction mixture was heated at 60 8C for ca. 1 h under an atmosphere of dinitrogen yielding a pale turquoise precipitate. This solid was isolated by filtration, rinsed with diethyl ether and dried in vacuo. Yield 0.049 g, 58% (Found: C, 34.0; H, 5.4. Calc. for C12H24Cl2NiS4: C, 33.8; H, 5.6%). n& /cm21 (Ni]Cl) 224. m 3.0 mB. [NiBr2([16]aneS4)]. To a solution of NiBr2 (0.044 g, 2.0 × 1024 mol) in nitromethane (10 cm3) was added a solution of [16]aneS4 (0.061 g, 2.0 × 1024 mol) in dichloromethane (3 cm3) via a syringe.The reaction mixture was heated at 60 8C for ca. 1 h under an atmosphere of dinitrogen yielding a pale green precipitate. This solid was isolated by filtration, rinsed with diethyl ether and dried in vacuo. Yield 0.065 g, 63% (Found: C, 27.9; H, 4.4. Calc. for C12H24Br2NiS4: C, 28.0; H, 4.7%). m 2.95 mB. [NiI2([16]aneS4)]. Prepared as above from a solution of NiI2 (2.0 × 1024 mol) in nitromethane (10 cm3) and a solution of [16]aneS4 (0.061 g, 2.0 × 1024 mol) in dichloromethane (3 cm3), as a brick-red precipitate.Yield 0.080 g, 66% (Found: C, 23.2; H, 4.1. Calc. for C12H24I2NiS4: C, 23.7; H, 3.9%). m 3.1 mB. Crystallography Lime green blocks of [NiCl2(MeSeCH2CH2SeMe)2] were obtained from n-butanol solution. The selected crystal (0.40 × 0.20 × 0.15 mm) was coated with mineral oil and mounted on a glass fibre under a cold stream of nitrogen gas. Crystal data. C8H20Cl2NiSe4, M = 561.69, monoclinic, space group P21/c, a = 14.466(4), b = 7.838(2), c = 15.641(5) Å, b = 114.86(2)8, U = 1607.9(8) Å3 [from 2q values of 16 reflections measured at ±w (2q = 21.7–27.58, l = 0.710 73 Å)], Z = 4, Dc = 2.320 g cm23, m = 105.67 cm21, F(000) = 1064.Data collection and processing. Data collection used a Rigaku AFC7S diVractometer equipped with an Oxford Systems cryostream operating at 150 K, using graphite monochromated Mo-Ka radiation (w–2q scan technique). 3198 Data collected (2qmax 50.08), 3072 unique (Rint = 0.040 based on F2).An absorption correction was applied via y-scans (maximum transmission factor = 1.000, minimum transmission factor = 0.435). No significant crystal decay or movement was observed. Structure solution and refinement. The structure was solved by heavy atom methods28 and expanded using Fourier techniques to locate all non-H atoms for the two half molecules in the asymmetric unit, each of which possesses crystallographic i symmetry.29 All non-H atoms were refined anisotropically and hydrogen atoms were included in fixed, calculated positions [d(C]H) = 0.96 Å] but not refined.The final cycle of full-matrix least-squares refinement (on F) was based on 2053 observed reflections [I > 2.5s(I )] and 139 variable parameters and converged with R = 0.037, Rw 0.049 and S = 1.48, using the weighting scheme w21 = s2( F). The maximum residual peak and minimum residual trough corresponded to 10.81 and 20.96 e Å23. CCDC reference number 186/1003.EXAFS data refinement Typically two or three data sets were collected for each complex and the analyses were carried out on the averaged spectra. The raw data were background-subtracted using the program PAXAS30 by fitting a six- or eight-order split polynomial to the pre-edge subtracted spectrum between k = 2 up to 13–15 Å21. Curve fitting was carried out using the program EXCURV- 92.31 Ground state potentials of the atoms were calculated using Von Barth theory and phase shifts using Hedin–Lundqvist potentials.Two shells (4 Se and 2 X) were fitted in each case. EXAFS Refinements were also carried out for the bromocomplexes using 6 Se or 6 Br, but here as well the two-shell model was statistically better.26 The distances and Debye– Waller factors were refined for all the shells, as well as the Fermi energy diVerence. No attempt was made to refine the carbons of the ligand backbones since these occur over a range of distances and are not expected to be well defined.The [NiCl2- (MeSeCH2CH2SeMe)2] complex served as a model to check data collection and refinement.J. Chem. Soc., Dalton Trans., 1998, Pages 2185–2189 2189 Acknowledgements We thank the Leverhulme Trust for a postdoctoral fellowship (M. K. D.) and the EPSRC for provision of the X-ray diffractometer. We also thank the Director of the Synchrotron Radiation Source at the Daresbury Laboratory for access to the facilities. References 1 S.G. Murray and F. R. Hartley, Chem. Rev., 1981, 81, 365. 2 E. G. Hope and W. Levason, Coord. Chem. Rev., 1993, 122, 109. 3 A. J. Blake and M. Schröder, Adv. Inorg. Chem., 1990, 35, 1; S. R. Cooper and S. C. Rawle, Struct. Bonding (Berlin), 1990, 72, 1. 4 R. J. Batchelor, F. W. B. Einstein, I. D. Gray, J.-H. Gu, B. D. Johnson and B. M. Pinto, J. Am. Chem. Soc., 1989, 111, 6582. 5 N. R. Champness, P. F. Kelly, W. Levason, G. Reid, A. M. Z. Slawin and D. J. Williams, Inorg. Chem., 1995, 34, 651. 6 W. Levason, J. J. Quirk, G. Reid and C. S. Frampton, Inorg. Chem., 1994, 33, 6120. 7 W. Levason, J. J. Quirk and G. Reid, J. Chem. Soc., Dalton Trans., 1996, 3713. 8 W. Levason, J. J. Quirk, G. Reid and S. M. Smith, J. Chem. Soc., Dalton Trans., 1997, 3719. 9 R. J. Batchelor, F. W. B. Einstein, I. D. Gray, J.-H. Gu, B. M. Pinto and X. M. Zhou, J. Am. Chem. Soc., 1990, 112, 3706; J. Organomet. Chem., 1991, 411, 147. 10 W. Levason, G. Reid and S. M. Smith, Polyhedron, 1997, 16, 4253. 11 A. J. Blake, M. A. Halcrow and M. Schröder, J. Chem. Soc., Dalton Trans., 1994, 1463. 12 L. R. Gray, S. J. Higgins, W. Levason and M. Webster, J. Chem. Soc., Dalton Trans., 1984, 1433; E. G. Hope, W. Levason, M. Webster and S. G. Murray, J. Chem. Soc., Dalton Trans., 1986, 1003. 13 L. Y. Martin, C. R. Sperati and D. H. Busch, J. Am. Chem. Soc., 1977, 99, 2968. 14 W. Rosen and D. H. Busch, J. Am. Chem. Soc., 1969, 91, 4694. 15 A. B. P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Amsterdam, 1984; D.A. Rowley and R. S. Drago, Inorg. Chem., 1968, 7, 795. 16 W. Levason, C. A. McAuliVe and S. G. Murray, Inorg. Chim. Acta, 1976, 17, 247. 17 D. Reinen, C. Friebel and V. Propach, Z. Anorg. Allg. Chem., 1974, 408, 187. 18 A. J. Blake, M. A. Halcrow and M. Schröder, J. Chem. Soc., Dalton Trans., 1992, 2803. 19 A. J. Blake, R. O. Gould, M. A. Halcrow, A. J. Holder, T. I. Hyde and M. Schröder, J. Chem. Soc., Dalton Trans., 1992, 3427. 20 L. F. Warren and M. A. Bennett, Inorg. Chem., 1976, 15, 3126; L. R. Gray, S. J. Higgins, W. Levason and M. Webster, J. Chem. Soc., Dalton Trans., 1984, 459. 21 S. K. Harbron, S. J. Higgins, E. G. Hope, T. Kemmitt and W. Levason, Inorg. Chim. Acta, 1987, 130, 43. 22 N. L. Hill and H. Hope, Inorg. Chem., 1974, 13, 2079. 23 T. Ito, M. Kato and H. Ito, Bull. Chem. Soc. Jpn., 1984, 57, 2641 and refs. therein. 24 S. J. Higgins, W. Levason, M. C. Feiters and A. T. Steel, J. Chem. Soc., Dalton Trans., 1986, 317; L. R. Hanton, J. Evans, W. Levason, R. J. Perry and M. Webster, J. Chem. Soc., Dalton Trans., 1991, 2039. 25 A. J. Blake, M. J. Bywater, R. D. Crofts, A. M. Gibson, G. Reid and M. Schröder, J. Chem. Soc., Dalton Trans., 1996, 2979. 26 N. Binsted, S. L. Cook, J. Evans, G. N. Greaves and R. J. Price, J. Am. Chem. Soc., 1987, 109, 3669; R. W. Joyner, K. J. Martin and P. Meehan, J. Phys. C, 1987, 20, 4005. 27 D. J. Gulliver, E. G. Hope, W. Levason, S. G. Murray, D. M. Potter and G. L. Marshall, J. Chem. Soc., Perkin Trans. 2, 1984, 429. 28 SHELXS 86, program for crystal structure solution, G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467. 29 TEXSAN Crystal Structure Analysis Package, Molecular Structure Corporation, The Woodlands, TX, 1995. 30 N. Binsted, PAXAS, Program for the analysis of X-ray absorption spectra, University of Southampton, 1988. 31 N. Binsted, J. W. Campbell, S. J. Gurman and P. C. Stephenson, EXCURV 92, SERC Daresbury Laboratory, 1992. Received 24th March 1998; Paper 8/02300J

ISSN:1477-9226    

DOI:10.1039/a802300j

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2189–2196 2189 Complexes of the lanthanide metals (La–Nd, Sm–Lu) with hypophosphite and phosphite ligands: crystal structures of [Ce(H2PO2)3(H2O)], [Dy(H2PO2)3] and [Pr(H2PO2)(HPO3)- (H2O)]?H2O Joanne A. Seddon, Andrew R. W. Jackson, Roman A. Kresin� ski * and Andrew W. G. Platt School of Sciences, StaVordshire University, College Road, Stoke-on-Trent, StaVordshire, UK ST4 2DE. E-mail: sctrak@staVs.ac.uk Received 5th October 1998, Accepted 29th April 1999 Reactions of lanthanide chlorides LnCl3 with NaH2PO2 in aqueous solution aVorded a series of complexes [Ln(H2PO2)3(H2O)n] (Ln = La–Tb, n = 1; Ce–Nd, Dy–Lu; n = 0) with members falling into at least four separate structural types.The crystal structures of members of two of these types, [Ce(H2PO2)3(H2O)] and [Dy(H2PO2)3], have been determined for the first time, along with that of [Pr(H2PO2)(HPO3)(H2O)]?H2O, one of a new series of complexes [Ln(H2PO2)(HPO3)(H2O)n]?nH2O (Ln = La–Gd, n = 1; Tb–Lu; n = 0) obtained by controlled oxidation of [Ln(H2PO2)3(H2O)n].The hydrated members of this series are notable due to their incorporation of chiral channels inhabited by water molecules, and to their ability reversibly to dehydrate. Steric angle sum calculations have been used to rationalise the morphologies of the new complexes. Tripositive lanthanide ions are influenced only slightly by their own d or f orbitals in their bonding with ligands, these interactions being largely electrostatic.Others 1 have expounded from this that the concept of co-ordination saturation becomes equated with one of steric saturation in the case of lanthanide complexes. Thus, a wide variety of physicochemical properties of lanthanide complexes can vary smoothly when surveyed across the lanthanide series, until, at a certain limit, an abrupt variation is encountered.2 This phenomenon is ascribable to the ionic radius of the lanthanide metal decreasing smoothly up to a point where the metal environment is suYciently crowded as to eject one or more ligand atoms from the primary co-ordination sphere. In a desire to survey systematically the structures of a family of simple lanthanide ion complexes we sought a ligand system which was uncomplicated, but nonetheless relatively unexplored, and this prompted our study of hypophosphite (phosphinate) complexes of lanthanides.Hypophosphitecontaining structures appear to be well distributed around the Periodic Table: structures reported to date include those of d-block,3–5 s-block,6–9 p-block,10,11 and actinide metals,12,13 and an early structure of hypophosphite as its ammonium salt.14 These show the hypophosphite ion to be very flexible in its co-ordination, doubly bridging 11,13 m(k1,k1), triply bridging 3,5 m3(k1,k1,k1), and quadruply bridging 4,6 m4(k1,k1,k1,k1) modes all being represented.Four structures of lanthanide hypophosphite complexes have been elucidated to date.These are consistent with the expectation that later lanthanide ions should be less able to accommodate high co-ordination numbers than the larger, earlier lanthanides. Thus, the closely related complexes [La(H2PO2)3- (H2O)] and [Eu(H2PO2)3(H2O)], belonging to structural types H P O H O Ln Ln H P O H O Ln Ln Ln Ln H P O H O Ln Ln Ln m(k1, k1) m3(k1, k1, k1) m4(k1, k1, k1, k1) denoted by us here as A and A9 respectively, accommodate a water ligand in their co-ordination spheres.15,16 Two of the hypophosphite ligands adopt the m(k1,k1) mode and the third m3(k1,k1,k1), the co-ordination number thus being eight in both structures.Despite their evident close similarity, the A and A9 structures diVer in the disposition of the m3(k1,k1,k1) ligand, and therefore cannot be considered isostructural.16 The transition point between them in the lanthanide series has not yet been located and, in planning so to do, we considered that the close similarity of these structural types may prohibit unambiguous attribution of class to intervening lanthanide analogues simply by means of spectroscopic techniques.We anticipated that powder X-ray diVraction and, given the ability to grow suitable crystals, single-crystal X-ray diVraction, would prove our most valuable tools in achieving this and our other aims, which also include establishing for which metals anhydrous structural types may be formed.An example is the recently discovered17 structural type B adopted by [Pr(H2PO2)3], which achieves 8-coordination by use of the m(k1,k1) mode for one ligand only, the other two being m3(k1,k1,k1). In contrast, the late lanthanide complex [Er(H2PO2)3] is reported 18 to be 6-co-ordinate, having an approximately octahedral geometry about the metal ion, all hypophosphite ligands adopting the m(k1,k1) mode; this structure is denoted by us here as belonging to type C. Our final aim was to explore whether other lanthanide structures might adopt types B, C, or an entirely new structural form, potentially one adopting the comparatively rare 1 7-co-ordination. Results and discussion Synthetic studies The reaction of aqueous solutions of lanthanide chlorides with sodium hypophosphite gave rise to the corresponding lanthanide hypophosphites.The compounds are all poorly soluble in water, but dissolve in dilute HCl. Their spectroscopic and other properties, and subsequent structural studies (discussed below), showed that the compounds form four distinct series of structural types depending on the metal and the reaction conditions.These and their interconversions are summarised in Table 1. In some cases air oxidation results in the formation of2190 J. Chem. Soc., Dalton Trans., 1999, 2189–2196 Table 1 Formation of the various classes of lanthanide hypophosphite complexes La Ce Pr Nd (Pm) Sm Eu Gd Tb Dy Ho Er Tm Yb Lu AA 9 B C ! ! b ! b ! b ! ! c ! ! c ! ! ! ! ! ! !, Formed on mixing reagents; b, formed from type A by digestive dehydration; c, formed on forced dehydration of type A9.phosphite, manifest in the 31P NMR spectra of the praseodymium and neodymium products completely dissolved in aqueous HCl. This oxidation is suppressed by carrying out the reaction under nitrogen or by buVering the solution to pH 1.4. Digestion of the type A complexes on a water-bath over one day leads to the formation of anhydrous type B complexes for Ce, Pr and Nd.Interestingly no type B complex is observed for lanthanum and the type A9 compounds do not undergo similar reactions. On prolonged digestion open to the air well defined mixed hypophosphite–phosphite complexes are formed. Two distinct forms of the mixed complex are observed, type 1, [Ln(H2PO2)(HPO3)(H2O)]?H2O (Ln = Pr–Gd) and an anhydrous type 2, [Ln(H2PO2)(HPO3)] (Ln = Tb–Lu), but we have never unambiguously identified the lanthanum and cerium type 1 analogues.Over prolonged periods evidence of further oxidation to phosphate is observed in the 31P NMR spectra of solutions of the products which show, in addition to HPO3 22 and H2PO2 2, a singlet due to PO4 32. The substitution of lanthanide chlorides by the nitrates, whilst giving the same hypophosphite complexes, leads to the acceleration of the formation of type 1 and 2 materials; in these cases the oxidation of hypophosphite by nitrate was confirmed by the identification of the main gaseous nitrogen containing product as N2O contaminated with smaller amounts of NO, the infrared spectrum of the gas collected from the reaction mixture being identical with that expected from the literature.19 Of note here is the observation that the cerium type B complex does not easily appear to undergo oxidation under these conditions.In view of the formation of anhydrous hypophosphites for the heavier lanthanides it seemed reasonable to suppose that at some point the type A9 and type C structures might possess similar stabilities and thus be interconvertible.Indeed, reaction of [Tb(H2PO2)3(H2O)], the last type A9 complex, with refluxing HC(OMe)3 gives a type C complex which is considerably more soluble in water than the other type C compounds and can be precipitated therefrom as type A9 by the addition of acetone. When Ln = Eu a type C compou is also formed, which rapidly rehydrates in air.Attempts to convert type 1 into type 2 materials by dehydration with HC(OMe)3 have not been successful. Spectroscopic and thermal studies All type A, A9, B and C complexes produced possess spectral and thermal properties consistent with their known15–18 structures. Thus the types A and A9 have very similar infrared spectra. Both are indicative of the presence of two or more diVerent types of hypophosphite environment, and the presence of water (Fig. 1). Types A9 have only three P–H stretching bands, presumably due to overlap.Thermal analysis shows an endotherm at around 210 8C, associated with a loss of ca. 5% mass, and consistent in all cases with loss of water. At around 310 8C there is a further compound exothermic event, resulting in a further 2% loss of mass; infrared investigation of the gaseous products of this decomposition revealed that phosphine 20 is evolved, and we believe the change to be attributable to the known21 disproportionation of hypophosphite, occurring concomitantly with its partial oxidation. Type B complexes possess infrared spectra indicative of the absence of water ligands and the presence of two or more diVerent types of hypophosphite. They lose no significant mass below 310 8C at which point an exothermic loss of 5% mass occurs.This is also attributable to the disproportionation of hypophosphite and, in common with the cases of A and A9 above, is associated with another, concomitant, event, although much less in evidence here than in A or A9.Type C complexes possess uncomplicated infrared spectra indicative of rather uniform hypophosphite environments. They lose no significant mass below 340 8C, at which point there is an exothermic gain in mass of ca. 4% occurring over ca. 40 8C. Presumably this is air oxidation of hypophosphite, no loss of phosphine being observed; this fact can be rationalised by the structural studies discussed below. For all the above type A, A9, B and C complexes, their 31P NMR spectra measured in aqueous HCl show only hypophosphite ion in solution. Infrared spectra of the new type 1 complexes show intense broad bands in the appropriate regions indicating the presence of water.The P–H region is simple relative to type A complexes, but the P–O region is rather more complex. Thermal analysis reveals an endothermic loss of mass of ca. 11% at 130 8C, which corresponds to a loss of two water molecules per metal atom, followed by no further events up to 460 8C.Samples heated to 270 8C and allowed to stand in air appear to rehydrate to regenerate materials with type 1 infrared spectra. Most notably, however, 31P NMR spectra of types 1 in aqueous HCl indicate the presence of both phosphite and hypophosphite, suggesting an empirical formulation of Ln(H2PO2)(HPO3)(H2O)2 for type 1 complexes. Proton coupled 31P NMR spectra of the complexes dissolved in concentrated HCl clearly show the presence of both phosphite (doublet) and hypophosphite (triplet).The integrated peak area ratios of these, measured using diVering pulse delays and pulse widths, remains unaltered at 1 : 1, implying that rapid relaxation is occurring due to the presence of the paramagnetic lanthanide ions, and thus the measured ratio is a good reflection of the relative amounts of phosphite and hypo- Fig. 1 Typical infrared spectra of all structural types.J. Chem. Soc., Dalton Trans., 1999, 2189–2196 2191 Table 2 Crystal data for lanthanide hypophosphite complexes Formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 Dc/g cm23 Colour F(000) Size/mm q Range/8 hkl ranges Total data Unique data Merging R m/mm21 tmin, tmax R (all data) wR2 (all data) Goodness of fit [Ce(H2PO2)3(H2O)] 353.09 Triclinic P1� 7.1729(10) 7.9827(9) 8.8710(6) 110.643(12) 98.101(13) 104.970(11) 2.642 None 334 0.20 × 0.25 × 0.30 2.54–24.92 28 £ h £ 5, 29 £ k £ 8, 210 £ l £ 10 1964 1274 0.0580 5.661 0.532, 1.000 0.0374 0.0922 1.112 [Dy(H2PO2)3] 357.46 Monoclinic C2/m 14.368(3) 5.7340(10) 12.1230(10) 122.33(2) 2.813 Lilac 660 0.35 × 0.24 × 0.24 1.99–24.84 216 £ h £ 16, 26 £ k £ 5, 210 £ l £ 13 1816 717 0.0495 9.398 0.584, 1.000 0.0309 0.0850 1.129 [Pr(H2PO2)(HPO3)(H2O)]?H2O 1287.62 Orthorhombic P212121 6.6558(5) 7.1539(5) 16.5506(18) 2.713 Light green 608 0.25 × 0.28 × 0.30 3.10–25.03 27 £ h £ 7, 27 £ k £ 6, 218 £ l £ 17 3274 1220 0.0670 6.574 0.740, 1.000 0.0430 0.1029 1.051 phosphite present.The spectral properties of type 2 materials are similar to those of type 1 mentioned above, with the exception that no bands arising from water are evident in their infrared spectra. Their thermogravimetric traces are almost featureless below 460 8C. The infrared spectra of the materials obtained by thermal dehydration of type 1 complexes are very similar to those of type 2, and we believe type 2 complexes to be the anhydrous analogues of type 1, the absence of water being necessitated by smaller ionic radii of the later lanthanides, in the same way as type C are analogues of type A or A9.We therefore tentatively assign the formulation Ln(H2PO2)(HPO3) to type 2. There is some evidence here of the existence of alternative structural types which might be denoted 19 and 29, by analogy with A9. This arises from the interesting fact that type 1 materials when heated to 160 8C are completely dehydrated, and upon rehydration in air revert to type 1.When heated to 270 8C, however, they possess diVerent IR spectra after complete rehydration. These transformations are irreversible, but the products still contain the same 1 : 1 ratio of hypophosphite to phosphite (NMR evidence). Structural studies Powder X-ray diVraction patterns were simulated for all of types A, A9, B and C based upon the literature.15–18 Experimental traces were recorded for all the new and known type A, A9, B and C complexes and showed four families of patterns, in accordance with the categories assigned to each complex by spectroscopic and thermal means.Good agreement was also obtained between each pattern prediction and the experimental trace in all cases, the worst fit being for types C. Patterns were also recorded for all type 1 materials, and also showed a familial resemblance. As a final verification of the compositions of these materials, and in order to clarify the discrepancy between the predicted and observed powder patterns of type C complexes, we sought to examine one of each type by single-crystal X-ray diVraction and found Ce to give satisfactory crystals of type A, Dy of C, and Pr of types B and 1.No satisfactory crystals were obtained of any type A9 complex except for Eu, or of any type 2 complex. Each of the above crystals aVorded a structural solution. Details salient to data collection and structural refinement are presented in Table 2 (and elsewhere for [Pr(H2PO2)3]).17 The structure of the cerium type A complex was confirmed to be [Ce(H2PO2)3(H2O)] and is depicted in Fig. 2. It is, as indicated by supporting methods, virtually isostructural 15 with [La(H2PO2)3(H2O)], the structure of which is outlined briefly above. The Ln–O (hypophosphite) distance therein is 2.560[7] Å, but only 2.492[2] Å ([smean] = i = n i = 1 S(si 2)/n) in the cerium analogue (Table 3). There appears to be some compensation for this contraction in an extension of the hypophosphite ligands; the P–O (hypophosphite) lengths in [Ce(H2PO2)3(H2O)] average 1.495[2] Å as compared with 1.478[6] Å in the lanthanum analogue, the O–P–O angles likewise extending to average 117.77[17]8 as compared to 115.6[5]8 in [La(H2PO2)3(H2O)]. The hydrogen atoms of the waters were not locateable, but their presence was inferred from two, and only two, close contacts between O(1) and hypophosphite atoms O(21)iv and O(22)v which subtend almost tetrahedral angles for O(21)iv ? ? ? O(1)– Ce and O(21)iv ? ? ? O(1) ? ? ? O(22)v.The O(22)v ? ? ? O(1)–Ce Fig. 2 A view22 of [Ce(H2PO2)3(H2O)] along the unit cell b axis. The Ce, P, and H atoms are represented by spheres of decreasing relative arbitrary size. Only the water H atoms are shown, for reasons of clarity, along with their hydrogen-bonding contacts. Symmetry operators used throughout: i = 2x, 2y, 2z; ii = x 1 1, y, z; iii = 1 2 x, 1 2 y, 1 2 z; iv = 1 2 x, 2y, 2z; v = x 1 1, y 1 1, z; vi = 2x, 2y, 1 2 z; vii = x, 2y, z; viii = x, 1 2 y, z; ix = 2 2 x, y 1 1– 2, 1– 2 2 z; x = 2 2 x, y 2 1– 2, 1– 2 2 z; xi = x 2 1, y, z; xii = x 2 1– 2, 11– 2 2 y, 2z; xiii = 11– 2 2 x, 1 2 y, z 2 1– 2; xiv = 11– 2 2 x, 2 2 y, z 2 1– 2; xv = 1 2 x, 1 2 y, 2z; xvi = 2x, y 2 1, 1 2 z; xvii = x, y 2 1, z; xviii = 2x, y, 1 2 z; xix = 2x, 1 2 y, 1 2 z; xx = 2x, y 2 1, 2z; xxi = 2x, y, 2z; xxii = 2x, 1 2 y, 2z; xxiii = 11– 2 2 x, 1 2 y, z 1 1– 2; xxiv = 11– 2 2 x, 2 2 y, z 1 1– 2; xxv = x 1 1– 2, 11– 2 2 y, 2z; xxvi = x, y 1 1, z.2192 J.Chem. Soc., Dalton Trans., 1999, 2189–2196 angle, however, is far larger, which implies that, assuming an sp3 hybridisation at O(1), the attitude of the lone pairs of O(1) to Ce is not one of direct alignment. This is, however, a common phenomenon, manifest also in other structures,23–25 and probably implies a degree of interaction between Ce and both lone pairs; indeed, in this very structure, the orientations of the hypophosphite ligands also are not consistent with an sp3 hybridisation at oxygen atoms and direct alignment between only one oxygen lone pair and Ce.The overall co-ordination geometry (Fig. 3) around Ce conforms most closely to bicapped trigonal prismatic (BTP), although polytopal analysis shape parameters 26 indicate that a degree of square antiprismatic (SAP) character is also present (Table 4; DOD = dodecahedral) which is manifest mainly in the elongation of the O(1) ? ? ? O(31) distance so as to destroy the coplanarity of the sides of the prism.The important bond distances and angles of the type B complex [Pr(H2PO2)3] have been communicated elsewhere.17 Its overall co-ordination geometry conforms fairly closely to square antiprismatic (Table 4). The structure reported 18 for [Er(H2PO2)3] and that determined by us for our dysprosium type C complex are diVerent, Fig. 3 The co-ordination polyhedron in [Ce(H2PO2)3(H2O)].Table 3 Selected interatomic separations (Å) and angles (8) for [Ce(H2PO2)3(H2O)] Ce–O(11) Ce–O(31) Ce–O(12)i Ce–O(22)i P(1)–O(11) P(2)–O(22) P(3)–O(31) O(1) ? ? ? O(21)iv O(31)–Ce–O(11) O(11)–Ce–O(32)iii O(11)–Ce–O(22)i O(31)–Ce–O(21) O(32)iii–Ce–O(21) O(31)–Ce–O(1) O(32)iii–Ce–O(1) O(21)–Ce–O(1) O(11)–Ce–O(12)i O(22)i–Ce–O(12)ii O(1)–Ce–O(12)i O(11)–Ce–O(12)ii O(22)i–Ce–O(12)ii O(1)–Ce–O(12)ii O(11)–P(1)–O(12) O(31)–P(3)–O(32) Ce–O(1) ? ? ? O(22)v 2.432(4) 2.416(5) 2.574(4) 2.482(5) 1.483(5) 1.496(5) 1.484(5) 2.714(7) 86.59(17) 79.92(17) 81.64(16) 78.99(18) 143.03(16) 102.88(18) 72.20(17) 140.46(15) 119.21(15) 77.19(15) 77.56(15) 144.17(15) 130.51(14) 67.61(14) 115.59(28) 118.48(32) 142.04(22) Ce–O(21) Ce–O(1) Ce–O(12)ii Ce–O(32)iii P(1)–O(12) P(2)–O(21) P(3)–O(32) O(1) ? ? ? O(22)v O(31)–Ce–O(32)iii O(31)–Ce–O(22)i O(32)iii–Ce–O(22)i O(11)–Ce–O(21) O(22)i–Ce–O(21) O(11)–Ce–O(1) O(22)i–Ce–O(1) O(31)–Ce–O(12)i O(32)iii–Ce–O(12)i O(21)–Ce–O(12)i O(31)–Ce–O(12)ii O(32)iii–Ce–O(12)ii O(21)–Ce–O(12)ii O(12)i–Ce–O(12)ii O(22)–P(2)–O(21) Ce–O(1) ? ? ? O(21)iv O(21)iv ? ? ? O(1) ? ? ? O(22)v 2.502(5) 2.515(5) 2.607(4) 2.434(5) 1.514(5) 1.504(5) 1.489(5) 2.834(7) 75.64(18) 150.06(18) 75.24(16) 72.10(15) 122.41(15) 146.97(16) 74.52(15) 132.11(16) 143.38(15) 73.06(15) 71.36(15) 119.25(15) 76.11(14) 64.69(16) 119.19(28) 110.75(19) 107.06(21) but we note that the veracity of the former has been queried elsewhere.23 Although the structures do not agree, the axial lengths of the two unit cells do, only the b angles being diVerent.The two structures share the common characteristic of consisting a framework of metal atoms linked by m(k1,k1)- hypophosphite bridges extending along the principal axes of the lattice. The metal atoms (of which there are two crystallographically unique) in [Dy(H2PO2)3] are thereby six-coordinate. The co-ordination geometry is near-octahedral (Fig. 4), the trans angles being perfectly 1808 and the cis angles ranging close around 908, both extremes of this range being found at Dy(2).The mean Dy–O distance is 2.253[1] Å (Table 5), shorter than in any other lanthanide hypophosphite complex (leaving aside [Er(H2PO2)3]).18 The presence of two waters per metal ion for the Type 1 complexes is substantiated by the emergent structure of [Pr- (H2PO2)(HPO3)(H2O)]?H2O (a formulation to be preferred over our former interpretation).17 Only one of these waters is associated directly with the Pr.The metal is once again 8-co-ordinate by means of additional contributions from m(k1,k1)-hypophosphite and a m4(k2,k1,k1,k1)-phosphite (Fig. 5). As in [Ce(H2PO2)3(H2O)], the water H atoms were not definitively located, but were clearly implied by interoxygen distances and angles: as a result it is clear that the structural units are bound together by means of the non-ligand water molecules, which bridge between hypophosphite O atoms as hydrogen-bonding acids, in turn acting as hydrogen-bonding bases to the ligand waters (Fig. 6). The result is a region of the structure inhabited by water molecules associated by hydrogen-bonding and extending along the screw axes. The space group itself being chiral, this area resembles a ‘screw thread’ of hydrogen bonds. Again, as in [Ce(H2PO2)3(H2O)], the geometry at the ligand water is far from tetrahedral. The O(2) ? ? ? O(1) ? ? ? O(2)xii angle is almost tetrahedral, but the corresponding angles between Pr and O(2) or O(2)xii (these are the O atoms which act as hydrogen-bonding bases to H(13) and H(14) respectively) are obtuse; as in [Ce(H2PO2)3(H2O)], no other close contacts are made with O(1) to imply a demand on the remaining lone pair, the implication being, in view of the angles at O(1), that it interacts somewhat with Pr.The geometry at O(2) is more regular (Table 6). The mean hypophosphite P–O Fig. 4 A view22 of [Dy(H2PO2)3]. The Dy, P and O atoms are represented by spheres of decreasing relative arbitrary size, and H atoms are omitted. H P O O O Ln Ln Ln Ln m4(k2, k1, k1, k1)J.Chem. Soc., Dalton Trans., 1999, 2189–2196 2193 Table 4 Polytopal a analysis shape parameters for 8-co-ordinate lanthanide hypophosphite complexes [Ce(H2PO2)3(H2O)] [Pr(H2PO2)3] b [Pr(H2PO2)(HPO3)(H2O)]?H2O BTP SAP DOD d 1(57)3/8 d 2(68)4/8 d 2(58)3/8 d 1(67)4/8 f 7–1–2–8/8 f 5–3–4–6/8 13.8 2.9 45.6 42.9 16.0 16.6 8.0 7.6 50.0 57.4 24.2 37.7 34.1 16.0 50.7 45.6 5.1 20.4 21.8 0.0 48.2 48.2 14.1 14.1 0.0 0.0 52.5 52.5 24.5 24.5 29.5 29.5 29.5 29.5 0.0 0.0 a Vertices are assigned, for the above three structures respectively, as follows: 1 [O(12)ii, O(11), O(21)], 2 [O(21), O(21), O(22)], 3 [O(32)iii, O(31), O(23)xi], 4 [O(22)i, O(12)xv, O(1)], 5 [O(31), O(32)xix, O(11)], 6 [O(12)i, O(22)iv, O(12)ix], 7 [O(1), O(22), O(22)ix], 8 [O(11), O(12)xi, O(21)x].b See ref. 17. distance of 1.491[4] Å in this structure appears to be shorter than the 1.513[2] Å seen in [Pr(H2PO2)3], but this is to be interpreted in the light of the fact that both the co-ordination mode of the hypophosphites and the nature of the coligands is diVerent in both structures.In the phosphite ligand the P(2)–O(23) distance is shorter than the distances to O(21) and O(22), which situation has been observed before 27,28 and is analogous to the asymmetry of the m3(k1,k1,k1)-hypophosphite ligands, caused by diVerent ligating demands on the two O atoms.In [Pr(H2- PO2)(HPO3)(H2O)]?H2O the co-ordination polyhedron is a dodecahedron, perhaps rather distorted in the direction of SAP by the loss of planarity of the O(11), O(23)xi, O(1), O(12)ix trapezoid (Fig. 7). The degree of steric crowding in the above complexes can be compared by the use of steric angle sum (SAS) calculations,1 which express the fraction of surface area of a notional 1 Å Fig. 5 A view22 of [Pr(H2PO2)(HPO3)(H2O)]?H2O.The Pr, P, O and H atoms are depicted with decreasing arbitrary radii. Only H atoms, and their hydrogen-bonds to surrounding atoms, are shown for purposes of clarity. Table 5 Selected interatomic separations (Å) and angles (8) for [Dy(H2PO2)3] Dy(1)–O(11) Dy(2)–O(12) P(1)–O(12) P(2)–O(21) O(11)–Dy(1)–O(21) O(21)vi–Dy(1)–O(21)vii O(11)–Dy(1)–O(11)vi O(12)–Dy(2)–O(31) O(31)–Dy(2)–O(31)vii O(12)i–Dy(2)–O(12) O(12)–P(1)–O(11) O(31)–P(3)–O(31)viii 2.243(6) 2.246(6) 1.439(7) 1.486(5) 91.3(2) 89.5(2) 180.0 88.4(2) 90.1(2) 180.0 121.1(5) 117.0(4) Dy(1)–O(21) Dy(2)–O(31) P(1)–O(11) P(3)–O(31) O(11)–Dy(1)–O(21)vi O(21)–Dy(1)–O(21)vii O(21)–Dy(1)–O(21)vi O(12)i–Dy(2)–O(31) O(31)i–Dy(2)–O(31)vii O(31)–Dy(2)–O(31)i O(21)–P(2)–O(21)viii 2.256(4) 2.259(5) 1.465(7) 1.489(5) 88.7(2) 90.5(2) 180.0 91.6(2) 89.9(2) 180.0 116.6(4) radius sphere, at a metal’s centre, which is covered by conic projections of the ligating atoms.Computationally this is done by summing all of the individual atoms’ contributions but, since overlap between the individual atoms’ projections is not counted twice, an overlap correction is then applied.Values calculated for the above complexes are presented in Table 7 along with those for some related complexes. The table is arranged according to atomic weight of the metal, and the eVects of the lanthanide contraction are immediately evident in the general increase in SAS values for the later lanthanides. The lanthanum complex has the smallest value, and there is no overlap correction required.In the case of the isostructural type A cerium complex a very small overlap correction is present, which arises from a close approach of atoms O(12)i and O(12)ii which reside in two m3(k1,k1,k1)-hypophosphite ligands. This contact may be expected to become closer in the later lanthanide structures, and suggests that the structural change from A to A9 occurs when it reaches a limiting value. The SAS calculation for the type A9 [Eu(H2PO2)3(H2O)] requires an overlap correction, but this arises mainly from a contact between the Fig. 6 The packing arrangement of [Pr(H2PO2)(HPO3)(H2O)]?H2O seen 22 along the unit cell a axis. Some bonds are omitted for clarity. The symbol X denotes the approximate location of a screw axis consisting the centre of a ‘screw thread’ of water molecules. Fig. 7 The co-ordination around the Pr atom in [Pr(H2PO2)(HPO3)- (H2O)]?H2O.2194 J. Chem. Soc., Dalton Trans., 1999, 2189–2196 Table 6 Selected interatomic separation (Å) and angles (8) for [Pr(H2PO2)(HPO3)(H2O)]?H2O Pr–O(11) Pr–O(22) Pr–O(12)ix Pr–O(22)ix P(1)–O(11) P(2)–O(21) P(2)–O(23) O(1) ? ? ? O(2)xii O(2) ? ? ? O(11)xiv O(23)xi–Pr–O(21)x O(21)x–Pr–O(22)ix O(21)x–Pr–O(1) O(23)xi–Pr–O(12)ix O(22)ix–Pr–O(12)ix O(23)xi–Pr–O(11) O(22)ix–Pr–O(11) O(12)ix–Pr–O(11) O(21)x–Pr–O(22) O(1)–Pr–O(22) O(11)–Pr–O(22) O(21)x–Pr–O(21) O(1)–Pr–O(21) O(11)–Pr–O(21) O(11)–P(1)–O(12) O(23)–P(2)–O(22) Pr–O(1) ? ? ? O(2) O(2) ? ? ? O(1) ? ? ? O(2)xii O(1) ? ? ? O(2) ? ? ? O(11)xiv 2.479(6) 2.570(5) 2.479(6) 2.395(5) 1.478(6) 1.540(6) 1.490(6) 2.827(9) 2.866(8) 90.82(20) 171.07(21) 79.98(23) 132.99(21) 82.07(20) 77.29(23) 94.55(20) 147.52(21) 66.84(19) 123.70(22) 77.55(20) 122.41(15) 137.49(20) 77.99(22) 118.86(33) 113.05(34) 133.35(30) 101.48(26) 112.18(32) Pr–O(21) Pr–O(1) Pr–O(21)x Pr–O(23)xi P(1)–O(12) P(2)–O(22) O(1) ? ? ? O(2) O(2) ? ? ? O(12)xiii O(23)xi–Pr–O(22)ix O(23)xi–Pr–O(1) O(22)ix–Pr–O(1) O(21)x–Pr–O(12)ix O(1)–Pr–O(12)ix O(21)x–Pr–O(11) O(1)–Pr–O(11) O(23)xi–Pr–O(22) O(22)ix–Pr–O(22) O(12)ix–Pr–O(22) O(23)xi–Pr–O(21) O(22)ix–Pr–O(21) O(12)ix–Pr–O(21) O(22)–Pr–O(21) O(23)–P(2)–O(21) O(21)–P(2)–O(22) Pr–O(1) ? ? ? O(2)xii O(1) ? ? ? O(2) ? ? ? O(12)xiii O(11)xiv ? ? ? O(2) ? ? ? O(12)xiii 2.639(6) 2.475(7) 2.390(6) 2.367(6) 1.505(7) 1.547(6) 2.784(9) 2.794(8) 80.27(20) 70.85(21) 96.31(23) 103.82(20) 68.29(21) 84.06(20) 143.93(23) 147.80(19) 121.53(13) 76.93(20) 135.61(19) 65.63(18) 71.17(19) 56.01(18) 114.37(32) 104.86(33) 123.82(27) 88.62(27) 114.58(29) m3(k1,k1,k1) and the water ligands, rather than between like ligands.The type B [Pr(H2PO2)3] contains no strong contacts such as would necessitate an overlap correction, despite possessing a larger SAS value than [Ce(H2PO2)3(H2O)] and being presumably more sterically crowded. The distribution of ligand atoms17 around the metal ion in the type B materials is evidently quite eYcient, which is in accordance with the observed SAP co-ordination geometry.This might explain why type B forms by dehydration of type A, even in the presence of water. The complex [Dy(H2PO2)3] contains two crystallographically inequivalent dysprosium ions, and thus has two ascribable SAS values, the comparatively small magnitudes of which reflect the fact that this structure is a 6-co-ordinate one. This allows the ligands to move well away from one another, which is manifest in the lack of any overlap correction and the lower density of [Dy(H2PO2)3] compared to 17 [Pr(H2PO2)3]. Furthermore, it might also aVord type C complexes their resistance to disproportionation of hypophosphite, which occurs readily in types A, A9 and B at elevated temperatures.Since one of the products of this process is phosphine, interphosphorus oxygen transfer is a requisite, but there are no P ? ? ? O approaches in [Dy(H2PO2)3] closer than 3.508(6) Å.This can be compared with values of 3.126(5) Å in [Ce(H2PO2)3(H2O)] and 2.918(4) Å in [Pr(H2- PO2)3], both of which fall well inside the sum of van der Waals Table 7 Steric angle sums (SASs) for lanthanide hypophosphite complexes SAS Complex Uncorrected Corrected [La(H2PO2)3(H2O)] a [Ce(H2PO2)3(H2O)] [Pr(H2PO2)3] b [Pr(H2PO2)(HPO3)H2O]?H2O [Eu(H2PO2)3(H2O)] c [Dy(H2PO2)3] 0.653 0.691 0.698 0.705 0.738 0.6503, 0.6486 0.653 0.691 0.698 0.699 0.733 0.6503, 0.6486 a See ref. 15. b See ref. 17. c See ref. 16. radii of P and O for these type A and B complexes both of which undergo thermal disproportionation. Conclusion Whilst the hypophosphite–lanthanide system has not proven uncomplicated in its behaviour, relatively simple analyses, such as SAS calculations, appear to have aVorded some fundamental insights to the structural preferences and reactivities of lanthanide hypophosphite complexes. These studies have established the classes of structures adopted by these materials and the ranges over which each is formed in the lanthanide series. The structure of type A has been verified by examination of a new member, and that of type C established correctly for the first time.No evidence for a 7-co-ordinate structural type, between the former 8- and the latter 6-co-ordinate complexes, has been found. A new class of mixed-ligand hypophosphite– phosphite complex, containing interesting chiral channels of water molecules, has been synthesized and characterised structurally.Experimental Instrumentation JEOL JNM-FX270 and FX90Q (NMR), ATI Mattson Genesis single beam (FTIR) Philips 1050 Cu-Ka (powder diVraction) and Netzch STA 409 EP (TGA) instruments were used for routine analysis. Analysis Oxidisable phosphorus was determined by treatment of samples with an excess of bromine (generated quantitatively from bromate and bromide). The sample was stirred with bromine for 3 h in a stoppered flask, cooled in ice and an excess of potassium iodide added.The iodine liberated was titrated with standard sodium thiosulfate solution. For parity of reporting for pure hypophosphite and mixed-ligand systems, the results are expressed in terms of calculated molar mass. Percentage phosphorus values were determined by DCP (direct current plasma) atomic absorption spectroscopy.J. Chem. Soc., Dalton Trans., 1999, 2189–2196 2195 Syntheses [Ln(H2PO2)3(H2O)n] (types A and A9, n 5 1; C, n 5 0), general procedure.Sodium hypophosphite (ca. 1.00 g) was dissolved in pH 1.4 (KCl–HCl) buVer solution (10 ml). Hydrated lanthanide chloride (ca. 1.20 g) in the buVer solution (10 ml) was added. The mixture was allowed to stand in air at room temperature for one hour. A solid precipitated from solution where Ln = La–Eu, Dy–Lu. For Ln = Gd or Tb addition of a seed crystal resulted in rapid precipitation from the supersaturated solution. The resulting solids, bearing the characteristic colour of the Ln31 ions, were collected by suction filtration, washed with water, and dried at the pump. Yields 61– 89%.Representative analyses: [Ce(H2PO2)3(H2O)], found P 26.1, H8CeO7P3 requires 26.3%; [Dy(H2PO2)3], found P 25.6. H6DyO6P3 requires 26.0%; [Sm(H2PO2)3(H2O)], M found 366, theoretical 363; [Eu(H2PO2)3(H2O)], M found 362, theoretical 365. [Ln(H2PO2)3] (type B). Stoichiometric amounts of sodium hypophosphite and the lanthanide chloride were dissolved separately in the minimum amount of water.On mixing a precipitate was formed immediately, and the reaction mixture heated under reflux under nitrogen for several hours. Needle-like crystals formed of the colour of the corresponding Ln31 ion, which were collected by suction filtration, washed with water, and dried at the pump. Yields 51–69%. [Pr(H2PO2)3)], M found 336, theoretical 336. [Tb(H2PO2)3] (type C) from [Tb(H2PO2)3(H2O)] (type A9). A small quantity of [Tb(H2PO2)3(H2O)] was stirred under reflux with excess of trimethyl orthoformate in a nitrogen atmosphere for 2 h.The resulting material was filtered in a dry-box, washed with dry thf and allowed to dry. [Ln(H2PO2)(HPO3)(H2O)n]?H2O (type 1, n 5 1; 2, n 5 0). Air oxidation of the lanthanide hypophosphite complexes, monitored by IR spectroscopy, was achieved by in situ air oxidation on heating the lanthanide chloride with sodium hypophosphite in aqueous solution on a steam-bath for several hours.Needle like crystals were formed for the praseodymium and neodymium complex, whilst for the later lanthanides the complexes were obtained as fine powders. The products were filtered oV, washed with water and dried in air at the pump. Representative analyses: [Nd(H2PO2)(HPO3)(H2O)]?H2O, M found 301, theoretical 325; [Tm(H2PO2)(HPO3)], M found 316, theoretical 314; [Lu(H2PO2)(HPO3)], M found 325, theoretical 320. Crystallography DiVraction data were collected, using Mo-Ka radiation, according to previously published procedures.29 Non-H atoms were modelled 30 anisotropically, and H atoms isotropically, these being placed in theoretical positions.Following convergence of full-matrix least-squares refinement30 using merged data, these were corrected 31 for absorption eVects and refinement resumed to convergence. [Ce(H2PO2)3(H2O)]. The structure was solved by isomorphous replacement.15 A common refined P–H distance (1.309(14) Å) was used, and water H atoms were restrained to sit 30% along the length of their putative hydrogen-bonding vectors and, as a result, the refinement was unstable and required slight damping.Final error limits were estimated using undamped cycles of refinement. The largest hole and peak in the final Fourier-diVerence map were 21.08 and 1.40 e Å23 (at Ce). [Dy(H2PO2)3]. Data were collected as for triclinic symmetry, and transformed to the above system. The structure was solved by trial placement of heavy atoms at special positions.A common refined P–H distance (1.245(15) Å) was used for the refinement. The largest hole and peak in the final Fourierdi Verence map were 20.86 and 0.74 e Å23 (ca. 1.2 Å from Dy(1) and O(11)). [Pr(H2PO2)(HPO3)(H2O)]?H2O. The structure was solved by Patterson methods.32 A common refined P–H distance (1.266(26) Å) was used, which was considered a reasonable step in the light of the similarity of the IR stretching frequencies.Some systematic error in the data necessitated that phosphite O atoms be weakly restrained to be isotropic to prevent ‘nonpositive definite’ collapse. Water H atoms were restrained to sit 30% along the length of their putative hydrogen-bonding vectors and, as a result, the refinement was unstable and required damping. Final error limits were estimated using undamped cycles of refinement. The largest hole and peak in the final Fourier-diVerence map were 21.29 and 3.99 e Å23 (at Pr).CCDC reference number 186/1450. Acknowledgements The authors gratefully acknowledge the use of the EPSRC’s X-Ray Crystallography Service, and Chemical Database Service at Daresbury. Thanks are due to Stephanie Barnett for simulations of powder patterns, and to all in the Divison of Ceramics for use of apparatus. References 1 X.-Z. Zhang, A.-L. Guo, Y.-T. Xu, X.-F. Li and P.-N. Sun, Polyhedron, 1987, 6, 1041. 2 F. A. Hart, in Comprehensive Coordination Chemistry, eds. G.Wilkinson, R. D. Gillard and J. A. McCleverty, Pergamon Press, Oxford, 1987, vol. 3. 3 M. D. Marcos, R. Ibanez, P. Amoros and A. LeBail, Acta Crystallogr., Sect. C, 1991, 47, 1152. 4 T. J. R. Weakley, Acta Crystallogr., Sect. B, 1979, 35, 42. 5 M. D. Marcos, P. Amoros, F. Sapina, A. Beltran-Porter, R. Martinez-Manez and J. P. Attfield, Inorg. Chem., 1993, 32, 5044. 6 T. Matsuzaki and Y. Itaka, Acta Crystallogr., Sect. B, 1969, 25, 1932. 7 B. O. Loopstra, Int. Estab. Nucl. Energy Res.Publ., 1958, 15, 64. 8 A. R. Pedrazuela, S. Garcia-Blanco and L. Rivoir, An. Soc. Esp. Fis. Quim., 1953, 49, 255. 9 T. Akimoto, Ph.D. Thesis, University of Tokyo, 1965. 10 T. J. R. Weakley, J. Chem. Soc. Pak., 1983, 5, 279. 11 T. J. R. Weakley and W. W. L. Watt, Acta Crystallogr., Sect. B, 1979, 35, 3023. 12 P. A. Tanner, T. Sze, T. C. Mak and W. Yip, J. Cryst. Spectrosc. Res., 1992, 22, 25. 13 P. A. Tanner, S.-T Hung, T. C. W. Mak and W. Ru-Ji, Polyhedron, 1992, 11, 817. 14 W. H. Zachariasen and R. C. L. Mooney, J. Chem. Phys., 1934, 2, 34. 15 V. M. Ionov, L. A. Aslanov, V. B. Rybakov and M. A. Porai-Koshits, Kristallografiya, 1973, 18, 403. 16 V. M. Ionov, L. A. Aslanov, M. A. Porai-Koshits and V. B. Rybakov, Kristallografiya, 1973, 18, 405. 17 J. A. Seddon, A. R. W. Jackson, R. A. Kresinski and A. W. G. Platt, Polyhedron, 1996, 15, 1899. 18 L. A. Aslanov, V. M. Ionov, M. A. Porai-Koshits, V. G. Lebedev, B. N. Kulikovskii, O. N. Gilyarov and T. L. Novoderezhkina, Izv. Acad. Nauk. SSSR, Neorg. Mater., 1975, 11, 96. 19 J. Laane and J. R. Ohlsen, Prog. Inorg. Chem., 1980, 27, 465. 20 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 4th edn., Wiley, New York, 1986. 21 J. W. Mellor, Comprehensive Treatise on Inorganic and Theoretical Chemistry, Longmans, New York, London, 1971, vol. 8, suppl. 3. 22 E. K. Davies, SNOOPI, Chemical Crystallography Laboratory, University of Oxford, 1982. 23 The United Kingdom Chemical Database Service, D. A Fletcher, R. F. McMeeking and D. Parkin, J. Chem. Inf. Comput. Sci., 1996, 36, 746. 24 D. L. Faithfull, J. M. Harrowfield, M. I. Ogden, B. W. Skelton, K. Third and A. H. White, Aust. J. Chem., 1992, 45, 583. 25 M. C. Favas, D. L. Kepert, B. W. Skelton and A. H. White, J. Chem. Soc., Dalton Trans., 1980, 454. 26 M. A. Porai-Koshits and L. A. Aslanov, J. Struct. Chem., 1978, 13, 244.2196 J. Chem. Soc., Dalton Trans., 1999, 2189–2196 27 Y.-P. Zhang, H. Hu and A. Clearfield, Inorg. Chim. Acta, 1992, 193, 35. 28 J.-D. Foulon, N. Tijani, J. Durand, M. Rafiq and L. Cot, Acta Crystallogr., Sect. C, 1993, 49, 1. 29 J. A. Darr, S. R. Drake, M. B. Hursthouse and K. M. A. Malik, Inorg. Chem., 1993, 32, 5704. 30 G. M. Sheldrick, SHELXL 93, Program for Crystal Structure Refinement, University of Göttingen, 1993. 31 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158. 32 G. M. Sheldrick, SHELXS 86, Program for the Solution of Crystal Structures, University of Göttingen, 1986. Paper 8/07727D

ISSN:1477-9226    

DOI:10.1039/a807727d

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2191–2198 2191 Synthesis, spectroscopic and EXAFS studies of vanadium complexes of trithioether ligands and crystal structures of [VCl3([9]aneS3)] and [VI2(thf)([9]aneS3)] ([9]aneS3 = 1,4,7-trithiacyclononane) † Sian C. Davies,a Marcus C. Durrant,a David L. Hughes,a Christine Le Floc’h,a Simon J. A. Pope,b Gillian Reid,*,b Raymond L. Richards *,a and J. Roger Sanders a a Nitrogen Fixation Laboratory, John Innes Centre, Colney Lane, Norwich, UK NR4 7UH b Department of Chemistry, University of Southampton, Highfield, Southampton, UK SO17 1BJ A series of vanadium-(II), -(III) and -(IV) macrocyclic thioether complexes has been synthesized and characterised by analytical, magnetic and spectroscopic methods.The new complexes reported are [{V([9]aneS3)}2(m-Cl)3]Cl ([9]aneS3 = 1,4,7-trithiacyclononane), [VI2(thf)([9]aneS3)], [VI2(ttob)] (ttob = 2,5,8-trithia[9]-o-benzenophane), [VX3([9]aneS3)] (X = Cl, Br or I), [VX3([10]aneS3)] ([10]aneS3 = 1,4,7-trithiacyclodecane), [VCl3(ttob)], [VCl3- ([16]aneS4)] ([16]aneS4 = 1,5,9,13-tetrathiacyclohexadecane), [(VX3)2(m-[18]aneS6)] (X = Cl or Br, [18]aneS6 = 1,4,7,10,13,16-hexathiacyclooctadecane) and [VOCl2(ttob)].The crystal structures of [VI2(thf)([9]aneS3)] and [VCl3([9]aneS3)] and EXAFS structural data for [VX3([9]aneS3)] and [VX3([10]aneS3)] are presented and discussed. The acyclic trithioether complexes [VX3{MeC(CH2SMe)3}] (X = Cl or Br) and the complex [VI2(py)4] are also reported.Vanadium–sulfur chemistry has recently become an active area of research due inter alia to the existence of a vanadium nitrogenase system 1 and the involvement of vanadium sulfide species in the refining of crude oils.2 It has been proposed that in the Fe/S/V cluster in the active site of vanadium nitrogenase the co-ordination at vanadium involves one nitrogen, two oxygen and three confacial sulfur atoms, similar to that at molybdenum in the crystallographically characterised iron– molybdenum cofactor of nitrogenase.1 This proposal is supported by the fact that the EXAFS spectrum of the vanadium nitrogenase cofactor resembles that of the synthetic cluster [VFe3S4Cl3(dmf)3]2.3 In view of this work, noting that the only well characterised metal–sulfur site at which dinitrogen is bound and reduced is in the thioether complex trans-bis- (dinitrogen)(3,3,7,7,11,11,15,15-octamethyl-1,5,9,13-tetrathiacyclohexadecane) molybdenum,4 and in the knowledge that early transition metal thioether compounds are rare, we have initiated a study of vanadium thioether macrocyclic chemistry.In particular with regard to understanding the nature of the vanadium site in nitrogenase, we considered that as well as introducing the correct sulfur ligand environment at vanadium (three confacial S donors), macrocyclic trithioethers would also facilitate more stable complexes and may enable N- and O-donor ligands to be introduced at the other co-ordination sites. Accordingly, in this paper we report the preparation and spectroscopic characterisation of vanadium-(II), -(III) and -(IV) complexes involving trithioethers and also other macrocyclic and acyclic thioether ligands.Vanadium K-edge extended X-ray absorption fine structure (EXAFS) measurements have been used to determine V]S and V]X distances for several of these compounds and single crystal X-ray structural analyses of [VCl3([9]aneS3)] and [VI2(thf)([9]aneS3)] are also reported.A preliminary communication on some aspects of this work has been published.5 Prior to this study the only vanadium thioether complexes to be structurally characterised were the vanadium(IV) species [VOCl2([9]aneS3)] 6 and [VOCl2([9]aneN2S)]?MeCN7 ([9]aneN2S = 1-thia-4,7-diazacyclononane), both of which were † Non-SI units employed: eV ª 1.60 × 10219 J, mB ª 9.27 × 10224 J T21. obtained fortuitously from VCl3 and have distorted octahedral geometry. Results and Discussion Preparations and spectroscopy Vanadium(II) derivatives of thioether macrocycles have been prepared.Reaction of [VI2(thf)4] (thf = tetrahydrofuran) with 1 molar equivalent of [9]aneS3 (1,4,7-trithiacyclononane) or ttob (2,5,8-trithia[9]-o-benzenophane) (L9) in thf solution yields [VI2(thf)([9]aneS3)] or [VI2(thf)(ttob)] respectively as a light blue solid [reaction (1)]. Infrared spectroscopy confirms the [VI2(thf)4] 1 L9 æÆ [VI2(thf)L9] 1 3thf (1) presence of the thioether ligand as well as co-ordinated thf, while magnetic measurements are consistent with VII.In addition, reaction of the triply chloride-bridged species [{V(thf)3}2- (m-Cl)3][AlCl2Et2] 8 in CH2Cl2 with [9]aneS3 gives the poorly soluble and highly air-sensitive complex [{V([9]aneS3)}2- (m-Cl)3]Cl, whose characterisation is on the basis of analytical and magnetic data. Reaction of [VX3L3] (L = MeCN, thf or Me2PhPO; X = Cl, Br or I) with 1 molar equivalent of L9 [L9 = [9]aneS3, [10]aneS3 (1,4,7-trithiacyclodecane) or ttob] or with 0.5 molar equivalent of [18]aneS6 (1,4,7,10,13,16-hexathiacyclooctadecane) in anhydrous CH2Cl2 at room temperature under a dinitrogen atmosphere yields the neutral vanadium(III) species [VX3(L9)] or [(VX3)2(m-[18]aneS6)] as a highly coloured solid in good yield.Similar reaction of [VX3(thf)3] (X = Cl or Br) with the tripodal ligand MeC(CH2SMe)3 yields the neutral species [VX3{MeC(CH2SMe)3}] {reaction (2); L9 = [9]aneS3, [10]aneS3, ttob, MeC(CH2SMe)3 or ��� [18]aneS6}.[VX3L3] 1 L9 æÆ [VX3(L9)] or ��� [(VX3)2(m-[18]aneS6)] 1 3L (2) The tetrathioether macrocycle 1,5,9,13-tetrathiacyclohexadecane ([16]aneS4) reacted with [VCl3(thf)3] to give [VCl3([16]- aneS4)], in which the S4 ligand may be tridentate {as in [Mo- (CO)3([16]aneS4)] and [WI(CO)3(Me8[16]aneS4-S,S9,S0)]}.9,102192 J. Chem. Soc., Dalton Trans., 1998, Pages 2191–2198 Alternatively the fourth sulfur atom could ligate to another vanadium atom, as in [{Cu(m-h1 :h3-([14]aneS4)}n],11 giving a polymer formulated as [{VCl2[m-h1 :h3-([16]aneS4)]}n]Cln.Unfortunately the compound was too insoluble for studies in solution or to obtain crystals for a definitive structural study. These thioether compounds are poorly soluble in common solvents; however, they are relatively stable in the solid state when contained in a dry, O2-free atmosphere. The binuclear [18]aneS6 complexes appear to be rather less stable to moist air than the trithioether compounds, decolourising readily upon exposure. The trithioether complexes are all constrained by the ligand geometry to be fac trisubstituted; however, in principle, [18]aneS6 could yield either mer- or fac-trisubstituted isomers.In fact, comparison of the IR and UV/VIS spectroscopic data for these compounds with those for all of the other complexes prepared suggests that they too are fac trisubstituted.In each case the IR spectra confirm the presence of the thioether ligand and in addition the chloro and bromo derivatives show peaks in the region 200–450 cm21 which are tentatively assigned as n(V]Cl) or n(V]Br). Owing to their poor solubilities and sensitivity to moisture, FAB and electrospray mass spectra proved unhelpful. However, IR and UV/VIS spectroscopy and microanalytical data were consistent with the proposed formulations. The UV/VIS spectrum of a vanadium(III) (d2) complex in octahedral symmetry is expected to show three spin-allowed d–d transitions.These correspond to, in order of increasing energy: 3T2g(F) �æ 3T1g(F) (v1), 3T1g(P) �æ 3T1g(F) (v2) and 3A2g(F) �æ 3T1g(F) (v3). Typically v3 is not observed, since it is obscured by much more intense charge-transfer transitions. While the local symmetry at VIII in the compounds reported here is approximately C3v, the absence of any discernible splitting of the d–d bands allows the spectra to be analysed in terms of Oh symmetry.The values of Dq and B were obtained from the appropriate Tanabe–Sugano diagram, and the data for the compounds in this work and some other octahedral vanadium( III) compounds for comparison are presented in Table 1. The individual values from such an analysis are not of high precision, but the usually reliable. The ligand field strengths for the thioether species reported here are higher than for [VCl3(thf)3] or [VCl3(MeCN)3],12 but lower than in the complex anion [V(CN)6]32.13 Also, Dq is higher in the vanadium( III) species than in the corresponding chromium(III) complexes.14–16 The vanadium(IV) species [VOCl2([9]aneS3)] 6 and [VOCl2- (ttob)] were prepared in high yield (>90%) as blue ([9]aneS3) or turquoise (ttob) solids by the direct reaction of the vanadium(IV) precursor [VOCl2(MeCN)2] with the appropriate thioether L9 in CH2Cl2 solution [reaction (3)].Their IR spectra [VOCl2(MeCN)2] 1 L9 æÆ [VOCl2(L9)] 1 2MeCN (3) Table 1 Electronic spectroscopic data for vanadium(III) thioether macrocyclic compounds a Compound [VCl3([9]aneS3)] [VBr3([9]aneS3)] [VI3([9]aneS3)] [VCl3([10]aneS3)] [VBr3([10]aneS3)] [(VCl3)2([18]aneS6)] [(VBr3)2([18]aneS6)] [VCl3(MeCN)3] c [VCl3(thf)3] c [VCl6]32 c [V(CN)6]32d Colour Pink Brick red Brown-black Pink Orange Pink Red Green Orange n& 1/ cm21 18 590 17 890 16 050 19 050 18 250 19 380 17 930 14 400 13 300 16 650 22 200 n& 2/ cm21 27 620 24 020 27 030 27 700 23 810 28 010 23 320 21 400 19 900 18 350 28 600 Dq/ cm21 1932 1857 1783 2048 1866 2064 1825 1550 1400 1265 2385 Bb/ cm21 690 502 770 640 445 635 445 540 553 513 550 a Recorded as a solid diluted with BaSO4 by diVuse reflectance.b C = 4.5B. c Taken from ref. 11. d Taken from ref. 12. clearly show the V]] O stretching band at ca. 960 cm21, as well as bands of the co-ordinated thioether. As expected for a vanadium(IV) (d1) species, [VOCl2(ttob)] is EPR active and shows a very broad resonance in the solid state (g = 1.995).X-Ray crystallography In view of the paucity of structural data on vanadium thioether compounds, single crystal X-ray determinations were undertaken on the vanadium(III) complex [VCl3([9]aneS3)] and the vanadium(II) compound [VI2(thf)([9]aneS3)]. The structure of [VCl3([9]aneS3)] (Fig. 1 and Table 2) shows the trithioether ligand bonded in a facial manner to the VIII, with the three chloride ligands completing the distorted octahedral geometry.A pseudo-threefold symmetry axis passes through the thioether ligand and the vanadium atom; the regularity of the ligand about this axis can be seen in Fig. 1, and mean dimensions in the ligand are listed in Table 3 with those of other complexes and in the free molecule. The angles subtended by the macrocycle at the vanadium atom, mean value 82.6(2)8, suggest that the nine-membered ring is too small to give an ideal octahedral co-ordination pattern.However, the Fig. 1 View of the structure of [VCl3([9]aneS3)] with the numbering scheme adopted Table 2 Selected molecular dimensions in the [9]aneS3 complexes of vanadium. Bond lengths are in Å, angles in 8; estimated standard deviations in parentheses V]S(1) V]S(2) V]S(3) V]X(4) V]X(5) V]X(6) S(1)]V]S(2) S(1)]V]S(3) S(1)]V]X(4) S(1)]V]X(5) S(1)]V]X(6) S(2)]V]S(3) S(2)]V]X(4) S(2)]V]X(5) S(2)]V]X(6) S(3)]V]X(4) S(3)]V]X(5) S(3)]V]X(6) X(4)]V]X(5) X(4)]V]X(6) X(5)]V]X(6) [VCl3([9]aneS3)] 2.469(2) 2.501(2) 2.515(2) X = Cl 2.277(2) X = Cl 2.304(2) X = Cl 2.296(2) 82.34(8) 83.03(8) 87.52(9) 86.68(8) 168.69(10) 82.32(8) 85.02(8) 166.31(9) 89.55(11) 165.09(9) 88.26(9) 88.10(10) 102.72(10) 99.66(11) 100.10(11) [VI2(thf)([9]aneS3)] Sample II 2.492(2) 2.490(2) 2.495(2) X = I 2.7961(14) X = I 2.8021(13) X = O 2.133(5) 84.03(8) 84.71(8) 90.02(6) 90.86(7) 172.9(2) 83.45(8) 89.23(6) 169.92(7) 90.1(2) 171.38(7) 87.44(6) 90.7(2) 99.48(4) 93.9(2) 94.4(2)J.Chem. Soc., Dalton Trans., 1998, Pages 2191–2198 2193 S ? ? ? S distances in the complex are slightly shorter than in the free thioether molecule 17 which has a very similar shape to that shown for the ligand; the angular requirements of the sulfur atoms are the most likely determining factor of the molecular geometry. The conformation of the molecule has been adjusted so that one of the lone pairs of electrons, in a tetrahedral arrangement, on each sulfur atom is pointing more directly at a common point (viz.the vanadium atom in the complex) than in the free molecule. The other co-ordinating atoms, chloride ions in this case, may also influence the distortions from the octahedral pattern. Two polymorphs of [VI2(thf)([9]aneS3)] were examined by X-ray crystallography. The analysis of sample I of this complex (blue-green plates) shows two virtually identical molecules in the crystal but the intensity data were from a weakly diVracting crystal and the results were not precise so they are not recorded nor discussed here.Therefore, the second sample (greenish blue prisms), II, was examined and showed the same molecular complex (Fig. 2 and Tables 2 and 3) but with more satisfactory dimensions. In each sample, the VII is co-ordinated to two terminal iodide ions, the oxygen atom of a thf ligand and the three sulfur atoms of the [9]aneS3 molecule. In sample II the thf ligand is disordered with two distinct orientations of the fivemembered ring; the oxygen atom site is common to both arrangements. Mean dimensions of the thioether ligands and its coordination to the vanadium atom in several complexes are shown in Table 3.The V]S distances in these vanadium-(II), -(III) and -(IV) compounds appear to be almost independent of the formal oxidation state of the vanadium centre. Evidently, there is a balance between the s and p components of the V]S bonding systems in these complexes which compensates for the variation of charge at the metal.Comparison of V]S separations in crown thioether complexes with other types of V]S bonds The shortest known V]S separations in monomeric complexes are in thiovanadyl groups e.g. in [VS(SPh)4]22 (2.078 Å) 19 and [VS(SCH2CH2S)2]22 (2.087 Å).20 The single-bond V]S separations in these anions are considerably longer, at 2.391 and 2.367 Å respectively, and these are typical of cases where the sulfur donor atom is from a thiolate(12) group.Other examples Fig. 2 View of the structure of [VI2(thf)([9]aneS3)], sample II, with the numbering scheme adopted. One of the two orientations of the disordered thf ligands is shown: the two molecules of [VI2(thf)([9]aneS3)], sample I, have very similar structures to that shown here include V]S at 2.378 Å in [VO(SCH2CH2S)2]22,21 2.32 Å (mean) in [V(SC6H2Pri 3-2,4,6)3(thf)2],22 2.290 Å (mean) in [V{N(CH2- CH2S)3}(NH3)],23 2.263 Å (mean) in [V{N(CH2CH2S)3}- (NNMe2)] 22 and 2.381 Å (mean) in [VO(L-O,S)2] (HL = 2-mercaptopyridine N-oxide).24 The complex [V(2-SC2H4SCH2CH2SCH2CH2C6H4S-2)(Me2- NCH2CH2NMe2)] 25 is the only structurally characterised complex where vanadium is ligated by both thiolate and thioether donor functions.In it all the V]S separations fall within the narrow range 2.476–2.485 Å, suggested to be due to electron delocalisation through the phenyl rings.25 These separations are considerably longer than those in vanadium thiolate complexes; they suggest that pure vanadium–thioether bonds should be longer still.In view of this the long V]S separations found in our crown thioether complexes [range 2.469(2)–2.515(2) Å] are not surprising. The other class of complex to which crown thioether vanadium compounds may be compared comprises iron– vanadium–sulfur clusters, which may be regarded as structural models for the vanadium site of vanadium nitrogenase. The geometry about the vanadium atom in clusters and in crown thioether complexes is directly comparable as there are three fac-ligating sulfur atoms in each case; thus both V]S separations and S]V]S angles can be compared. The most straightforward comparison may be made between the structure of [VCl3([9]aneS3)] and [VFe3S4Cl3(dmf)3]2 (containing vanadium essentially as VIII).26 Both have local C3v symmetry at vanadium, but the following remarks also apply to the other crown thioether complexes discussed in this paper and to other cluster complexes where dmf has been substituted by bipyridine or a diphosphine.27 In [VCl3([9]aneS3)] the mean V]S separation is 2.495(14) Å with a mean S]V]S angle of 82.6(2)8.The mean S ? ? ? S nonbonded distance is approximately 3.29(1) Å. In the cluster Table 3 Mean dimensions in the thioether ligands of [9]aneS3 complexes of vanadium. Distances are in Å, angles in 8. Standard deviations in parentheses [VCl3- ([9]aneS3)] [VI2(thf)- ([9]aneS3)] Sample II [VCl2O- ([9]aneS3)] 6 [9]aneS3 17 Metal co-ordination V]S S]V]S 2.495(14) 82.6(2) 2.492(1) 84.1(4) 2.53(4) a 81.2(9) In the thioether ligand S]Ci b S]Co b C]C C]S]C S]C1]Co Ci]Co]S S ? ? ?S 1.805(1) 1.815(6) 1.497(3) 102.6(2) 113.5(2) 115.5(7) 3.29(1) 1.833(5) 1.812(5) 1.509(8) 102.0(2) 113.2(4) 115.7(3) 3.338(12) 1.803(6) 1.797(4) 1.507(7) 102.6(3) 112.3(3) 115.0(3) 3.293(7) 1.820(5) 1.823(5) 1.510(6) 102.8(3) 113.0(4) 117.0(4) 3.451(2) Torsion angles S]C]C]S C]Co]S]C C]S]Ci]C 248.8(14) 264.6(12) 131(2) 250.9(12) 262.4(11) 132.0(6) 252.7(6) 261.2(7) 132.9(4) 2 58.5 55.1 131.1 a The mean (from values in two independent molecules) of two V]S (trans to O) at 2.634 and 2.653 Å and four V]S (trans to Cl) distances in the range 2.463–2.481 Å.b Subscripts ‘i’ and ‘o’ indicate the inand out-of-plane carbon atoms as identified by Blower and coworkers. 18 In the vanadium complexes each VS2C2 chelate ring has an envelope shape in which one atom is displaced from the almost planar group of the other four atoms; the out-of-plane atoms in each of our molecules are C(13), C(32) and C(21); the free [9]aneS2 molecule adopts a very similar shape.2194 J.Chem. Soc., Dalton Trans., 1998, Pages 2191–2198 Table 4 Vanadium K-Edge EXAFS structural data a for vanadium(III) thioether macrocyclic compounds Complex [VCl3([9]aneS3)] [VCl3([9]aneS3)] f [VBr3([9]aneS3)] [VI3([9]aneS3)] [VCl3([10]aneS3)] [VBr3([10]aneS3)] [VCl3(thf)3] [VBr3(thf)3] d(V]S) b/Å 2.498(4) 2.495(14) 2.486(4) 2.486(4) 2.411(11) 2.482(7) d(V]O)b/Å 2.044(9) 2.036(5) 2s2 c/Å2 0.0116(7) 0.0165(12) 0.0083(8) 0.0200(24) 0.0105(18) 0.0182(19) 0.0098(9) d(V]X)b/Å 2.309(2) 2.292(8) 2.472(2) 2.661(3) 2.283(8) 2.472(4) 2.344(6) 2.517(3) 2s2 c/Å2 0.0062(3) 0.0093(2) 0.0091(4) 0.0178(17) 0.0087(5) 0.0138(7) 0.0096(2) Rd 19.8 22.6 24.9 20.2 23.6 23.6 21.0 Fit index e 3.5 3.4 6.6 5.5 9.1 7.1 4.4 a Recorded in transmission mode on station 7.1, using powdered sample diluted with BN.b Standard deviations in parentheses. Note that the systematic errors in bond distances arising from data collection and analysis procedures are ±0.02–0.03 Å for well defined co-ordination shells. AFAC = 0.80 in all cases. c Debye–Waller factor. d Defined as [Ú(cT 2 cE)k3dk/ÚcEk3dk] × 100%. e Defined as Si[(cT 2 cE)ki 3]2. f Average bond distances from X-ray crystallographic data (see Table 2). [VFe3S4Cl3(dmf)3]2 the V]S separations are 2.338, 2.340 and 2.331 Å and S]V]S angles are 101.4, 102.2 and 102.38, the nonbonding S ? ? ? S distances being around 3.6 Å.The longer V]S separation in the crown thioether complexes is not due to the fact that the S3 plane has larger S ? ? ? S dimensions (in fact it has smaller dimensions). It reflects the much steeper nature of the pyramid (of which V is the apex and S3 is the base) in the crown thioether complex. In the cluster the V is much more firmly embedded in the S3 plane. If the data for all crown thioether compounds and all clusters are considered, it is seen that V]S separations are longer (by 6–8%) and S]V]S angles are smaller (80 against 1008) in crown thioethers than in clusters.The V]S separations in clusters resemble far more closely typical V]S separations in thiolates. Vanadium K-Edge EXAFS structural studies Owing to the limited solubilities displayed by many of the compounds isolated, and their sensitivity to moisture, in most cases crystals suitable for an X-ray study could not be obtained.However, given the lack of structural data on compounds of this type, vanadium K-edge EXAFS data were used to provide important structural information for the metal–ligand bond lengths in the first co-ordination sphere, i.e. d(V]S) and d(V]X). The spectroscopic studies carried out in parallel provided key information concerning the donor sets involved in these products. Details of the refined EXAFS data for the complexes are given in Table 4 and Fig. 3 shows a typical example. Vanadium K-edge EXAFS spectra were also recorded for the [VX3(thf)3] (X = Cl or Br) model compounds and for [VCl3- ([9]aneS3)] in order to compare the V]S and V]X distances derived from this method with the average values obtained from X-ray crystallographic studies noted above. These model compounds also allow us to check that the data treatment and analyses are satisfactory. The EXAFS data for the thf adducts, [VX3(thf)3], were satisfactorily modelled by a first shell of three oxygens giving V]O distances of 2.04 Å for both X = Cl and Br, with a second shell of three halides giving d(V]Cl) = 2.34 and d(V]Br) = 2.52 Å.In the case of [VCl3([9]aneS3)] the data were satisfactorily modelled by an S3Cl3 donor set with d(V]Cl) = 2.31, d(V]S) = 2.50 Å. These results correlate very well with the average V]S, V]O or V]X distances derived from the X-ray crystallographic studies, and provide further supporting evidence for the structures of the remaining compounds.For [VX3([9]aneS3)] and [VX3([10]aneS3)] the EXAFS data were modelled for three sulfurs and three halogen atoms (Cl, Br or I as appropriate). In all cases the EXAFS data gave d(V]S) values very similar to those obtained crystallographically for vanadium(III)–thioether interactions (ca. 2.5 Å) and signifi- cantly longer than d(V]Cl) (ca. 2.3 Å). This is consistent with the interaction between the hard vanadium(III) centre and the thioether functions being weak, as might be anticipated for such a hard metal–soft ligand combination.The V]Br and V]I bond lengths of ca. 2.45 and 2.66 Å respectively are in accord with the trend expected on the basis of the increasing size of the halogen. Furthermore, the VIII]I distances are shorter than the VII]I distances determined crystallographically for [VI2(thf)([9]aneS3)] (see above), consistent with the increase in oxidation state in the former, and hence smaller metal ion radius.We have also reported the preparation and structural characterisation (through EXAFS studies and X-ray crystallography) of a series of chromium(III) thioether and selenoether macrocyclic complexes.14,16 In the thioether species d (Cr]S) is ca. 2.4 Å, while d (Cr]X) is 2.3 Å for X = Cl and 2.45 Å for X = Br. Thus the metal–thioether distance is significantly shorter than in the vanadium species reported here, while for a given halogen the metal–halogen distances are virtually the same.Some reactions of [9]aneS3 compounds We have made a brief examination of the reactions of [VCl3([9]aneS3)] and [VI2(thf)([9]aneS3)]. We find that pyridine Fig. 3 (a) Background subtracted vanadium K-edge EXAFS data and (b) the corresponding Fourier transform for [VBr3([9]aneS3)] (solid line = experimental, dashed line = calculated data)J. Chem. Soc., Dalton Trans., 1998, Pages 2191–2198 2195 displaces the thioether ligands from these complexes to give [VCl3(py)3] and [VI2(py)4] respectively [reactions (4) and (5)].[VCl3([9]aneS3)] 1 C5H5N (excess) æÆ [VCl3(py)3] 1 [9]aneS3 (4) [VI2(thf)([9]aneS3)] 1 C5H5N (excess) æÆ [VI2(py)4] 1 [9]aneS3 (5) Neither thioether complex reacted with anhydrous HCl in thf and repeated attempts to obtain tractable products after reduction of these compounds with sodium or magnesium under N2 or H2 were unsuccessful. Conclusion These results illustrate that thioether ligands bond readily to vanadium; in particular [9]aneS3 is capable of stabilising vanadium-(II), -(III) and -(IV) centres, although the V]S interaction in each case is relatively weak.It is notable that within the vanadium series the V]S distances trans to halide are relatively insensitive to the vanadium oxidation state. The introduction of O-donor coligands such as thf into these compounds indicates that a wider variety of coligands with the S3 core can be anticipated in future studies.Experimental Infrared spectra were measured as Nujol mulls between CsI plates using Perkin-Elmer 883 or 983 spectrometers over the range 200–4000 cm21, UV/VIS spectra of samples diluted with BaSO4 were recorded by diVuse reflectance using a Perkin- Elmer Lambda 19 spectrophotometer. Microanalytical data were obtained from the University of Surrey Microanalytical Service, the University of Southampton (C, H and N), and the Butterworth Laboratories Ltd.(S). Magnetic moments were measured at 20 8C by the Faraday method, using Hg[Co- (NCS)4] as standard and making the usual diamagnetic corrections using Pascal’s constants. The EXAFS measurements were made at the Daresbury Laboratory, operating at 2.0 GeV with typical currents of 200 mA. Vanadium K-edge data were collected on station 7.1 using a silicon(111) order-sorting monochromator, with harmonic rejection achieved by stepping oV the peak of the rocking curve by 50% of full height level.Data were collected in transmission mode from samples diluted with boron nitride and mounted between Sellotape sheets in 1 mm aluminium holders. The compounds PMe2Ph, VCl3 and VBr3 were from Aldrich Chemical Co., as were some samples of [9]aneS3 and [16]aneS4; [VOCl2(H2O)2] was from BDH Chemical Co. Samples of [9]aneS3 28 and [16]aneS4,29 as well as Me8[16]aneS4 and ttob,30 were made by published procedures, as were the vanadium complexes [V2(m-Cl)3(thf)6]2[AlCl2Et2],7 [VCl3(thf)3],31 [VBr3- (thf)3],31 [VCl3(MeCN)3],32 [VO(acac)2],33 [VI2(thf)4],34 [VOCl2- (NCMe)2],35 and [VCl3(OPMe2Ph)(PMe2Ph)2].36 All reactions were performed in anhydrous solvents under an atmosphere of dry N2 using standard Schlenk techniques.Preparations Vanadium(II) complexes. [{V([9]aneS3)}2(m-Cl)3]Cl. The complex [{V(thf)3}2(m-Cl)3][AlCl2Et2] (0.65 g, 0.8 mmol) and [9]aneS3 (0.21 g, 1.2 mmol) were heated under reflux in CH2Cl2 (100 cm3) giving a purple solid which was filtered oV, washed with dichloromethane (2 × 20 cm3), diethyl ether and dried in vacuo.Yield 0.42 g, 85% (Found: C, 23.6; H, 4.0; S, 30.4. C6H12Cl2S3V requires C, 23.9; H, 4.0; S, 31.8%). meff = 3.5 mB. [VI2(thf)([9]aneS3)]. Solutions of [VI2(thf)4] (0.59 g, 1.0 mmol) in thf (20 cm3) and [9]aneS3 (0.18 mmol) in thf (5 cm3) were mixed. An immediate light blue precipitate was produced, and this was filtered oV, washed with thf and diethyl ether and dried in vacuo.Yield = 0.43 g, 77% (Found: C, 21.7; H, 3.6; S, 16.6. C10H20I2OS3V requires C, 21.5; H, 3.6; S, 17.2%). meff = 3.7 mB. [VI2(thf)(ttob)]. This complex was prepared in a similar manner and yield to the above, but using ttob instead of ([9]aneS3) (Found: C, 27.2; H, 3.5. C16H24I2OS2V requires C, 30.3; H, 3.8%). meff = 3.6 mB. [VI2(C5H5N)4]. A solution of pyridine (0.8 g, 10 mol) in thf (5 cm3) was added to a solution of [VI2(thf)4] (0.59 g, 1 mmol) in thf (20 cm3).Red crystals precipitated immediately. After an hour they were filtered oV, washed with thf and ether and dried in vacuo. Yield 0.57 g, 0.92 mmol, 92% (Found: C, 39.1; H, 3.3; N, 8.8. C20H20I2N4V requires C, 38.6; H, 3.2; N, 9.0%). meff = 3.6 mB. Vanadium(III) complexes. [VBr3(thf)3]. This compound was made by refluxing VBr3 in thf for 6 h, evaporating to dryness and recrystallising from thf–hexane in 85% yield (Found: C, 28.6; H, 4.5. Calc. for C12H24Br3O3V: C, 28.4; H, 4.7%).[VI3(thf)3]. A solution of [VI2(thf)4] (0.59 g, 1.0 mmol) in thf (40 cm3) and I2 (0.127 g, 0.5 mmol) in thf (10 cm3) were mixed at 0 8C. Black crystals quickly precipitated. After the flask was cooled at 220 8C overnight they were filtered oV and washed with thf and diethyl ether, yield 68% (Found: C, 22.4; H, 3.8; I, 59.7. C12H24I3O3V requires C, 22.2; H, 3.7; I, 58.8%). meff = 2.88 mB. [VCl3([9]aneS3)]. The complex [VCl3(thf)3] (0.75 g, 2.0 mmol) was treated with [9]aneS3 (0.43 g, 2.0 mmol) in refluxing toluene, thf or CH2Cl2 (120 cm3) for 1 h, giving a pink solid which was isolated by filtration, washed with thf and hexane, and dried in vacuo.Yield = 0.64 g, 94% (Found: C, 21.3; H, 3.6; S, 29.2. C6H12Cl3S3V requires C, 21.3; H, 3.6; S, 28.5%). IR spectrum (Nujol): 1402s, 840m, 350m and 320w cm21. meff = 2.55 mB. Similar reaction of [VCl3(MeCN)3] or [VCl3(OPMe2Ph)- (PMe2Ph)2] with [9]aneS3 also yielded [VCl3([9]aneS3)] in high yield.[VBr3([9]aneS3)]. Method as for [VCl3([9]aneS3)] above, using [VBr3(thf)3] (0.142 g, 0.28 mmol) and [9]aneS3 (0.05 g, 0.28 mmol), giving a brown solid. Yield = 0.09 g, 68% (Found: C, 15.3; H, 2.7; S, 19.4. C6H12Br3S3V requires C, 15.5; H, 2.5; S, 20.4%). IR (Nujol mull): 1404s, 826m and 306w cm21 [n(V]Br)]. meff = 2.59 mB. [VI3([9]aneS3)]. Method 1. The complex [VI2(thf)4] (0.40 g, 0.67 mmol) and I2 (0.084 g, 0.33 mmol) were heated to reflux in thf solution (80 cm3) and then filtered. To the cooled solution was added [9]aneS3 (0.12 g, 0.67 mmol) in thf (20 cm3), resulting in the immediate precipitation of a dark brown-black powder which was filtered oV, washed with thf and diethyl ether and dried.Yield 0.2 g, 48% (Found: C, 12.1; H, 2.1. C6H12I3S3V requires C, 11.8; H, 2.0%). IR (Nujol mull): 1404s and 826m cm21. Method 2. Trimethylsilyl iodide (2 cm3) was added to a mixture of [VCl3(NCMe)3] (0.27 g, 1.0 mmol) and [9]aneS3 (0.18 g, 1 mmol) in MeCN (25 cm3).The mauve precipitate dissolved and the mixture was distilled to 50% volume to expel SiMe3Cl. The residue was then cooled to give a dark precipitate which was filtered oV, washed with MeCN and diethyl ether and dried in vacuo. Yield 0.3 g, 74% (Found: C, 12.1; H, 2.1; S, 15.7. C6H12I3S3V requires C, 11.8; H, 2.0; S, 15.7%). meff = 2.80 mB. [VCl3([10]aneS3)]. Method as for [VCl3([9]aneS3)] above, using VCl3 (0.34 mmol) and [10]aneS3 (0.066 g, 0.34 mmol), giving a pink solid.Yield = 0.097 g, 81% (Found: C, 23.4; H, 3.9. C7H14Cl3S3V requires C, 23.9; H, 4.0%). IR (Nujol mull): n(V]Cl) 440s (br) cm21. [VBr3([10]aneS3)]. Method as for [VCl3([9]aneS3)] above, using [VBr3(thf)3] (0.103 g, 0.20 mmol) and [10]aneS3 (0.039 g, 0.20 mmol), giving an orange solid. Yield 0.064 g, 66% (Found: C, 17.0; H, 3.1. C7H14Br3S3V requires C, 17.3; H, 2.9%). IR (Nujol mull): n(V]Br) 329w and 305 (br) cm21.2196 J. Chem. Soc., Dalton Trans., 1998, Pages 2191–2198 [(VCl3)2(m-[18]aneS6)].Method as for [VCl3([9]aneS3)] above. using VCl3 (0.56 mmol) and [18]aneS6 (0.025 g, 0.28 mmol), giving a pink solid. Yield 0.12 g, 64% (Found: C, 20.9; H, 3.5. C6H12Cl3S3V requires C, 21.3; H, 3.6%). IR (Nujol mull): 858m, 353 (br) m and 288w cm21. [(VBr3)2(m-[18]aneS6)]. Method as for [VCl3([9]aneS3)] above, using [VBr3(thf)3] (0.05 g, 0.099 mmol) and [18]aneS6 (0.018 g, 0.049 mmol), giving a brown solid. Yield 0.031 g, 67% (Found: C, 15.1; H, 2.6.C6H12Br3S3V requires C, 15.3; H, 2.5%). IR (Nujol mull): n(V]Br) 315m and 296w cm21. [VCl3(ttob)]. The complex [VCl3(thf)3] (0.087 g, 0.23 mmol) and ttob (0.059 g, 0.23 mmol) were heated to reflux in CH2Cl2 solution (25 cm3) for 15 min. The resulting pink solid was filtered oV, washed with CH2Cl2 and hexane and dried in vacuo. Yield 0.085 g, 90% (Found: C, 34.6; H, 3.9; S, 23.0. C12H16Cl3S3V requires C, 34.8; H, 3.9; S, 23.2%). meff = 2.76 mB. Vanadium(IV) complexes. [VOCl2([9]aneS3)].Method 1. The complex [VOCl2(MeCN)2] (0.122 g, 0.55 mmol) was dissolved in CH2Cl2 (30 cm3) to give a blue solution, [9]aneS3 (0.099 g, 0.5 mmol) was then added, and stirring for 1 h gave a blue precipitate which was filtered oV, washed with thf and diethyl ether and dried in vacuo. Yield 0.16 g, 95% (Found: C, 22.5; H, 3.7; S, 29.5. Calc. for C6H12Cl2OS3V: C, 22.6; H, 3.7; S, 30.2%). IR spectrum (Nujol mull): n(V]] O) 962 cm21. Method 2. The complex [VO(acac)2] (0.294 g, 1.10 mmol) was dissolved in toluene (50 cm3), MeOH (0.23 cm3, 5.6 mmol) and SiMe3Cl (0.70 cm3, 5.6 mmol) were added, giving a dark green solution.The compound [9]aneS3 (0.200 g, 1.10 mmol) was then added and the resulting blue suspension was refluxed for 45 min before filtering. The residue was washed with CH2Cl2, thf and diethyl ether and dried in vacuo. Yield 0.29 g, 95% (Found: C, 22.6; H, 3.6; S, 29.7. Calc. for C6H12Cl2OS3V: C, 22.6; H, 3.7; S, 30.2%). meff = 1.73 mB.[VOCl2(ttob)]. The complex [VOCl2(MeCN)2] (0.18 g, 0.82 mmol) and ttob (0.21 g, 0.82 mmol) were stirred in CH2Cl2 solution for 1 h to give a pale turquoise suspension. The precipitate was then filtered oV, washed with CH2Cl2 and thf and dried in vacuo. Yield 0.29 g, 90% (Found: C, 36.3; H, 4.1; S, 24.2. C12H16Cl2OS3V requires C, 36.5; H, 4.1; S, 24.4%). meff = 1.85 mB. IR spectrum (Nujol mull): n(V]] O) 982; n(V]Cl) 415 cm21. Reactions of [9]aneS3 complexes [VI2(thf)([9]aneS3)] with pyridine.A solution of pyridine (0.6 g, 7.5 mmol) in thf (5 cm3) was added to a suspension of [VI2- (thf)([9]aneS3)] (0.41 g, 0.75 mmol) in thf (20 mmol). There was an immediate red colour. The mixture was refluxed for 4 h then the suspension of red product was cooled and the product filtered oV, washed with thf and ether, dried in vacuo and identified by its IR spectrum as [VI2(py)4]. Yield 0.35 g (0.56 mmol, 75%). The filtrate was taken to dryness and the crude residue identified as [9]aneS3 by its IR spectrum (80% yield).[VCl3([9]aneS3)] with pyridine. In a similar reaction to the above, treatment of [VCl3([9]aneS3)] gave [VCl3(py)3] 37 and [9]aneS3 in 85% yield. Neither [9]aneS3 complex reacted with anhydrous HCl in thf even at reflux and repeated attempts to obtain tractable products after reduction of these compounds with sodium or magnesium under N2 or H2 in thf were unsuccessful. X-Ray crystallography The crystallographic data for the three samples are presented in Table 5.[VCl3([9]aneS3)]. Ruby-red crystals suitable for X-ray analysis were obtained by mixing filtered solutions of [VCl3- (MeCN)3] and [9]aneS3 (0.05 mmol of each) in MeCN (125 cm3). The solution turned red over 15 min and red needles grew over 3 d. The same reaction carried out in thf, CH2Cl2 or MeOH did not give satisfactory crystals. A ruby-red, square prism crystal, was mounted on a glass fibre, examined photographically, then transferred to an Enraf- Nonius CAD4 diVractometer (with monochromated radiation) for determination of accurate cell parameters and measurement of diVraction intensities (1125 unique reflections to qmax = 258, 846 ‘observed’ with I > 2sI).Intensities were corrected for absorption (by semiempirical y-scan methods) and to eliminate negative net intensities (by Bayesian statistical methods); no deterioration correction was necessary. The structure was determined by direct methods in SHELXS.38 Refinement was by full-matrix least-squares methods, initially on F in SHELX,39 then on F2 in SHELXL.40 Hydrogen atoms were included in idealised positions but with independent Uiso.All the non-hydrogen atoms were refined anisotropically. The polarity of the crystal was checked by refinement of the structure at 1 2 x, 0.5 2 y, 1 2 z; this gave marginally lower R factors, but a significantly lower Flack parameter,40 viz. 0.01(7) vs. 0.18(7). Scattering factor curves for neutral atoms were taken from ref. 41. Computer programs used in this analysis have been noted above or in Table 4 of ref. 42, and were run on a DECAlphaStation 200 4/100 computer in the Nitrogen Fixation Laboratory, John Innes Centre. [VI2(thf)([9]aneS3)]. Two polymorphs were obtained from the same recrystallisation solution, dark greenish blue plates (sample I) and dark greenish blue prisms (sample II). Crystals of each were mounted on glass fibres and sealed with epoxy resin.Photographic and diVractometric procedures similar to those described above were followed. Both crystals showed a decline in the intensities of three reflections monitored throughout the data collections, and the intensities of each were corrected accordingly. The structures of both were solved by direct methods in SHELXS38 and refined, on F2 in SHELXL.40 In sample I there are two independent, virtually identical molecules in the crystal. The intensity data for this crystal were, overall, rather weak and there were few ‘observed’ data.The results from the refinement are not precise, and sample II was examined for better results. In sample II the thf ligand is disordered approximately equally in two distinct orientations; the O atom is common to both orientations and the planes of the four carbon atoms in the two arrangements diVer by a rotation of ca. 458 about the V]O bond. The carbon atoms of the thf ligands were refined isotropically and their hydrogen atoms included in idealised positions, all parameters riding on those of the parent atoms.The remaining non-hydrogen atoms were refined anisotropically, and the hydrogen atoms in the [9]aneS3 ligand included in calculated positions with freely refined Uiso. CCDC reference number 186/1005. EXAFS Refinements Typically two or three data sets were collected for each complex and the analyses carried out on the averaged spectra. The raw data were background-subtracted using the program PAXAS43 by fitting a six- or eight-order split polynomial to the pre-edge subtracted spectrum between k = 2 and 13–15 Å21.Curve fitting was carried out using the program EXCURV 92.44 Ground state potentials of the atoms were calculated using Von Barth theory and phase shifts using Hedin–Lundqvist potentials. Two shells (3S and 3X) were fitted in each case. Refinements were also carried out using 6S or 6X, as well as other combinations, and in the case of X = Br or I the results clearly supported the S3Br3 or S3I3 donor sets expected. In the case of the chlorine derivatives, the very similar back scattering from S and Cl made the assignment of the donor set diYcult on the basis of the EXAFSJ.Chem. Soc., Dalton Trans., 1998, Pages 2191–2198 2197 Table 5 Crystallographic data for [VCl3([9]aneS3)] and [VI2(thf)([9]aneS3)] a [VI2(thf)([9]aneS3)] Complex Elemental formula M Crystal system, space group (no.) a/Å b/Å c/Å b/8 U/Å3 Z Dc/g cm23 F(000) m(Mo-Ka)/cm21 Crystal colour, shape Crystal size/mm On diVractometer: q range for centred reflections/8 qmax for data collection/8 h, k, l ranges Crystal degradation (% overall) Absorption: transmission factor range Total no.reflection measured (not including absences) Rint for equivalents Total no. unique reflections No. ‘observed’ reflections (I > 2sI) Refinement: final R1 final wR2 no. reflections used R1 for the ‘observed’ data goodness of fit (on F 2), S reflections weighted, w = Final diVerence map highest peaks/ e Å23, location [VCl3([9]aneS3)] C6H12Cl3S3V 337.6 Tetragonal, I41cd (no. 110) 17.2808(10) 17.2808 16.4654(11) 4917.0(5) 16 1.824 2720 19.2 Ruby-red, square prisms with good faces/edges 0.035 × 0.035 × 0.52 10–11 25 0–20, 0–20, 0–19 0 0.042–0.063 2189 0.035 1125 846 0.052 0.069 1125 (all data) 0.037 1.003 s22(Fo 2) 0.5, close to the V atom Sample I C10H20I2OS3V 557.2 Monoclinic, P21/n (equiv. to no. 14) 7.8864(10) 33.284(4) 13.2548(14) 95.144(10) 3465.2(7) 8 2.136 2120 44.8 Dark greenish blue plates 0.88 × 0.24 × 0.04 10–11 20 0–7, 0–32, 212 to 12 39 0.58–0.79 3478 0.057 3187 1710 0.133 0.261 3184 (all but 3 suspect) 0.081 1.057 [s2(Fo 2) 1 (0.152P)2]21 b 1.5, near the I ligands Sample II C10H20I2OS3V 557.2 Monoclinic, B21/c (equiv.to no. 14) 16.0550(12) 8.6760(10) 24.975(3) 91.681(8) 3477.3(6) 8 2.128 2120 44.7 Dark greenish blue prisms 0.23 × 0.14 × 0.12 10–11 23 0–17, 0–9, 227 to 27 12 0.84–0.99 2511 0.015 2406 1811 0.055 0.083 2406 (all data) 0.037 1.062 [s2(Fo 2) 1 23.6P]21 b 1.3, close to an I ligand a Details in common: 293 K, l(Mo-Ka) 0.710 69 Å. b P = (Fo 2 1 2Fc 2)/3.data alone, although a better fit was obtained using two shells (3S and 3Cl) and, in addition, the UV/VIS and IR spectroscopic data provide very strong evidence for the donor sets chosen. The distances and Debye–Waller factors were refined for all the shells, as well as the Fermi energy diVerence.No attempt was made to refine the carbons of the ligand backbones since these occur over a range of distances and are not expected to be well defined. Acknowledgements We thank the BBSRC for support and the EPSRC for an Earmarked Studentship (to S. J. A. P.). We also thank the Director of the SRS at Daresbury for the use of the facilities and are indebted to Dr. W. Levason (University of Southampton) for help in collecting the EXAFS data. References 1 R.R. Eady, Chem. Rev., 1996, 96, 3013 and refs. therein. 2 J. F. Reynolds, W. R. Briggs and J. C. Fetzer, Liq. Fuel Technol., 1985, 3, 423. 3 J. M. Arber, B. R. Dobson, R. R. Eady, P. Stevens, S. S. Hasnain, C. D. Garner and B. E. Smith, Nature (London), 1987, 325, 372. 4 T. Yoshida, T. Adachi, T. Ueda, M. Kaminaka, N. Sasaki, T. Higuchi, T. Aoshima, I. Mega, Y. Mizobe and M. Hidai, Angew. Chem., Int. Ed. 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Received 30th March 1998; Paper 8/02404I

ISSN:1477-9226    

DOI:10.1039/a802404i

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2197–2203 2197 Oxygenation of heterodinuclear di(Ï-phenoxo) CoIIMII (M 5 Mn, Fe or Co) complexes having a “Co(salen)” entity in a macrocyclic framework † Hideki Furutachi,*a Shuhei Fujinami,a Masatatsu Suzuki a and Hisashi O— kawa*b a Department of Chemistry, Faculty of Science, Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan b Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan Received 19th April 1999, Accepted 18th May 1999 Heterodinuclear di(m-phenoxo) CoIIMII complexes [CoM(L)(AcO)]ClO4 (M = Mn 1, Fe 2 or Co 3) and [CoM(L)(NCS)]ClO4 (M = Mn 4, Fe 5 or Co 6) have been obtained where L22 is a heterodinucleating macrocycle derived by the 2:1:1 condensation of 2,6-diformyl-4-methylphenol, ethylenediamine and diethylenetriamine and has a “salen”-like N2O2 metal-binding site and a “saldien”-like N3O2 site sharing the phenolic oxygens.The CoM(AcO) complexes 1 and 3 show reversible oxygenation at 0 8C in dmf, whereas 2 is irreversibly oxidized under the same conditions.The structures of the dioxygen adducts of 1 and 3 have been determined by X-ray crystallography. In that of 1, [{CoMn(L)(AcO)}2(O2)][ClO4]2?4CH3CN oxy-1, the Co resides in the “salen” site and the Mn in the “saldien” site. An exogenous acetate group bridges the two metal ions in the h1 :h1 mode together with the two phenolic oxygens. The peroxo group bridges two {CoMn(L)(AcO)} molecules at the Co forming a Co–O–O–Co linkage.The peroxo O(1)–O(2) bond distance is 1.416(5) Å and the Co(1) ? ? ? Co(2) intermetallic separation is 4.359(1) Å. The geometry about the Co is pseudo octahedral with a peroxo oxygen and an acetate oxygen at the axial sites and the Mn has a distorted six-co-ordination. The dioxygen adduct of 3, [{Co2(L)(AcO)}2(O2)][ClO4]2? 4CH3CN oxy-3, is isomorphous with oxy-1: the peroxo O(1)–O(2) bond distance is 1.415(4) Å and the Co(1) ? ? ? Co(3) intermetallic separation is 4.3527(8) Å.Within the CoM(NCS) complexes 4–6, 4 shows reversible oxygenation at 230 8C, whereas irreversible oxidation is observed for 5 and 6. Introduction Dioxygen binding and activation on dinuclear metal complexes are of current interest relating to the physiological metabolism of dioxygen at bimetallic biosites.1–5 Oxygenation of homodinuclear metal complexes like CuICuI 4 and FeIIFeII 5 have been extensively studied with the aim of providing models for hemocyanin and hemerythrin, but less attention has been paid to oxygenation of heterodinuclear complexes.6–9 It is well known that dioxygen reduction in cytochrome c oxidase is promoted by a CuFe pair in close proximity,10,11 and this has stimulated studies of the oxygenation behaviour of heterodinuclear complexes having diVerent combinations of metal ions.Recently some CuFe and CoCu complexes have been prepared and their oxygenation behaviour examined,8,9 but such studies are still limited because of the diYculty in preparing suitable heterodinuclear core complexes. The phenol-based compartmental ligand L22, having a “salen”-like N2O2 metal-binding site and a “saldien”-like N3O2 site sharing the phenolic oxygen, was developed in our laboratory for the study of heterodinuclear complexes (H2salen = N,N9-bis(salicylidene)ethylenediamine; H2saldien = N,N0-bis- (salicylidene)diethylenetriamine).12–21 Since [Co(salen)] is well known for its reactivity toward dioxygen,22,23 the dinuclear CoIIMII complexes with CoII in the “salen”-like site of the macrocycle are of great interest for studying oxygenation at the “Co(salen)” center with respect to the participation of the adjacent metal(II) ion.† Supplementary data available: ORTEP drawing of part of oxy-3, electronic spectra of 1–5. For direct electronic access see http : // www.rsc.org/suppdata/dt/1999/2197/, otherwise available from BLDSC (No.SUP 57560, 9 pp.) or the RSC Library. See Instructions for Authors, 1999, Issue 1 (http://www.rsc.org/dalton). Previously we reported the synthesis and the structures of the CoIIMII complexes [CoM(L)(AcO)]ClO4 (M = Mn 1, Fe 2 or Co 3) and [CoM(L)(NCS)]ClO4 (M = Mn 4, Fe 5 or Co 6).16 They have a di(m-phenoxo) CoIIMII core with the CoII in the “salen” site and the MII in the “saldien” site. The MII in the “saldien” site largely deviates from the mean molecular plane, leaving the “closed” and the “open” faces for dioxygen.In complexes 1–3 an acetate group is involved in an additional bridge at the closed face (Scheme 1, (a)), leaving only the open face of “Co(salen)” for oxygenation. Complexes 4–6 assume a chain structure extended by a thiocyanate bridge in the solid but a discrete dinuclear core structure with isothiocyanato donation to the MII in solution. Thus, both the closed and open faces of “Co(salen)” are available for oxygenation of 4–6 (Scheme 1, (b)).The oxygenation behaviour of 1–6 has now been studied in dmf by means of visible and EPR methods and discussed in view of the dinuclear core structure and the participation of the neighboring metal(II) ion. A part of this work was briefly reported previously.19 O– CH3 O– CH3 N N N NH N (L)2–2198 J. Chem. Soc., Dalton Trans., 1999, 2197–2203 Experimental Measurements Elemental analyses of C, H and N were obtained from the Service Center of Elemental Analysis at Kyushu University.Infrared spectra were recorded on a JASCO IR-810 spectrophotometer using KBr discs, electronic spectra in dmf or acetonitrile (ª1 × 1023 M) on Shimadzu MPS-2000 and UV- 3100 spectrophotometers and X-band EPR spectra on a JEOL JEX-FE3X spectrometer at liquid nitrogen temperature. Preparation The complexes [CoM(L)(AcO)]ClO4 (M = Mn 1, Fe 2 or Co 3) and [CoM(L)(NCS)]ClO4 (M = Mn 4, Fe 5 or Co 6) were prepared by methods in our previous paper.16 Oxygenation studies A dmf solution of a CoIIMII complex was prepared in a nitrogen or argon atmosphere and the reactivity towards dioxygen examined by means of electronic and EPR spectroscopy.The oxygenated complexes of 1 and 3, [{CoMn(L)(AcO)}2(O2)]- [ClO4]2?4CH3CN (oxy-1) and [{Co2(L)(AcO)}2(O2)][ClO4]2? 4CH3CN (oxy-3), were isolated as good crystals when each oxygenated solution in acetonitrile was diVused with diethyl ether at 230 8C. Found: C, 41.83; H, 4.39; N, 9.37.Calc. for C26H34ClCoMnN5O11 oxy-1: C, 42.09; H, 4.62; N, 9.44. Found: C, 42.38; H, 4.35; N, 9.49. Calc. for C52H66Cl2Co4N10O21 oxy-3: C, 42.38; H, 4.51; N, 9.50%. The oxidized complex of 6, [Co2(L)(NCS)(OH)]ClO4?1.5H2O 69, was obtained as brown crystals when an oxygenated dmf solution of 6 in the presence of an excess of NaClO4 was diVused with 2-propanol at 230 8C. Calc. for C25H31- ClCo2N6O8.5S: C, 40.75; H, 4.24; N, 11.40. Found: C, 40.69; H, 4.29; N, 11.55%.X-Ray crystallography Single crystals of complexes oxy-1 and oxy-3 were picked up on a hand-made cold copper plate mounted inside a liquid N2 Dewar vessel and mounted on a glass rod at 280 8C. Measurements were made on a Rigaku RAXIS-IV imaging plate area detector using graphite monochromated Mo-Ka radiation (l = 0.71070 Å) at 280 8C. Crystal-to-detector distance was 120 mm. In order to determine the cell constants and the orientation matrix, three oscillation photographs were taken with oscillation angle 28 and exposure time of 8 min for oxy-1 and 6 min for oxy-3 for each frame.The accurate unit-cell parameters used for the refinement were determined by least-squares calculations on the setting angles for 25 reflections with 2q = 22.08– 24.768 for oxy-1 and 25.20–29.178 for oxy-3 collected on a Rigaku AFC7R diVractometer with graphite monochromated Mo-Ka radiation and a rotating anode generator. Intensity data were collected by taking oscillation photographs (total oscillation range 1628, 54 frames, oscillation angle 38, and exposure time 18 min for oxy-1, 1658, 55 frames, 38, and 10 min Scheme 1 Possible oxygenation sites of CoM(AcO) 1–3 and CoM- (NCS) 4–6 complexes.N O N N N M N O Co N N N M N O Co SCN N O O O open face open face closed face (a) CoMAcO core (b) CoMNCS core for oxy-3). The data were corrected for Lorentz-polarization eVects, but not for absorption. The structure was solved by direct methods and expanded using Fourier techniques.Nonhydrogen atoms were refined anisotropically. Hydrogen atoms were included but not refined. The final cycle of full-matrix least-squares refinement was based on observed reflections (I > 3.00s(I)). Crystal data and details of the structure determinations are summarized in Table 1. CCDC reference number 186/1470. See http://www.rsc.org/suppdata/dt/1999/2197/ for crystallographic files in .cif format. Results and discussion [CoMn(L)(AcO)]ClO4 1 and [Co2(L)(AcO)]ClO4 3 These complexes have similar oxygenation behaviours. Introduction of dioxygen into a dmf solution of 1 at 0 8C caused an immediate change from red to dark red, suggesting formation of an oxygenated complex.Complex 1 shows an intense absorption band at 362 nm (e 10500 M21 cm21) and weaker bands near 460 (shoulder) and 560 nm (e 990 M21 cm21) (Fig. 1a) whereas its oxygenated complex shows an intense band at 382 nm (e 11750 M21 cm21) and an enhanced band at 550 nm (e 1700 M21 cm21) (Fig. 1b). The latter band of moderate intensity is characteristic of cobalt–dioxygen complexes and can be attributed to a LMCT band.22–24 The oxygenated complex was stable at 0 8C for several days. When the oxygenated solution was purged with argon the original red solution was recovered. The reversible oxygenation/deoxygenation cycle for 1 is confirmed by observing the electronic spectral interconversion between traces a and b (Fig. 1). A similar reversible oxygenation/ deoxygenation has been established for 3 at 0 8C (UV-vis: 3, 365 (e 10000), 480 (shoulder) and 565 nm (e 1100); oxygenated complex of 3, 392 (e 11200) and 560 nm (e 1500 M21 cm21)).19 In order to characterize the oxygenated complex in solution, EPR spectra of the oxygenated solution of 1 were studied (Fig. 1, insert). The observed isotropic EPR signal near g ª 2.0 has a well resolved six-line hyperfine structure attributable to isolated MnII (Aiso = 90 G).This result demonstrates that the oxygenated complex is a peroxo dimer having the MnIICoIII–O– O–CoIIIMnII linkage. This was demonstrated by X-ray crystallography for [{CoMn(L)(AcO)}2(O2)][ClO4]2?4CH3CN (oxy-1) and [{Co2(L)(AcO)}2(O2)][ClO4]2?4CH3CN (oxy-3) isolated from the oxygenated solutions of 1 and 3, respectively. An ORTEP25 drawing of the cationic part of [{CoMn(L)- (AcO)}2(O2)][ClO4]2?4CH3CN oxy-1 with 30% probability thermal ellipsoids is shown in Fig. 2 together with the atomnumbering scheme and the framework of the complex.Relevant bond distances and angles are given in Table 2. The cation Fig. 1 Electronic spectra for complex 1 in dmf: (a) in the absence of O2. (b) oxygenated at 0 8C. Insert: EPR spectrum of the oxygenated species in dmf at liquid nitrogen temperature.J. Chem. Soc., Dalton Trans., 1999, 2197–2203 2199 consists of two {CoMn(L)(AcO)} entities and a peroxo group; four acetonitrile molecules and two perchlorate ions are free from co-ordination and captured in the lattice.The {CoMn(L)(AcO)} part is very similar to the di(m-phenoxo)- (m-acetato) CoMn core of 1,16 having the Co in the “salen” site and the Mn in the “saldien” site. The acetate group bridges the metal ions at the closed face. Oxygenation occurs at the open face of “Co(salen)”, trans to the bridging acetate oxygen, forming a m-h1 :h1 peroxo dimer with a Mn(1)Co(1)–O(1)–O(2)– Co(2)Mn(2) linkage; the Co(1) ? ? ? Co(2) intermetallic separation is 4.359(1) Å.The two {CoMn(L)(AcO)} parts in oxy-1 are not equivalent; the Co(1) ? ? ? Mn(1) and Co(2) ? ? ? Mn(2) intermetallic separations are 3.124(1) and 3.123(1) Å, respectively. The peroxo O(1)–O(2) bond distance is 1.416(5) Å that is long relative to those of [{Co(salen)(dmf)}2(O2)] (1.339(6) Å)22e,26 and [{Co(salen)(pip)}2(O2)] (1.383(7) Å; pip = Fig. 2 (a) An ORTEP drawing of the [{CoMn(L)(AcO)}2(O2)]21 part of oxy-1 with the atom numbering scheme.(b) The framework of oxy-1. piperidine).22e,27 Instead, the Co(1)–O(1) and Co(2)–O(2) bond distances (1.866(4) and 1.849(4) Å, respectively) are shortened relative to those of the Co(salen) peroxo complexes (1.909(5)– Table 1 Crystallographic data for [{CoM(L)(AcO)}2(O2)][ClO4]2? 4CH3CN (M = Mn, oxy-1; Co, oxy-3) oxy-1 oxy-3 Formula M Crystal size/mm Crystal system Space group a/Å b/Å c/Å a/ 8 b/ 8 g/ 8 U/Å3 Z Dc /g cm23 m/cm21 No. reflections No of data used (I > 3.00s(I)) No.variables RR 9 C60H72Cl2Co2Mn2N14O18 1575.96 0.20 × 0.10 × 0.10 Triclinic P1� 15.296(4) 17.578(5) 14.224(3) 99.57(2) 113.00(2) 80.14(2) 3447(1) 2 1.518 9.87 10375 7271 884 0.051 0.066 C60H72Cl2Co4N14O18 1583.95 0.50 × 0.25 × 0.15 Triclinic P1� 14.833(2) 17.962(2) 13.820(3) 98.656(9) 110.540(8) 82.378(9) 3395.9(7) 2 1.549 11.19 11147 9158 884 0.058 0.083 Table 2 Selected bond distances (Å) and angles (8) of [{CoMn(L)- (AcO)}2(O2)][ClO4]2?4CH3CN oxy-1 Co(1)–O(1) Co(1)–O(4) Co(1)–N(1) Co(2)–O(2) Co(2)–O(8) Co(2)–N(6) Mn(1)–O(3) Mn(1)–O(5) Mn(1)–N(4) Mn(2)–O(7) Mn(2)–O(9) Mn(2)–N(9) O(1)–Co(1)–O(3) O(1)–Co(1)–O(6) O(1)–Co(1)–N(2) O(3)–Co(1)–O(6) O(3)–Co(1)–N(2) O(4)–Co(1)–N(1) O(6)–Co(1)–N(1) N(1)–Co(1)–N(2) O(2)–Co(2)–O(8) O(2)–Co(2)–N(6) O(7)–Co(2)–O(8) O(7)–Co(2)–N(6) O(8)–Co(2)–O(10) O(8)–Co(2)–N(7) O(10)–Co(2)–N(7) O(3)–Mn(1)–O(4) O(3)–Mn(1)–N(3) O(3)–Mn(1)–N(5) O(4)–Mn(1)–N(3) O(4)–Mn(1)–N(5) O(5)–Mn(1)–N(4) N(3)–Mn(1)–N(4) N(4)–Mn(1)–N(5) O(7)–Mn(2)–O(9) O(7)–Mn(2)–N(9) O(8)–Mn(2)–O(9) O(8)–Mn(2)–N(9) O(9)–Mn(2)–N(8) O(9)–Mn(2)–N(10) N(8)–Mn(2)–N(10) Co(1)–O(3)–Mn(1) Co(2)–O(7)–Mn(2) 1.866(4) 1.918(4) 1.881(5) 1.849(4) 1.921(4) 1.875(5) 2.189(4) 2.119(4) 2.379(4) 2.195(4) 2.109(4) 2.385(5) 89.0(2) 173.0(2) 88.7(2) 94.2(1) 177.2(2) 177.6(2) 87.9(2) 85.3(2) 90.9(2) 90.2(2) 86.6(1) 92.8(2) 90.3(2) 95.4(2) 91.0(2) 72.0(1) 147.3(1) 79.1(2) 79.9(1) 129.0(1) 84.6(1) 75.6(2) 74.1(2) 84.3(1) 132.7(2) 89.1(1) 152.9(2) 108.2(2) 133.4(2) 107.0(2) 98.8(2) 98.2(2) Co(1)–O(3) Co(1)–O(6) Co(1)–N(2) Co(2)–O(7) Co(2)–O(10) Co(2)–N(7) Mn(1)–O(4) Mn(1)–N(3) Mn(1)–N(5) Mn(2)–O(8) Mn(2)–N(8) Mn(2)–N(10) O(1)–Co(1)–O(4) O(1)–Co(1)–N(1) O(3)–Co(1)–O(4) O(3)–Co(1)–N(1) O(4)–Co(1)–O(6) O(4)–Co(1)–N(2) O(6)–Co(1)–N(2) O(2)–Co(2)–O(7) O(2)–Co(2)–O(10) O(2)–Co(2)–N(7) O(7)–Co(2)–O(10) O(7)–Co(2)–N(7) O(8)–Co(2)–N(6) O(10)–Co(2)–N(6) N(6)–Co(2)–N(7) O(3)–Mn(1)–O(5) O(3)–Mn(1)–N(4) O(4)–Mn(1)–O(5) O(4)–Mn(1)–N(4) O(5)–Mn(1)–N(3) O(5)–Mn(1)–N(5) N(3)–Mn(1)–N(5) O(7)–Mn(2)–O(8) O(7)–Mn(2)–N(8) O(7)–Mn(2)–N(10) O(8)–Mn(2)–N(8) O(8)–Mn(2)–N(10) O(9)–Mn(2)–N(9) N(8)–Mn(2)–N(9) N(9)–Mn(2)–N(10) Co(1)–O(4)–Mn(1) Co(2)–O(8)–Mn(2) 1.916(4) 2.003(4) 1.872(4) 1.931(4) 2.046(4) 1.866(4) 2.243(3) 2.222(5) 2.223(4) 2.233(3) 2.223(5) 2.207(5) 96.2(2) 85.8(2) 85.6(1) 92.9(2) 90.3(2) 96.3(2) 87.8(2) 81.2(2) 172.8(2) 96.0(2) 91.8(1) 176.6(2) 178.6(2) 88.4(2) 85.3(2) 88.6(1) 131) 87.8(1) 151.0(2) 107.1(2) 133.0(2) 107.4(2) 73.3(1) 151.3(2) 79.1(2) 81.0(2) 125.9(1) 86.8(2) 75.0(2) 74.0(2) 97.0(1) 97.2(2)2200 J.Chem. Soc., Dalton Trans., 1999, 2197–2203 1.914(5) Å).22e,26,27 This fact suggests that the axial acetate coordination is strong compared with dmf or pip co-ordination, aVording a high aYnity towards dioxygen for the CoII in the “salen” site. The Co(1)–O(1)–O(2) and Co(2)–O(2)–O(1) angles are 109.1(3) and 116.3(3)8, respectively, typical for Co(salen) peroxo complexes.22e,26,27 The Co(1), Co(2), O(1), and O(2) are not coplanar and the Co(1)–O(1)–O(2)–Co(2) torsion angle with respect to the O(1)–O(2) edge is 149.5(2)8.In each {CoMn(L)(AcO)} unit the Co assumes a pseudo octahedral geometry with the N2O2 donor atoms of the macrocycle on the equatorial plane and the bridging acetate oxygen and the peroxo oxygen at the axial positions. The in-plane Co– N and Co–O bond distances fall in the range 1.866(4)–1.931(4) Å, slightly longer than those of 1 (1.864(6)–1.916(4) Å).The axial Co–O (acetate) bond distance in oxy-1 (Co(1)–O(6) 2.003(4), Co(2)–O(10) 2.046(4) Å), on the other hand, is considerably short relative to that of 1 (2.129(4) Å). The {CoN2O2} part forms a good coplane; the sum of the bite angles about the Co is 360.18 (mean value for the two units). The O (acetate)– Co–O (peroxo) angle is 172.98 (mean). The Mn in the “saldien” site is not involved in the oxygenation and retains a distorted trigonal-prismatic geometry as found for complex 1, but some geometric changes occur upon oxygenation. The Mn–O (phenolate) and Mn–N (imine) bond distances of oxy-1 (2.189(4)–2.243(3) Å) are slightly shortened relative to the corresponding bond distances of 1 (2.221(5)– 2.258(4) Å).The Mn–N (amine) bond distances of oxy-1 Table 3 Selected bond distances (Å) and angles (8) of [{Co2(L)- (AcO)}2(O2)][ClO4]2?4CH3CN oxy-3 Co(1)–O(1) Co(1)–O(4) Co(1)–N(1) Co(2)–O(3) Co(2)–O(5) Co(2)–N(4) Co(3)–O(2) Co(3)–O(8) Co(3)–N(6) Co(4)–O(7) Co(4)–O(9) Co(4)–N(9) O(1)–Co(1)–O(3) O(1)–Co(1)–O(6) O(1)–Co(1)–N(2) O(3)–Co(1)–O(6) O(3)–Co(1)–N(2) O(4)–Co(1)–N(1) O(6)–Co(1)–N(1) N(1)–Co(1)–N(2) O(3)–Co(2)–O(5) O(3)–Co(2)–N(4) O(4)–Co(2)–O(5) O(4)–Co(2)–N(4) O(5)–Co(2)–N(3) O(5)–Co(2)–N(5) N(3)–Co(2)–N(5) O(2)–Co(3)–O(7) O(2)–Co(3)–O(10) O(2)–Co(3)–N(7) O(7)–Co(3)–O(10) O(7)–Co(3)–N(7) O(8)–Co(3)–N(6) O(10)–Co(3)–N(6) N(6)–Co(3)–N(7) O(7)–Co(4)–O(9) O(7)–Co(4)–N(9) O(8)–Co(4)–O(9) O(8)–Co(4)–N(9) O(9)–Co(4)–N(8) O(9)–Co(4)–N(10) N(8)–Co(4)–N(10) Co(1)–O(3)–Co(2) Co(3)–O(7)–Co(4) 1.878(3) 1.895(3) 1.866(4) 2.168(3) 2.056(3) 2.297(4) 1.854(3) 1.917(3) 1.870(4) 2.161(3) 2.053(3) 2.281(4) 90.5(1) 173.3(1) 88.0(2) 92.8(1) 178.0(2) 176.8(1) 88.2(2) 85.4(2) 85.9(1) 128.4(1) 89.2(1) 155.3(1) 103.1(2) 133.1(1) 108.9(2) 83.1(1) 175.3(1) 95.5(1) 92.2(1) 177.0(2) 177.1(1) 88.9(2) 84.9(2) 84.8(1) 123.2(1) 88.2(1) 158.2(1) 98.2(1) 138.0(1) 109.4(2) 99.5(1) 98.0(1) Co(1)–O(3) Co(1)–O(6) Co(1)–N(2) Co(2)–O(4) Co(2)–N(3) Co(2)–N(5) Co(3)–O(7) Co(3)–O(10) Co(3)–N(7) Co(4)–O(8) Co(4)–N(8) Co(4)–N(10) O(1)–Co(1)–O(4) O(1)–Co(1)–N(1) O(3)–Co(1)–O(4) O(3)–Co(1)–N(1) O(4)–Co(1)–O(6) O(4)–Co(1)–N(2) O(6)–Co(1)–N(2) O(3)–Co(2)–O(4) O(3)–Co(2)–N(3) O(3)–Co(2)–N(5) O(4)–Co(2)–N(3) O(4)–Co(2)–N(5) O(5)–Co(2)–N(4) N(3)–Co(2)–N(4) N(4)–Co(2)–N(5) O(2)–Co(3)–O(8) O(2)–Co(3)–N(6) O(7)–Co(3)–O(8) O(7)–Co(3)–N(6) O(8)–Co(3)–O(10) O(8)–Co(3)–N(7) O(10)–Co(3)–N(7) O(7)–Co(4)–O(8) O(7)–Co(4)–N(8) O(7)–Co(4)–N(10) O(8)–Co(4)–N(8) O(8)–Co(4)–N(10) O(9)–Co(4)–N(9) N(8)–Co(4)–N(9) N(9)–Co(4)–N(10) Co(1)–O(4)–Co(2) Co(3)–O(8)–Co(4) 1.895(3) 2.002(4) 1.856(4) 2.174(3) 2.074(4) 2.111(4) 1.913(3) 2.003(3) 1.854(4) 2.148(3) 2.100(4) 2.104(4) 95.7(1) 85.8(2) 84.0(1) 93.1(1) 90.4(1) 97.5(1) 88.6(1) 71.5(1) 153.8(1) 80.3(1) 83.9(1) 127.0(1) 79.1(1) 77.8(1) 75.3(1) 90.6(1) 91.1(2) 85.4(1) 92.5(2) 89.2(1) 97.2(2) 89.2(1) 74.2(1) 158.8(1) 80.5(1) 84.9(1) 124.3(1) 81.1(1) 77.9(1) 74.8(2) 99.3(1) 98.3(1) (Mn(1)–N(4) 2.379(4); Mn(2)–N(9) 2.385(4) Å) are also shortened relative to that of 1 (2.407(5) Å).Instead, the Mn–O (acetate) bond distances (Mn(1)–O(5) 2.119(4); Mn(2)–O(9) 2.109(4) Å) are slightly elongated relative to that of 1 (2.099(4) Å). The least-squares plane of the “salen” site and that defined by the two phenolic oxygens and two iminic nitrogens of the “saldien” site are bent at the O(3)–O(4) (O(7)–O(8)) edge.The dihedral angle between the two least-squares planes is 10.38 (mean for the two units) which is large compared with 4.68 for 1. The {CoMn(L)(AcO)} unit also shows a distortion with respect to the Co–Mn edge, aVording a saddle-like shape for the molecule. The dihedral angle between the two aromatic rings is 29.38 (mean) that is slightly smaller than the corresponding dihedral angle for 1 (31.38). Complex oxy-3 (M = Co) is isomorphous with oxy-1.19 Relevant bond distances and angles are given in Table 3.Some geometrical features for oxy-1 and oxy-3 are summarized in Table 4. The peroxo O(1)–O(2) bond distance (1.415(4) Å), the Co(1)–O(1)–O(2), Co(3)–O(2)–O(1) angles (110.0(2) and 117.0(2)8, respectively), and the Co(1) ? ? ? Co(3) intermetallic separation (4.3527(8) Å) for oxy-3 are comparable to the respective values for oxy-1. The Co(1)–O(1)–O(2)–Co(3) torsion angle of oxy-3 (143.7(2)8) is smaller than that of oxy-1 (149.5(2)8). The “Mn(saldien)” part of oxy-1 and the “Co(saldien)” part of oxy-3 diVer from each other because of the different ionic radii of MnII and CoII.The Mn-to-ligand bond distances in the former (2.217 Å, mean) are evidently longer than the Co-to-ligand bond distances in the latter (2.130 Å, mean). The distortions in the {CoM(L)(AcO)} core with respect to the O (phenolate)–O (phenolate) edge (t) and the Co–M edge (f) are both larger in oxy-3. The above X-ray crystallographic studies indicate that the acetate bridge is retained in the oxygenation process to allow oxygenation at the open face of “Co(salen)”.The initial oxygenation product must be the superoxo complex [CoIIIMII(L)- (AcO)(O2 2)]1 that then reacts with another CoIIMII complex (1 or 3) to form the peroxo dimer (oxy-1 or oxy-3); eqns. (1) and (2). [CoIIMII(L)(AcO)]1 1 O2 [CoIIIMII(L)(AcO)(O2 2)]1 (1) [CoIIMII(L)(AcO)]1 1 [CoIIIMII(L)(AcO)(O2 2)]1 [{CoIIIMII(L)(AcO)}2(O2 22)]21 (2) Table 4 Structural parameters of [{CoM(L)(AcO)}2(O2)][ClO4]2? 4CH3CN (M = Mn, oxy-1; Co, oxy-3) oxy-1 oxy-3 O(1)–O(2)/Å Co–O(1)–O(2)/8 Co–O(2)–O(1)/8 Co–O(1)–O(2)–Co/8 Co(1) ? ? ? M(1) (unit 1)/Å (unit 2)/Å Co(1) ? ? ? Co(2) (unit 1–unit 2)/Å Co(1) ? ? ? M(2) (unit 1–unit 2)/Å Co(2) ? ? ? M(1) (unit 1–unit 2)/Å M(1) ? ? ? M(2) (unit 1–unit 2)/Å d(Co) a/Å d(M)b/Å (unit 1) (unit 2) t c/8 (unit 1) (unit 2) fd/8 (unit 1) (unit 2) 1.416(5) 109.1(3) 116.3(3) 149.5(2) 3.124(1) 3.123(1) 4.359(1) 6.143(1) 5.617(1) 7.160(1) 0 0.70 0.69 9.30 11.37 27.21 31.41 1.415(4) 110.0(2) 117.0(2) 143.7(2) 3.105(8) 3.0785(8) 4.3527(8) 6.0776(8) 5.5295(9) 7.0428(1) 0 0.61 0.57 12.27 14.52 34.14 31.81 a Deviation from the least-squares plane defined by the basal donor atoms at the “salen” site.b Deviation from the least-squares plane defined by the basal donor atoms at the “saldien” site. c The bending at O (phenolate)–O (phenolate) edge between the plane defined by the basal donor atoms at the “salen” site and the plane defined by the basal donor atoms at the “saldien” site. d Dihedral angle between the two aromatic rings.J.Chem. Soc., Dalton Trans., 1999, 2197–2203 2201 Such a stepwise formation of a peroxo dimer through a superoxo complex has been demonstrated for Co(salen) and related SchiV base complexes.22,23 It must be noted that Co(salen) itself predominantly forms the superoxo complex [Co(salen)(O2 2)] in dmf22,23 whereas 1 and 3 form the peroxo dimer.The X-ray crystallographic results for oxy-1 and oxy-3 indicate that the peroxo O–O bond is elongated whereas the Co–O (peroxo) bond is shortened relative to the corresponding bonds of the Co(salen) peroxo complexes. As discussed above the axial acetate oxygen is a strong enough donor to cause an eYcient electron transfer from the CoII to dioxygen in oxy-1 and oxy-3. Such axial ligation of an acetate group is diYcult for mononuclear Co(salen) and analogs. Thus, the MII in the “saldien” site contributes to the axial acetate ligation to the “Co(salen)” through the acetate bridge formation.When a solution of complex oxy-1 was warmed to room temperature the spectrum changed with the decrease of the absorption bands at 382 and 550 nm, forming a yellow solution within 2 h, probably due to decomposition of oxy-1. Similarly the solution of oxy-3 faded within 2 h when warmed to room temperature. [CoFe(L)(AcO)]ClO4 2 This complex was very sensitive toward molecular dioxygen so as to be oxidized even at 230 8C with a change from red to yellow.Complex 2 shows an intense absorption band at 358 nm (e 10900 M21 cm21) and weaker bands near 460 (shoulder) and 560 nm (e 1400 M21 cm21), whereas its oxidized yellow solution shows an intense band at 385 nm (e 11200 M21 cm21) but no distinct absorption in the visible region. The resulting yellow solution showed EPR signals at g = 4.26 and 2.01 that are attributable to isolated high-spin FeIII (in frozen solution at liquid nitrogen).This result indicates that a CoIIIFeIII species is formed. The mechanism for the conversion of 2 into the CoIIIFeIII complex is not straightforward because the facile oxidation of FeII in the “saldien” site is recognized for analogous [CuIIFeII( L)]21 and [NiIIFeII(L)]21 complexes.13,14 [CoMn(L)(NCS)]ClO4 4 Complex 4 in dmf formed a dioxygen adduct at 230 8C with a change from red to dark red. Purging to the oxygenated solution with argon at 230 8C resulted in the recovery of the original red colour of 4.The reversible oxygenation/deoxygenation was confirmed by the interconversion of the electronic spectra of 4 and its dioxygen adduct. Complex 4 shows an intense absorption band at 370 (e 11000 M21 cm21) and a weaker band at 540 nm (e 500 M21 cm21). The oxygenated solution of 4 (oxy-4) has an intense absorption band at 377 nm (e 11400 M21 cm21) and a moderately intense band at 595 nm (e 2700 M21 cm21).The latter band in the visible region (LMCT band) is located at longer wavelength relative to the corresponding bands for oxy-1 and oxy-3 (ca. 560 nm). The red-shift of the peroxide-to-CoIII charge transfer band for oxy-4 can be explained by no axial donation to “Co(salen)”. That is, the cobalt d orbitals of oxy-4 are low-lying relative to those of oxy- 1 and oxy-3. The EPR spectrum of the oxygenated solution of 4 (in frozen dmf solution) shows an isotropic signal with six-line hyperfine structure near g ª 2.0 (Aiso = 93 G) typical of isolated MnII as observed for oxy-1.The EPR result is in harmony with the formulation MnIICoIII–O–O–CoIIIMnII for the oxygenated complex. As mentioned in the Introduction, both the open and closed faces of the “Co(salen)” can be available for oxygenation of complex 4. A peroxo dimer formed at the closed face of “Co(salen)” is ruled out because this would give rise to a severe steric repulsion between two {CoMn(L)(NCS)} entities.Thus, the oxygenation of 4 to form the peroxo dimer (oxy-4) occurs at the open face of “Co(salen)” as provided for oxy-1 and oxy-3 (see Scheme 2, left). When the oxygenated solution of complex 4 was warmed to 0 8C the spectrum of the peroxo dimer changed with a decrease of the bands at 377 and 595 nm, forming a yellow solution due to decomposition of oxy-4 as observed for oxy-1 and oxy-3. [CoFe(L)(NCS)]ClO4 5 Complex 5 was very sensitive to dioxygen like 2 and instantaneously oxidized at 230 8C when exposed. The oxidized solution showed an absorption spectrum very similar to that of the oxidized solution of 2.Further, it showed EPR signals (g = 4.24 and 2.01) very similar to those of 2. Evidently both the CoII and FeII are oxidized with dioxygen to form a CoIIIFeIII species. [Co2(L)(NCS)]ClO4 6 Complex 6 was also sensitive to dioxygen and irreversibly oxidized even at 230 8C within 20 min and the formation of a peroxo complex was not confirmed.Thus, 6 and 3 diVer in oxygenation behaviour in spite of the same Co2 pair. Fig. 3 shows the electronic spectral changes of 6 upon oxidation at 230 8C. The absorption spectrum of 6 has two bands near 360 and 550 nm which are replaced by one at 393 nm on oxidation. The facile oxidation of 6 even at 230 8C may proceed by a mechanism involving a neighbouring CoII in the “saldien” site. We have noticed that the lifetime of the oxygenated solution of 6 varies with the complex concentration; the higher the concentration the longer is the lifetime.This fact suggests that a peroxo dimer and superoxo complex exist in an equilibrium in solution and the superoxo complex as a minor species is associated with the high sensitivity of 6. As mentioned above the oxygenation can occur either at the open or the closed face of “Co(salen)”. Oxygenation at the open face forms the peroxo dimer [{CoIIICoII(L)(NCS)}2- (O2 22)]21 as a dominant species.If oxygenation occurs at the closed face of “Co(salen)” a superoxo complex [CoIIICoII( L)(NCS)(O2 2)]1 is formed because of steric reasons as Scheme 2 A possible oxygenation mechanism for complexes 4 and 6. N O N N N M N O Co SCN N O N N N M N O Co SCN N N N M N O Co SCN O N O O O– O– N N N Mn N O Co SCN O N O N N NCS N O Co O N O N Mn N O N N N Co N O Co O O intramolecular peroxo complex O2 irreversible oxidation for CoMn (4) for CoCo (6) intermolecular peroxo complex2202 J.Chem. Soc., Dalton Trans., 1999, 2197–2203 discussed above. The terminal superoxo oxygen can make a bridge to the adjacent CoII in the “saldien” site, by kicking out the thiocyanate ion, forming an intramolecular peroxo complex [CoIIICoIII(L)(O2 22)]21 (see Scheme 2, right). The intramolecular peroxo complex must be formed as a minor species in the equilibrium, but 6 is oxidized to a CoIIICoII species through this complex at 230 8C. In our preliminary study the final product was shown to be the CoIIICoII complex [Co2(L)(NCS)(OH)]ClO4?1.5H2O 69.It appears that the resulting “CoIII(saldien)” center may act as a strong oxidant of the oxidized complex 6 as in eqn. (3). {CoIIICoIII(L)} 1 {CoIICoII(L)} 2{CoIIICoII(L)} (3) It must be noted that complexes 4 (CoMn) and 6 (Co2) have essentially the same core structure but diVer in oxygenation behaviour; 4 forms a stable peroxo dimer at 230 8C whereas 6 is oxidized at this temperature through an intramolecular peroxo intermediate.This can be explained by the participation of the adjacent metal in oxygenation. In the case of 4, the adjacent MnII cannot be involved in two-electron reduction of dioxygen to form an intramolecular CoIII–O–O–MnIII peroxo bond because of the preferred d5 electronic configuration of MnII. In the case of 6, the Co in the “saldien” site can be involved in such a two-electron reduction forming the intramolecular peroxo complex. Further, it should be noted that oxygenation of 3 significantly diVers from that of 6 in spite of the same Co2 pair.In the case of 3, the formation of the peroxo bridge over the Co2(AcO) core at the open face is diYcult as judged from the core structure. Thus, the core structure bridged by an acetate group at the closed face suppresses a neighbouring eVect of the adjacent metal(II) ion. Conclusion The CoIIMII complexes of the macrocyclic ligand L22 show diVerent oxygenation behaviours at the “Co(salen)” center, depending upon the dinuclear core structure and the nature of the MII in the adjacent “saldien” site.Complexes [CoMn(L)- (AcO)]ClO4 1 and [Co2(L)(AcO)]ClO4 3 have an acetatebridged core in solution leaving the open face of “Co(salen)” for oxygenation. The resulting peroxo dimers [{CoM(L)- (AcO)}2(O2)][ClO4]2 (M = Mn, oxy-1; Co, oxy-3) were stable at 0 8C and deoxygenated by purging with argon at this temperature. The complexes [CoFe(L)(AcO)]ClO4 2 and [CoFe(L)- (NCS)]ClO4 5 were immediately oxidized to CoIIIFeIII species at 230 8C.The mechanism for the oxidation was complicated because the FeII in the “saldien” site is air-sensitive. Complex [CoMn(L)(NCS)]ClO4 4 showed reversible oxygenation at Fig. 3 Electronic spectral changes of complex 6 in dmf upon oxygenation at 230 8C. 230 8C forming the peroxo dimer [{CoMn(L)(NCS)}2(O2)]21, whereas [Co2(L)(NCS)]ClO4 6 showed a high sensitivity toward dioxygen and was oxidized even at 230 8C. The marked sensitivity of 6 is explained by a participation of the adjacent CoII in the oxidation; the CoII in the “saldien” site can be involved in two-electron reduction of dioxygen to form an intramolecular peroxo intermediate [Co2(L)(O2)]21. 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Koikawa, J. Chem. Soc., Dalton Trans., 1999, 367. 22 (a) R. D. Jones, D. A. Summerville and F. Basolo, Chem. Rev., 1979, 79, 139; (b) C. Floriani and F. Calderazzo, Coord. Chem. Rev., 1972, 8, 57; (c) T. D. Smith and J. R. Pilbow, Coord. Chem. Rev., 1981, 39, 295; G. McLendon and A. E. Martell, Coord. Chem. Rev., 1976, 19, 1; (e) E. C. NiederhoVer, J. H. Timmons and A. E. Martell, Chem. Rev., 1984, 84, 137. 23 T. Tsumaki, Bull. Chem. Soc. Jpn., 1938, 13, 252; D. Chen and A. E. Martell, Inorg. Chem., 1987, 26, 1026; D. Chen, A. E. Martell and Y. Sun, Inorg. Chem., 1989, 28, 2647; K. Nakamoto, Y. Nonaka, T. Ishiguro, M. W. Urban, M. Suzuki, M. Kozuka, Y. Nishida and S. Kida, J. Am. Chem. Soc., 1982, 104, 3386; W. Kanda, H. O—kawa, S. Kida, J. Goral and K. Nakamoto, Inorg. Chim. Acta, 1988, 146, 193; E. Ochiai, J. Inorg. Nucl. Chem., 1973, 35, 1727; C. Floriani and F. Calderazzo, J. Chem. Soc. A, 1969, 946. 24 D. H. Busch and N. W. Alcock, Chem. Rev., 1994, 94, 585; T. Kayatani, Y. Hayashi, M. Suzuki and A. Uehara, Bull. Chem. Soc. Jpn., 1994, 67, 2980. 25 C. K. Johnson, Report 3794, Oak Ridge National Laboratory, Oak Ridge, TN, 1965. 26 M. Calligaris, G. Nardin and L. Randaccio, Chem. Commun., 1969, 763; M. Calligaris, G. Nardin, L. Randaccio and A. Ripamonti, J. Chem. Soc. A, 1970, 1069. 27 A. Audeef and W. P. Schaefer, Inorg. Chem., 1976, 15, 1432. Paper 9/03099I

ISSN:1477-9226    

DOI:10.1039/a903099i

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2199–2204 2199 X-Ray absorption fine structure study of the bound state electronic transitions at the vanadium K and L edges in low symmetry, molecular, vanadium-(IV) and -(V) complexes with oxyoxime and oxyoximate ligands ‡ David Collison,*,a C. David Garner,*,a Julian Grigg,a Catherine M. McGrath,b J. Frederick W. Mosselmans,c Elna Pidcock,a Mark D. Roper,c Jon M. W. Seddon,b Ekk Sinn,b Peter A. Tasker,d,e GeoV Thornton,f John F.Walsh f and Nigel A. Young *,†,b a Department of Chemistry, The University of Manchester, Oxford Road, Manchester, UK M13 9PL b Department of Chemistry, The University of Hull, Hull, UK HU6 7RX c CCLRC Daresbury Laboratory, Warrington, Cheshire, UK WA4 4AD d Zeneca Specialties Research Centre, Blackley, Manchester, UK M9 3DA e Department of Chemistry, The University of Edinburgh, Kings Building, West Mains Road, Edinburgh, UK EH9 3JJ f IRC in Surface Science, Department of Chemistry, The University of Manchester, Oxford Road, Manchester, UK M13 9PL A combination of vanadium K- and L-edge XAFS has been used to characterise a series of monomeric oxovanadium(IV), monomeric dioxovanadium(V) and dimeric oxovanadium(V) complexes with oxyoxime and oxyoximate ligands.The K- and L-edge spectra confirm the presence of VV in the dimeric species and the L-edge spectra have been used to discriminate between six-co-ordinate V]N]O]V bridged oxovanadium(V) dimers and seven-co-ordinate phenolate bridged oxovanadium(V) dimers containing h2-N]O groups.The bound state electronic transitions in the X-ray absorption fine structure (XAFS) spectra of 3d transition elements at their K- and L-edges have very diVerent intensities because of the dipole selection rules.1 Thus, at the K-edge, the 1s æÆ 3d transitions are dipole-forbidden and therefore in general are only seen as weak ‘pre-edge’ features prior to the onset of the absorption edge and the subsequent extended X-ray absorption fine structure (EXAFS) which can be used to give structural information.1 In the case of vanadium the intensity of the 1s æÆ 3d transitions can be significantly enhanced depending upon: (i) the extent of 3d–4p mixing at the vanadium; (ii) the overlap of the vanadium 3d orbitals with ligand 2p orbitals (especially in compounds containing V]] O moieties); and (iii) deviations from high symmetry geometries.The position, shape and relative intensity of these pre-edge features are dependent on oxidation state and co-ordination environment, and hence they have been used to investigate vanadoenzymes and synthetic analogues of their active sites,2,3 as well as an extensive range of vanadium compounds and complexes.4,5 Although useful information has been obtained using this approach, Weidemann et al.3 have advised exercising caution against over interpretation of the data.In contrast to the K-edge, the L-edge spectra are dominated by intense, well structured transitions which arise from dipoleallowed 2p63dn æÆ 2p53dn11 transitions which have about a quarter of the natural linewidths of the corresponding K-edge features;6 whilst 2p æÆ 4s transitions are allowed, their transition probabilities are much smaller.7 The L3 (2p3/2) and L2 (2p1/2) components are split by spin–orbit coupling of the core–hole, and as there is a strong interaction between the 2p core–hole and the valence 3d orbitals, the position of, and structure on, † E-Mail: n.a.young@chem.hull.ac.uk ‡ Non-SI units employed: eV ª 1.60 × 10219 J, bar = 105 Pa.the L2,3 absorptions are very sensitive to oxidation state, spin state, ligand field and local environment, as well as being element specific.7 This can be especially powerful for d0 electronic con- figurations, and where d–d transitions are obscured by (intense) charge transfer bands in the optical spectra. The technique has found use in the study of minerals, metalloproteins and coordination compounds.8 The application of L-edge spectroscopy to solid state physics and chemistry has also been reviewed.9 Abbate et al.have shown that vanadium L-edge XAFS is suYciently sensitive to distinguish between V2O5, VO2 and V2O3,10 and that there are observable diVerences in the spectrum of VO2 above and below its first order phase transition at 67 8C.11 However, in the case of LiVO2 there was very little change in the spectra above and below the phase transition. 12 Polarisation dependent, single crystal vanadium L-edge experiments have been used to study the 2p æÆ 3d transitions in greater detail in V2O5,13–15 VO2,13 V2O3 13 and V6O13.13,14 Chen et al.16 have demonstrated a shift in the vanadium L-edge features of vanadium oxide model compounds of 0.68 ± 0.03 eV per oxidation state, and have used this to identify the oxidation state of vanadium carbide on a vanadium (110) surface. A comparison of the experimental and theoretical spectrum of VF3 has been reported,17 and vanadium L-edge XAFS has also been used for oxidation state identification and quantification in a range of vanadium-containing minerals.18,19 We have recently developed the synthesis and structural characterisation of a series of oxovanadium-(IV) and -(V) complexes containing oxyoxime and oxyoximate ligands.20–22 Fig. 1(a) shows the formulae of these proligands, which bond to vanadium either as mononegative oxyoxime units by deprotonation of the phenol function or as dinegative oxyoximate ligands when the N-hydroxy group is additionally deprotonated. Fig. 1(b)–(e) shows the various structural types which we have identified using single crystal X-ray diVraction on2200 J. Chem. Soc., Dalton Trans., 1998, Pages 2199–2204 selected complexes. The monomeric oxovanadium(IV) complexes [Fig. 1(b)] show a typical hydrogen-bonded uninegative form of the ligand in a bis complex. They are stable over a period of months in the solid state, but in chlorinated or hydrocarbon solvents the solutions rapidly darken as the complexes undergo oxidation to dimeric species.The particular structural type formed depends on the substituent in the hydroxyoxime proligand and also the starting material since some of the dimers can be formed without oxidation using [NH4][VO3] as the vanadium precursor. In these proposed higher oxidation state dimers the oxovanadium(V) centres are bound by both mononegative oxyoxime and dinegative oxyoximate ligands.The V]N]O]V bridged structure [Fig. 1(c)] has two six-co-ordinate pseudo-octahedral metal centres, whereas the phenolate-bridged structure [Fig. 1(d)] has pseudopentagonal bipyramidal seven-co-ordination at each metal, which includes the h2-N]O bonding mode of the oxyoximate ligands. Reaction of the oxovanadium(IV) monomers with nitriles (MeCN, PhCN and 4-O2NC6H4CN) led to oxidation to dioxovanadium(V) monomers [Fig. 1(e)] with the formation of a novel organic ligand.23 The assignment of (formal) metal oxidation state in the dimeric compounds can be non-trivial as the magnetic distinction between vanadium-(IV) and -(V) is no longer present if there is strong antiferromagnetic coupling between the oxovanadium( IV) centres. The identification of the dimeric species [Fig. 1(c) and (d)] as oxovanadium(V) followed from a consideration of the bond lengths in the structurally characterised compounds20,21 in conjunction with Bond Valence Sum Analysis,24 together with the observation and position of 51V NMR resonances.21 Whilst the EPR signal characteristic of monomeric vanadium(IV) complexes was absent from the Fig. 1 Representation of the structures of: (a) proligands (R1 = H, R2 = H, H2LH; R1 = H, R2 = Me, H2LMe; R1 = H, R2 = Et, H2LEt; R1 = Octt, R2 = H, H2LOctt; R1 = But, R2 = H, H2LBut; R1 = Cl, R2 = H, H2LCl; (b) five-co-ordinate monomeric bis(oxyoxime)oxovanadium( IV) complex: (c) six-co-ordinate oxyoximate-bridged oxovanadium( V) dimer containing m-N]O units; (d) seven-co-ordinate, phenolate-bridged, oxovanadium(V) dimer, containing h2-N]O units; (e) dioxovanadium(V) monomer, [VO2{C6H4(O)C(R)]] NOC(R9)]] NH}] (R = Me, R9 = Ph; R = H, R9 = Me, Ph or 4-O2NC6H4) spectra of the dimeric complexes, this could be due to the presence of vanadium(V) or the spin pairing of the single unpaired electron of two vanadium(IV) centres in the dimers.Therefore, the present study explored the use of vanadium K- and L-edge XAFS spectroscopy to probe the oxidation state of the vanadium centres in several monomeric and dimeric oxyoxime and oxyoximate complexes of vanadium-(IV) and -(V). This work also assesses the applicability of bound state transitions at these edges to the discrimination of co-ordination environment. Experimental Sample preparation Vanadium(V) oxide and [NH4][VO3] were obtained from Aldrich and used as received.The complexes [VO(acac)2],21 [VO(acac)2(py)],25 [VO(salen)],21 K3[V O(O2)2(C2O4)] 26 and [VO2{C6H4(O)C(R)]] NOC(R9)]] NH}] 23 (R = Me, R9 = Ph; R = H, R9 = Me, Ph or 4-O2NC6H4) [Fig. 1(e)] were synthesized using previously published methods.§ The synthesis and characterisation of the hydroxyoxime proligands [Fig. 1(a)] will be published elsewhere.20,21,27 The synthesis of the oxovanadium( IV) oxyoxime complexes [VO(HLR)2] (R = H, Me, Et, But or Cl) [Fig. 1(b)] from vanadyl sulfate and the appropriate proligand, and the oxovanadium(V) oxyoxime oxyoximate complexes [{VO(HLR)LR}2] [R = H, Me, Et or Octt (Octt = Me3CCH2CMe2)] [Fig. 1(c) and (d)] from either oxidation of the vanadium(IV) complex in chlorocarbon or hydrocarbon solvents or the addition of the proligand to [NH4][VO3], will be published in detail elsewhere, together with the spectroscopic and crystallographic data.20,21,27 The numbering scheme for the compounds is given in Table 1.K-edge X-ray absorption spectroscopy The vanadium K-edge X-ray absorption data were collected on station 4.2 28 at the Daresbury Laboratory Synchrotron Radiation Source (SRS) operating at 2 GeV with circulating currents of 220–240 mA. The samples were investigated as a slurry in hexane (reagent grade), evaporated onto vanadiumfree stainless steel holders and mounted in an ultra-high vacuum chamber. Total electron yield detection was used for all experiments and the spectra were calibrated using the maximum intensity position of the V2O5 1s æÆ 3d pre-edge transition at 5470.60 eV.5 The accuracy of the measurement of the absolute energy is estimated to be ±0.5 eV, and that of the relative energy to be ±0.25 eV.L-edge X-ray absorption spectroscopy The vanadium L-edge data were obtained on station 5U.1 29 of the undulator beamline at the SRS operating at 2 GeV with circulating currents of 150–250 mA. The general features of the experimental set-up employed have been described in detail elsewhere.8 The samples were prepared either as slurries of graphite (99.999%; Goodfellows, Cambridge) with CH2Cl2 or EtOH and left to evaporate on aluminium plates or as powders on conductive epoxy resin on aluminium plates.The aluminium plates were mounted in an ultra-high vacuum chamber with a base pressure of ca. 1027 mbar. Data were collected as total electron yield using drain current methods which gives an estimated sampling depth of ca. 30–50 Å. The spectra were normalised to the intensity of the L3 feature and were calibrated using oxygen K-edge features in the I0 channel, these having been referenced to the vanadium L3 peak maximum of V2O5 at 516.9 eV, based on the reported XPS 2p3/2 binding energy of V2O5 at 516.9 eV.30 The oxygen K-edge features starting at ca. 528 eV have been removed from the spectra for clarity. Whilst § Hacac = Acetylacetone = pentane-2,4-dione; H2salen = N,N9-bis(salicylidene) ethane-1,2-diamine.J.Chem. Soc., Dalton Trans., 1998, Pages 2199–2204 2201 the accuracy of the absolute energy measurement is estimated to be ±0.2 eV, the relative energies are considered to be accurate to at least ±0.1 eV due to the use of in situ calibration. Results and Discussion Vanadium K-edge spectra Vanadium K-edge spectra of [VO(salen)] 3 and V2O5 4, with pre-edge features of moderate intensity about 10 eV below the absorption edge, are shown in Fig. 2, and these were essentially identical to those observed previously.2–5 The pre-edge feature in the spectrum of [VO(salen)] was at 5469.0 eV, compared to a literature value of 5469.1 eV,¶,2 and previous workers have reported values for the position of the pre-edge features for molecular oxovanadium(IV) complexes of 5469.1 to 5469.8,2 5469.05 to 5469.8,3 and 5469.7 to 5469.9 eV.4 For V2O5 the preedge feature in the spectrum was observed at 5470.6 eV, ca. 1.5 eV higher in energy than the above values, as to be expected for vanadium-(V) vs.-(IV). Previously reported values of the positions of the pre-edge features for molecular oxovanadium( V) complexes are in the range 5470.1 to 5470.7,2 5469.9 to 5471.1 and 5470.2 to 5470.8 eV.4 Therefore, the position of the pre-edge peaks in the vanadium K-edge spectra will be able to identify with reasonable certainty the oxidation state in the oxyoxime and oxyoximate complexes. The vanadium K-edge spectra (Fig. 2, Table 1) of the oxo- Fig. 2 Vanadium K-edge spectra of [VO(salen)] 3, [VO(HLH)2] 7, [VO(HLMe)2] 8, [VO(HLEt)2] 9, V2O5 4, [{VO(HLMe)LMe}2] 15, [{VO- (HLEt)LEt}2] 16, [{VO(HLH)LH}2] 17 and [{VO(HLEt)LEt}2] 18 ¶ This value has been amended from the published value of 5459.1 eV, since the original work2 used a value of 5456.0 eV for the pre-edge feature in vanadium foil, whereas a value of 5466.0 eV (see ref. 5) is more compatible with the calibration used herein. The other data taken from ref. 2 have been treated in a similar manner.vanadium(IV) complexes containing oxyoxime ligands (7–9) have 1s æÆ 3d transitions in the range 5469.3 to 5469.8 eV, consistent with the presence of VIV. In contrast, the position of the pre-edge features in the vanadium K-edge spectra (Fig. 2, Table 1) of the complexes formulated as dimeric oxovanadium( V) species (15–18) are in the range 5470.6 to 5470.8 eV, indicative of the presence of VV. Therefore, vanadium K-edge XAFS confirms the presence of VV in the dimeric species. The vanadium K-edge spectra of 15 and 16 are virtually identical, confirming the same type of structural motif (seven-coordinate, phenolate bridged dimer containing an h2-N–O group [see Fig. 1(d)] is present in both complexes. The spectrum of 17 is diVerent to those of 15 and 16, indicating the presence of a diVerent structural type (six-co-ordinate, V]N]O]V bridged dimers [see Fig. 1(c)]. The spectrum of 18 is broadly similar to that of 17 and very diVerent from those of 15 or 16, indicating that the same structural type is probably present in 17 and 18.Whilst the spectra of the dimeric complexes have indicated the sensitivity of vanadium K-edge XAFS to changes in structural type at the metal centre, the diVerences are fairly small and subtle. Therefore, we decided to investigate the applicability of vanadium L-edge XAFS to the identification of the structural form present in the oxovanadium(V) dimers, as this technique is very sensitive to changes in the electronic and geometric structure at the metal centre.Vanadium L-edge spectra Compounds for calibration and comparison. Fig. 3 shows the vanadium L-edge spectra obtained for several oxocompounds of VIV and VV. These spectra are split into the L3 (2p3/2) and L2 (2p1/2) components by spin–orbit coupling (ca. 7 eV) of the core–hole, and the structure on each of these components is related to the ligand field at, and site symmetry of, the vanadium.The structure on the higher energy L2 feature is less well resolved than that at the L3 edge due to interaction with the L3 continuum states.7 The maxima of the L3 components for [VO(acac)2] 1, [VO(acac)2(py)] 2 and [VO(salen)] 3 all occur at 515.7 eV, with shoulders at 512.7 (512.8 for 1) and 513.4 eV in each case. The maxima of the broad, slightly asymmetric L2 Fig. 3 Vanadium L-edge XAFS spectra of [VO(acac)2] 1, [VO(acac)2- (py)] 2, [VO(salen)] 3, V2O5 4, [NH4][VO3] 5, K3[VO(O2)2(C2O4)] 62202 J.Chem. Soc., Dalton Trans., 1998, Pages 2199–2204 Table 1 Vanadium K- and L-edge XAFS data (eV) for some vanadium-(IV) and -(V) compounds Compound 1 [VO(acac)2] 2 [VO(acac)2(py)] 3 [VO(salen)] 4 V2O5 5 [NH4][VO3] 6 K3[VO(O2)2(C2O4)] 7 [VO(HLH)2] 8 [VO(HLMe)2] 9 [VO(HLEt)2] 10 [VO(HL(Cl))2] 11 [VO2{C6H4(O)CH]] NOC(Me)]] NH}] 12 [VO2{C6H4(O)CH]] NOC(Ph)]] NH}] 13 [VO2{C6H4(O)C(Me)]] NOC(Ph)]] NH}] 14 [VO2{C6H4(O)CH]] NOC(4-O2NC6H4)]] NH}] 15 [{VO(HLMe)LMe}2] (h2-N]O)i 16 [{VO(HLEt)LEt}2] (h2-N]O)i 17 [{VO(HLH)LH}2] (m-N]O)i 18 [{VO(HLEt)LEt}2] (m-N]O)i 19 [{VO(HLoct)Loct}2] K edge 1s æÆ 3d transition a 5469.05;c 5469.4 d f 5469.0;e 5469.1 d 5470.6 e 5470.6;g 5470.67;c 5470.3 d 5469.8;g 5470.1 d 5470.61 c 5469.8 e 5469.7 e 5469.3 e fffff 5470.7 e 5470.6 e 5470.6 e 5470.8 e f L3 edge b 512.8, 513.4, 515.7 e 512.7, 513.4, 515.7 e 512.7, 513.4, 515.7 e 513.9, 515.3, (516.2), 516.9 e 513.5, 514.7, 515.5, 516.7 e 513.6, 515.3, 517.0 e h 512.8, 513.6, 515.7 e 512.8, 513.6, 515.7 e 512.7, 513.6, 515.6 e 515.3, 516.9 e 515.0, 516.6 e 514.9, 516.8 e 515.0, 516.7 e 514.9, 515.8, 516.8 e 515.0, 515.8, 516.8 e 514.0, 515.1, 517.1 e (513.9), 514.9, (516.3), 517.1 e 515.1, 517.1 e L2 edge b 522.6 e 522.6 e 522.4 e 523.7 e 523.5 e 522.4, 523.9 e h 522.6 e 522.6 e 522.4 e 523.5 e 523.3 e 523.4 e 523.3 e (522.6), 523.4 e 523.3 e 523.7 e (522.2), 523.7 e (522.7), 523.7 e a Peak maxima ± 0.25 eV, referenced to V2O5 1s æÆ 3d transition at 5470.6 eV.b Peak maxima ± 0.1 eV referenced to L3 maximum of V2O5 at 516.9 eV; figures in parentheses are poorly defined shoulders. c Ref. 3. d Ref. 2 [value amended from that given in the original work which used a value for the vanadium foil pre-edge feature of 5456.0 eV; a value of 5466.0 eV was used herein (see ref. 5)]. e This work. f Vanadium K-edge data not recorded. g Ref. 5. h Reliable vanadium L-edge data could not be obtained. i The bonding mode of the deprotonated oxime moiety (see Fig. 1). features are observed at 522.6 eV for [VO(acac)2] and [VO(acac)2(py)] and 522.4 eV for [VO(salen)]. The spectra for all three complexes are very similar, implying that vanadium L-edge XAFS is not suYciently sensitive to discriminate between the small changes in the ligand field experienced by the vanadium in these compounds. (Single crystal electronic absorption measurements have shown that the 3dz2 orbitals is at least 4000 cm21 higher in energy in six-co-ordinate VO21 complexes than in their five-co-ordinate counterparts.31) Therefore, we believe that the profile observed could be useful as a spectroscopic signature for VO21 bound to O,N-donor ligands.For V2O5 4 the L3 maximum was observed at 516.9 eV, with well defined features at 513.9 and 515.3 eV and a weak shoulder at 516.2 eV. In the case of [NH4][VO3] 5 the L3 maximum was at 516.7 eV together with shoulders at 513.5, 514.7 and 515.5 eV.For K3[VO(O2)2(C2O4)] 6 the L3 maximum at 517.0 eV was accompanied by a well defined shoulder at 515.3 eV and a weaker feature at 513.6 eV. The L2 features for V2O5, [NH4][VO3] and K3[VO(O2)2(C2O4)] were observed at 523.7, 523.5 and 523.9 eV, respectively. For the last of these features there was a shoulder at 522.4 eV, whereas in the other two spectra the L2 band was asymmetric. The shift of ca. 1 eV in the maxima of both the L3 and L2 peaks on going from VIV to VV clearly indicates the sensitivity of vanadium L-edge XAFS spectra to changes in oxidation state.Chen at al.16 have previously observed a shift of 0.68 eV per oxidation state for vanadium oxocomplexes, but the resolution obtained was very poor (e.g. the spectrum of V2O5 contained only a broad feature at both the L3 and L2 edges) casting some doubt on the accuracy of this value. Whilst the L-edge spectra of the oxovanadium( IV) compounds appear to be very similar, there are significant diVerences between the spectra of the vanadium(V) systems, presumably related to the diVerences in the local environment of the vanadium which aVect the relative energies of the 3d orbitals.Previously, it has been noted that the simulation of L-edge spectra for d0 configurations is complicated because of the large number of individual dipole-allowed 2p æÆ 3d transitions.7 Although polarisation-dependent, single crystal measurements on V2O5 have been used to identify the spectroscopic features arising from the diVerent 3d orbitals,15 we have been unable to collect polarisation-dependent data on molecular complexes due to the loss of crystallinity, presumably related to the loss of solvent from the top (ca. 30–50 Å) layer of the compounds under the ultra-high vacuum conditions required for the experiment. The complexity of the L-edge spectra observed for the vanadium(V) systems reported herein also calls into question the approach previously used for identification of oxidation state in vanadium-containing minerals.18,19 This assumed that any VV present would be represented by a single peak in the L3-edge region of the spectrum.Thus, whilst we have observed one major peak at the L3 edge, lower energy shoulders associated with the vanadium(V) spectra may overlap with, or could be misassigned to, features from lower oxidation state species. Oxovanadium oxyoxime and oxyoximate complexes. The vanadium L-edge spectra obtained from the oxovanadium-(IV) and -(V) complexes containing oxyoxime and oxyoximate ligands are shown in Fig. 4. Essentially identical spectra were observed for all of the oxovanadium(IV) oxyoxime complexes studied (8–10) and representative spectra of [VO(HLMe)2] 8 and [VO(HLEt)2] 9 are given in Fig. 4. The L3 maxima were observed at 515.7 eV, together with lower energy features at 512.8 and 513.6 eV, whilst the L2 absorption band was observed at 522.6 eV for 8 and 9 and at 522.4 eV for 10.These spectra and values are very similar to those observed for [VO(acac)2], [VO(acac)2(py)] and [VO(salen)], consistent with the presence of VIV in these complexes, further supporting the idea that this spectroscopic motif is characteristic of VO21 bound to O,Ndonor ligands. For the vanadium(V) complexes 11–19 a much wider variation in the nature of the L-edge spectra was observed. For the monomeric, five-co-ordinate, dioxovanadium(V) complexes 11– 14 [see Fig. 1(e)] the spectra were similar, with the L3 maxima at 516.6–516.9 eV with low energy shoulders at ca. 515.0 eV and the L2 maxima at ca. 523.4 eV; Fig. 4 shows the spectrum obtained for 14. The position of the L3 maxima at ca. 516.7 eV suggests that this feature is indicative of VV in such systems which have been shown unambiguously to be VV from 51V NMR spectroscopy, consistent with the lack of an EPR signal.23 For the oxovanadium(V) dimeric species 15–18, two diVerent structural forms have been identified using X-ray crystallography.Red-brown, [{VO(HLMe)LMe}2] 15 has a seven-co-J. Chem. Soc., Dalton Trans., 1998, Pages 2199–2204 2203 ordinate, dimeric structure [Fig. 1(d)] with bridging phenolate ligands from two monodeprotonated hydroxyoxime ligands and the other two oximes co-ordinated via h2-N]O units.21 The vanadium L-edge spectrum (Fig. 4) of this material consists of three features (514.9, 515.8 and 516.8 eV) at the L3 edge and a broad, asymmetric peak at 523.4 eV at the L2 edge.The lowest and highest energy components at the L3 edge, and the shape and position of the L2 band, correlate very well with those observed for the monomeric dioxovanadium(V) complexes, confirming the presence of VV in these dimeric complexes. We do not believe that the central component of the L3 band at 515.8 eV is a genuine part of the spectral profile of the oxovanadium( V) dimer spectrum as its intensity was found to depend upon the length of time the sample was exposed to the soft X-ray beam (the intensity increased with successive scans) and whether epoxy- or graphite-mounted samples were used, even though the same batch of compound was used in both cases.The energy of this band (515.8 eV) is very similar to that observed for the vanadium(IV) complexes and therefore it is most likely to be due to the presence of some VIV in the sample. Previously, we have observed soft X-ray induced spin state transitions and photochemistry in some iron complexes,8 soft X-ray induced photoreduction and photoisomerisation in nickel complexes,32 and diVerent rates of photoreduction in a number of vanadium(V) compounds.33 Therefore, the 515.8 eV feature in the spectra of some of the oxovanadium(V) oxyoxime oxyoximate complexes is probably due to VIV caused by some photoreduction of the sample on exposure to soft X-rays.As 3d L-edge XAFS is essentially a surface sensitive technique (with a penetration depth of ca. 30–50 Å) the vanadium(IV) component in the spectra is most likely to be located in the Fig. 4 Vanadium L-edge XAFS spectra of [VO(HLMe)2] 8, [VO- (HLEt)2] 9, [VO2{C6H4(O)CH]] NOC(4-O2NC6H4)]] NH}] 14, [{VO- (HLMe)LMe}2] 15, [{VO(HLEt)LEt}2] 16, [{VO(HLH)LH}2] 17, [{VO- (HLEt)LEt}2] 18, [{VO(HLoct)Loct}2] 19 surface layer, rather than as a result of bulk decomposition of the sample. Black, [{VO(HLH)LH}2] 17 has a six-co-ordinate, dimeric structure [Fig. 1(c)] with V]N]O]V bridging.20 The vanadium L-edge spectrum of this compound has an L3 band with features at 514.0, 515.1 and 517.1 eV, and a broad asymmetric L2 band with a maximum at 523.7 eV.There is no evidence of a feature at 515.8 eV, indicating the absence of any significant photoreduction. Of interest is the eVect of changes in molecular geometry on the rate of soft X-ray photoreduction in these two oxovanadium(V) complexes. The L3 maximum at 517.1 eV for 17 is 0.3 eV higher in energy than that for 15 and the L2 band is also ca. 0.3 eV higher in energy. These shifts were consistently observed for diVerent samples and are considered to be indicative of changes in the 3d orbital energies due to changes in bonding and site symmetry at the vanadium between the two structural forms. Deconvolution of the spectrum of the sevenco- ordinate species 15 using a vanadium(IV) spectrum 9 and a spectrum of the six-co-ordinate species 17 showed that this shift of ca. 0.3 eV cannot be accounted for by the presence of the 515.8 eV band in the spectrum of the seven-co-ordinate species.Therefore, we believe that the position of the L3 maximum can be used to diVerentiate between the two types of dimeric structures. In respect of the synthesis of complexes 15 and 17, the same product was obtained from either oxidation of the corresponding vanadium(IV) complex or the addition of the proligand to a vanadium(V) precursor such as [NH4][VO3].20,21 However, in the case of [{VO(HLEt)LEt}2], the nature of the product depended on the synthetic route chosen.Oxidation of [VO(HLEt)2] in CHCl3 led to the production of black crystals of [{VO(HLEt)- LEt}2] 18 which have been shown by X-ray crystallography 21 to possess a structure of the type shown in Fig. 1(c). The vanadium L-edge spectrum of 18 is similar to that of 17, with L3 components at 514.9 and 517.1 eV, together with weak shoulders at 513.9 and 516.3 eV, and a broad asymmetric L2 peak at 523.7 eV.The positions of the L3 and L2 maxima and the general form of the spectral profile are very similar to those observed for 17, as expected since both 18 and 17 have the same structural form. The origin of the subtle change in relative intensity and slight energy shift of the shoulders at the L3 peak is unclear, and it should be noted that there were also small diVerences between the vanadium K-edge spectra of these two complexes. Crystallographic studies have revealed that whilst both complexes have the structure type of Fig. 1(c), there are statistically significant diVerences in the angles subtended at the vanadium in the two compounds.20,21 Thus, the experimental data indicate the sensitivity of L-edge spectroscopy to small changes in the local environment of d0 systems. Reaction of proligand H2LEt with [NH4][VO3] led to the synthesis of brown [{VO(HLEt)LEt}2] 16. Whilst we have not been able to determine the structure of 16 by X-ray crystallography, the spectroscopic data (IR, NMR, UV/VIS) indicate a structure of the type Fig. 1(d).21 The vanadium L-edge spectrum of 16 was essentially identical to that of 15, with L3 features at 515.0, 515.8 and 516.8 eV and a broad L2 peak at 523.3 eV, consistent with the structure of 16 being very similar to that of 15, as indicated by other spectroscopic data. Given the above results which show that vanadium L-edge XAFS is able to discriminate between the two structural forms observed for the oxovanadium(V) dimers, we employed this approach to investigate the nature of the vanadium centre present in a material that was only available as an amorphous solid but has industrial importance given the use of the proligand in metal extraction.Attempts to synthesize an oxovanadium(IV) complex using a toctyl substituted hydroxyoxime proligand (R1 = Octt, R2 = H in Fig. 1(a)] invariably led to a rapid darkening of the reaction solution and the formation of an almost black amorphous product formulated as [{VO(HLoct)Loct}2] 19 on the basis of microanalytical and IR data.21 The vanadium2204 J.Chem. Soc., Dalton Trans., 1998, Pages 2199–2204 L-edge spectrum obtained for this product is shown in Fig. 4 with the L3 maximum at 517.1 eV and a low energy shoulder at 515.1 eV, together with a broad asymmetric L2 peak with a maximum at 523.7 eV. This spectrum is very similar to that obtained from the six-co-ordinate V]N]O]V bridged [{VO- (HLEt)LEt}2] dimer 18 at both the L3 and L2 edges and this, together with the observed colour, strongly implies that the structure of this compound is based on a six-co-ordinate vanadium(V) dimer with V]N]O]V bridging.This is in good agreement with the solid state IR spectroscopic experiments which also indicated a structure based on a six-co-ordinate dimeric structure.21 Conclusion The position of the pre-edge features in the vanadium K-edge XAFS spectra gives a clear indication of the oxidation state in the molecular compounds.Subtle changes in the edge structure give a probable indication of the structural type present in the dimeric species, but this is not suYciently diagnostic to be used as a fingerprint of co-ordination environment. In contrast, vanadium L-edge XAFS has been shown to be a powerful fingerprint of both the oxidation state and the local geometry of the vanadium in a range of oxyoxime and oxyoximate complexes. In particular vanadium L-edge XAFS spectra have shown that the dimeric vanadium oxime oxyoximate complexes should be formulated as vanadium(V) systems with the L3 maximum being diagnostic of the presence of either a V]N]O]V bridged structure with two six-co-ordinate pseudo-octahedral metal centres, or a phenolate-bridged structure with h2-N]O bonding mode of the oxyoximate ligands and pseudo-pentagonal bipyramidal seven-co-ordination at each metal.Acknowledgements We thank the SERC/EPSRC for financial support including an Advanced Fellowship (N.A. Y.), equipment and SRS beamtime (GR/J 34200), post-doctoral provision (C. M. McG., GR/K 64662), and Ph.D. studentships (J. G., CASE with Zeneca Specialties; J. F. W., CASE with ICI Chemicals & Polymers; J. M. W. S.). The Royal Society is thanked for a University Research Fellowship (D. C.) and The University of Manchester for a Rona Robinson Scholarship (E. P.). The Director of the Synchrotron Radiation Department at the SRS is thanked for access to experimental and computational facilities.References 1 B. K. Teo, EXAFS Basic Principles and Data Analysis, Springer, Berlin, 1986; X-Ray Absorption: Principles, Applications and Techniques of EXAFS, SEXAFS and XANES, eds. D. C. Koningsberger and R. Prins, Wiley, New York, 1988. 2 J. M. Arber, E. De Boer, C. D. Garner, S. S. Hasnain and R. Wever, Biochemistry, 1989, 28, 7968. 3 C. Weidemann, D. Rehder, U. Kuetgens, J. Hormes and H.Vilter, Chem. Phys., 1989, 136, 405. 4 K. H. Hallmeier, R. Szargan, G. Werner, R. Meier and M. A. Sheromov, Spectrochim. Acta, Part A, 1986, 42, 841. 5 J. Wong, F. W. Lytle, R. P. Messmer and D. H. Maylotte, Phys. Rev. B, 1984, 30, 5596. 6 M. O. Krause and J. H. Oliver, J. Phys. Chem. Ref. Data, 1979, 8, 329. 7 G. van der Laan and I. W. Kirkman, J. Phys.: Condens. Matter, 1992, 4, 4189. 8 D. Collison, C. D. Garner, C. M. McGrath, J. F. W. Mosselmans, M. D. Roper, J. M.W. Seddon, E. Sinn and N. A. Young, J. Chem. Soc., Dalton Trans., 1997, 4371 and refs. therein. 9 F. M. F. de Groot, J. Electron Spectrosc. Relat. Phenom., 1994, 67, 529. 10 M. Abbate, H. Pen, M. T. Czyzyk, F. M. F. de Groot, J. C. Fuggle, Y. J. Ma, C.-T. Chen, F. Sette, A. Fujimori, Y. Ueda and K. Kosuge, J. Electron Spectrosc. Relat. Phenom., 1993, 62, 185. 11 M. Abbate, F. M. F. de Groot, J. C. Fuggle, Y. J. Ma, C.-T. Chen, F. Sette, A. Fujimori, Y. Ueda and K. Kosuge, Phys.Rev. B, 1991, 43, 7263. 12 H. F. Pen, L. H. Tjeng, E. Pellergrin, F. M. F. de Groot, G. A. Sawatzky, M. A. van Veenendaal and C.-T. Chen, Phys. Rev. B, 1997, 55, 15 500. 13 E. Goering, O. Müller, M. L. denBoer and S. Horn, Physica B, 1994, 194, 1217. 14 E. Goering, O. Müller, M. Klemm, J. P. Urbach, H. Petersen, C. Jung, M. L. denBoer and S. Horn, Physica B, 1995, 208 and 209, 300. 15 E. Goering, O. Müller, M. Klemm, M. L. denBoer and S. Horn, Phil. Mag. B, 1997, 75, 229. 16 J. G. Chen, C. M. Kim, B. Fruhberger, B. D. de Vries and M. S. Touvelle, Surf. Sci., 1994, 321, 145. 17 F. M. F. de Groot, J. C. Fuggle, B. T. Thole and G. A. Sawatzky, Phys. Rev. B, 1990, 42, 5459. 18 G. Cressey, C. M. B. Henderson and G. van der Laan, Phys. Chem. Min., 1993, 20, 111. 19 P. F. Schofield, C. M. B. Henderson, G. Cressey and G. van der Laan, J. Synchrotron Rad., 1995, 2, 93. 20 J. M. Thorpe, Ph.D. Thesis, The University of Manchester, 1992. 21 J. Grigg, Ph.D. Thesis, The University of Manchester, 1995. 22 J. Grigg, D. Collison, C. D. Garner, M. Helliwell and P. A. Tasker, J. Inorg. Biochem., 1993, 51, 172. 23 J. Grigg, D. Collison, C. D. Garner, M. Helliwell, P. A. Tasker and J. M. Thorpe, J. Chem. Soc., Chem. Commun., 1993, 1807. 24 C. D. Garner, D. Collison and E. Pidcock, Philos. Trans. R. Soc. London, Ser. A, 1996, 354, 325. 25 A. Rosenheim and H. Y. Mong, Z. Anorg. Allg. Chem., 1925, 148, 25. 26 N. J. Campbell, M. V. Capparelli, W. P. GriYth and A. C. Skapski, Inorg. Chim. Acta, 1983, 77, L215. 27 R. L. Beddoes, D. Collison, C. D. Garner, J. Grigg, M. Helliwell, P. A. Tasker, D. Thorp and J. M. Thorpe, to be published. 28 V. R. Dhanak, A. W. Robinson, G. van der Laan and G. Thornton, Rev. Sci. Instrum., 1992, 63, 1342. 29 C. S. Mythen, G. van der Laan and H. A. Padmore, Rev. Sci. Instrum., 1992, 63, 1313. 30 G. A. Sawatzky and D. Post, Phys. Rev. B, 1979, 20, 1546. 31 D. Collison, B. Gahan, C. D. Garner and F. E. Mabbs, J. Chem. Soc., Dalton Trans., 1980, 667. 32 D. Collison, C. D. Garner, C. M. McGrath, J. F. W. Mosselmans, E. Pidcock, M. D. Roper, B. G. Searle, J. M. W. Seddon, E. Sinn and N. A. Young, to be published. 33 D. Collison, C. D. Garner, C. M. McGrath, J. F. W. Mosselmans, M. D. Roper, J. M. W. Seddon, E. Sinn and N. A. Young, unpublished work. Received 21st January 1998; Paper 8/00568K

ISSN:1477-9226    

DOI:10.1039/a800568k

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2205–2210 2205 Using pseudohalides (NCS2, N3 2) as a probe for the active site of (Ï-alkoxo)diiron(III) complexes and to reveal a novel asymmetrical structure Den-Nan Horng * and Kwang-Ming Lee Department of Chemistry and Physics, The Chinese Military Academy, PO Box 90602-6, Fengshan, 830 Taiwan Received 10th March 1999, Accepted 30 April 1999 A series of (m-alkoxo)diiron(III) complexes [Fe2(L)Cl4]Cl?2H2O 1, [Fe2(L)(NCS)n(Cl)42n]Cl? 4H2O 2–5 (n = 1–4) and [Fe2(L)(N3)n(Cl)42n] NO3?3H2O 6–9 (n = 1–4), where HL is N,N,N9,N9-tetrakis(2-benzimidazolylmethyl)-2- hydroxy-1,3-diaminopropane, have been synthesized and their structures, magnetic and redox properties and Mössbauer spectra have been investigated.Three complexes 1, 3 and 9 were characterized by single crystal structure analysis. The structures of 1 and 9 are geometrically symmetric, but 3 is asymmetric. The Mössbauer spectra of all complexes are typical of high-spin (m-alkoxo)diiron(III) complexes. Complexes 2–9 exhibit intense IR bands (2022– 2081 cm21) which are characteristic of terminally bound thiocyanate (N-bound) and azide ligands.The E1/2 and the DEpc of 1, 3 and 9 increase with p-donor eVectiveness of the exogenous ligands in the following order: NCS2 < Cl2 < N3 2. The 2J (30024.2 K) of 1, 3 and 9 are in the range of 13.3–16.4 cm21, indicating that the iron(III) sites are antiferromagnetically coupled.Introduction The chemistry of dinuclear iron complexes is of particular importance to gain insight into the structures and functions of the active forms of proteins such as hemerythrin (Hr),1,2 ribonucleotide reductase (RRB2) 3,4 and methane monooxygenase (MMO).5–7 Dinuclear metal complexes with sterically and electronically controlled environments are expected to make diVerent biofunctions. It is of interest not only to understand how these non-heme diiron proteins aVect their respective chemical transformations but also to determine what factors direct the reactivity of their metallocenters to achieve a particular function.It is often found that the dinuclear site of the metalloenzyme situates its metal ions in chemically distinct environments. From the perspective of the metal, four distinct environments can readily be identified:8 (1) symmetric, (2) donor asymmetry, (3) geometrical asymmetry and (4) co-ordination number asymmetry. Many geometric symmetry or asymmetry model complexes have been reported, however the eVects of changing from geometric symmetry into asymmetry on the physical properties and function of dinuclear sites are much less studied.Pseudohalides, such as thiocyanate and azide ions, can be used as probes for the active-site structures of non-heme diiron proteins. For example, crystallographic investigations revealed that the binding modes of azidomethemerythrin and oxyhemerythrin (oxyHr) are almost identical.9,10 Recent examples of azide adducts 11 have also been reported.Nevertheless, only two crystal structures of thiocyanate-bound diiron model compounds had been published so far.12,13 Our interest in the active sites of dinuclear iron proteins has led us to the exploration of pseudohalide-bound diiron(III) complexes and to study the influence of pseudohalides, such as thiocyanate and azide ions, on the structure of (m-alkoxo)diiron( III) complexes of HL (N,N,N9,N9-tetrakis(2-benzimidazolylmethyl)- 2-hydroxy-1,3-diaminopropane). The bis-octahedral [Fe2(L)X4]1 complexes comprise two five-membered rings involving 2-hydroxypropane chains and four five-membered rings resulting from the co-ordination of the (benzimidazolylmethyl) amino fragments of the polydentate ligand.Scheme 1 shows three possible isomer structures for [Fe2(L)X4]1; the two pairs of benzimidazole rings of the ligand can have three possible arrangements, such as facial–facial, meridional– meridional and meridional–facial forms.We have synthesized a series of diiron complexes [Fe2(L)(X)n(Cl)42n]Cl (X = NCS2 or N3 2, n = 0–4) and three crystal structures were determined. It is interesting that [Fe2(L)Cl4]Cl?2H2O and [Fe2(L)(N3)4]NO3? 3H2O are mer, mer geometrically symmetric structures, but [Fe2(L)(NCS)2Cl2]Cl?4H2O is a fac, mer asymmetric one. To our best knowledge, this is the first example that pseudohalide can induce asymmetric geometry from symmetric.In this paper we report the characterization of the complexes by single crystal X-ray diVraction, magnetic susceptibility, Mössbauer, redox Scheme 1 Three possible conformations of [Fe2(L)X4]1. Fe1 Fe2 N O N X4 X1 X3 N N N N X2 Fe1 Fe2 N O N NCS NCS Cl N N N N Cl Fe1 Fe2 N O N O O N N OPPh3 N Ph3PO N N HN N (a) fac, fac (b) mer, mer (c) mer, fac = X1, X2, X3, X4 = Cl, N3, NO, O2P(OPh)2, MeOH, m-CO2R, m-O2AsMe2, H2O, etc.2206 J. Chem. Soc., Dalton Trans., 1999, 2205–2210 and optical spectroscopic techniques and explore the influence of pseudohalide on geometric symmetry.Experimental 1,2-Diaminobenzene was sublimed before use, while all other chemicals were A.R. grade used without further purification. Preparations N,N,N9,N9-Tetrakis(2-benzimidazolylmethyl)-2-hydroxy-1,3- diaminopropane trihydrate HL?3H2O. The ligand, HL was synthesized by condensing 1,2-diaminobenzene with 2-hydroxy- 1,3-diaminopropane-N,N,N9,N9-tetraacetic acid, utilizing the procedure reported earlier by Reed and co-workers.14 It was characterized by 1H NMR in DMSO-d6 (Calc.for C35H40N10O4: C, 63.24; H, 6.06; N, 21.07. Found: C, 63.15; H, 6.01; N, 20.98%). [Fe2(L)Cl4]Cl?2H2O 1. Iron(III) chloride (0.324 g, 2 mmol) and HL (0.665, 1 mmol) were mixed in 50 ml EtOH and stirred for 10 min. After standing for about 1 d, the dark orange solution yielded red rhombic crystals. The crystals were suitable for single-crystal structure analysis.Yield 0.81 g (85%) (Calc. for C35H37Cl5Fe2N10O3: C, 45.06; H, 4.00; N, 15.02. Found: C, 43.88; H, 4.01; N, 14.58%). [Fe2(L)(NCS)n(Cl)42n]Cl?4H2O 2–5 (n 5 1–4). A solution of complex 1 (0.191 g, 0.2 mmol) in 50 ml methanol was treated with n × 0.2 mmol of AgNO3. After stirring overnight, the white precipitate of AgCl was removed by filtration and the solution mixed with n × 0.1 mmol of KSCN in 20 ml methanol. The resulting red-wine solution was allowed to crystallize at room temperature for about 2 d, yielding wine-colored microcrystals (72–80% yield).Only the crystals of 3 were suitable for single-crystal structure analysis [Calc. for C36H41Cl4Fe2N11O5S 2: C, 43.53; H, 4.16; N, 15.51. Found: C, 43.30; H, 4.08; N, 15.42%. nCN 2031 cm21 (KBr pellet). Calc. for C37H41Cl3Fe2- N12O5S2 3: C, 43.74; H, 4.07; N, 16.54. Found: C, 43.48; H, 3.95; N, 16.37%. nCN 2023 cm21. Calc. for C38H41Cl2Fe2N13O5S3 4: C, 43.95; H, 3.98; N, 17.53. Found: C, 43.88; H, 3.88; N, 17.38%.nCN 2023 cm21. Calc. for C39H41ClFe2N14O5S4 5: C, 44.14; H, 3.89; N, 18.48. Found: C, 44.12; H, 3.75; N, 18.32%. nCN 2022 cm21]. [Fe2(L)(N3)n(Cl)42n]NO3?3H2O 6–9 (n 5 1–4). The preparative procedure is almost identical with that described above, except that KSCN was replaced by NaN3. Only the crystals of 9 were suitable for single-crystal structure analysis (Calc. for C35H39Cl3Fe2N14O7 6: C, 42.64; H, 3.99; N, 19.89. Found: C, 41.02; H, 3.90; N, 19.05%. nNN 2076 cm21.Calc. for C35H39- Cl2Fe2N17O7 7: C, 42.36; H, 3.96; N, 23.99. Found: C, 41.48; H, 3.87; N, 22.87%. nCN 2081 cm21. Calc. for C35H39ClFe2N20O7 8: C, 42.08; H, 3.94; N, 28.04. Found: C, 41.78; H, 4.01; N, 27.58%. nCN 2081 cm21. Calc. for C35H39Fe2N23O7 9: C, 41.81; H, 3.91; N, 32.04. Found: C, 41.82; H, 3.80; N, 31.62%. nCN 2051 and 2077 cm21). Physical measurements Elemental analyses: Heraeus CHN-O-Rapid Analyzer. 1H NMR: Bruker AC300 spectrometer at 300 MHz. Infrared spectrum: Perkin-Elmer FT-IR spectrometer using KBr pellets.Electronic spectra: Shimadzu UV-210 spectrometer at room temperature in MeOH. Cyclic voltammetry: BAS-100A Electrochemical Analyzer using a three-compartment cell. A platinum working electrode, platinum-wire auxiliary and a Ag–Ag1 (0.01 mmol dm23 AgNO3 in CH3CN–DMSO 10: 1) reference electrode were employed. All solutions were degassed by purging with nitrogen for at least 15 min prior to use. The ferrocene–ferrocenium couple was employed as an internal reference.The magnetic susceptibility of a polycrystalline sample was measured by using a Quantum Design SQUID susceptometer. The sample was loaded anaerobically into a gel capsule and suspended in a plastic straw. A background correction for the empty capsule and straw was applied to the data; a total of 31 data points were collected in the temperature range 4.2 to 300 K. 57Fe Mössbauer measurements were made on a constant-velocity instrument, previously described.15 Velocity calibration was made using a 10 mg 99.99% pure iron foil.Typical linewidths for all three pairs of iron foil lines fell in the range 0.24–0.27 mm s21. Isomer shifts are reported relative to iron foil at 300 K. Crystal structure determination Single crystals of complexes 1, 3 and 9 were obtained by vapor diVusion of diethyl ether into concentrated ethanol solutions of the respective complexes. The crystal data of 1 and 9 were collected on a Enraf-Nonius CAD4 four-circle diVractometer equipped with a graphite monochromator using Mo-Ka radiation (l = 0.71073 Å).The data of 3 were collected on a Siemens P4 diVractometer equipped with a graphite monochromator using Mo-Ka radiation. Details of crystal parameters, data collection and structure refinement are summarized in Table 1. The structures were solved by the direct method using SHELXTL PLUS16 and refined using SHELXL 93.17 All non-hydrogen atoms, except for some belonging to the solvent molecules, were refined anisotropically.All H atoms, except for water, at calculated positions with thermal parameters equal to 1.2 times that of the attached C atoms were not refined. The counter anion chloride of 3 and the water of complexes 3 and 9 are disordered over several positions, to which some restraints were applied and modeled using diVerent molecules with occupancies of 0.15–0.5. CCDC reference number 186/1448. See http://www.rsc.org/suppdata/dt/1999/2205/ for crystallographic files in .cif format.Results and discussion The ligand HL, which has four benzimidazole fragments, is known to act as a bridge in diiron(III) complexes and has proven to be suitable for the synthesis of dinuclear metal complexes.18–25 The syntheses of [Fe2(L)(X)n(Cl)42n]Cl?3H2O complexes with X2 = NCS2 or N3 2 proceed in excellent yield, chloride being displaced from Fe2(L)(Cl)52n(NO3)n by pseudohalide nucleophiles. The presence of NCS2 (N-bonded) or N3 2 ligands in complexes 2–9 is indicated by sharp CN or NN stretches between 2030 and 2070 cm21.Reaction of 2 molar equivalents of FeCl3 in ethanol with one of HL leads to red crystals of [Fe2(L)Cl4]Cl?2H2O 1. In an earlier study, Sakurai et al.18 reported a diiron(III) complex Fe2(L)Cl5 and a m-alkoxo diiron core structure capped by the L ligand and four chloro ligands was proposed. The structure of complex 1 agrees with the proposed structure. The complex [Fe2(L)Cl4]Cl?2H2O crystallized in the monoclinic space group C2/c.An ORTEP26 drawing of the cation is shown Fig. 1(a), and selected interatomic distances and angles are listed in Table 2. The structure reveals that the iron(III) ions in the dinuclear complex are six-co-ordinated in a distorted octahedral geometry. Each metal atom has two benzimidazole moieties, a tertiary nitrogen atom, a bridging alkoxo oxygen atom and two chloro ligands. The Fe ? ? ?Fe separation of 3.712(5) Å, similar to those found in related complexes which do not have bridging ligands,21 but larger than that found in complexes having bridged ligands, for example [Fe4O2(L)2(O2CPh)2][ClO4]2- [O3SC6H4Me-p]2 and [Fe4O2(L9)2(OAc)2][BF4]4,22 (L9 is the 1-ethylbenzimidazole derivative of L) that exhibit Fe ? ? ? Fe distances between 3.539 and 3.488(2) Å in their carboxylato bridged Fe2 units.Each iron core has two benzimidazole ligands co-ordinated cis to each other (fac form), with two ring planesJ.Chem. Soc., Dalton Trans., 1999, 2205–2210 2207 perpendicular to each other (85–908). One benzimidazole ligand is co-ordinated trans to a chloride and another trans to an alkoxide ligand. The co-ordination sphere is completed by a chloride and tertiary amine ligands in trans position. The Fe–Cl bond length is aVected by trans influence; those trans to tertiary amine (2.207(4) and 2.226(4) Å) are shorter than those trans to benzimidazole (2.391(4) and 2.352(4) Å).Treatment of complex 1 with two equivalents of KNCS yields [Fe2(L)(NCS)2Cl2]Cl?4H2O 3, in which two chloro ligands (in 1) have been displaced by two thiocyanate ligands. Most of the known related compounds have two of the benzimidazoles bound to an iron atom in a cis fashion (Scheme 1(a), fac, fac form). Only one structurally characterized iron(III) complex has been found to have two benzimidazoles bound to one iron atom in a trans form (Scheme 1(b), mer, mer form).To our best knowledge, no example has been found where L is bound in an asymmetric manner (Scheme 1(c), mer, fac form). The Fig. 1 The crystal structures of the complex cations of complexes 1 (a), 3 (b) and 9 (c). Thermal ellipsoids are at the 30% probability level. Hydrogen atoms are omitted for clarity. molecular structure of 3 is depicted in Fig. 1(b), and selected interatomic distances and angles are listed in Table 3. When compared with 1, each iron atom has one chloride replaced by one thiocyanate ligand.It is interesting that the two iron centers have the same N4OCl co-ordination sphere, but diVerent coordination mode. For the Fe1 center the two benzimidazole ligands are co-ordinated cis to each other and one thiocyanate is trans to N5(benzimidazole). At Fe2, the two benzimidazole ligands co-ordinate trans to each other and the two benzimidazole rings are perpendicular to the plane defined by the two iron atoms and the alkoxide; the thiocyanate ligands are trans to the tertiary amine(N10).Complex 3, therefore, is not only one of the three known examples having a terminal thiocyanate coordinated at an iron(III) center, but also the first example of a dinuclear iron(III) complex having asymmetrically bonded benzimidazole moieties in a mer, fac form. The co-ordination sphere around the Fe2 center is similar to that of [Fe2(L)Cl4]Cl, while that of Fe1 is similar to that of [Fe2(m-1,2-O2)(L9)(Ph3PO)2] reported by Que and co-workers.24 Especially, the mean Fe1–N (benzimidazole) distance of 2.078(13) Å is similar to that of [Fe2(m-1,2-O2)(L9)(Ph3PO)2] (2.088(4) Å).The structural similarity between the co-ordination spheres of Fe1 and that of the O2 adduct in the non-heme diiron complex [Fe2(m-1,2-O2)- (L9)(Ph3PO)2] suggests that NCS indeed is a good ligand to probe the active site of non-heme diiron proteins. The asymmetrical structure of 3 has two interesting features as compared with that of 1 and [Fe2(m-1,2-O2)(L9)(Ph3PO)2].First, the conformations of the two irons are independent, although L is a symmetrical ligand. This property is similar to that of diiron proteins such as hemerythrin. Secondly, the co-ordination sites of the two irons are distinct; only when the iron center bonds to one thiocyanate which is trans to a tertiary amine, the two benzimidazoles are in a trans form. The azide adduct [Fe2(L)(N3)4]NO3?3H2O 9 crystallized in the monoclinic space group C2/c.An ORTEP drawing of the structure is shown in Fig. 1(c), and selected interatomic distances and angles are listed in Table 4. A general feature of 9 is that its structural parameters are similar but not identical with those of 1, two pairs of benzimidazoles also bound to each iron atom in a cis form. Table 5 compares the partial structural parameters of 1, 3 and 9 with those of related (m-alkoxo)- diiron(III) complexes. Complex 10, [Fe2(L){O2P(OPh)2}Cl2- (MeOH)]21, is a mono-bridged complex of the m-alkoxo variety, [Fe4O2(L9)2(OAc)2]41 11;22 [Fe2(L)(O2AsMe2)Cl(H2O)]31 12;23 [Fe2(m-1,2-O2)(L9)(PH3PO)2]31 13;24 and [Fe2(NO)2(L9)(O2CPh)] 21 14 25 are dibridged complexes.A general feature of the monobridged species is that their structural parameters are diVerent from those of dibridged ones. Thus, 1, 3 and 10 have longer Fe ? ? ?Fe distances (3.700(2)–3.717(6) Å) and larger Fe– O–Fe angles (130.9(2)–132.0(4)8) than the others.It is noticeable that the Fe–O–Fe angle of 9 (127.9(5)8) is the smallest among those of other monobridged complexes. The alkoxobridge in 9 constrains the Fe ? ? ?Fe distance to 3.642 Å. These values are comparable to those found for the dibridged complex 12. The two other dibridged complexes 11 and 13 have somewhat shorter Fe ? ? ?Fe distances (3.49 and 3.46 Å) and smaller Fe–O–Fe angles (120.9, 120.88). It is interesting that both the azide adduct 9 and the dioxygen adduct 13 have longer Fe–N (tertiary) bond distances (2.315(11) for 9, 2.364(5) for 13, 2.25– 2.30 Å for the other complexes), which can be explained by the trans influence of azide on tertiary amine.The Fe-N (benzimidazole) distances (2.049(12)–2.154(10) Å) of 1, 3 and 9 also fall in the range found in 10–14 (2.06–2.23 Å). Cyclic voltammetry Cyclic voltammograms of these complexes were recorded in a mixed-solvent system (CH3CN–DMSO 10: 1) owing to the insolubility of the compounds in CH3CN.The redox processes are in a region (20.7 to 10.2 V) free from solvent interference.2208 J. Chem. Soc., Dalton Trans., 1999, 2205–2210 Table 1 Crystallographic data for complexes 1, 3 and 9 1 3 9 Chemical formula M Crystal system Space group a/Å b/Å c/Å b/8 V/Å3 ZT /K Dc /g cm23 F(000) m/mm21 Reflections collected/unique (Rint) Data/restraints/parameters Final R1, wR2 [I > 2s(I)] Largest diVerence peak and hole/e Å23 C35H37Cl5Fe2N10O3 934.70 Monoclinic C2/c 22.365(3) 13.812(2) 28.778(4) 105.05(1) 8585(2) 8 293(2) 1.446 3824 1.033 5552 5552/0/487 0.0744, 0.1990 1.176, 20.495 C37H41Cl3Fe2N12O5S2 1015.99 Monoclinic P21/c 13.638(3) 22.508(3) 17.667(3) 99.56(2) 5348(2) 4 293(2) 1.262 2088 0.817 7271/6933(0.0566) 6930/21/576 0.0894, 0.2420 0.587, 20.482 C35H39Fe2N23O7 1005.59 Monoclinic C2/c 21.338(4) 15.685(3) 28.017(6) 102.68(3) 9148(3) 8 293(2) 1.460 4144 0.707 9175/8980(0.0875) 8971/20/612 0.0828, 0.1944 0.623, 20.373 Ferrocene was used as internal standard, yielding the Fc–Fc1, one-electron couple at Em = 0.2 V vs.Ag–Ag1. The cyclic voltammograms of complexes 1, 3 and 9 are shown in Fig. 2. Complex 1 exhibits an irreversible reduction at 20.51 V and a coupled oxidation–reduction wave at 20.218 and 20.345 V, respectively. The E1/2 value for this process is 20.282 V, however, DE is 0.12 V. The redox process therefore by definition is quasi-reversible.27 The voltammograms of complexes 3 and 9 are displayed in Fig. 2(b) and 2(c). Two quasireversible redox processes are observed for each complex corresponding to successive one-electron-transfer steps. The redox steps at 20.227 and 20.423 V for 3 and at 20.356 and 20.508 V for 9 correspond to the FeIIIFeIII–FeIIFeIII and FeIIFeIII–FeIIFeII couples, respectively. The HOMO level has the correct symmetry to interact with benzimidazole p* orbitals and pp-donor orbitals of halide and pseudohalide ligands. The E1/2 of complexes 1, 3 and 9 are 20.282, 20.227 and 20.356 V and the DEpc of complexes 1, 3 and 9 are 20.160, 20.169 and 20.145 V.Both increase with p-donor eVectiveness of the exogenous ligands,28 in the following order: NCS2 < Cl2 < N3 2. Mössbauer spectrum The Mössbauer spectra for complexes 1, 3 and 9 were recorded Table 2 Selected bond lengths (Å) and angles (8) for [Fe2(L)Cl4]1 Fe(1) ? ? ?Fe(2) Fe(2)–O(1) Fe(1)–N(3) Fe(1)–Cl(1) Fe(2)–N(5) Fe(2)–N(10) Fe(2)–Cl(4) Fe(1)–O(1)–Fe(2) O(1)–Fe(1)–N(3) O(1)–Fe(1)–Cl(1) N(1)–Fe(1)–N(3) N(1)–Fe(1)–Cl(1) N(3)–Fe(1)–N(9) N(3)–Fe(1)–Cl(2) N(9)–Fe(1)–Cl(2) O(1)–Fe(2)–N(5) O(1)–Fe(2)–N(10) O(1)–Fe(2)–Cl(4) N(5)–Fe(2)–N(10) N(5)–Fe(2)–Cl(4) N(7)–Fe(2)–Cl(3) N(10)–Fe(2)–Cl(3) Cl(3)–Fe(2)–Cl(4) 3.712(5) 2.021(8) 2.154(10) 2.226(4) 2.108(11) 2.257(10) 2.391(4) 132.0(4) 154.3(4) 107.7(3) 89.5(4) 95.4(3) 73.4(4) 86.6(3) 88.7(3) 89.3(3) 78.9(3) 93.0(2) 78.4(4) 166.8(3) 99.4(3) 172.3(3) 93.9(2) Fe(1)–O(1) Fe(1)–N(1) Fe(1)–N(9) Fe(1)–Cl(2) Fe(2)–N(7) Fe(2)–Cl(3) O(1)–Fe(1)–N(1) O(1)–Fe(1)–N(9) O(1)–Fe(1)–Cl(2) N(1)–Fe(1)–N(9) N(1)–Fe(1)–Cl(2) N(3)–Fe(1)–Cl(1) N(9)–Fe(1)–Cl(1) Cl(1)–Fe(1)–Cl(2) O(1)–Fe(2)–N(7) O(1)–Fe(2)–Cl(3) N(5)–Fe(2)–N(7) N(5)–Fe(2)–Cl(3) N(7)–Fe(2)–N(10) N(7)–Fe(2)–Cl(4) N(10)–Fe(2)–Cl(4) 2.043(8) 2.122(10) 2.279(10) 2.352(4) 2.119(10) 2.207(4) 89.1(3) 81.2(3) 88.7(2) 77.8(4) 166.5(3) 98.0(3) 169.0(3) 97.92(14) 152.7(4) 107.8(3) 84.7(4) 97.8(3) 73.7(4) 87.3(3) 89.3(3) Table 3 Selected bond lengths (Å) and angles (8) for [Fe2(L)(NCS)2- Cl2]1 Fe(1) ? ? ?Fe(2) Fe(2)–O(1) Fe(1)–N(3) Fe(1)–Cl(1) Fe(2)–N(5) Fe(2)–N(10) Fe(2)–Cl(2) Fe(1)–O(1)–Fe(2) O(1)–Fe(1)–N(3) O(1)–Fe(1)–Cl(1) N(1)–Fe(1)–N(3) N(1)–Fe(1)–Cl(1) N(3)–Fe(1)–N(9) N(3)–Fe(1)–N(11) N(9)–Fe(1)–N(11) O(1)–Fe(2)–N(5) O(1)–Fe(2)–N(10) O(1)–Fe(2)–N(12) N(5)–Fe(2)–N(10) N(5)–Fe(2)–N(12) N(7)–Fe(2)–Cl(2) N(10)–Fe(2)–Cl(2) Cl(2)–Fe(2)–N(12) 3.717(6) 2.065(9) 2.087(13) 2.382(5) 2.142(11) 2.257(11) 2.220(8) 131.9(4) 92.4(4) 168.4(3) 154.1(6) 87.0(3) 77.3(5) 103.6(6) 179.0(6) 89.0(4) 79.1(4) 87.2(4) 79.0(5) 167.5(6) 97.6(5) 170.9(4) 97.1(4) Fe(1)–O(1) Fe(1)–N(1) Fe(1)–N(9) Fe(1)–N(11) Fe(2)–N(7) Fe(2)–N(12) O(1)–Fe(1)–N(1) O(1)–Fe(1)–N(9) O(1)–Fe(1)–N(11) N(1)–Fe(1)–N(9) N(1)–Fe(1)–N(11) N(3)–Fe(1)–Cl(1) N(9)–Fe(1)–Cl(1) Cl(1)–Fe(1)–N(11) O(1)–Fe(2)–N(7) O(1)–Fe(2)–Cl(2) N(5)–Fe(2)–N(7) N(5)–Fe(2)–Cl(2) N(7)–Fe(2)–N(10) N(7)–Fe(2)–N(12) N(10)–Fe(2)–N(12) 2.005(9) 2.068(12) 2.257(12) 1.920(13) 2.109(12) 2.045(13) 89.0(4) 81.5(4) 98.1(6) 77.3(5) 101.8(6) 86.6(4) 87.0(4) 93.4(5) 154.3(5) 108.1(3) 88.5(4) 95.4(4) 75.4(5) 89.8(5) 88.6(5) Table 4 Selected bond lengths (Å) and angles (8) for [Fe2(L)(N3)4]1 Fe(1) ? ? ?Fe(2) Fe(2)–O(1) Fe(1)–N(3) Fe(1)–N(11) Fe(2)–N(5) Fe(2)–N(10) Fe(2)–N(20) Fe(1)–O(1)–Fe(2) O(1)–Fe(1)–N(3) O(1)–Fe(1)–N(11) N(1)–Fe(1)–N(3) N(1)–Fe(1)–N(11) N(3)–Fe(1)–N(9) N(3)–Fe(1)–N(14) N(9)–Fe(1)–N(14) O(1)–Fe(2)–N(5) O(1)–Fe(2)–N(10) O(1)–Fe(2)–N(20) N(5)–Fe(2)–N(10) N(5)–Fe(2)–N(20) N(7)–Fe(2)–N(17) N(10)–Fe(2)–N(17) N(17)–Fe(2)–N(20) 3.642(6) 2.014(7) 2.106(10) 1.893(13) 2.049(12) 2.255(12) 1.996(13) 127.9(5) 152.1(5) 107.3(5) 90.3(4) 90.4(6) 74.6(5) 86.4(5) 98.3(7) 88.7(3) 78.1(4) 91.8(4) 78.1(5) 165.7(6) 98.8(5) 172.3(5) 96.6(6) Fe(1)–O(1) Fe(1)–N(1) Fe(1)–N(9) Fe(1)–N(14) Fe(2)–N(7) Fe(2)–N(17) O(1)–Fe(1)–N(1) O(1)–Fe(1)–N(9) O(1)–Fe(1)–N(14) N(1)–Fe(1)–N(9) N(1)–Fe(1)–N(14) N(3)–Fe(1)–N(11) N(9)–Fe(1)–N(11) N(11)–Fe(1)–N(14) O(1)–Fe(2)–N(7) O(1)–Fe(2)–N(17) N(5)–Fe(2)–N(7) N(5)–Fe(2)–N(17) N(7)–Fe(2)–N(10) N(7)–Fe(2)–N(20) N(10)–Fe(2)–N(20) 2.039(7) 2.068(12) 2.315(11) 2.01(2) 2.103(10) 1.838(14) 92.3(4) 79.1(4) 88.5(5) 76.4(6) 174.4(7) 100.5(6) 165.7(5) 94.7(7) 153.1(5) 108.0(5) 85.7(3) 96.9(6) 75.0(5) 87.5(4) 87.9(5)J. Chem.Soc., Dalton Trans., 1999, 2205–2210 2209 Table 5 Comparison of relevant distances, angles and physical properties for (m-alkoxo)diiron(III) complexes Feature 1 3 9 10 11 12 13 14 Fe ? ? ? Fe Fe–O–Fe Fe–O Fe–N(38) b Fe–N(Bim)c 2J/cm21 d/mm s21 DEQ/mm s21 Ref. 3.712(5) 132.0(4) 2.043(8) 2.021(8) 2.279(10) 2.257(10) 2.122(10) 2.154(10) 2.108(11) 2.119(10) 13.3 0.36 0.54 This work 3.717(6) 131.9(4) 2.005(9) 2.065(9) 2.257(12) 2.257(11) 2.068(12) 2.087(13) 2.142(11) 2.109(12) 16.4 0.35 0.51 This work 3.642(6) 127.9(5) 2.039(7) 2.014(7) 2.315(11) 2.255(12) 2.068(12) 2.106(10) 2.049(12) 2.103(10) 15.1 0.37 0.58 This work 3.700(2) 130.9(2) 2.011(4) 2.056(4) 2.295(4) 2.276(4) 2.120(5) 2.106(4) 2.138(5) 2.073(4) 13.7 0.46 0.59 21 3.488(2) 120.9(4) 1.995(2) 2.018(2) 2.25(1) 2.26(1) 2.22(1) 2.16(1) 2.23(1) 2.16(1) 83 a a 22 3.580(2) 127.3(3) 1.971(6) 2.025(6) 2.288(7) 2.269(7) 2.063(7) 2.086(7) 2.077(8) 2.055(7) 10.3 0.35, 0.35 0.37, 0.65 23 3.462(3) 120.8(3) 1.991(3) 1.991(3) 2.364(5) 2.364(5) 2.082(4) 2.094(4) 2.082(4) 2.094(4) a 0.52 0.72 24 a 117.7(2) 2.017(5) 2.006(5) 2.290(6) 2.282(7) 2.119(7) 2.117(7) 2.114(7) 2.135(7) 23 0.67 1.44 25 a Not reported. b N(38) refers to the tertiary amine nitrogen.c N(Bim) refers to the benzimidazole nitrogen. at room temperature and all show a slight asymmetrical quadruple doublet. The isomer shifts (d) and quadruple splitting (DEQ) are summarized in Table 5. Since the isomer shifts for high-spin mononuclear and alkoxo-bridged binuclear iron(III) complexes generally fall in the range 0.3–0.6 mm s21,29 the present isomer shifts (0.35–0.37 mm s21) are consistent with the presence of high-spin iron(III) ions.Magnetic susceptibility The magnetic susceptibility of complexes 1, 3 and 9 were measured in the temperature range 4.2 to 300.0 K, and the coupling constants found are listed in Table 5. Fig. 3 shows the experimental data and fitted curves of magnetic susceptibility of 3. The magnetic moment at room temperature is 3.88 mB. With lowering of the temperature the magnetic moment decreases and reaches 0.13 mB at 4.2 K.This magnetic behavior suggested the operation of an antiferromagnetic spin exchange. The Fig. 2 Cyclic voltammograms of complexes 1 (a), 3 (b) and 9 (c), scan rate 0.5 V s21. magnetic data could be fitted on the basis of an isotropic Heisenberg model H9 = 22JS1S2 (S1 = S2 = 5/2), eqn. (1), where cm = C(1 2 P)? A B 1 4.37 2p T 1 t.i.p. (1) A = 2e2x 1 10e6x 1 28e12x 1 60e20x 1 110e30x, B = 1 1 3e2x 1 5e6x 1 7e12x 1 9e20x 1 11e30x, C = Nb2g2/kT and x = J/kT. The symbols N, b, g and k in these expressions have their usual meanings, and p represents the fraction of mononuclear paramagnetic impurity present.The shapes of the plots in Fig. 3 are clearly indicative of antiferromagnetic exchange interactions. All the three diiron(III) complexes 1, 3 and 9 are weakly antiferromagnetic, the 2J values decreasing in the order 3 (16.4) > 9 (15.1) > 1 (13.3 cm21). This order is consistent with the magnetostructural relationship proposed by Gorun and Lippard.30 These values are in the typical range for m-alkoxo or m-hydroxo bridged systems.Electronic spectroscopy Electronic absorption spectra in the UV-visible region of 1, 3 and 9 complexes were recorded in methanol solution and the data are collected in Table 6. The absorption bands below 300 nm are due to “free” ligand, and their absorption coeYcients are typical of p æÆ p* transitions. Complex 1 exhibits intense UV bands in MeOH but no significant visible absorption.Complex 3 shows a more intense peak at 480 nm (em 4816 M21 cm21), while this region of 1 is featureless. Complex 9 show a peak at 342 nm (em 4291 M21 cm21) with a less intense shoulder at about 450 nm. These two bands of 3 and 9 originate from N(N3) and N(NCS) to iron charge transfer and give information on the energy separation between the ground and excited Fig. 3 The experimental data and fitted curves of magnetic susceptibility (.) and moments (h) of complex 3.2210 J.Chem. Soc., Dalton Trans., 1999, 2205–2210 states. In the crystal structure of 9, the four N3 2 have N–N–N angles in the range of 173–1788. Bent N3 2 bound to FeIII will have two allowed LMCT transitions.31 This is also consistent with the CV measurement, in that the reduction potential Epc(3) is more positive than Epc(9). Acknowledgements Research grants from the National Science Council of Taiwan and The Chinese Military Academy are highly appreciated. References 1 R.E. Stenkamp, Chem. Rev., 1994, 94, 715. 2 M. A. Holmes, I. L. Trong, S. Turley, L. C. Sieker and R. E. Stenkamp, J. Mol. Biol., 1991, 218, 583. 3 J. Stubbe, Adv. Enzymol., 1989, 63, 349. 4 P. Nordlund and H. Eklund, J. Mol. Biol., 1993, 232, 123. 5 J. D. Lipscomb, Annu. Rev. Microbiol., 1994, 48, 371. 6 A. C. Rosenzweig, C. A. Frederick, S. J. Lippard and P. Nordlund, Nature (London), 1993, 366, 537. 7 A. C. Rosenzweig, P. Nordlund, P. M. Takahara, C. A. Frederick and S. J.Lippard, Chem. Biol., 1995, 2, 409. 8 J. H. Satcher, Jr., M. W. Droege, T. J. R. Weakley and R. T. Taylor, Inorg. Chem., 1995, 34, 3317. 9 R. E. Stenkamp, L. C. Sieker and L. H. Jensen, Acta Crystallogr., Sect. B, 1983, 39, 697. Table 6 Quantitative spectral data of complexes 1, 3 and 9 Complex lmax/nm e/M21 cm21 1 3 9 239 272 278 333 243 272 279 331 480 242 272 279 342 13040 15760 15328 3136 16208 17088 16880 3120 4816 15439 16566 16087 4291 10 P. E. Clark and J. Webb, Biochemistry, 1981, 20, 4628. 11 J. Ai, J. A. Broadwater, T. M. Loehr, J. Sanders-Loehr and B. G. Fox, JBIC, 1997, 2, 37. 12 T. J. Mizoguchi and S. J. Lippard, Inorg. Chem., 1997, 36, 4526. 13 J. H. Satcher, Jr., A. L. Balch, M. M. Olmstead and M. W. Droege, Inorg. Chem., 1996, 35, 1749. 14 V. McKee, M. Zvagulis, J. V. Dagdigian, M. G. Patch and C. A Reed, J. Am. Chem. Soc., 1984, 106, 4765. 15 T.-Y. Dong, C. H. Huang, C. K. Chang, Y. S. Wen, L. S. Lee, J. A. Chen, W. Y. Yeh and A. Yeh, J. Am. Chem. Soc., 1993, 115, 6357. 16 G. M. Sheldrick, SHELXTL PLUS, Program Package for Structure Solution and Refinement, Siemens Analytical Instruments, Madison, WI, 1990. 17 G. M. Sheldrick, SHELXL 93, Program for Crystal Structure Refinement, University of Göttingen, 1993. 18 T. Sakurai, H. Kaji and A. Nakahara, Inorg. Chim. Acta, 1982, 67, 1. 19 Y. Nishida, M. Takeuchi, H. Shimo and S. Kida, Inorg. Chim. Acta, 1984, 96, 115. 20 P. Mathur, M. Crowder and G. C. Dismukes, J. Am. Chem. Soc., 1987, 109, 5227. 21 B. Bremer, K. Schepers, P Fleischhauer, W. Haase, G. Henkel and B. Krebs, J. Chem. Soc., Chem. Commun., 1991, 510. 22 Q. Chen, J. B. Lynch, P. Gomez-Romero, A. Ben-Hussein, G. B. Jameson, C. J. O’Connor and L. Que, Jr., Inorg. Chem., 1988, 27, 2673. 23 B. Eulering, F. Ahlers, F. Zippel, M. Schmidt, H.-F. Nolting and B. Krebs, J. Chem. Soc., Chem. Commun., 1995, 1305. 24 Y. H. Dong, S. P. Yan, V. G. Young, Jr. and L. Que, Jr., Angew. Chem., Int. Ed. Engl., 1996, 35, 6618. 25 A. L. Feig, M. T. Bautista and S. J. Lippard, Inorg. Chem., 1996, 35, 6892. 26 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 27 A. J. Bard and L. R. Faulkner, Electrochemical Methods, Wiley, New York, 1980. 28 T. F. Tekut, C. J. O’Connor and R. A. Holwerda, Inorg. Chem., 1993, 32, 324. 29 T. C. Gibb and N. N. Greenwood, Mössbauer Spectroscopy, Chapman and Hall, London, 1971, p. 148. 30 S. M. Gorun and S. J. Lippard, Inorg. Chem., 1991, 30, 1625. 31 J. M. McCormick, R. C. Reem and E. I. Solomon, J. Am. Chem. Soc., 1991, 113, 9066. Paper 9/01905G

ISSN:1477-9226    

DOI:10.1039/a901905g

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2211–2217 2211 Electrochemical synthesis and structural characterisation of transition metal complexes with 2,6-bis(1-salicyloylhydrazonoethyl) pyridine, H4daps Manuel R. Bermejo,*a Matilde Fondo,a Ana M. González,a Olga L. Hoyos,a Antonio Sousa,*a Charles A. McAuliVe,*b Wasif Hussain,b Robin Pritchard b and Vladimir M. Novotorsev c a Departamento de Química Inorgánica, Facultad de Química, Universidad de Santiago, E-15706 Santiago de Compostela, Spain.E-mail: qimb45@uscmail.usc.es; qiansoal@uscmail.usc.es b Department of Chemistry, University of Manchester Institute of Science and Technology, Manchester, UK M60 1QD c N.S. Kurnakov Institute of General and Inorganic Chemistry, 31 Leninsky prosp., 117907 Moscow, Russian Federation Received 15th March 1999, Accepted 11th May 1999 Neutral manganese, cobalt and nickel complexes of the pentadentate hydrazone 2,6-bis(1-salicyloylhydrazonoethyl) pyridine (H4daps) have been prepared by means of electrochemical syntheses.They have been characterised by elemental analyses, IR spectroscopy, fast atom bombardment mass spectrometry (FAB) and magnetic susceptibility measurements. The molecular structures of [Mn(H2daps)(py)2] 1, [Co(H2daps)(py)2] 2, [Ni2(H2daps)2]?CH2Cl2 3, and [Ni2(H2daps)2(py)2]?CH2Cl2 4 have been determined by X-ray diVraction. Depending on the nature of the metal ion, the dianionic [H2daps]22 ligand shows diVerent co-ordination modes in these complexes: 1 and 2 are mononuclear with the metal atom in a pentagonal bipyramidal environment, 3 and 4 are binuclear with a helicate structure in which the nickel atoms attain octahedral co-ordination.Introduction In the past few years the co-ordination properties of hydrazone ligands have extensively been investigated.1–9 The development of this co-ordination chemistry is, in part, the result of the interesting donor systems which could result.Many ligands, mainly containing nitrogen donors in heterocyclic rings, but also in hydrazones, have been investigated in an attempt to predict their behaviour upon co-ordination. The structural characterisation of the resultant mononuclear or polynuclear complexes has led to some emerging patterns and has improved the design of molecular threads which may be twisted, yielding helical molecular systems.6,7 Nevertheless many questions still remain and the predicted systems are not always obtained.The desire for an in depth understanding of the rules that lead to systems of diVerent nuclearity, together with their pharmacological activity,10–12 as well as their interesting electric and magnetic properties,13–15 make research on the co-ordination chemistry of hydrazone ligands even more attractive. Part of our research program is directed towards the synthesis and structural characterisation of transition metal complexes with SchiV bases.16 Many methods of synthesis have been tried in an attempt to obtain compounds of this kind.Recently we have turned our attention to electrochemical synthesis, as it has been found to be a convenient route for the preparation of neutral SchiV base metal complexes through the oxidation of a metal anode in a solution of a SchiV base bearing weakly acidic groups, e.g. salicylaldimines (phenol OH) or pyrrolaldimines (pyrrole NH).17 In this paper we apply this methodology to synthesize neutral complexes of Mn, Co and Ni containing 2,6-bis(1-salicyloylhydrazonoethyl)pyridine, H4daps with high purity and good yield.Results and discussion A series of neutral chelate complexes has been synthesized by electrochemical oxidation of the corresponding metal anode in the presence of the neutral ligand H4daps in an organic solvent. The electrochemical eYciency of the cell (Table 1) was close to 0.5 mol F21, which is compatible with Scheme 1. Cathode: H4daps 1 2e2 æÆ H2(g) 1 H2daps22 Anode: H2daps22 1 M æÆ M(H2daps) 1 2e2 Scheme 1 Elemental analyses (Table 2) show that all metals react with the ligand in molar ratio 1 : 1 to aVord solvated complexes of the bis-deprotonated ligand [H2daps]22 in high purity.These neutral metal complexes are obtained in high yields and appear to be stable in the solid state and in solution. Most of them are Table 1 Experimental conditions for the electrochemical syntheses (initial current 10.0 mA, electrolysis time 2.5 h) Metal Amount (mg) dissolved Voltage (V) Ef a/ mol F21 Mn Co Ni 30.4 30.2 25.1 17.5 4.2 3.3 0.59 0.55 0.52 a Electrochemical eYciency of the cell, defined as the amount of metal dissolved per Faraday of charge.2212 J.Chem. Soc., Dalton Trans., 1999, 2211–2217 Table 2 Analytical and some selected data for the complexes Analysis (%) a Complex C N H meff/mB FABb m/z Colour Mn(H2daps)(H2O)0.5 Co(H2daps)(H2O)1.5(CH3CN) Ni(H2daps)(H2O)1.5(CH3CN) Ni(H2daps)(CH2Cl2)0.5 56.0 (55.9) 54.3 (53.9) 53.6 (53.9) 53.5 (53.2) 14.4 (14.2) 14.9 (15.1) 15.4 (15.1) 13.3 (13.2) 3.6 (4.0) 4.4 (4.4) 4.6 (4.5) 3.9 (3.8) 5.7 4.0 2.9 2.9 485 489 488–491; 976* 488–491; 976* Dark orange Yellow-orange Yellow-brown Yellow-brown a Found (calculated). b Peaks corresponding to [ML]1 except * that correspond to [M2L2]1.Table 3 Selected bond lengths (Å) and angles (8) for complexes 1 and 2 with estimated standard deviations (e.s.d.s) in parentheses 1 2 Mn1–O2 Mn1–N1 Mn1–N2 Mn1–N6 O2–Mn1–O29 O2–Mn1–N1 O2–Mn1–N2 O2–Mn1–N29 O2–Mn1–N6 O2–Mn1–N69 N1–Mn1–N2 N1–Mn1–N29 N1–Mn1–N6 N2–Mn1–N29 N2–Mn1–N6 N2–Mn1–N69 N6–Mn1–N6 2.243(4) 2.380(6) 2.267(5) 2.297(4) 88.2(2) 135.9(1) 68.4(2) 156.1(2) 87.6(2) 86.6(1) 67.7(1) 67.7(1) 94.0(1) 135.3(3) 87.8(2) 95.2(2) 172.0(2) Co1–O2 Co1–O1 Co1–N1 Co1–N3 O2–Co1–O1 O2–Co1–N1 O2–Co1–N3 O2–Co1–N2 O2–Co1–N6 O2–Co1–N7 O1–Co1–N1 O1–Co1–N3 O1–Co1–N2 O1–Co1–N6 O1–Co1–N7 2.153(5) 2.171(5) 2.213(6) 2.181(6) 78.3(2) 140.2(2) 149.2(2) 70.6(2) 89.8(2) 87.6(2) 141.2(2) 70.9(2) 148.6(2) 88.1(2) 89.4(2) Co1–N2 Co1–N6 Co1–N7 N1–Co1–N3 N1–Co1–N2 N1–Co1–N6 N1–Co1–N7 N3–Co1–N2 N3–Co1–N6 N3–Co1–N7 N2–Co1–N6 N2–Co1–N7 N6–Co1–N7 2.210(6) 2.168(6) 2.193(6) 70.5(2) 70.1(2) 94.7(2) 88.6(2) 140.1(3) 88.9(2) 92.3(2) 88.3(2) 92.8(2) 176.7(2) insoluble or sparingly soluble in water and common organic solvents but soluble in polar co-ordinating solvents such as DMF, DMSO and pyridine.All the complexes melt above 300 8C.FAB mass and IR spectra All the FAB mass spectra show peaks (Table 2) due to the fragments [M(H2daps)]1. A peak at m/z 976 due to the fragment [Ni(H2daps)]2 1 is also observed for 3 and for Ni(H2daps)- (H2O)1.5(CH3CN). The IR spectra show that in all cases the Fig. 1 Molecular structure of [Mn(H2daps)(py)2] 1 showing the atomic numbering scheme. bands due to the amide I [n(CO)] and amide II [d(NH) 1 n(CN)] modes undergo negative shifts of 19–60 and 46–64 cm21, respectively.This behaviour is compatible with the participation of the oxygen atoms of both carbonyl CO groups in the co-ordination to the metal, in agreement with previous results.18 The spectra also show the absence of the n(N–H) bands, which for the “free” ligand appear at 3208 cm21. This is in accordance with the dianionic nature of the ligand. X-Ray studies Crystal structures of [Mn(H2daps)(py)2] 1 and [Co(H2daps)- (py)2] 2. The crystal structures of complexes 1 and 2 are shown in Figs. 1 and 2 and selected bond lengths and angles are given in Table 3. Both structures consist of discrete [M(H2daps)(py)2] molecules, with a crystallographic twofold axis bisecting the Fig. 2 Molecular structure of [Co(H2daps)(py)2] 2 showing the atomic numbering scheme.J. Chem. Soc., Dalton Trans., 1999, 2211–2217 2213 Table 4 Selected bond lengths (Å) and angles (8) for complexes 3 and 4 with estimated standard deviations (e.s.d.s) in parentheses 3 4 Ni1–N1 Ni1–N19 Ni1–N4 Ni1–N49 Ni1–O2 Ni1–O29 Ni1 ? ? ? Ni2 N4–Ni1–N49 N4–Ni1–O29 N4–Ni1–O2 N4–Ni1–N1 N4–Ni1–N19 N49–Ni1–O29 N49–Ni1–O2 N49–Ni1–N1 N49–Ni1–N19 O29–Ni1–O2 O29–Ni1–N1 O29–Ni1–N19 O2–Ni1–N1 O2–Ni1–N19 N1–Ni1–N19 Ni2–N1–Ni1 2.281(5) 2.430(4) 1.962(4) 1.965(4) 2.026(4) 2.010(3) 3.06(2) 174.34(18) 106.31(16) 79.35(16) 76.14(18) 100.53(16) 79.35(16) 99.86(16) 104.64(17) 73.81(16) 104.37(15) 84.49(15) 153.05(14) 155.14(15) 82.80(15) 99.88(15) 80.73(14) Ni2–N1 Ni2–N19 Ni2–N2 Ni2–N29 Ni2–O1 Ni2–O19 Ni2–N1–Ni1 N2–Ni2–O1 N2–Ni2–O19 N2–Ni2–N19 N29–Ni2–N2 N29–Ni2–O1 N29–Ni2–O19 N29–Ni2–N19 N1–Ni2–N2 N1–Ni2–N29 N1–Ni2–N19 N1–Ni2–O1 N1–Ni2–O19 O1–Ni2–O19 O1–Ni2–N19 O19–Ni2–N19 2.454(4) 2.300(4) 1.956(4) 1.953(4) 2.002(3) 2.019(4) 89.74(13) 79.10(17) 100.08(17) 104.37(17) 173.70(17) 107.14(16) 79.06(17) 75.80(17) 73.92(16) 99.80(16) 98.64(17) 152.73(17) 80.86(16) 108.04(15) 84.17(15) 154.41(15) Ni1–N1 Ni1–N2 Ni1–O1 Ni2–N4 Ni2–N5 Ni2–O3 Ni1 ? ? ? Ni2 N2–Ni1–N29 N2–Ni1–O1 N2–Ni1–O19 N2–Ni1–N19 N2–Ni1–N1 O1–Ni1–O19 O1–Ni1–N19 O1–Ni1–N1 N19–Ni1–N1 N4–Ni2–N49 N4–Ni2–N5 N4–Ni2–N59 N5–Ni2–N59 O3–Ni2–N5 O3–Ni2–N59 O39–Ni2–N49 2.175(11) 1.990(12) 2.120(10) 2.136(13) 2.148(12) 2.036(10) 4.51(9) 165.1(7) 76.9(4) 93.0(4) 76.7(5) 113.1(5) 95.1(5) 153.6(4) 87.5(4) 101.7(6) 87.9(7) 162.5(5) 85.0(4) 106.0(6) 76.5(4) 106.2(5) 87.4(5) O3–Ni2–N49 O3–Ni2–N4 O3–Ni2–O39 89.4(5) 87.4(5) 175(6) molecule in complex 1.The metal atom is in a distorted pentagonal bipyramidal environment [MN5O2] in both complexes.The equatorial plane of the bipyramid is occupied by the N3O2 donor set of the [H2daps]22 ligand, giving rise to four fivemembered chelate rings. Four of the five angles subtended at Mn by adjacent equatorial atoms are slightly smaller than the value of 728 for an ideal pentagonal bipyramidal arrangement, ranging from 67.7(1) to 68.4(2)8, while the fifth angle [O2–Mn1–O29] is 88.2(2)8. The pentagon is less distorted in the cobalt complex [four angles ranging from 70.1 to 70.98 and the fifth O2–Co1–O1 78.3(2)8].The deviations of the pentagon from planarity are also somewhat diVerent in the two cases. The five atoms of the donor set are planar within the experimental errors for the manganese complex (maximum deviation from the N3O2 least squares plane = 0.084 Å, with the manganese atom sitting on the plane) while the deviation from planarity is slightly higher for the cobalt compound (maximum = 0.098 Å, with the cobalt atom 0.004 Å below this plane).In both cases the apical positions are filled by two pyridine molecules, which come from the solvent of crystallisation. The interaxial angle is closer to the ideal value in the cobalt (176.7(2)8) than in the manganese complex (172.0(2)8). The structures of complexes 1 and 2 feature intramolecular hydrogen bonds between the phenol hydrogen atom and the hydrazide nitrogen atom, O (phenol) ? ? ? N (hydrazide) of ca. 2.5 Å for the manganese and cobalt complexes.This interaction resulted in O3–C14 acquiring some double bond character (1.323(8) Å for Mn and 1.331(9) Å for Co; ideal value for C–OH (phenol) = 1.36 Å). These data are in agreement with the bisdeprotonated nature of the ligands in 1 and 2. All the angles and bond distances are similar to the values found in related seven-co-ordinate complexes of Co and Mn containing acylhydrazones 19–23 and do not merit further discussion. Intermolecular interactions by p–p stacking between two very close capping pyridines and between two phenol rings are observed in 1 but not in 2.Crystal structure of [Ni2(H2daps)2]?CH2Cl2 3. The crystal structure of [Ni2(H2daps)2]?CH2Cl2 is shown in Fig. 3, together with the atom numbering scheme. Bond angles and distances are contained in Table 4. The compound is a binuclear nickel complex, with a helicate structure, solvated with one dichloromethane molecule. Each H4daps behaves as a dianionic ligand using five [ONNNO] donor atoms, viz.the pyridine nitrogen, both imine nitrogen and both carbonyl oxygen atoms, as in 1 and 2. However, the co-ordination mode of the ligand is found to diVer from that in 1 and 2. In 3 each ligand uses one imine nitrogen atom and one carbonyl oxygen atom to bind one metal centre. A rotation around the C–C bond adjacent to the pyridine ring allows the pyridine nitrogen atom to act as a bridge between the two nickel atoms. A further rotation about the symmetrical adjacent C–C bond leads to chelation of the remaining imine nitrogen and carbonyl oxygen atoms to a second metal centre, generating a double helical structure.This co-ordination mode produces four five-membered chelate rings around each nickel atom, which are in a distorted octahedral environment [NiN4O2]. The Ni ? ? ? Ni distance is 3.06(2) Å. This short distance is the result of the distortion of the central rhombus Ni1–N1–Ni2–N19, formed by both pyridine bridges and the two nickel atoms, with higher angles around each Ni atom (ca. 1008) and smaller than 908 around the pyridine nitrogen atoms. The Ni–N bond lengths are rather diVerent from one Fig. 3 An ORTEP24 view of the crystal structure of [Ni2- (H2daps)2]?CH2Cl2 3. Thermal ellipsoids are drawn at the 30% probability level. Lattice CH2Cl2 is not depicted. Hydrogen atoms, except those attached to oxygen atoms, are omitted for clarity.2214 J. Chem. Soc., Dalton Trans., 1999, 2211–2217 another; the Ni–N (imine) bonds (of ca. 1.96 Å) are shorter than the Ni–N (pyridine) bonds [ranging from 2.281(5) to 2.454(4) Å]. For each metal ion, one of the Ni–N (pyridine) bond lengths [Ni1–N1 2.281(5) and Ni2–N19 2.300(4) Å] is shorter than the other one [Ni1–N19 2.430(4) Å and Ni2–N1 2.454(4) Å]. The shorter distance corresponds to the interaction between the nickel atom and the pyridine ring in an equatorial plane and the longer one to the interaction with the pyridine group in an axial position.The Ni–O distances are similar for both metals (ca. 1.27 Å) and do not deserve further consideration. The four C–N (imine) bond distances are ca. 1.28 Å, typical of a double C]] N bond, and show the lack of electronic delocalisation as a consequence of the non-planar conformations of the ligands. The N (hydrazide) ? ? ? O (phenol) distances of ca. 2.5 Å, typical of intramolecular hydrogen bonds, indicate deprotonation of the hydrazide nitrogen atoms of the ligand.The most interesting feature of this compound lies in the octahedral environment around each metal centre and the double helical structure, as hydrazone ligands of this type usually lead to seven-co-ordinated complexes with a pentagonal bipyramidal geometry,1–4,11–15 as has also been found in 1 and 2. Helicates containing pyridine as a bridge have previously been described, mainly containing ligands with nitrogen donor atoms in heterocyclic rings or in acyclic imines,7 but few of them contain hydrazones. As far as we know, the most similar complex reported is [Ni(dapz)]2 25 [H2dapz = 2,6-diacetylpyridinebis( 19-phthalozinylhydrazone)] and a comparison between bond distances and angles for both complexes is shown below (see Table 5).Another important fact in relation with this structure is that it was thought that if a metal ion with a strong ligand fieldimposed preference for an octahedral geometry was selected, and a ligand with central pyridine and two other bidentate domains in each thread was used, a double helicate would result.7 The only diYculty would be to prevent the metal centres from adopting a pentagonal bipyramidal geometry.This could be avoided by introducing bulky substituents on the hydrazone. However these do not seem to be the unique reasons for obtaining a double helicate. The structure of a monomeric nickel compound [Ni(H4daps)(H2O)2]21, containing H4daps as a neutral ligand, has been described.26 The nickel atom is in a [NiN3O4] pentagonal bipyramidal environment, H4daps forming the equatorial plane and the water molecules filling the axial positions. The diVerent structures observed in 3 and in [Ni(H4daps)(H2O)2]21 cannot be attributed to the diVerent charge of the ligand (dianionic and neutral), as similar monomers have been found for manganese complexes containing dianionic and neutral H2dappc ligands (H2dappc = 2,6- diacetylpyridinebis(picolinylhydrazone)].20 In addition, reasons adducing diVerent nuclearity based on acidity of the reaction medium27 seem not to be valid in this case, as both compounds [Ni2(H2daps)2]?CH2Cl2 and [Ni(H4daps)(H2O)2][NO3]2 were obtained in a neutral medium.In an attempt to obtain the mononuclear neutral complex, 3 was treated with pyridine. This method has been previously reported to be successful for obtaining monomeric cobalt complexes with 2,29:69,20:60,2-:6-,2+-quinquepyridine ligands from binuclear complexes.28 However, in this case the experiment led to asymmetric cleavage of the pyridine bridges, yielding another helicate binuclear compound [Ni2(H2daps)2(py)2]? CH2Cl2, 4.Crystal structure of [Ni2(H2daps)2(py)2]?CH2Cl2 4. The molecular structure of [Ni2(H2daps)2(py)2]?CH2Cl2 4 is shown in Fig. 4, together with the atom numbering scheme and main bond distances and angles are given in Table 4. The compound is a binuclear nickel derivative, with the Ni atoms located on a crystallographic twofold axis.The [H2daps]22 ligand spans both metal atoms, and each nickel atom is in a distorted octahedral [NiN4O2] environment. However the nickel environments are diVerent. One arises from co-ordination of one nickel atom to the pyridine nitrogen, the imine nitrogen and one carbonyl oxygen atom of two [H2daps]22 ligands, the other from coordination of the nickel atom to one imine nitrogen and one carbonyl oxygen atom of two [H2daps]22 ligands and to the two nitrogen atoms of two pyridine molecules.Again, the Ni–N bond lengths are diVerent from one another and, as in complex 3, the Ni–N (imine) bonds are shorter than the Ni–N (pyridine) bonds. In addition, the Ni–N lengths corresponding to the isolated pyridine molecules are shorter than the one corresponding to the pyridine fragment of [H2daps]22. This is most probably due to steric hindrance. It should be noted that these distances are shorter than the corresponding distances in 3.This is a reflection of the pyridine in 3 acting as a bridging N donor rather than a terminal donor in 4. The cleavage of the pyridine bridges also leads to a longer Ni ? ? ? Ni distance in 4, 4.51(9) Å, than in 3, 3.06(2) Å. The C–O (phenol) distances of 1.27(2) and 1.34(2) Å are shorter than the ideal value. These data and the distances N (hydrazide) ? ? ? O (phenol) of ca. 2.5 Å suggest the presence of an intramolecular hydrogen bond between the phenol oxygen and the hydrazide nitrogen atoms, as a result of the bisdeprotonation of the ligand. It should be stressed that although the interaction of 3 with pyridine results is breaking of the pyridine bridges, the product of the reaction is not the expected mononuclear complex but a binuclear compound with both nickel atoms in diVerent environments.This behaviour contrasts with the symmetric breaking of the pyridine bridges in a binuclear complex containing quinquepyridine ligands, to yield mononuclear compounds.7,28 If we compare the binuclear compounds 3 and 4 with the related complexes [Ni2(dapz)2] and [Ni(H4daps)(H2O)2]21 (Table 5), some conclusions can be drawn.(1) The complexes [Ni2- (H2daps)2] and [Ni2(dapz)2] present very similar double helical structures, with both hydrazone ligands adopting the same conformation. The most remarkable diVerence is a more distorted Ni1–N1–Ni2–N19 central rhombus for 3, leading to a shorter Ni–Ni distance (3.06(2) Å in 3 and 3.125(2) Å in [Ni2(dapz)2]).All the other distances are quite similar and in the range of those expected for complexes containing hydrazone ligands. (2) The comparison of 3 and 4 with [Ni(H4daps)(H2O)2]21 is maybe more interesting and clearly shows a longer Ni–N (pyridine) distance in the binuclear complexes {ranging from 2.281(5) to 2.454(4) for 3, 2.175(11) for 4 and 2.028(6) Å for [Ni(H4daps)- Fig. 4 An ORTEP view of the crystal structure of [Ni2(H2daps)2- (py)2]?CH2Cl2 4.Lattice CH2Cl2 is not depicted. Thermal ellipsoids are drawn at the 30% probability level.J. Chem. Soc., Dalton Trans., 1999, 2211–2217 2215 Table 5 Comparison of bond lengths (Å) in 3, 4 and related complexes [Ni(H4daps)(H2O)]21a [Ni2(H2dapz)2] b [Ni2(H2daps)2] c [Ni2(H2daps)2(py)2] c Ni1–N (pyridine) Ni2–N (pyridine) Ni1–N (imine) Ni2–N (imine) Ni1–O (carbonyl) Ni2–O (carbonyl) Ni1 ? ? ? Ni2 C–N (pyridine) C (pyridine)–C (imine) C–N (imine) N (imine)–N (hydrazine) N (hydrazine)–C (carbonyl) C–O (carbonyl) C–O (phenol) N (hydrazine) ? ? ? O (phenol) 2.028(6) — 2.194(6); 2.081(6) — 2.628(6); 2.247(6) —— 1.347(10); 1.319(11) 1.490(11); 1.487(12) 1.288(10); 1.275(10) 1.342(10); 1.332(10) 1.371(11); 1.354(11) 1.221(10); 1.217(10) 1.377(9); 1.356(10) 2.62(1); 2.58(1) 2.347(7); 2.348(6) 2.313(7); 2.249(6) 1.985(7); 1.974(7) 1.975(7); 1.967(7) —— 3.125(2) 1.37(1); 1.36(1) 1.36(1); 1.36(1) 1.48(1); 1.39(1) 1.47(1); 1.45(1) 1.30(1); 1.30(1) 1.30(1); 1.28(1) 1.38(1); 1.36(1) 1.38(1); 1.36(1) — — — — 2.430(4); 2.281(5) 2.454(4); 2.300(4) 1.965(4); 1.962(4) 1.956(4); 1.953(4) 2.026(4); 2.010(3) 2.019(4); 2.002(3) 3.06(2) 1.357(7); 1.345(6) 1.364(7); 1.340(7) 1.481(8); 1.475(8) 1.466(8); 1.460(8) 1.284(6); 1.279(6) 1.288(7); 1.285(7) 1.377(6); 1.373(6) 1.375(6); 1.369(6) 1.342(7); 1.340(7) 1.340(7); 1.327(7) 1.276(6); 1.263(6) 1.277(6); 1.266(6) 1.346(7); 1.332(7) 1.351(8); 1.335(8) 2.56(2); 2.54(2) 2.175(11); 2.175(11) — 1.990(12); 1.990(12) 2.148(12); 2.148(12) 2.120(10); 2.120(10) 2.036(10); 2.036(10) 4.51(9) 1.36(2); 1.34(2) 1.36(2); 1.34(2) 1.50(2); 1.44(2) 1.50(2); 1.44(2) 1.30(2); 1.30(2) 1.30(2); 1.30(2) 1.39(2); 1.39(2) 1.39(2); 1.39(2) 1.35(2); 1.34(2) 1.35(2); 1.34(2) 1.28(2); 1.25(2) 1.28(2); 1.25(2) 1.34(2); 1.27(2) 1.34(2); 1.27(2) 2.56(2); 2.56(2) a Ref. 26. b Ref. 25. c This work. (H2O)2]21}, even when the pyridine ring is acting as a terminal donor (4). In contrast to this, the Ni–N (imine) and Ni–O (carbonyl) bonds are shorter in the binuclear complexes.The non-planar conformation of the ligands and the consequent lack of delocalisation is shown in all cases by the short C–N (imine) bonds (ca. 1.28 Å). The dianionic nature of the ligand in 3 and 4 is pointed out by the C–O (phenol) distances: these are slightly shorter for the binuclear compounds and reflect the intramolecular hydrogen bond between the phenol oxygen and the hydrazide nitrogen atoms.Magnetic measurements All the compounds show magnetic moment values per atom very close to that expected for their magnetically dilute metal(II) ions at room temperature. This confirms the oxidation state 1II of the metal centre and indicates the bis-deprotonation of H4daps. Magnetic measurements at variable temperature have been performed for the binuclear nickel compounds, 3 and 4. Magnetic susceptibility data for 3 were collected in the 78–289 K range, using a Faraday balance, and in the 5–300 K range for 4 in a SQUID at a small applied field of 5000 G.The magnetic behaviour of 3 and 4 is shown in Figs. 5 and 6, respectively, as plots of meff per Ni atom versus temperature. The eVective magnetic moments of complex 3 were calculated by formula (1). The value per Ni atom at room tempermeff = (8cMT)1/2 (1) Fig. 5 Plot of eVective magnetic moment versus T for complex 3, in the range 78–300 K; j represents the experimental data and the solid line the best fit of the data. ature is 2.88 mB and it decreases gradually with decreasing temperature, indicative of an antiferromagnetic exchange.The best fit of the values was obtained with the Heisenberg– Dirac–van Vleck (HDVV) theoretical model for two exchangecoupled nickel(II) ions in the absence of orbital degeneracy of the complex ground states. The spin Hamiltonian has the form (2) where J is the isotropic exchange coupling, g the isotropic g H = 22JS1S2 1 gbH(S1z 1 S2z) (2) factor and S are the spins of the exchange coupled ions (in this case S1 = S2 = 2). The calculation of the theoretical meff values and the least squares treatment were carried out as reported.29 The best fit values are 22J = 54 cm21, g = 2.2 which are within the usual range expected for binuclear nickel(II) complexes, showing antiferromagnetic exchange.The amount of paramagnetic impurity is negligible within experimental error. The eVective magnetic moments of complex 4 versus temperature are shown in Fig. 6. The temperature dependency first increases with decreasing temperature and then passes through a maximum at 19 K, clearly indicating the existence of ferromagnetic exchange between the Ni atoms. The experimental results were fitted using eqn. (3). The isotropic spin Hamiltonian c = (1 2 a)cdim 1 amon 1 Na (3) has the form (4) where a is the molar fraction of magnetic H = 22JS1S2 2 2zJMs ·SzÒ (4) Fig. 6 Plot of eVective magnetic moment versus T for complex 4, in the range 5–300 K.Details as in Fig. 5.2216 J. Chem. Soc., Dalton Trans., 1999, 2211–2217 Table 6 Crystal data and details of refinement for complexes 1–4 1 2 3 4 Formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 V/Å3 T/K Crystal size/mm Z m/cm21 Reflections collected No. unique reflections RR 9 C33H29MnN7O4 642.57 Monoclinic C2/c 18.528(1) 12.783(7) 14.274(1) — 112.36(5) — 3126.7(5) 296(2) 0.40 × 0.25 × 0.25 4 4.51 2982 2884 (Rint = 0.096) 0.061 0.050 C33H29CoN7O4 646.60 Monoclinic P21/n 14.315(8) 13.67(1) 16.126(5) — 106.82(3) — 3021(5) 296(2) 0.30 × 0.30 × 0.30 4 6.15 5810 5572 (Rint = 0.134) 0.043 0.043 C47H38Cl2N10Ni2O8 1059.19 Triclinic P1� 12.739(3) 14.266(3) 14.699(3) 77.00(3) 84.61(3) 63.04(3) 2139.9(9) 293(2) 0.40 × 0.22 × 0.10 2 9.93 3603 3391 (Rint = 0.0161) 0.036 0.036 C28.5H31ClN6NiO6 647.75 Monoclinic C2/c 20.993(4) 20.649(4) 16.821(3) — 122.32(2) — 6162(2) 293(2) 0.40 × 0.30 × 0.20 8 2.135 2791 2791 0.123 0.124 impurities, Na refers to the temperature-independent paramagnetism (250 × 1026 cm3 mol21 per NiII) and 2zJMs ·SzÒ describes the interbinuclear interaction;30 S are the spins of the exchange coupled ions (in this case S1 = S2 = 1 without zero- field splitting for the binuclear complex).The values of the parameters obtained from non-linear fits of the experimental data by eqn. (3) are 22J = 2.55 and g = 2.0, and agree fairly well with previous results for ferromagnetic exchange between nickel(II) ions.31 While antiferromagnetic interaction in binuclear nickel(II) complexes is often observed, the presence of a ferromagnetic exchange is quite unusual 31 and shows the very diVerent exchange mechanism between 3 and 4.This is in accordance with the very diVerent environments around the nickel atoms in the two cases. Conclusion The electrochemical synthetic methodology has been shown to be a new and simple way to prepare first row transition neutral metal(II) complexes of hydrazone ligands with high purity and good yield. The same reaction conditions lead to complexes of diVerent nuclearity (mononuclear and binuclear), suggesting that Ni has a low preference for a pentagonal bipyramidal geometry.It thus seems that the central ion plays a more important role in producing helicates than the ligand itself. Previous results seemed to indicate that the presence of a good donor solvent could break the pyridine bridges in a double helical complex to give rise to monomeric compounds with a co-ordination number of seven.The reaction mechanism must be more complicated as the presence of pyridine is not able to convert helicate 3 into the expected monomer. The addition of pyridine does indeed break the pyridine bridges, as predicted, but rather than producing the expected monomer it yields another binuclear compound. As a result, it appears that we must think about new reasons to explain which variables really favour the production of helicates and what are the reasons for retention of the helicate structure in some hydrazone complexes in the presence of strong donors.Experimental Chemicals All solvents, 2,6-diacetylpyridine and salicylhydrazide are commercially available and were used without further purifi- cation. Metals (Ega Chemie) were used as ca. 2 × 2 cm2 plates. Physical measurements Elemental analyses were performed on a Carlo Erba EA 1108 analyser.The NMR spectra were recorded on a Bruker WM- 250 spectrometer using DMSO-d6 as solvent, infrared spectra as KBr pellets on a Bio-Rad FTS 135 spectrophotometer in the range 4000–600 cm21 and fast atom bombardment (FAB) mass spectra on a Kratos MS-50 mass spectrometer, employing Xe atoms at 70 keV in m-nitrobenzyl alcohol as a matrix. Room-temperature magnetic susceptibilities were measured using a Digital Measurement system MSB-MKI, calibrated using tetrakis(isothiocyanato)cobaltate(II).Measurements of the binuclear nickel complexes were taken by the Faraday technique in the range 78–289 K for 3 and in a SQUID using an applied field of 5000 G in the range 5–300 K for 4. Ligand preparation The ligand H4daps was prepared as previously described.2 Its purity was checked by elemental analyses, 1H NMR and IR spectroscopy. The yield was almost quantitative (Found: C, 64.1; H, 4.8; N, 16.1. Calc. for C23H21N5O4: C, 64.0; H, 4.9; N, 16.2%). 1H NMR (DMSO-d6): d 2.50 (s, 6 H), 6.97–8.17 (m, 11 H), 11.51 (s, br, 2 H) and 11.80 (br, 2 H). Syntheses of the complexes The compounds were obtained using an electrochemical procedure. 17,32 An acetonitrile solution of the ligand containing about 10 mg of tetramethylammonium perchlorate, as supporting electrolyte, was electrolysed using a platinum wire as the cathode and a metal plate as the anode. The cell can be summarised as: Pt(2)|H4daps 1 MeCN|M(1), where M stands for the metal.The synthesis is typified by the preparation of Ni2(H2daps)2(H2O)1.5(CH3CN). A suspension (0.2 g, 0.464 mmol) of the ligand in acetonitrile (80 cm3), containing 10 mg of tetramethylammonium perchlorate, was electrolysed for 2.5 h using a current of 10 mA. Concentration of the resulting solution to a third of its initial volume yielded a yellow-brown solid that was washed with diethyl ether and dried under vacuum. Crystallisation from dichloromethane–hexane produced dark red crystals of [Ni2(H2daps)2]?CH2Cl2, suitable for X-ray diVraction.Slow evaporation of pyridine–dichloromethane solutions containing Mn(H2daps)(H2O)0.5, Co(H2daps)(H2O)1.5(CH3CN) and [Ni2(H2daps)2]?CH2Cl2 yielded crystals of [Mn(H2daps)- (py)2], [Co(H2daps)(py)2] and [Ni2(H2daps)2(py)2]?CH2Cl2, respectively, suitable for X-ray diVraction. Crystallographic measurements Crystal data and details of refinement are given in Table 6 for all the structures.J. Chem. Soc., Dalton Trans., 1999, 2211–2217 2217 [Mn(H2daps)(py)2] 1 and [Co(H2daps)(py)2] 2.Data were collected using an Enraf-Nonius CAD-4 diVractometer for complex 1 and a Rigaku AFC6S diVractometer for 2. The structures were solved by direct methods 33 and refined by fullmatrix least squares on F2. Lorentz-polarisation corrections were applied. Hydrogen atoms attached to oxygen ats were located in the Fourier map and isotropically refined. All calculations were performed using the TEXSAN crystallographic software package.34 [Ni2(H2daps)2]?CH2Cl2 3.Data were collected using a CAD-4 diVractometer. The structure was solved by direct methods and refined using Fourier techniques. Hydrogen atoms attached to oxygen atoms were located. Data processing and computation were carried out by using the SHELXL 97 program package.35 [Ni2(H2daps)2(py)2]?CH2Cl2 4. Data were collected using a Nicolet P-3 diVractometer. The crystals were extremely unstable under X-ray irradiation and we were unable to prevent decomposition (standards decay = 51%).This is the reason for the rather poor resolution of the structure. The structure was solved by direct methods33a and refined using Fourier techniques.36 CCDC reference number 186/1458. See http://www.rsc.org/suppdata/dt/1999/2211/ for crystallographic files in .cif format. Acknowledgements The authors thank Xunta de Galicia (XUGA 20901B97) and Ministerio de Educación y Ciencia (Spain) (PB95-0827) for financial support.References 1 D. Wester and G. J. Palenik, Inorg. Chem., 1976, 15, 755. 2 C. Pelizzi and G. Pelizzi, J. Chem. Soc., Dalton Trans., 1980, 1970. 3 C. Pelizzi, G. Pelizzi and F. Vitali, J. Chem. Soc., Dalton Trans., 1987, 177. 4 C. Carini, G. Pelizzi, P. Tarasconi, C. Pelizzi, K. C. Molloy and P. C. Waterfield, J. Chem. Soc., Dalton Trans., 1989, 289. 5 A. Bonardi, C. Carini, C. Merlo, C. Pelizzi, G. Pelizzi, P. Tarasconi, F. Vitali and F. Cavatorta, J.Chem. Soc., Dalton Trans., 1990, 2771. 6 E. C. Constable, Tetrahedron, 1992, 48, 10013. 7 E. C. Constable, in Comprehensive Supramolecular Chemistry, eds. J. L. Atwood, J. E. D. Davies, D. D. McNicol, F. Vögtle, J. P. Sauvage and M. W. Hosseini, Pergamon, Oxford, 1996, vol. 9, p. 213. 8 K. Andjelkovic, Y. Ivanovic, S. R. Niketic, B. Prelesnik and V. M. Leovac, Polyhedron, 1997, 16, 4221. 9 S. Abram, C. Maichle-Mössmer and U. Abram, Polyhedron, 1998, 17, 131. 10 M. Carcelli, P.Mazza, C. Pelizzi, G. Pelizzi and F. Zani, J. Inorg. Biochem., 1995, 57, 43 and refs. therein. 11 A. Bacchi, A. Bonardi, M. Carcelli, P. Mazza, P. Pelagatti, C. Pelizzi, G. Pelizzi, C. Solinas and F. Zani, J. Inorg. Biochem., 1998, 69, 101. 12 A. R. Todeschini, A. L. P. De Miranda, K. C. M. Da Silva, S. C. Parrini and E. J. Barreiro, Eur. J. Med. Chem., 1998, 33, 189. 13 O. Kahn, Angew. Chem., Int. Ed. Engl., 1985, 24, 834. 14 J. M. Williams, M. A. Beno, K. D. Carlson, U. Geiser, H.C. J. Kao, A. M. Kini, L. C. Porter, A. J. Schultz, R. J. Thorn, H. H. Wang, M.-H. Wanyho and M. Evain, Acc. Chem. Res., 1988, 21, 1. 15 R. Sumita, D. D. Mishra, R. V. Maurya and N. Nageswara, Polyhedron, 1997, 16, 1825. 16 M. R. Bermejo, M. Fondo, A. García-Deibe, M. Rey, J. Sanmartín, A. Sousa, M. Watkinson, C. A. McAuliVe and R. G. Pritchard, Polyhedron, 1996, 15, 4185; C. E. Hulme, M. Watkinson, R. G. Pritchard, C. A. McAuliVe, N. Jaiboon, B. Beagley, A. Sousa, M.R. Bermejo and M. Fondo, J. Chem. Soc., Dalton Trans., 1997, 1805; M. Watkinson, M. Fondo, M. R. Bermejo, A. Sousa, C. A. McAuliVe, R. G. Pritchard, N. Jaiboon, N. Aurangzeb and M. Naeem, J. Chem. Soc., Dalton Trans., 1999, 31. 17 M. L. Durán, J. A. García-Vázquez, J. Romero, A. Castiñeiras, A. Sousa, A. D. Garnovskii and D. A. Garnovskii, Polyhedron, 1997, 16, 1707; J. A. García-Vázquez, J. Romero, M. L. Durán, A. Sousa, A. D. Garnovskii, A. S. Burlov and D. A. Garnovskii, Polyhedron, 1998, 17, 1547. 18 A. Bonardi, C. Merlo, C. Pelizzi, G. Pelizzi, P. Tarasconi and F. Cavatorta, J. Chem. Soc., Dalton Trans., 1991, 1063. 19 M. Nardelli, C. Pelizzi and G. Pelizzi, Transition Met. Chem., 1977, 2, 35. 20 C. Pelizzi, G. Pelizzi, G. Predieri and S. Resola, J. Chem. Soc., Dalton Trans., 1982, 1349. 21 C. Pelizzi, G. Pelizzi, G. Predieri and F. Vitali, J. Chem. Soc., Dalton Trans., 1985, 2387. 22 T. J. Giordano, G. J. Palenik, R. Palenik and D. A. Sullivan, Inorg. Chem, 1979, 18, 2445. 23 S. Ianelli, G. Minardi, C. Pelizzi, G. Pelizzi, L. Reverberi, C. Solinas and P. Tarasconi, J. Chem. Soc., Dalton Trans., 1991, 2113. 24 C. K. Johnson, ORTEP, report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 25 G. Paolucci, S. Stelluto, S. Sitran, D. Ajo, F. Benetollo, A. Polo and G. Bombieri, Inorg. Chim. Acta, 1992, 193, 57. 26 C. Pelizzi, G. Pelizzi, S. Porretta and F. Vitali, Acta Crystallogr., Sect. C, 1986, 42, 1131. 27 A. Bino and N. Cohen, Inorg. Chim. Acta, 1993, 210, 11. 28 E. C. Constable, Prog. Inorg. Chem., 1994, 42, 42. 29 Y. V. Rakitin and V. T. Kalinnikov, Soviemennaya magnetokhimiya (Modern Magnetochemistry), Nauka, St. Petersburg, 1994, p. 272. 30 Y. V. Rakitin, V. M. Novotorsev, G. M. Larin, V. V. Zelentsov and V. T. Kalinnikov, J. Struct. Chem. (USSR), 1974, 15, 881. 31 D. Volkmer, B. Hommerich, K. Griesar, W. Haase and B. Krebs, Inorg. Chem., 1996, 35, 3792. 32 C. Oldham and D. G. Tuck, J. Chem. Educ., 1982, 59, 420. 33 (a) G. M. Sheldrick, SHELXS 86, in Crystallographic Computing, eds. G. M. Sheldrick, C. Krueger and R. Goddard, Oxford University Press, 1985, p. 175; (b) P. T. Beurskens, DIRDIF, Direct Methods for DiVerence Structures, an automatic procedure for phase extension and refinement of diVerence structure factors, technical report 1984/1, Crystallography Laboratory, Toernooiveld, Nijmegen, 1984. 34 TEXSAN, Structure Analysis Package, Molecular Structure Corp., The Woodlands, TX, 1985. 35 G. M. Sheldrick, SHELXL 97 (SHELXS 97 and SHELXL 97), Programs for Crystal Structure Analyses, University of Göttingen, 1998. 36 G. M. Sheldrick, SHELXL 93, University of Göttingen, 1993. Paper 9/02018G

ISSN:1477-9226    

DOI:10.1039/a902018g

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2215–2224 2215 Synthesis, structure and redox chemistry of 1,2-bis(ruthenocenyl)- ethylene derivatives: a novel structural rearrangement to a (Ï-Á6 :Á6- pentafulvadiene)diruthenium complex upon two-electron oxidation † Masaru Sato,*,a Yasushi Kawata,a Ayumi Kudo,a Ayako Iwai,a Hideki Saitoh b and Shukichi Ochiai c a Chemical Analysis Center, Saitama University, Urawa, Saitama 338, Japan b Department of Chemistry, Faculty of Science, Saitama University, Urawa, Saitama 338, Japan c S.T.JAPAN, Inc., Nihonbashi Kakigara-cho, Chuo-ku, Tokyo 103, Japan Formylruthenocene, 1-formyl-19,29,39,49,59-pentamethylruthenocene and 1-formyl-2,3,4,5-tetramethylruthenocene were treated with TiCl4–Zn in thf to aVord the corresponding ethylene derivatives trans-1,2- bis(ruthenocenyl)ethylene, trans-1,2-bis(19,29,39,49,59-pentamethylruthenocenyl)ethylene and trans-1,2-bis(2,3,4,5- tetramethylruthenocenyl)ethylene in excellent yields.Similarly, the dimethyl analogs were obtained from acetylruthenocene and 1-acetyl-19,29,39,49,59-pentamethylruthenocene in good yields. Cyclic voltammograms of the ethylene complexes showed an irreversible two-electron oxidation wave at significantly lower potential than that of pentamethylruthenocene or ruthenocene. Two-electron chemical oxidation of these complexes with p-benzoquinone– BF3?OEt2 gave stable dicationic (m-h6 :h6-pentafulvadiene)diruthenium complexes in moderate yields.The molecular structures of five complexes were determined by X-ray diVraction. Redox active binuclear organometallic complexes with a conjugated hydrocarbon bridging ligand, corresponding to organometallic versions of the multistage redox systems first described by Deuchert and Hünig,1 have attracted much attention in both fundamental and applied studies.2–7 A large number of dinuclear complexes with conjugated bridges have been reported, of which the chemistry of bis(ferrocenyl) compounds has been well investigated, particularly from the viewpoint of mixed valence, because ferrocene has a well defined and stable one-electron redox system.8 Ferrocene has also been recognized as a good trigger and termini for electronic switching phenomena. 9 Ruthenocene is a stable metallocene similar to ferrocene but shows diVerent electochemical properties.10 Owing to its irreversible two-electron oxidation process, there have been few reports about bis(ruthenocenyl) compounds.11–15 We have focused on redox-active heterobinuclear complexes (hetero species and/or co-ordination environment) including ferrocene or ruthenocene as part of the redox centers and investigated the electronic structures of the mixed-valence states,16a–e and the novel reactions 16d,f and the structural rearrangement17 upon one- or two-electron oxidation. The ruthenocene moiety in the ruthenium(II) ruthenocenylacetylide complexes showed a reversible one-electron oxidation process in the cyclic voltammogram and transformed into a fulvene-like complex upon two-electron oxidation.17 These findings stimulated us to investigate in detail the electronic structure of bis(ruthenocenyl) compounds connected by a conjugated hydrocarbon bridge in order to elucidate the electrochemical behaviour of the ruthenocene moiety and the metal–metal interaction.We here report the synthesis, structure and redox chemistry of 1,2-bis(ruthenocenyl)ethylene derivatives and oxidatively induced structural rearrangement to the unprecedented stable dicationic (m-h6 :h6-pentafulvadiene)diruthenium complexes.15 † According to IUPAC nomenclature pentafulvadiene is named 5,59- (1,2-ethanediylidene)biscyclopenta-1,3-diene.Also, it is called 6,69- bifulvenyl customarily. Results and Discussion 1,2,3,4,5-Pentamethylruthenocene 1 reacted with dmf and POCl3 (Vilsmeier’s complex) in 1,2-dichloroethane on reflux for 12 h to give 1-formyl-19,29,39,49,59-pentamethylruthenocene 2 in 87% yield.Complex 1 was oxidized with activated MnO2 in refluxing 1,2-dichloroethane to aVord 1-formyl-2,3,4,5-tetramethylruthenocene 3 and 1,2-diformyl-3,4,5-trimethylruthenocene in 37 and 7% yield, respectively, along with the starting material 1 in 40% yield. In another route, the tetramethylfulvene complex [Ru(h5-C5H5)(h6-C5Me4CH2)]1BF4 2, prepared in quantitative yield by the two-electron oxidation of 1 by p-benzoquinone–BF3?Et2O,16 was treated with aqueous KOH in thf to aVord a corresponding 1-hydroxymethyl-2,3,4,5- tetramethylruthenocene in 73% yield, which was oxidized with Scheme 1 (i) POCl3–dmf, (CH2Cl)2; (ii) activated MnO2, (CH2Cl)2; (iii) p-benzoquinone (2 equivalents)–BF3?OEt2 (10 equivalents), CH2Cl2; (iv) 10% aqueous KOH, thf; (v) activated MnO2, (CH2Cl)2 Ru Ru CH2OH Ru CHO Ru CHO CHO Ru Ru CHO 1 2 3 + (i) (ii) (iii) (iv) (v)2216 J.Chem. Soc., Dalton Trans., 1998, Pages 2215–2224 activated MnO2 in refluxing 1,2-dichloroethane to give the aldehyde 3, although in low (24%) yield, along with 1,2- diformyl-3,4,5-trimethylruthenocene in 21% yield (Scheme 1).Formylruthenocene 4 was prepared according to the literature. 18 Complexes 4, 2 and 3 were treated with low-valent titanium prepared from TiCl4–Zn in thf 19 to aVord the corresponding ethylene derivatives, trans-1,2-bis(ruthenocenyl)- ethylene 5, trans-1,2-bis(19,29,39,49,59-pentamethylruthenocenyl) ethylene 6 and trans-1,2-bis(2,3,4,5-tetramethylruthenocenyl) ethylene 7, in 66, 93 and 76% yield, respectively (Scheme 2).The structures of these ethylenes were determined by the spectroscopic data. For example, the strong C]] C stretching vibration of 6 was observed at 1646 cm21 in the Raman spectrum. The 1H NMR spectrum of 6 showed the vinyl proton signal at d 5.92 and the 13C NMR spectrum exhibited the vinyl carbon signal at d 121.69. A single crystal X-ray analysis Scheme 2 (i) TiCl4–Zn, thf Ru Ru Ru Ru Ru Ru CHO CHO Ru Ru Ru CHO 4 5 2 6 3 7 Ru Ru Ru COCH3 Ru Ru 9a 8 9b Ru Ru Ru COCH3 Ru Ru 11a 10 11b (i) (i) (i) (i) (i) confirmed the trans configuration in 6.15 Selected bond lengths and angles are summarized in Table 1.Acetylruthenocene 8 was treated with TiCl4–Zn in thf under gentle refluxing for 2 h to give the coupling products, a mixture of trans- (9a) and cis-1,2-dimethyl-1,2-bis(ruthenocenyl)- ethylenes (9b) in 83% yield.Similarly, 1-acetyl-19,29,39,49,59- pentamethylruthenocene 10 gave trans- (11a) and cis-1,2- dimethyl-1,2-bis(pentamethylruthenocenyl)ethylenes (11b) in 70% yield (Scheme 2). These isomers were separated through a fractional recrystallization. In the 1H NMR spectrum the product 9a showed the ring protons of the ruthenocenyl moiety at d 4.55 (10 H), 4.63 (4 H) and 4.54 (4 H), similar chemical shifts to those of the trans isomer of the parent 1,2-bis(ruthenocenyl)- ethylene 5 [d 4.49 (10 H), 4.74 (4 H) and 4.55 (4 H)]. On the other hand, the protons of the substituted C5H4 rings in 9b [d 4.43 (4 H) and 4.40 (4 H)] and the methyl signal (d 1.84) were at higher field than the corresponding signals of 9a.The total similarity in the chemical shifts of the ruthenocenyl moiety for 9a to those for 5 may suggest that 9a can be assigned to a trans isomer. This assignment was confirmed by X-ray diVraction (see below). The proton signals of the C5H4 ring of ruthenocene and the methyl group attached to the ethylene carbon for product 11a [d 4.35 (4 H), 4.15 (4 H) and 1.98 (6 H), respectively] were at lower field than those for product 11b [d 4.06 (4 H), 4.00 (4 H) and 1.86 (6 H), respectively].From the similarity of the chemical shifts with those for 9a and 9b it is suggested that 11a is a trans and 11b a cis isomer. Single crystals suitable for X-ray diVraction of 9a and 9b were obtained by recrystallization from chloroform–diethyl ether using a diVusion method.The ORTEP20 views are shown in Figs. 1 and 2, respectively. Half of the molecule for 9a is crystallographically unique, with the whole molecule located on an inversion center. Selected bond distances and angles for 9a and 9b are summarized in Table 1. The most significant diVer- Fig. 1 An ORTEP view of complex 9a Fig. 2 An ORTEP view of complex 9bJ. Chem. Soc., Dalton Trans., 1998, Pages 2215–2224 2217 Table 1 Selected bond distances (Å) and angles (8) for complexes 6, 9a and 9b 6 C(1)]C(1) C(1)]C(2) Ru(1)]C(ring) C]C(ring) C(1)]C(1)]C(2) C(1)]C(2)]C(3) 1.359 * 1.547 * 2.18 * 1.41 * 114.6 * 120.1 * 9a C(1)]C(1) C(1)]C(2) C(1)]C(3) Ru(1)]C(ring) C]C(ring) C(1)]C(1)]C(2) C(1)]C(1)]C(3) C(2)]C(1)]C(3) 1.348(5) 1.498(6) 1.487(6) 2.174 * 1.410 * 123.1(4) 122.5(4) 114.4(4) 9b C(1)]C(2) C(1)]C(3) C(2)]C(4) C(1)]C(5) C(2)]C(15) Ru(1)]C(ring) C]C(ring) C(2)]C(1)]C(3) C(1)]C(2)]C(4) C(2)]C(1)]C(5) C(1)]C(2)]C(15) C(3)]C(1)]C(5) C(4)]C(2)]C(15) 1.342(9) 1.509(8) 1.498(10) 1.475(9) 1.471(9) 2.174 * 1.418 * 121.0(6) 120.8(6) 124.4(6) 123.4(6) 114.6(5) 115.8(6) * Average. ences of 9a compared with complex 6 are the fact that the plane of the substituted C5H4 ring of the ruthenocene moiety is inclined by 37.27(2)8 towards the plane of the ethylene bond, probably because of the steric crowding of the methyl group on the ethylene bond, while the corresponding two planes in 6 are almost coplanar (1.228).Similarly the plane of the substituted C5H4 ring attached to the double bond in the cis isomer 9b inclines by 30.80(3) and 49.89(3)8 in order to avoid the steric repulsion between the methyl group on the ethylene and the hydrogen atom on the substituted C5H4 ring.The C]C and Ru]C distances of the ruthenocene parts in 9a and 9b are normal. Fig. 3 Cyclic voltammograms of complexes 5 (A), 6 (B), 7 (C), 9a (D) and 11a (E) in CH2Cl2 The cyclic voltammograms of 1,2-bis(ruthenocenyl)ethylenes 5–7, 9 and 11 in CH2Cl2 are shown in Fig. 3. The corresponding redox potentials and those of related compounds are summarized in Table 2. For complexes 6, 9 and 11 an irreversible oxidation wave, confirmed as corresponding to a two-electron process by using the Randles–Sevcik equation and, on the backward scan, an irreversible two-electron reduction wave having nearly the same magnitude as that of the oxidation wave were observed. On the other hand, 5 and 7 showed a quasireversible two-electron wave (Epc 2 Epa = 0.06 and 0.07 V, respectively) and small irreversible reduction wave.The diVerence in redox behavior among 5–7, 9 and 11 is probably explained as follows: these two-electron oxidation processes are regarded as an electrochemical–electrochemical–chemical process, in which the chemical step probably involves great structural rearrangement (see below). If the rate of the latter step is slow the oxidation wave would be accompanied by a reduction wave similar to the oxidation wave (as for 5 and 7), but if the rate is fast the new reduction wave would appear at a diVerent potential (as for 6, 9 and 11).Surprisingly, the oxidation potential of 6, 7 and 11 is remarkably lower (DE = 0.52, 0.43 and 0.32–0.34 V, respectively) than that of pentamethylruthenocene (Epa = 10.33 V). Similarly, complexes 5 and 9 showed lower oxidation potentials by 0.52 and 0.37–0.33 V than that of ruthenocene (Epa = 10.55 V). Another example of a compound containing two ruthenocene parts which shows such an unusual low oxidation potential was [1.1]ruthenocenophane,11a which is oxidized to the dicationic complex containing a direct RuIII] RuIII bond.11c The two-electron process observed in 5–7, 9 and 11 is considered to be due to two one-electron oxidation processes (of RuII/III) for each ruthenocene moiety, suggesting that there is a certain ligand-mediated metal–metal interaction between the two ruthenium atoms.This unique behavior in 1,2- bis(ruthenocenyl)ethylenes may be interpreted as follows. The crucial interaction takes place potentially between the two filled non-bonding d orbitals of the ruthenocene part and the filled Table 2 Redox potentials of bis(ruthenocenyl)ethylenes and related compoundsa Complex 1[ Ru(h5-C5H5)2] 567 9a 9b 11a 11b Epa b 10.33 10.55 10.03 20.19 20.10 10.18 10.22 10.01 20.01 Epc(1) —— 20.03 c 20.40 b 20.17 c 20.09 b 20.09 c 20.19 b 20.19 b Epc(2) —— 20.20 c — 20.27 c ———— a In V vs.ferrocene–ferrocenium. b Two-electron process. c The process involved less than two electrons.2218 J. Chem. Soc., Dalton Trans., 1998, Pages 2215–2224 bonding orbital of the ethylene part, leading to a splitting of these orbitals into three new filled orbitals, i.e. bonding, nonbonding and antibonding. This is similar to the result obtained from Fenske–Hall MO calculations on butadienediyl-bridged diiron complexes.21 The interaction does not contribute to the metal–metal interaction in the neutral complex because of no net stabilizing energy. However, on oxidation, an electron is removed from the new highest filled orbital and this reflects the lowering of the oxidation potential, as observed in complexes 5–7, 9 and 11.The extent of the shift to lower potential of the first oxidation wave would be modified by the methylsubstitution mode on the C5H5 ring or the bridging ethylene. The electron-donating eVect of the methyl group decreases the oxidation potential.Also, the eVect of the methyl substituent on the inclination of the plane of the C5H4 from the plane of the ethylene bond seems to reduce the extent of the lowpotential shift and to influence the stability of the two-electron oxidized species (see below). Complexes 5–7 were oxidized with 2 equivalents of benzoquinone –BF3?OEt2 at 0 8C in CH2Cl2 to give the corresponding dicationic complexes 12–14 as stable solids in moderate to good yields (Scheme 3).Dimethyl analogs 9a and 9b similarly gave the oxidized species 15a and 15b at 278 8C in CH2Cl2, respectively, but no stable oxidation product from 11a and 11b could be isolated. The oxidized complexes were soluble in CD3CN, but not in acetone and CH2Cl2. The complexes 12–14 were stable in CD3CN at room temperature for a long time, but solutions of 15a and 15b in CD3CN decomposed at room temperature within 1 h. The instability of the latter may be because of the increased strain induced by the methyl group on the exomethylene carbon.The IR spectrum of 13 showed very strong absorption of nBF at 1084 cm21, indicating that 13 is a cationic Scheme 3 (i) p-Benzoquinone (2 equivalents)–BF3?OEt2 (10 equivalents), CH2Cl2, 0 8C; (ii) p-benzoquinone (2 equivalents)–BF3?OEt2 (10 equivalents), CH2Cl2, 278 8C Ru Ru Ru Ru Ru Ru Ru Ru Ru Ru Ru Ru Ru Ru Ru Ru Ru Ru Ru Ru 5 12 6 13 7 14 9a 15a 9b 15b (i) (i) (i) (ii) (ii) [BF4]2 [BF4]2 [BF4]2 [BF4]2 [BF4]2 complex having BF4 2 as counter anion.The cyclopentadienyl protons in the oxidized complex 13 shifted downfield (D ª 1.4 ppm), implying the accumulation of positive charge on the Ru atom. In spite of this, a high-field shift of the olefinic proton from d 5.92 in the neutral complex 6 to d 5.60 in 13 was observed, suggesting co-ordination of the olefinic carbon. One of the most interesting points observed for the oxidized species is the chemical shift (d 96.76 for 13) and the 1JCH coupling constant (167 Hz for 13) of the carbon atoms connecting the two ruthenocenyl moieties. These values are very similar to those of the exo-methylene carbon in the tetramethylfulvene complex [Ru(h5-C5H5)(h6-C5Me4CH2)]BF4 (d 69.40 and 1JCH = 167 Hz)17 and [Ru(h5-C5Me5)(h6-C5Me4CH2)]PF6 (d 77.77 and 1JCH = 165 Hz),22a,b rather than those of the olefinic carbon (d 121.69 and 1JCH = 153 Hz in 6).Similar 13C spectral features were also observed for complexes 12 (d 91.34 1JCH = 170 Hz) and 14 (d 87.05, 1JCH = 165 Hz).The protons of the substituted C5H4 in 1H NMR spectrum of 13 were observed as two double triplets and two triple doublets, although the latter is somewhat broadened. Such asymmetric appearance is in accord with no rotation around the exo double bond. Based on the proton coupling pattern of the cyclopentadienyl rings in ferrocene derivatives,23,24 the double triplets at d 4.93 and 5.43 observed for complex 13 can be assigned as the a-C5H4 protons, and the triple doublets at d 5.86 and 5.98 as the b-C5H4 protons.This assignment was confirmed by two-dimensional H]H COSY measurement; the latter signals gave a correlation peak but the former no such peak. The appearance of the a-C5H4 protons at higher field than that of the b-C5H4 protons is characteristic of fulvene complexes.25 A similar asymmetric pattern of the C5H4 ring protons and a similar H]H COSY spectrum were observed for complex 12, as well as for 15a and 15b.These spectral data suggest that 12–15 can be assigned as (m-h6 :h6-pentafulvadiene) diruthenium complexes. The separation (D ª 15 ppm) of the a- and b-protons of the substituted C5H4 ring in 13 is rather larger than that (D ª 9 ppm) of 12, as well as that (D ª 11 ppm) of 15a and 15b, suggesting that the fulvenic structure may contribute more to the limiting structure in the former than in the latter complexes. A single crystal X-ray analysis of complex 13 was performed15 and selected bond distances and angles are summarized in Table 3.The C5Me5 ligand is normal (C]C average 1.43 Å). The distance of the C5H4 ring from the Ru atom is 1.811 Å and somewhat shorter than the distance between the C5Me5 ring and the Ru atom (1.825 Å). The tilt angle between the C5Me5 and C5H4 rings is 11.298 and significantly diVerent from the corresponding value (32.28) of [Ru(h5-C5H5)2I]I3 26 and similar to that (6.98) of the isomorphous osmium analog22c of the cationic fulvene complex [Ru(h5-C5Me5)(h6-C5Me4CH2)]- BPh4,22d respectively.This suggests that the oxidation state of the central atom of complex 13 remains RuII. Some bond alternation is observed in the substituted C5H4 ligand of 13, although it is somewhat obscure because of the disorder described above than that in the cationic fulvene complex [Ru(h5-C5Me5)(h6-C5Me4CH2)]BPh4.22d The C(1A/1B)]C(2) distance (average 1.48 Å) is shorter than the corresponding distance in the neutral complex 6 (average 1.55 Å).The Ru]C(2) distance [2.077(5) Å] is somewhat shorter than Ru]C(3) [2.159(6) Å] and Ru]C(6) [2.174(6) Å]. Moreover, the Ru] C(1A/1B) distance (average 2.41 Å) and the bending angle of the C(2)]C(1A/1B) bond from the plane of the substituted C5H4 ring to the Ru atom (40.48) are close to the corresponding values in [Ru(h5-C5Me5)(h6-C5Me4CH2)]BPh4 [2.270(3) Å and 40.38] 22d and the isoelectronic [Cr(h6- C5H4CH2)(CO)3] [ 2.352(9) Å and 358],25a respectively.The distance (average 1.46 Å) of the central bond connecting the halves of the molecule 13 is close to that of a sp2–sp2 single bond (1.47 Å). These features indicate that the halves of the molecule have the structure of a fulvene complex and therefore the total molecule of 13 is assigned as a (m-h6 :h6-pentafulva-J. Chem. Soc., Dalton Trans., 1998, Pages 2215–2224 2219 diene)diruthenium complex. Free pentafulvadiene was reported as unstable and reactive red-violet crystals by Prinzbach and co-workers in 1977.27 Complexes 12–14 are the first examples of transition-metal stabilized pentafulvadiene complexes, to the best of our knowledge.The pentafulvadiene ligand constitutes a plane with many folds, to which the two (h5-C5Me5)Ru parts are co-ordinated anti to each other. Moreover, the C5Me5 rings in the two parts are also parallel to each other. Single crystals of complex 15b were fortunately obtained by recrystallization from CH3CN–diethyl ether at low temperature, in spite of the instability of the complex in solution.Selected bond distances and angles are summarized in Table 3. The ORTEP view of the cationic part of 15b is given in Fig. 4. The structure is essentially similar to that of 13. The remarkable features are the appearance of a cationic pentafulvadiene complex and the maintenance of the original cis conformation. The C5H4 ring is practically flat and is located at somewhat shorter distance (1.810 and 1.799 Å) from the central Ru atom than that (1.825 and 1.825 Å) of the C5H5 ring.The tilt angles between the C5H5 and C5H4 rings are 11.04(3) and 12.94(3)8 similar to those in 13. In the substituted C5H4 ligand of 15b there is a more clear bond alternation compared with that in 13, as can been also seen in the cationic fulvene complex [Ru(h5- C5Me5)(h6-C5Me4CH2)]BPh4 22d and the fulvene complexes [Ru(h6-C5Me4CH2)(h4-C8H12)],28 [{RuCl2(h6-C5Me4CH2)}2],29 [RuCl(h2-ButNSPh)(h6-C5Me4CH2)] 30 and [Cr(h6-C5H4CH2)- (CO)3].25a The C(1)]C(5) and C(2)]C(15) distances [1.406(5) and 1.407(5) Å, respectively] are much shorter than the corresponding distances in the neutral complex 9b [1.475(9) and 1.471(9) Å, respectively]. The C(5)]C(6) and C(5)]C(9) distances [1.449(6) and 1.461(5) Å, respectively] are long and Table 3 Selected bond distances (Å) and angles (8) for complexes 13 and 15b 13 Ru(1)]C(1A) Ru(1)]C(1B) Ru(1)]C(2) Ru(1)]C(3) Ru(1)]C(4) Ru(1)]C(5) Ru(1)]C(6) C(1A)]C(1A) C(1B)]C(1B) C(1A)]C(2) C(1B)]C(2) C(2)]C(3) C(2)]C(6) C(3)]C(4) C(4)]C(5) C(5)]C(6) Ru(1)]C(C5Me5) C]C(C5Me5) 2.407(1) 2.413(1) 2.077(5) 2.174(6) 2.244(7) 2.225(7) 2.159(6) 1.467 1.444 1.453(6) 1.519(6) 1.445(10) 1.418(10) 1.376(11) 1.414(13) 1.373(12) 2.195 * 1.434 * 15b Ru(1)]C(1) Ru(1)]C(5) Ru(1)]C(6) Ru(1)]C(7) Ru(1)]C(8) Ru(1)]C(9) Ru(2)]C(2) Ru(2)]C(15) Ru(2)]C(16) Ru(2)]C(17) Ru(2)]C(18) Ru(2)]C(19) C(1)]C(2) C(1)]C(3) C(2)]C(4) C(1)]C(5) C(2)]C(15) C(5)]C(6) C(5)]C(9) C(6)]C(7) C(7)]C(8) C(8)]C(9) C(15)]C(16) C(15)]C(19) C(16)]C(17) C(17)]C(18) C(18)]C(19) Ru(1)]C(ring) Ru(2)]C(ring) C]C(ring) C(2)]C(1)]C(3) C(2)]C(1)]C(5) C(3)]C(1)]C(5) C(1)]C(2)]C(4) C(1)]C(2)]C(15) C(4)]C(2)]C(15) 2.571(4) 2.116(4) 2.180(4) 2.224(5) 2.217(4) 2.162(4) 2.474(4) 2.090(4) 2.175(4) 2.212(5) 2.216(4) 2.167(4) 1.491(5) 1.512(6) 1.514(6) 1.406(5) 1.407(5) 1.449(6) 1.461(5) 1.395(6) 1.414(7) 1.398(6) 1.445(6) 1.460(6) 1.398(7) 1.414(7) 1.403(6) 2.184 * 2.178 * 1.396 * 117.3(3) 121.1(3) 120.4(4) 116.4(4) 120.9(3) 121.0(4) * Average.C(6)]C(7) and C(8)]C(9) [1.395(6) and 1.398(6) Å] are short. A similar trend was observed in the C(15)–C(19) ring. The Ru(1)]C(5) distance [2.116(4) Å] is somewhat shorter than Ru(1)]C(6) and Ru(1)]C(9) [2.180(4) and 2.162(4) Å, respectively]. This trend can also be seen in the remaining half of the complex. Also, the Ru(1)]C(1) and Ru(2)]C(2) distances [2.571(4) and 2.474(4) Å, respectively] are somewhat longer than the corresponding values in 13 (average 2.41 Å), [Ru(h5- C5Me5)(h6-C5Me4CH2)]BPh4 [2.270(3) Å],22d [{RuCl2(h6-C5Me4- CH2)}2] [2.268(4) and 2.271(4) Å],29 and the isoelectronic [Cr(h6-C5H4CH2)(CO)3] [ 2.352(9) Å].25a Moreover, the bending angles of the C(5)]C(1) and C(15)]C(2) bonds from the plane of the substituted C5H4 ring to the Ru atom (29.1 and 29.18, respectively) are smaller than in other related complexes (35–408).These facts suggest that the bond between the Ru atom and the fulvene ligand in 15b is somewhat weak because of the steric strain due to the methyl group on the bridging carbons. The distance [1.491(5) Å] of the central bond connecting the halves of the molecule 15b is close to that (1.46 Å) in 13 and corresponds to a C]C single bond, implying that 15b can also be assigned as a (m-h6 :h6-pentafulvadiene)diruthenium complex. The torsion angle C(3)]C(1)]C(2)]C(4) is 55.1(5)8, suggesting retention of the s-cis conformation which originates in the cis configuration in 11b.The plane formed by C(2), C(1) and C(3) is inclined by 30.228 to that of the C5H4 ring [C(5)– C(9)] and the plane formed by C(1), C(2) and C(4) is inclined by 33.708 to that of the C5H4 ring [C(15)–C(19)] in 15b. Such a strongly twisted structure seems to weaken the bond between the Ru atom and the fulvene ligand and make complex 15b unstable.The formation of the (m-h6 :h6-pentafulvadiene)diruthenium complexes, 11–13, 15a and 15b, in the two-electron oxidation of the corresponding ethylene derivatives may be explained as follows. As described above, the interaction between the filled bonding orbital of the ethylene part and the two filled nonbonding d orbitals of the ruthenocene parts would result in three new filled MOs. The removal of two electrons from the highest filled orbital (HOMO) leaves two pairs of electrons in non-bonding and bonding orbitals.As a result, a three-center four-electron (3c4e)-like interaction may be expected in the ethylene-bridging bis(ruthenocenyl) system and seems to bring about a large stabilization of the system and a structural rearrangement, i.e. the formation of the (m-h6 :h6-pentafulvadiene) diruthenium complexes. This interaction is very similar to that in the conversion of a butadienediyldiiron complex into a bis(carbene)-type complex upon two-electron oxidation.31,32 A similar oxidative transformation accompanied by a structural rearrangement was also observed in sp carbon-bridged Fig. 4 An ORTEP view of the cationic part of complex 15b2220 J. Chem. Soc., Dalton Trans., 1998, Pages 2215–2224 dirhenium complexes,33 and fulvalene- 34 and cyclooctatetraenebridged dinuclear complexes.35 In CH2Cl2–CH3CN (6: 4 v/v) solution,‡ the neutral ethylene 6 shows an irreversible two-electron oxidation wave at 20.18 V (for RuII 2 æÆ RuIII 2) and a smaller irreversible reduction wave (Epc = 20.32 V) on the backward scan, and the dicationic complex 13 shows an irreversible two-electron reduction wave at 20.41 V (for RuII 2 æÆ RuI 2) and a smaller irreversible oxidation wave (Epa = 20.17 V) on the backward scan.These redox behaviors are very similar, although the redox potentials are slightly diVerent. This suggests that the structural rearrangement induced by electron transfer in 6 and 13 may be chemically reversible.Actually, two-electron chemical reduction of the dicationic complex 13 by 2 equivalents of cobaltocene (E89 = 21.34 V vs. ferrocene–ferrocenium in CH3CN) gave the neutral complex 6 in 97% yield, although the reaction is very slow. Then, the redox reaction interrelating 6 with 13 may be explained by the process shown in Scheme 4, which is similar to a square scheme proposed by Geiger.36 The reversibility of this redox system was confirmed by controlled potential electrolysis monitored by Raman spectra as shown in Fig. 5. The peak at 1641 cm21 assigned to the C]] C stretching vibration is weakened and that at 1530 cm21 is increased according to the progress of oxidation. On reduction the reverse phenomena took place. The spectral changes were reproduced repeatedly. However, in the optically transparent thin layer electronic spectra (OTTLE) recorded upon controlled potential electrolysis a somewhat different behavior was observed as shown in Fig. 6. On oxidation of complex 6 the peaks at 340 and 440 nm increased and the absorption at 290 nm decreased, showing an isobestic point (at 316 nm), but the reductive scan of the oxidized solution showed the reverse change and no isobestic point. This seems to suggest that the oxidation proceeds rapidly and the intermediate ([6]21) cannot be detected even if it exists, but that the reduction is slow and the intermediate ([13]0) may have a short lifetime. The latter observation is in accord with the slow chemical reduction of 13 by cobaltocene.The observation of good reversibility between 6 and 13 upon controlled potential electrolysis may be because Raman spectroscopy observes the stretching vibration of only the special bond in the molecule. Experimental All reactions were carried out under an atmosphere of N2 and/ or Ar and work-ups were performed without precautions to exclude air. The NMR spectra were recorded on Bruker AM400 or ARX400 spectrometers, IR and Raman (KBr disc) spectra on a Perkin-Elmer System 2000R spectrometer, electronic Scheme 4 Square scheme for complex 6 Ru Ru Ru Ru 6 13 2+ [6]2+ [13]0 –2e +2e –2e +2e ‡ In order to compare directly redox behavior of 8 with that of 11, the mixed solvent system was used for reasons of solubility.spectra on a Shimadz UV-2100 and Raman spectra upon controlled potential electrolysis on a Kaiser Optical Systems Holo Probe 532. Controlled potential electrolysis with a platinum mesh working electrode under an atmosphere of He and cyclic voltammetry were carried out by using BAS CV27 in 1021 M NBun 4ClO4 (polarography grade, Nacalai tesque) solution in CH2Cl2 and/or CH3CN.The cells were fitted with a glassy carbon (GC) working electrode, platinum wire counter electrode and a Ag–Ag1 pseudo-reference electrode, and the scan rate was 0.1 V s21. All potentials were referred to ferrocene– ferrocenium, the value for which was obtained by subsequent measurement under the same conditions.Solvents were purified by distillation from the drying agent prior to use as follows: CH2Cl2 (CaCl2), ClCH2CH2Cl (CaCl2), CH3CN (CaH2), thf (sodium–benzophenone) and diethyl ether (LiAlH4). Formylruthenocene 4,18 1,2,3,4,5-pentamethylruthenocene 137 and [Ru(h5-C5H5)(h6-C5Me4CH2)]BF4 17 were prepared according to the literature. Other reagents were used as received from commercial suppliers. Fig. 5 Raman spectra (interval ca. 3 min) in the controlled potential electrolysis of complex 6 (1 mM) in CH2Cl2–CH3CN (6: 4, v/v).Upper: anodic electrolysis (potential limit 1.04 to 15.4 V). Lower: cathodic re-electrolysis (potential limit 10.54 to 21.04 V) Fig. 6 Optical transparent thin layer electronic spectra (interval ca. 10 min) in the controlled anodic electrolysis (potential limit 20.40 to 10.50) of complex 6 in CH2Cl2–CH3CN (6: 4, v/v)J. Chem. Soc., Dalton Trans., 1998, Pages 2215–2224 2221 Preparations 1-Formyl-19,29,39,49,59-pentamethylruthenocene 2.A solution of Vilsmeier’s complex was prepared by adding dmf (0.7 cm3, 45 mmol) and subsequently POCl3 (0.8 cm3, 42 mmol) at 0 8C in 1,2-dichloroethane (15 cm3) and stirring for 0.5 h at room temperature. To the yellow solution was added 1,2,3,4,5- pentamethylruthenocene 1 (1.28 g, 4.2 mmol). The solution was stirred for 12 h at 80 8C (oil-bath temperature) and then poured into aqueous saturated Na2CO3 solution (50 cm3) and stirred for 0.5 h.The organic layer was separated and the aqueous layer extracted with CH2Cl2 (50 cm3 × 3). The organic layer and the extracts were collected, dried over MgSO4, and then evaporated by a rotary evaporator. The residue was subjected to column chromatography on alumina using CH2Cl2 as the eluent. The yellow fraction was collected and evaporated to give complex 2 as a yellow solid. An analytically pure sample was obtained by sublimation [100 8C, 1022 Torr, (ca. 1.33 Pa)] 1.20 g (87%).M.p. 82–84 8C (Found: C, 58.60; H, 6.13. C16H20ORu requires C, 58.34; H, 6.12%). IR (KBr disc): n& /cm21 1676 (C]] O). 1H NMR (CDCl3): d 1.87 (s, 15 H, Me), 4.53 (t, J = 1.8, 2 H, b-H), 4.65 (t, J = 1.8 Hz, 2 H, a-H) and 9.40 (s, 1 H, CHO). 13C NMR (CDCl3): d 11.63 (Me), 72.57 (b-C of C5H4), 77.31 (a-C of C5H4), 84.71 (ipso-C of C5H4), 87.18 (C5Me5) and 189.39 (CHO). 1-Formyl-2,3,4,5-pentamethylruthenocene 3. Path A. Complex 1 (589 mg, 1.95 mmol) was refluxed with activated MnO2 (Aldrich) (3.0 g) in 1,2-dichloroethane (60 cm3) for 4 h.After MnO2 had been filtered oV the filtrate was evaporated by a rotary evaporator. The residue was subjected to column chromatography on alumina using CH2Cl2 as the eluent. From the first colorless fraction the starting material 1 was recovered in 40% yield (236 mg). The second yellow fraction was collected and evaporated in vacuum to give complex 3 as a yellow solid. An analytically pure sample was obtained by recrystallization from hexane, 226 mg (37%).M.p. 151–152 8C (Found: C, 57.22; H, 5.79. C15H18ORu requires C, 57.13; H, 5.75%). IR (KBr disc): n& /cm21 1673 (C]] O). 1H NMR (CDCl3): d 2.01 (s, 6 H, b-Me), 2.18 (s, 6 H, a-Me), 4.35 (s, 5 H, C5H5) and 10.11 (s, 1 H, CHO). 13C NMR (CDCl3): d 11.64 (b-Me), 12.11 (a-Me), 73.49 (C5H5), 80.00 (b-C of C5Me4CHO), 87.26 (a-C of C5Me4CHO), 90.29 (ipso-C of C5Me4CHO) and 191.66 (CHO). The third yellow fraction gave 1,2-diformyl-3,4,5-trimethylruthenocene in 7% yield (45 mg) as yellow crystals.An analytically pure sample was obtained by recrystallization from hexane. M.p. 186– 187 8C (Found: C, 54.81; H, 4.88. C15H16O2Ru requires C, 54.70; H, 4.90%). IR (KBr disc): n& /cm21 1678 (C]] O). 1H NMR (CDCl3): d 2.08 (s, 3 H, b-Me), 2.28 (s, 6 H, a-Me), 4.55 (s, 5 H, C5H5) and 10.30 (s, 2 H, CHO). 13C NMR (CDCl3): d 11.13 (b- Me), 12.40 (a-Me), 74.92 (C5H5), 81.96 [b-C of C5Me3(CHO)2], 92.33 [a-C of C5Me3(CHO)2], 94.46 [ipso-C of C5Me3(CHO)2] and 191.34 (CHO).Path B. 1-Hydroxymethyl-2,3,4,5-pentamethylruthenocene (304 mg, 0.96 mmol) was refluxed with activated MnO2 (7.5 g) in 1,2-dichloroethane (40 cm3) for 4 h. After MnO2 had been filtered oV the filtrate was evaporated in vacuum. The residue was subjected to column chromatography on alumina using CH2Cl2 as the eluent. The first yellow fraction gave complex 3 as a yellow solid in 24% yield (73 mg). The second yellow fraction gave 1,2-diformyl-3,4,5-trimethylruthenocene in 21% yield (69 mg). 1-Hydroxymethyl-2,3,4,5-pentamethylruthenocene. To a solution of the fulvene complex [Ru(h5-C5H5)(h6-C5Me4CH2)]BF4 (605 mg, 1.6 mmol) in thf (15 cm3) was added 10% aqueous KOH solution (12 cm3) at room temperature. The mixture was stirred for 10 min. After the solvent had been removed by a rotary evaporator the residue was extracted with CH2Cl2 (20 cm3 × 3). The extracts were collected, washed with water (20 cm3 × 3), dried over MgSO4, and evaporated.The residue was recrystallized from hexane to give the analytically pure product as colorless crystals (464 mg, 96%). M.p. 109–110 8C (Found: C, 56.83; H, 6.32. C15H20ORu requires C, 56.76; H, 6.35%). IR (KBr disc): 3460 cm21 [n(OH)]. 1H NMR (CDCl3, 400 MHz): d 1.11 (t, J = 4.9, 1 H, OH), 1.94 (s, 6 H, b-Me of C5Me4), 1.96 (s, 6 H, a-Me of C5Me4), 3.97 (t, J = 4.9 Hz, 2 H, CH2) and 4.33 (s, 5 H, C5H5). 13C NMR (CDCl3, 100 MHz): d 11.83 (b-C of C5Me4), 12.01 (a-C of C5Me4), 54.73 (CH2), 72.04 (C5H5), 85.57 (b-CC5Me4), 86.31 (a-CC5Me4) and 94.49 (ipso-C of C5Me4).trans-1,2-Bis(ruthenocenyl)ethylene 5. To a low-valent titanium solution, prepared from TiCl4 (0.6 cm3, 5.3 mmol) in thf (30 cm3) and zinc powder (700 mg, 10.9 mmol) at 278 8C, was added dropwise a solution of complex 4 (465 mg, 1.8 mmol) in thf (10 cm3) at 278 8C. The brick-red reaction mixture was warmed to room temperature and then stirred for 12 h.To the resulting brown solution was slowly added water (15 cm3). The mixture was stirred for 10 min and then acidified (to pH < 2) with hydrochloric acid. The resulting pale yellow powder was filtered oV, washed with 10% aqueous HCl (10 cm3 × 3) and CH2Cl2 (3 cm3 × 3) and then dried in vacuum to give analytically pure 5, 288 mg (66%). M.p. >230 8C (Found: C, 54.08; H, 4.10. C11H10Ru requires C, 54.31; H, 4.14%). IR (KBr disc): n& /cm21 1645 (C]] C). 1H NMR (CDCl3): d 4.49 (s, 10 H, C5H5), 4.55 (t, J = 1.6, 4 H, b-2H of C5H4), 4.74 (t, J = 1.6 Hz, 4 H, a-H of C5H4) and 6.21 (s, 2 H, ]] CH). 13C NMR (CDCl3): d 68.71 (b-C of C5H4), 70.35 (a-C of C5H4), 71.05 (C5H5) and 122.38 (]] CH). trans-1,2-Bis(19,29,39,49,59-pentamethylruthenocenyl)ethylene 6. To a low-valent titanium solution, prepared from TiCl4 (0.15 cm3, 0.17 mmol) in thf (12 cm3) and zinc powder (174 mg, 2.7 mmol) at 278 8C, was added dropwise a solution of complex 2 (165 mg, 0.5 mmol) in thf (3 cm3) at 278 8C.The brick-red reaction mixture was warmed to room temperature and then stirred for 4 h. To the resulting brown solution was added slowly a 10% aqueous K2CO3 solution (15 cm3). The mixture was stirred for 10 min and then filtered. The filtrate was extracted with CH2Cl2 (20 cm3 × 3). The extracts were collected, washed with water, dried over MgSO4, and evaporated in vacuum. The residue was subjected to column chromatography on silica gel using a mixture of CH2Cl2 and hexane as the eluent.The first pale yellow fraction gave complex 6 as a yellow solid. An analytically pure sample was obtained by recrystallization from CH2Cl2–hexane, 146 mg (93%). M.p. 204–205 8C (Found: C, 60.84; H, 6.40. C16H20Ru requires C, 61.32; H, 6.43%). Raman (KBr disc): n& /cm21 1646 (C]] C). IR KBr disc): n& /cm21 1633 (C]] C). 1H NMR (CDCl3): d 1.86 (s, 30 H, Me), 4.19 (t, J = 1.4, 4 H, b-H of C5H4), 4.26 (t, J = 1.4 Hz, 4 H, a-H of C5H4) and 5.92 (s, 2 H, ]] CH). 13C NMR (CDCl3): d 11.81 (Me), 70.78 (b-C of C5H4), 72.72 (a-C of C5H4), 85.12 (C5Me5), 87.36 (ipso-C of C5H4) and 121.69 (]] CH). trans-1,2-Bis(2,3,4,5-tetramethylruthenocenyl)ethylene 7. Complex 7 was prepared from 3 (142 mg, 0.45 mmol) according to the procedure similar to that for 6. Pale yellow crystals (102 mg, 76%). M.p. 221–222 8C (Found: C, 60.24; H, 6.07. C15H18Ru requires C, 60.18; H, 6.06%). Raman (Kbr disc): n& /cm21 1643 (C]] C). 1H NMR (CDCl3): d 1.99 (s, 12 H, b-Me), 2.07 (s, 12 H, a-Me), 4.20 (s, 10 H, C5H5) and 6.45 (s, 2 H, ]] CH). 13C NMR (CDCl3): d 12.19 (b-Me), 13.16 (a-Me), 70.50 (C5H5), 84.08 (b-C of C5Me4), 86.28 (a-C of C5Me4), 87.15 (ipso-C of C5Me4) and 125.65 (]] CH). 1,2-Dimethyl-1,2-bis(ruthenocenyl)ethylene 9a and 9b. To a solution of low-valent titanium, prepared by slow addition of titanium tetrachloride (0.2 cm3, 1.8 mmol) to a suspension of zinc powder (0.23 g, 3.6 mmol) in thf (10 cm3) at 278 8C, was2222 J.Chem. Soc., Dalton Trans., 1998, Pages 2215–2224 added a solution of acetylruthenocene 8 (0.22 g, 0.8 mmol) at 0 8C. After stirring for 1 h on an ice-bath the mixture was gently refluxed for 2 h. An aqueous 10% potassium carbonate solution (10 cm3) was added and the mixture stirred for 1 h at room temperature. The mixture was filtered and the residue washed with CH2Cl2. The filtrate and washings were combined and the organic layer was separated, washed with water, and then dried over MgSO4.After evaporating under vacuum, the residue was subjected to column chromatography on SiO2 by elution of hexane–toluene (2 : 1). Pale yellow crystals (0.17 g, 83%) were obtained. This compound was a mixture of trans and cis isomers, the ratio of which was determined from integration of the 1H NMR spectrum to be ca. 2 : 3. The mixture was separated by a fractional recrystallization from chloroform–diethyl ether using the diVusion method.trans-9a: pale yellow, m.p. 210–211 8C (Found: C, 55.95; H, 4.67. C12H12Ru requires C, 56.02; H, 4.67%); Raman (KBr disc) n& /cm21 1622 (C]] C); 1H NMR (CDCl3) d 4.63 (t, J = 1.7, 4 H, a-H of C5H4), 4.55 (s, 10 H, C5H5), 4.54 (t, J = 1.7 Hz, 4 H, b-H of C5H4) and 1.97 (s, 6 H, Me); 13C NMR (CDCl3) d 24.15 (Me), 69.26 (b-C of C5H4), 70.88 (C5H5), 71.59 (a-C of C5H4), 95.21 (ipso-C of C5H4) and 127.08 (C]] ). cis-9b: pale yellow, m.p. 203–205 8C (Found: C, 56.13; H, 4.68.C24H24Ru2 requires C, 56.02; H, 4.67%); Raman (KBr disc) n& /cm21 1623 (C]] C); 1H NMR (CDCl3) d 4.50 (s, 10 H, C5H5), 4.43 (t, J = 1.7, 4 H, a-H of C5H4), 4.40 (t, J = 1.7 Hz, 4 H, b-H of C5H4) and 1.84 (s, 6 H, Me); 13C NMR (CDCl3) d 23.31 (Me), 69.02 (b-C of C5H4), 70.64 (C5H5), 72.02 (a-C of C5H4), 95.01 (ipso-C of C5H4) and 127.02 (C]] ). 1,2-Dimethyl-1,2-bis(19,29,39,49,59-pentamethylruthenocenyl)- ethylenes 11a and 11b. These compounds were prepared from 10 according to the procedure described above.Pale yellow crystals (0.183 g, 70%) were obtained of a mixture of trans and cis isomers, the ratio of which was determined from integration of the 1H NMR spectrum to be ca. 1 : 2. The mixture was separated by fractional recrystallization from benzene–diethyl ether using a diVusion method. trans-11a: pale yellow, m.p. 232– 234 8C (Found: C, 62.78; H, 6.83. C17H22Ru requires C, 62.36; H, 6.77%); Raman (KBr disc) n& /cm21 1609 (C]] C); 1H NMR (CDCl3) d 4.35 (t, J = 1.7, 4 H, a-H of C5H4), 4.15 (t, J = 1.7 Hz, 4 H, b-H of C5H4), 1.98 (s, 6 H, ]] CMe) and 1.90 (s, 30 H, Me); 13C NMR (CDCl3) d 11.88 (Me), 22.23 (]] CMe), 72.49 (b-C of C5H4), 73.40 (a-C of C5H4), 84.81 (C5Me5), 94.37 (ipso-C of C5H4) and 125.67 (C]] ).cis-11b: pale yellow, m.p. 221–223 8C (Found: C, 62.71; H, 6.82. C17H22Ru requires C, 62.36; H, 6.77%); Raman (KBr disc) n& /cm21 1620 (C]] C); 1H NMR (CDCl3) d 4.06 (t, J = 1.6, 4 H, a-H of C5H4), 4.00 (t, J = 1.6 Hz, 4 H, b-H of C5H4), 1.86 (s, 6 H, ]] CMe) and 1.88 (s, 30 H, Me); 13C NMR (CDCl3) d 11.92 (Me), 21.94 (]] CMe), 71.86 (b-C of C5H4), 73.64 (a-C of C5H4), 84.72 (C5Me5), 95.30 (ipso-C of C5H4) and 125.53 (C]] ).[Ru2(Ï-Á6 :Á6-C5H4CHCHC5H4)(Á5-C5H5)2][BF4]2 12. To a solution of complex 5 (48.6 mg, 0.1 mmol) and p-benzoquinone (21.6 mg, 0.2 mmol) in CH2Cl2 (35 cm3) was added BF3?OEt2 (0.13 cm3, 1.0 mmol) at room temperature. The solution was sonicated for 30 min.The resulting orange powder was filtered oV and washed with ether (2 cm3 × 3). An analytically pure sample was obtained by recrystallization repeatedly from CH3CN–diethyl ether, 66 mg (99%). M.p. >230 8C (Found: C, 40.15; H, 2.97. C11H10BF4Ru requires C, 40.03; H, 3.05%). IR (KBr disc): n& /cm21 1084 (BF4). 1H NMR (CD3CN): d 5.22 (m, 2 H, a-H of C5H4), 5.40 (s, 10 H, C5H5), 5.96 (broad d, J = 3.0, 2 H, a-H of C5H4), 6.19 (td, J = 3.0 and 0.9 Hz, 2 H, b-H of C5H4), 6.25 (s, 2 H, ]] CH) and 6.38 (broad t, 2 H, b-H of C5H4). 13C NMR (CD3CN): d 84.88 (a-C of C5H4), 85.52 (a-C of C5H4), 87.86 (C5H5), 91.34 (1JCH = 170 Hz, ]] CH), 94.02 (b-C of C5H4), 94.36 (b-C of C5H4) and 104.63 (ipso-C of C5H4). [Ru2(Ï-Á6 :Á6-C5H4CHCHC5H4)(Á5-C5Me5)2][BF4]2 13. To a solution of complex 6 (12.5 mg, 0.02 mmol) and p-benzoquinone (4.3 mg, 0.04 mmol) in CH2Cl2 (5 cm3) was added BF3?OEt2 (0.02 cm3, 0.2 mmol) at 0 8C. The solution was stirred for 10 min. The resulting red powder was filtered oV and washed with ether (2 cm3 × 3).An analytically pure sample was obtained by recrystallization from CH3CN–ether, 9.3 mg (58%). M.p. >230 8C (Found: C, 48.04; H, 5.11. C16H20BF4Ru requires C, 48.02; H, 5.04%). IR (KBr disc): n& /cm21 1084 (BF4). 1H NMR (CD3CN): d 1.90 (s, 30 H, Me), 4.93 (m, 2 H, a-H of C5H4), 5.43 (broad d, 2 H, a-H of C5H4), 5.60 (s, 2 H, ]] CH), 5.86 (td, J = 2.9 and 0.9 Hz, 2 H, C5H4) and 5.98 (broad t, 2 H, C5H4). 13C NMR (CD3CN): d 10.62 (Me), 81.59 (a-C of C5H4), 84.10 (a-C of C5H4), 96.76 (]] CH, 1JCH = 167 Hz), 97.32 (b-C of C5H4), 99.15 (b-C of C5H4), 100.87 (C5Me5) and 106.37 (ipso-C of C5H4). [Ru2(Ï-Á6 :Á6-C5Me4CHCHC5Me4)(Á5-C5H5)2][BF4]2 14. Complex 14 was prepared from 7 according to a procedure similar to that for 13. Orange crystals (9.4 mg, 61%). M.p. >230 8C (Found: C, 47.10; H, 4.54. C15H18BF4Ru requires C, 46.65; H, 4.70%). IR (KBr disc): n& /cm21 1084 (BF4). 1H NMR (CD3CN): d 1.79 (s, 6 H, Me), 2.12 (s, 6 H, Me), 2.23 (s, 6 H, Me), 2.29 (s, 6 H, Me), 5.19 (s, 10 H, C5H5) and 6.40 (s, 2 H, ]] CH). 13C NMR (CD3CN): d 10.13 (Me), 11.71 (Me), 11.90 (Me), 13.52 (Me), 87.05 (1JCH = 165 Hz, ]] CR), 99.70 (C5Me5), 100.14 (ipso-C of C5Me4), 100.55 (C5Me5), 109.34 (C5Me5) and 110.66 (C5Me5). s-cis-[Ru2(Ï-Á6 :Á6-C5Me4CMeCMeC5Me4)(Á5-C5H5)2][BF4]2 15b. cis Isomer 9b (30.8 mg, 0.06 mmol) and p-benzoquinone (13 mg, 0.12 mmol) were dissolved in CH2Cl2 (10 cm3) under N2 and the solution was cooled to 0 8C; BF3?OEt2 (0.2 cm3, 1.6 mmol) was added.After stirring for 1.5 h at 0 8C the red-brown oily product precipitated. The supernatant solution was removed by a syringe and MeCN (1 cm3) and subsequently acetone (1 cm3) was added. After addition of anhydrous ether (1 cm3), the solution was chilled at 278 8C for 1 h. The resulting red-brown micro crystals were filtered oV, 30 mg, (72%). M.p. 205 8C (decomp.) (Found: C, 41.85; H, 3.44. C12H12BF4Ru requires C, 41.89; H, 3.51%).IR (KBr disc): n& /cm21 1420, 1395, 1120–1000 and 859. 1H NMR (CD3CN): d 6.41 (td, 2 H, J = 3.0 and 1.0, b-H of C5H4), 6.12 (td, 2 H, J = 3.0 and 1.0, b-H of C5H4), 5.50 (s, 5 H, C5H5), 5.46 (dt, 2 H, J = 3.0 and 1.0, a-H of C5H4), 5.15 (dt, 2 H, J = 3.0 and 1.0 Hz, a-H of C5H4) and 1.93 (s, 3 H, Me). 13C NMR (CD3CN): d 28.05 (Me), 81.74 (b-C of C5H4), 83.04 (b-C of C5H4), 86.06 (C5H5), 92.89 (a-C of C5H4), 94.15 (ipso-C of C5H4) and 125.90 (]] CMe).s-trans-[Ru2(Ï-Á6 :Á6-C5Me4CMeCMeC5Me4)(Á5-C5H5)2]- [BF4]2 15a. trans Isomer 9a was oxidized according as described above giving red-brown micro crystals (32 mg, 77%) of 15a, m.p. 195 8C (decomp.) (Found: C, 42.04; H, 3.44. C12H12BF4Ru requires C, 41.89; H, 3.51%). IR (KBr disc): n& /cm21 1423, 1120–1000 and 850. 1H NMR (CD3CN): d 6.38 (td, 2 H, J = 3.0 and 1.0, b-H of C5H4), 6.09 (td, 2 H, J = 3.0 and 1.0, b-H of C5H4), 5.48 (s, 5 H, C5H5), 5.42 (dt, 2 H, J = 3.0 and 1.0, a-H of C5H4), 5.14 (dt, 2 H, J = 3.0 and 1.0 Hz, a-H of C5H4) and 2.35 (s, 3 H, Me). 13C NMR (CDCl3): d 28.02 (Me), 81.73 (b-C of C5H4), 83.04 (b-C of C5H4), 86.04 (C5H5), 92.85 (a-C of C5H4), 94.13 (a-C of C5H4) and 104.09 (ipso-C of C5H4). Two-electron reduction of complex 11 with cobaltocene. To a solution of complex 11 (32 mg, 0.04 mmol) in CH3CN (9 cm3) and CH2Cl2 (5 cm3) was added cobaltocene (20 mg, 0.11 mmol) at room temperature. The solution was stirred for 12 h.The solvent was removed by a rotary evaporator and the residue subjected to column chromatography on silica gel using CH2Cl2–hexane (1 : 1 v/v) as the eluent. The pale yellow first fraction was collected and evaporated to give pure 6 (24 mg,J. Chem. Soc., Dalton Trans., 1998, Pages 2215–2224 2223 Table 4 Crystal and intensity collection data for complexes 6, 9a, 9b, 13 and 15b Formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/g cm23 Crystal dimensions/mm m/cm21 hkl Limits Total reflections measured Unique reflections Reflections used Parameters RR 9 Maximum, minimum peaks in final Fourier map/e Å23 6 C22H40Ru2 626.80 Triclinic P1� 7.820(1) 8.573(3) 10.803(3) 93.83(2) 91.76(2) 102.00(2) 706.1(3) 1* 1.47 0.30 × 0.18 × 0.16 10.662 210 to 0, 210 to 11, 214 to 14 3581 3239 2511 241 0.021 0.028 2.14, 20.73 9a C24H24Ru2 514.59 Monoclinic P21/c 5.9060(6) 9.9670(9) 16.049(1) 93.640(6) 942.8(2) 2 1.812 0.5 × 0.15 × 0.15 15.768 0–8, 0–14, 222 to 22 3828 2335 2335 166 0.038 0.041 0.75, 20.90 9b C24H24Ru2 514.59 Monoclinic P21/c 11.5630(9) 9.8190(6) 16.501(1) 93.184(3) 1609.6(5) 4 1.817 0.35 × 0.14 × 0.14 15.895 0–16, 0–13, 223 to 23 5680 4275 4275 331 0.041 0.052 0.88, 20.77 13 C32H40B2F8Ru2 800.42 Monoclinic P21/a 13.905(3) 15.026(3) 7.900(3) 91.76(2) 1609.6(5) 2* 1.65 0.20 × 0.17 × 0.12 9.618 0–18, 0–19, 210 to 10 4208 3683 3094 284 0.040 0.045 1.08, 20.73 15b C24H24B2F8Ru2 688.21 Monoclinic P21/n 11.5740(6) 9.5430(6) 21.2030(8) 92.055(3) 2340.4(2) 4 1.953 0.12 × 0.12 × 0.1 13.409 0–16, 0–13, 224 to 20 6273 5080 5080 421 0.032 0.033 0.66, 20.75 * Crystal molecular symmetry 1. 97%) as a yellow solid. The spectroscopic data of the sample were identical with those of an authentic sample. Crystallography The crystallographic data are listed in Table 4. Data collections for complexes 6 and 13 were performed at room temperature on a Mac Science MXC18K diVractometer with graphite monochromated Mo-Ka radiation (l = 0.710 73 Å) and an 18 kW rotating anode generator.The structure was solved with the DIRDIF-PATTY or SIR method in CRYSTAN-GM38 and refined by full-matrix least squares. Absorption correction with the y-scan method and anisotropic refinement for nonhydrogen atom were carried out. Data collections for 9a, 9b, and 15b were performed by the Weissenberg method on a Mac Science DIP3000 image processor under similar conditions for those above. The structure was solved with the SIR method in CRYSTAN-GM and refined by full-matrix least squares.An absorption correction by the DIFABS method39 and anisotropic refinement for non-hydrogen atom were carried out. 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Rheingold, ibid., 1990, 112, 7113; T. T. Chin, W. E. Geiger and A. L. Rheingold, ibid., 1996, 118, 5002. 36 W. E. Geiger, Prog. Inorg. Chem., 1985, 33, 275. 37 A. R. Kudinov, M. I. Rybinskaya, Y. T. Struchkov, A. I. Yanovskii and P. V. Petrovskii, J. Organomet. Chem., 1987, 336, 187. 38 CRYSTAN-G, software package for structure determination attached to the MXC18K system. 39 N. Walker and D. Stuart, DIFABS, Acta. Crystallogr., Sect. A, 1983, 39, 158. Received 10th March 1998; Paper 8/01941J

ISSN:1477-9226    

DOI:10.1039/a801941j

出版商:RSC    

年代:1998

数据来源: RSC

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DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2217–2220 2217 Pentafluorophenylphosphine complexes of platinum(II); crystal structure of trans-[PtCl2(PEt3){PPh2(C6F5)}] Malcolm J. Atherton,a John Fawcett,b John H. Holloway,b Eric G. Hope,b David R. Russell b and Graham C. Saunders *,b a BNFL Fluorochemicals Ltd., Springfields, Salwick, Preston, UK PR4 0XJ b Department of Chemistry, University of Leicester, Leicester, UK LE1 7RH The reactions between the pentafluorophenylphosphines PPhx(C6F5)32x (x = 0–2) and the dimeric platinum(II) species [{Pt(PEt3)Cl(m-Cl)}2] yielded the complexes trans-[PtCl2(PEt3){PPhx(C6F5)32x}] (x = 0 1, 1 2 or 2 3).The molecular structure of complex 3 has been determined by single-crystal X-ray crystallography, it crystallizes in the triclinic space group P1� with Z = 4 with two independent molecules in the asymmetric unit, a = 12.067(2), b = 14.131(1), c = 16.393(2) Å, a = 76.92(1), b = 79.08(1), g = 89.40(1)8. Variable-temperature 19F NMR spectroscopic studies, performed at 282.41 MHz, were carried out and showed that there is hindered rotation about the P]C6F5 bonds of complex 1, which was frozen out at 197 K.There was no evidence of hindered rotation about the P]C bonds of complexes 2 and 3 down to 184 K. As part of our continuing study into the effects that the presence of fluorine at strategic sites in ligands can bestow upon transition-metal complexes, we have investigated rhodium and iridium complexes of P(C6F5)3,1,2 PPh(C6F5)2 1 and PPh2(C6F5).1 We have found that, for bis(phosphine) complexes of rhodium(I), the ligand P(C6F5)3 gives rise to dramatically different structural and spectroscopic properties from those of the ligands PPh(C6F5)2 and PPh2(C6F5). In particular, [{RhCl- [P(C6F5)3]2}n] is polymeric whereas [{RhCl[PPhx(C6F5)32x]2}2] (x = 1 or 2) are dimeric, and the absolute values of 1J(RhP) for trans-[RhCl(CO){PPhx(C6F5)32x}2] (x = 1 or 2) are similar, whilst that for trans-[RhCl(CO){P(C6F5)3}2] is considerably larger.We have extended our study to platinum(II) species of the form [PtCl2(PEt3)L] (L = fluorinated phosphines) and we report here the synthesis and characterization of these complexes and the structure of trans-[PtCl2(PEt3){PPh2(C6F5)}]. Results and Discussion The reactions between the pentafluorophenylphosphines PPhx- (C6F5)32x (x = 0–2) and the dimeric platinum(II) species [{PtCl- (m-Cl)(PEt3)}2] in refluxing acetone yielded the complexes trans-[PtCl2(PEt3){PPhx(C6F5)32x}] (x = 0 1, 1 2 or 2 3). The complexes were characterized by elemental analyses, mass spectroscopy, 1H, 19F and 31P NMR and IR spectroscopies (Table 1).The assignments of the phosphorus resonances were made by comparison of the 31P and 31P-{1H} NMR spectra. The magnitude of the platinum–phosphorus coupling constant, 1J(PtP), and for the complexes 1 and 2, the magnitude of the phosphorus–phosphorus coupling constant, 2J(PP), confirm that each complex possesses mutually trans phosphine ligands.This is further confirmed by the molecular structure of complex 3 (Fig. 1), which was determined by single-crystal X-ray diffraction. The 31P-{1H} NMR spectrum of 3 is second order exhibiting two signals at dP 14.4 and 14.3, each with platinum satellites. A simulation of this spectrum give values of dP of 13.9 and 14.8 with absolute values for 1J(PtP) of 2470 and 2615 Hz respectively, and an absolute value for 2J(PP) of 469 Hz.The assignment of the two resonances is difficult because of the very second-order nature of the spectrum. However, a careful inspection of the high frequency 195Pt satellites in the undecoupled 31P NMR spectrum allows assignment of the higherfrequency resonance (dP 14.8) to the PEt3 ligand, in line with that observed for complexes 1 and 2. The values of dP for the fluorine-containing phosphine resonances of complexes 1–3 are ca. 50 ppm to higher frequency than those for the free ligands.The magnitude of 1J[Pt]PPhx(C6F5)32x] increases in the order 1 < 2 < 3, which is consistent with previous observations and is accounted for by the expected increase in the C]P]C angles, and thus lower s-character of the Pt]P bond, as C6H5 is replaced by C6F5.3,4 (This series differs significantly from the sequence of the absolute values of the rhodium–phosphorus coupling constants, 1J(RhP), for the complexes trans-[RhCl(CO){PPhx- (C6F5)32x}], in which 1J(RhP) for the complexes x = 1 and 2 are similar and that for x = 0 is considerably greater.1) The value of d and the magnitude of 1J(PtP) for the PEt3 ligand follow the order 1 > 2 > 3.The magnitude of 2J(PP) follows the same order. The structure of complex 3 possesses two independent molecules in the asymmetric unit. Selected bond lengths, bond angles and torsion angles are given in Table 2. The trans geometry of the complex is confirmed by the crystal structure with P]Pt]P angles of ca. 1788 and Cl]Pt]Cl angles of ca. 1748. The P]Pt]Cl angles lie in the range 88.25(9)–92.93(7)8. The two independent molecules within the asymmetric unit possess Fig. 1 Molecular structure of one of the independent molecules of trans-[PtCl2(PEt3){PPh2(C6F5)}] 3. Displacement ellipsoids are shown at the 30% probability level. The hydrogen atoms are omitted for clarity2218 J. Chem. Soc., Dalton Trans., 1997, Pages 2217–2220 Table 1 Analytical, mass spectral and NMR spectroscopic data for compounds 1–3 Compound Analysis (%) a and m/z b NMR Spectroscopy c 1 d C, 29.6 (31.5); H, 2.0 (1.65) 915 (M1), 880 ([M 2 Cl]1), 843 ([M 2 2Cl 2 2H]1) 1H: 1.97 (6 H, m, CH2), 1.20 [9 H, dt, 3J(PH) 17.5, 3J(HH) 7.6, CH3] 19F: 2126.18 (6 F, br m, o), 2145.41 (3 F, unresolved t, p), 2159.29 (6 F, m, m) 19F(197 K): 2120.65 (2 F, m, o), 2127.97 (2 F, m, o), 2130.70 (2 F, m, o), 2142.14 (2 F, m, p), 2144.30 (1 F, m, p), 2158.29 (2 F, vt, J 23.2, m), 2158.77 (2 F, vt, J 20.7, m), 2159.50 (2 F, m, m) 31P-{1H}: 18.8 [d, 2J(PP) 532, 1J(PtP) 2918, PEt3], 218.1 [d, 2J(PP) 532, 1J(PtP) 2255, P(C6F5)3] 2 C, 35.1 (34.9); H, 2.4 (2.4) 826 ([M 1 H]1), 791 ([M 2 Cl 1 H]1), 755 ([M 2 2Cl]1) 1H: 7.90 (2 H, m, PPh), 7.52 (1 H, m, p), 7.45 (2 H, m, PPh), 1.98 (6 H, m, CH2), 1.22 [9 H, dt, 3J(PH) 17.0, 3J(HH), 7.7, CH3] 19F: 2124.88 [4 F, dm, 3J(FoFm) 19.3, o], 2147.13 [2 F, tm, 3J(FmFp) 20.8, p], 2159.95 (4 F, m, m) 31P-{1H}: 16.7 [d, 2J(PP) 508, 1J(PtP) 2792, PEt3], 0.8 [d, 2J(PP) 508, 1J(PtP) 2344, PPh(C6F5)2] 3 C, 39.4 (39.15); H, 3.5 (3.4) 736 ([M 1 H]1), 701 ([M 2 Cl 1 H]1), 665 ([M 2 2Cl]1) 1H: 7.97 (4 H, m, PPh2), 7.43 (6 H, m, PPh2), 2.01 (6 H, m, CH2), 1.25 [9 H, dt, 3J(PH) 17.3, 3J(HH) 7.4, CH3] 19F: 2124.80 [2 F, dm, 3J(FoFm) 20.8, o], 2149.39 [1 F, tm, 3J(FmFp) 20.7, p], 2161.05 [2 F, ddm, 3J(FmFp) ª 3J(FmFo) 20.9, m] 31P-{1H} ABX pattern, 14.8 [2J(PP) 469, 1J(PtP) 2615, PEt3], 13.9 [2J(PP) 469, 1J(PtP) 2470, PPh2(C6F5)] e a Required values are given in parentheses.b FAB mass spectra in m-nitrobenzyl alcohol matrix. c Recorded in CDCl3 at 298 K, unless stated otherwise. Data given as: chemical shift (d) [relative intensity, multiplicity (J in Hz), assignment], d = doublet, t = triplet, vt = virtual triplet, m = multiplet. d Samples of 1 were contaminated with small amounts of [{PtCl(m-Cl)(PEt3)}2], repeated recrystallizations failed to give satisfactory analysis.e Values obtained from simulation. Pt]PPh2(C6F5) bond lengths which are identical within experimental error. The Pt]PEt3 bond lengths in the two unique molecules are also identical, and they are shorter than the Pt] PPh2(C6F5) bonds by ca. 0.02 Å. In both molecules the planes defined by the Pt]PPh2(C6F5) and P]C6F5 bonds are almost coplanar with the PtP2Cl2 plane [i.e. the Cl(1)]Pt]P]C6F5 torsion angles are close to 08]. Both molecules show a similar disposition of the phenyl rings about the Pt]P axis.The planes defined by the C6H5 rings are twisted by ca. 208 from parallel with the Pt]P bond giving the Pt]P]C]C torsion angles close to 20 and 1608 for each ring. The plane defined by the C6F5 ring is twisted away from perpendicular to the Pt]P bond at ca. 208 such that the absolute Pt]P]C]C torsion angles are ca. 70 and 1108. The P]C bond lengths of the PPh2(C6F5) ligand arehe same within experimental error. Both Pt]P]C6F5 angles are ca.Table 2 Selected bond lengths (Å), angles (8) and torsion angles (8) with estimated standard deviations (e.s.d.s) in parentheses for trans- [PtCl2(PEt3){PPh2(C6F5)}] 3 Pt(1)]Cl(1) Pt(1)]Cl(2) Pt(1)]P(1) Pt(1)]P(2) P(1)]C(11) P(1)]C(21) P(1)]C(31) 2.305(2) 2.307(2) 2.318(2) 2.299(2) 1.852(8) 1.802(9) 1.814(8) Pt(2)]Cl(1a) Pt(2)]Cl(2a) Pt(2)]P(1a) Pt(2)]P(2a) P(1a)]C(11a) P(1a)]C(21a) P(1a)]C(31a) 2.303(2) 2.318(2) 2.322(2) 2.300(2) 1.849(9) 1.809(9) 1.813(8) Cl(1)]Pt(1)]Cl(2) P(1)]Pt(1)]Cl(1) P(1)]Pt(1)]Cl(2) P(2)]Pt(1)]Cl(1) P(2)]Pt(1)]Cl(2) P(1)]Pt(1)]P(2) Pt(1)]P(1)]C(11) Pt(1)]P(1)]C(21) Pt(1)]P(1)]C(31) C(11)]P(1)]C(21) C(11)]P(1)]C(31) C(21)]P(1)]C(31) 174.03(9) 92.93(7) 88.61(8) 88.25(9) 90.21(9) 178.82(9) 113.8(2) 112.9(3) 117.6(3) 105.3(4) 100.2(4) 105.7(4) Cl(1a)]Pt(2)]Cl(2a) P(1a)]Pt(2)]Cl(1a) P(1a)]Pt(2)]Cl(2a) P(2a)]Pt(2)]Cl(1a) P(2a)]Pt(2)]Cl(2a) P(1a)]Pt(2)]P(2a) Pt(2)]P(1a)]C(11a) Pt(2)]P(1a)]C(21a) Pt(2)]P(1a)]C(31a) C(11a)]P(1a)]C(21a) C(11a)]P(1a)]C(31a) C(21a)]P(1a)]C(31a) 173.45(9) 91.58(7) 89.43(7) 88.31(8) 90.40(8) 117.52(9) 112.8(2) 111.0(3) 118.4(3) 105.7(4) 100.9(4) 107.0(4) C(11)]P(1)]Pt(1)]Cl(1) Pt(1)]P(1)]C(11)]C(12) Pt(1)]P(1)]C(11)]C(16) Pt(1)]P(1)]C(21)]C(22) Pt(1)]P(1)]C(21)]C(26) Pt(1)]P(1)]C(31)]C(32) Pt(1)]P(1)]C(31)]C(36) 22.6 111.1 267.1 158.4 224.0 156.5 222.2 C(11a)]P(1a)]Pt(2)]Cl(1a) Pt(2)]P(1a)]C(11a)]C(12a) Pt(2)]P(1a)]C(11a)]C(16a) Pt(2)]P(1a)]C(21a)]C(22a) Pt(2)]P(1a)]C(21a)]C(26a) Pt(2)]P(1a)]C(31a)]C(32a) Pt(2)]P(1a)]C(31a)]C(36a) 8.1 74.1 2104.2 2165.6 19.0 15.5 2160.0 1138 with each unique molecule possessing one smaller Pt]P]C6H5 angle at ca. 1128 and one larger angle of ca. 1188. These values may be compared to those in the platinum(II) complex trans-[PtMe{PPh2(C6F5)}(OC6F4PPh2-2)],5 in which the P]C6F5 bond is significantly longer than the P]C6H5 bonds and the Pt]P]C6F5 angle of 109.7(3)8 is considerably smaller than the Pt]P]C6H5 angles of 114.4(2) and 116.8(2)8. The C]P]C angles of the PPh2(C6F5) ligand in 3 lie in the range 100.2(4)–107.0(4)8. The bond lengths and angles of the C6F5 rings in the structure of 3 are similar to those in trans- [PtMe{PPh2(C6F5)}(OC6F4PPh2-2)].The 19F NMR spectrum of complex 1, recorded at 282.41 MHz, in CDCl3 at 298 K shows three resonances at dF 2126.18, 2145.41 and 2159.29 assigned to the o-, p- and m-fluorine atoms respectively. The resonance assigned to the o-fluorines is broad, indicative of a fluxional process.At 348 K the o-fluorine resonance is considerably sharper. Upon cooling from 298 K the three resonances broaden significantly and at 197 K there are eight sharp resonances (Fig. 2, Table 1). The presence of only two resonances at d 2140.0 to 2145.0, with intensities in a ratio of 2 : 1, assigned to the p-fluorines is consistent with two equivalent and one unique C6F5 ring (Fig. 3, Fh and Fc). The presence of three resonances at d 2118.0 to 2132.0, with equal intensities, assigned to the ortho fluorine atoms and three reson- Fig. 2 Variable-temperature 19F NMR spectra of trans-[PtCl2(PEt3)- {P(C6F5)3}] 1 in CDCl3 at 282.41 MHzJ. Chem. Soc., Dalton Trans., 1997, Pages 2217–2220 2219 ances at d 2156.0 to 2160.0, with equal intensities, assigned to the meta fluorine atoms is consistent with the two ortho fluorine atoms on the unique C6F5 ring being equivalent (Fa), the two meta fluorine atoms on the unique C6F5 ring being equivalent (Fb), and the two ortho fluorine atoms on each equivalent ring being non-equivalent (Fd and Fe) and the two meta fluorine atoms on each equivalent ring being non-equivalent (Ff and Fg).These data are similar to those of the low-temperature 19F NMR spectra of trans-[PtCl2(PPh3){P(C6F5)3}] and trans- [PtBr2(PPhMe2){P(C6F5)3}] 3 and are consistent with hindered rotation about the P]C6F5 bonds of the two equivalent C6F5 rings. It is not essential to infer hindered rotation about the unique P]C6F5 bond to explain these data, but investigations into the molecular dynamics of trans-platinum(II) bis(phosphine) complexes, in particular trans-[PtCl(Ph)(PMePh2)- {P(C6F5)3}],3 indicate that there is hindered rotation about all the P]C bonds of the P(C6F5)3 ligand in this case.It could well be that this is also the case for complex 1. It seems likely that, at the low-temperature limit, the P(C6F5)3 ligand adopts a conformation where the plane of the unique C6F5 ring lies almost perpendicular to the Pt]P bond, such that the two Pt]P]C]C torsion angles are close to 90 and 2908, and the pair of identical C6F5 rings adopt conformations twisted from parallel to the Pt]P bond by the same amount such that the absolute values of the Pt]P]C]C torsion angles for each ring are very different.Such a conformation is, however, not consistent with conformations adopted by the P(C6F5)3 ligands of the four-co-ordinate, bis(phosphine) complexes trans-[IrBr(CO){P(C6F5)3}],2 trans- [PtX2{P(C6F5)3}2] (X = Cl 6 or I 7) and trans-[PdCl2{P(C6F5)3}2] 8 in the solid state.In these complexes the P(C6F5)3 ligands adopt conformations in which one C6F5 ring is parallel to the Pt]P bond (absolute Pt]P]C]C torsion angles of 0–13 and 172–1808) and two C6F5 rings lie twisted by ca. 308 from perpendicular to the Pt]P bond (absolute Pt]P]C]C torsion angles of 51–67 and 105–1208). The compounds trans-[PtX2{P(C6F5)3}2] (X = Cl or I) 3 show similar fluxional behaviour to trans-[PtCl2- {P(C6F5)3}L] (L = PMe3 or PPh3) 3 and trans-[PtBr2(PPhMe2)- {P(C6F5)3}] 3 and thus it appears that, in four-co-ordinate platinum(II) complexes, the P(C6F5)3 ligand adopts a different conformation in solution to that in the solid state.A variabletemperature 31P-{1H} NMR spectroscopic study (121.50 MHz) of complex 1 in CD2Cl2 shows no fluxional processes, with only a slight broadening of the signals at 184 K. Thus, there is no evidence to suggest hindered rotation about the Pt]P bonds in complex 1 under the conditions of the study.Complexes 2 and 3 do not show fluxional behaviour similar to that of 1. The 19F (282.41 MHz) and 1H (300.14 MHz) NMR spectra show only sharp resonances at 298 K, and at 184 K in CD2Cl2 no significant broadening of either the 19F or 1H spectroscopic resonances is observed. The replacement of one C6F5 group in P(C6F5)3 by a phenyl ring is evidently sufficient to allow essentially unhindered rotation about all the P]C bonds.Fig. 3 Diagrammatic representation of the arrangement of the C6F5 rings of P(C6F5)3 in trans-[PtCl2(PEt3){P(C6F5)3}] 1 at the lowtemperature limit In summary, the complexes trans-[PtCl2(PEt3){PPhx- (C6F5)32x}] have been synthesized and their molecular dynamics studied by variable-temperature 1H, 19F and 31P NMR spectroscopy. Our investigation shows that the electronic properties of the ligands in these complexes vary regularly, unlike those in the system trans-[RhCl(CO){PPhx(C6F5)32x}],1 but that rotation about the P]C bonds of P(C6F5)3 in complex 1 is considerably more hindered than that of PPh(C6F5)2 and PPh2(C6F5) in complexes 2 and 3 respectively.Experimental Physical measurements The 1H, 19F and 31P NMR spectra were recorded on a Bruker AM300 spectrometer at 300.14, 282.41 and 121.50 MHz respectively, 1H referenced internally using the residual protio solvent resonance relative to tetramethylsilane (d 0), 19F externally to CFCl3 (d 0) and 31P externally to 85% H3PO4 (d 0).Infrared spectra were recorded as Nujol mulls between KBr plates on a Digilab FTS40 Fourier-transform spectrometer. Elemental analyses were performed by Butterworth Laboratories Ltd. and FAB mass spectra were recorded on a Kratos Concept 1H mass spectrometer. Materials The phosphines P(C6F5)3, PPh(C6F5)2 and PPh2(C6F5) (Fluorochem) were used as supplied. The platinum complex [{PtCl- (m-Cl)(PEt3)}2] was prepared as described previously.9 Light petroleum (b.p. 40–60 8C) was used throughout. Preparations trans-[PtCl2(PEt3){P(C6F5)3}] 1. A slurry of [{PtCl(m-Cl)- (PEt3)}2] (0.24 g, 0.31 mmol) and P(C6F5)3 (0.27 g, 0.50 mmol) in acetone (30 cm3) was refluxed for 1 min to give a pale yellow solution. The solution was allowed to cool and filtered. The solvent was removed by rotary evaporation to give 1 as a yellow solid, which was dried in vacuo. Yield 0.17 g, 31%.IR: 1646m, 1520s, 1488s, 1391m, 1297m, 1264w, 1239w, 1150w, 1097s, 1038m, 1012w, 986s, 856w, 785m, 739w, 724w, 639w, 631w, 589w, 520w and 459w cm21. trans-[PtCl2(PEt3){PPh(C6F5)2}] 2. A slurry of [{PtCl- (m-Cl)(PEt3)}2] (0.15 g, 0.20 mmol) and PPh(C6F5)2 (0.17 g, 0.38 mmol) in acetone (50 cm3) was refluxed for 5 min to give a pale yellow solution. The solution was allowed to cool, filtered and concentrated by rotary evaporation to ca. 10 cm3. Addition of light petroleum (30 cm3) afforded yellow crystals of 2, which were washed with light petroleum and dried in vacuo.Yield 0.13 g, 41%. IR: 1644m, 1522s, 1488s, 1437m, 1413w, 1394m, 1312w, 1293m, 1260w, 1096s, 1040m, 979s, 849w, 772m, 744m, 724m, 704w, 688m, 633m, 588w, 524m, 513w, 487w, 476m and 451w cm21. trans-[PtCl2(PEt3){PPh2(C6F5)}] 3. A slurry of [{PtCl(m-Cl)- (PEt3)}2] (0.145 g, 0.19 mmol) and PPh2(C6F5) (0.122 g, 0.35 mmol) in acetone (50 cm3) was refluxed for 5 min to give a pale yellow solution.The solvent was removed by rotary evaporation to yield a yellow solid, which was recrystallized from dichloromethane. Yield 0.06 g, 21%. IR: 1645m, 1522s, 1488s, 1439w, 1412w, 1391w, 1290m, 1261w, 1085s, 1040m, 979s, 851w, 841w, 770m, 743m, 724m, 704w, 689m, 632m, 587w, 525m, 511m, 486w, 475w, 449w and 430m cm21. Crystal-structure determination of complex 3 Crystal data and data collection parameters. C24H25Cl2F5- P2Pt, M = 736.37, triclinic, a = 12.067(2), b = 14.131(1), c = 16.393(2) Å, a = 76.92(1), b = 79.08(1) g = 89.40(1)8, U = 2672.0(6) Å3 (by least-squares refinement on diffractometer2220 J.Chem. Soc., Dalton Trans., 1997, Pages 2217–2220 angles from 28 centred reflections, 10.0 < 2q < 24.68), T = 190(2) K, space group P1� , graphite-monochromated Mo-Ka radiation, l = 0.710 73 Å, Z = 4 with two independent molecules in the asymmetric unit, Dc = 1.831 g cm21, F(000) = 1424, dimensions 0.48 × 0.41 × 0.21 mm, m(Mo-Ka) = 5.618 mm21, semiempirical absorption correction based on y scans, maximum and minimum transmission factors 0.95 and 0.365, Siemens P4 diffractometer, w scans, data collection range 5.2 < 2q < 54.08, 21 < h < 14, 217 < k < 17, 220 < l < 20, no crystal decay was detected from periodically measured check reflections; 11 607 reflections measured, 11 395 unique (Rint = 0.0280).The data were corrected for Lorentz and polarization effects. Structure solution and refinement. Structure solution by Patterson methods was carried out using the SHELXTL PC program.10 Refinement by full-matrix least squares on F 2 was carried out using the program SHELXL 93.11 An initial data set collected at room temperature was solved satisfactorily except that all ethyl carbon atoms had excessive anisotropic parameters indicative of disorder which could not be adequately modelled.The highest residual electron density was 1.6 e Å23 lying in the bond between Pt(2) and Cl(2a), 1.3 Å from Pt(2).A second data set was collected from a new crystal at 190 K in an attempt to minimize the disorder. These data provided a molecular structure which displayed smaller, but still excessive, anisotropic displacement parameters for the ethyl groups suggesting that the disorder persists at 190 K. The final refinement allowed for disordered ethyl groups with restraints to the P]C [1.86(1) Å], C]C9 [1.46(1) Å] and P]C9 [2.80(5) Å] distances and isotropic displacement parameters.Essentially the disorder model allows two alternative sites for all 12 ethyl carbon atoms with 50% occupancy, but for three methylene carbon atoms [C(1), C(1b) and C(3b)] the alterative sites could not be resolved. All other non-hydrogen atoms were refined as anisotropic atoms. The hydrogen atoms of the disordered ethyl groups were not included in the refinement, all other hydrogen atoms were included in calculated positions (C]H = 0.96 Å) using a riding model.Final R1 = 0.0484 and wR2 = 0.1083 for 8266 observed reflections [I > 2s(I)] and R1 = 0.0798 and wR2 = 0.1221 (all data) for the 589 parameters and 33 restraints refined with largest D/s 0.012, goodness of fit = 1.043. The highest residual electron density peak from this data set is 3.25 e Å23 and, as with the room temperature data, is 1.3 Å from Pt(2), approximately on the Pt(2)]Cl(2a) bond. The residual density, although obviously an artefact in the data, does not appear to arise from absorption.Empirical absorption corrections based on y scan data from over 40 reflections from both crystals were applied. A DIFABS-type refinement12 was attempted on the 190 K data, but did not result in any signifi- cant reduction in this residual density, indicating that this problem was not due to absorption. An analytical absorption correction was not possible as the crystal did not have clearly defined faces. An analysis of the weighting scheme over |Fo| and sin q/l was satisfactory.Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/533. Acknowledgements We thank K. S. Coleman for preliminary work, Dr. G. A. Griffith for assistance with the NMR spectroscopy experiments and the simulation, BNFL Fluorochemicals Ltd. (G. C. S.) and the Royal Society (E. G. H.) for support. References 1 M. J. Atherton, K. S. Coleman, J. Fawcett, J. H. Holloway, E. G. Hope, A. Karaçar, L. A. Peck, D. R. Russell and G. C. Saunders, J. Chem. Soc., Dalton Trans., 1995, 4029. 2 J. H. Holloway, E. G. Hope, D. R. Russell, G. C. Saunders and M. J. Atherton, Polyhedron, 1996, 15, 173. 3 J. B. Docherty, D. S. Rycroft, D. W. A. Sharp and G. A. Webb, J. Chem. Soc., Chem. Commun., 1979, 336. 4 R. Mason and D. W. Meek, Angew. Chem., Int. Ed. Engl., 1978, 17, 183. 5 S. Park, M. Pointer-Johnson and D. M. Roundhill, Inorg. Chem., 1990, 29, 2689. 6 W. P. Schaefer, D. K. Lyon, J. A. Labinger and J. E. Bercaw, Acta Crystallogr., Sect. C, 1992, 48, 1582. 7 W. N. Hunter, K. W. Muir and D. W. A. Sharp, Acta Crystallogr., Sect. C, 1986, 42, 1743. 8 B. Berstch-Frank and W. Frank, Acta Crystallogr., Sect. C, 1996, 52, 328. 9 R. J. Goodfellow and L. M. Venanzi, J. Chem. Soc. A, 1965, 7533. 10 G. M. Sheldrick, SHELXTL PC, Release 4.2, Siemens Analytical X-Ray Instruments, Madison, WI, 1991. 11 G. M. Sheldrick, SHELXL 93, Program for Crystal Structure Refinement, University of Göttingen, 1993. 12 R. H. Blessing, Acta Crystallogr., Sect. A, 1995, 51, 33. Received 6th December 1996; Paper 6/0825

ISSN:1477-9226    

DOI:10.1039/a608253j

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2219–2223 2219 The reaction of N-methylbenzothiazole-2-selone with the interhalogens iodine monobromide and iodine monochloride Philip D. Boyle,a Wendy I. Cross,a Stephen M. Godfrey,a Charles A. McAuliVe,a Robin G. Pritchard a and Simon Teat b a Department of Chemistry, University of Manchester Institute of Science and Technology, PO Box 88, Manchester, UK M60 1QD. E-mail: stephen.m.godfrey@umist.ac.uk b Daresbury Laboratory, Warrington, UK WA4 4AD Received 19th March 1999, Accepted 13th May 1999 Two 1 : 1 interhalogen adducts of N-methylbenzothiazole-2-selone (mbts) have been prepared and crystallographically characterised: mbts?IBr (1) and mbts?ICl (2).Both exhibit the charge transfer ‘spoke’ structure consisting of a linear Se–I–X arrangement (X = Br or Cl) where d(C–Se) increases from that seen for mbts by 0.058(5) and 0.062(8) Å (1 and 2 respectively); d(C–N) decreases by 0.019(4) and 0.019(9) Å.This indicates electron density moves towards the Se–I–X moiety upon co-ordination, causing a partial positive charge to reside on the nitrogen atom. The I–X bond lengthens with respect to the unco-ordinated species for both molecules. The addition of two equivalents of ICl to mbts gave a dark purple material of stoichiometry C8H7Cl2.9I1.1NSSe 3; the fractional stoichiometry for iodine and chlorine may be indicative of ‘halogen scrambling’. An additional product from this reaction was examined crystallographically and found to consist of the ion pair [C8H7NSCl]1[ICl2]2 4, i.e.the C–Se double bond has been completely cleaved and replaced by a C–Cl single bond. The positive charge is again supported mostly by the nitrogen atom; d(C–N) decreases to 1.294(10) Å indicating a double bond. Introduction The ability of selenoamides to form 1 : 1 addition products with equimolar quantities of diiodine has been extensively investigated by Devillanova and co-workers 1–7 who reported the charge transfer (CT) ‘spoke’ structure consisting of a linear Se– I–I arrangement and bent geometry at the selenium atom.4,7 Interestingly, however, variations in the organic fragment of the selenoamide can result in a T-shaped I–Se–I arrangement7 which contains a hypervalent selenium atom.A further structural type described is that of the ionic product from the 1 : 1 reaction of N-methylbenzothiazole-2-selone, mbts, with diiodine; this consists of an [(mbts)2I]1 cation and I3 2 anion.5 Fig. 1 represents the three structural types so far elucidated for products of these reactions. Clearly, the nature of 1 : 1 selenoamide–diiodine addition compounds is highly dependent on subtle electronic eVects from the organic fragment of the selenoamide employed. Two further addition compounds of mbts have been described.5 The 2: 1 reaction of mbts and diiodine produces an ‘extended spoke’ which is perhaps best thought of as an [mbts–I]1 moiety strongly interacting with an I3 2 anion; i.e.the presence of two molecules of I2 per mbts molecule produces a CT structure whereas one would appear not to. A directly comparable structure exists for the 2 : 1 addition product of mbts and IBr; here the [mbts–I]1 moiety interacts (albeit weakly) with an IBr2 2 anion. Fig. 2 represents these two molecular structures. The carbon–selenium bond lengthens in all of the aforementioned molecules; however, it is noteworthy that the double bond character is essentially preserved, e.g.for the diiodine adduct of 5,5-dimethyl-2-selenoxoimidazolin-4-one, d(C–Se) = 1.861(4) Å.* The exception to this is for the T-shaped adduct in Fig. 1 (b) where the d(C–Se) of 1.893(6) Å indicates a purely single bond. We are currently engaged in a comprehensive study of the * Normal range for a carbon–selenium double bond taken as 1.817 to 1.866 Å based on crystallographic values reported in refs. 8–13. interaction of a variety of organo Group 15 and 16 compounds with dihalogen and interhalogen molecules and have also found that the geometrical nature of the adducts produced frequently varies with changes in organo-substituents. Further, the identity of the dihalogen and the solvent employed for the reaction is of importance.For example, Me2Se reacts with diiodine to produce the CT adduct Me2Se–I–I whereas the same diorganoselenide reacts with dibromine or dichlorine to produce the disphenoidal ‘see-saw’ structure Me2SeX2 (X = Br or Cl).14,15 Additionally, Knobler and McCullough 16 reported the crystal structure of the iodine monochloride complex of 1-oxa-4- selenacyclohexane, C4H8OSe?ICl, this is also a CT adduct con- Fig. 1 The three types of 1 : 1 product from the reactions of selenoamides and diiodine: (a) the ‘spoke’ structure of N-methyl-1,3- thiazolidine-2-selone–diodine; (b) the T-shape structure of (1,3- dimethylimidazolidin-2-yl)diiodoselenium; (c) the ionic N-methylbenzothiazole- 2-selone iodonium salt.N S Se Me I I N N Me Me Se I I N S Se Me I + Se S N Me (a) (b) (c) – +2220 J. Chem. Soc., Dalton Trans., 1999, 2219–2223 taining the linear arrangement Se–I–Cl. More recently, we have extended our studies to investigate the reaction of certain tertiary phosphine chalcogenides with dihalogens. In all cases, reaction of R3PSe with diiodine in a 1: 1 stoichiometry produces the CT adducts R3PSeI–I,17 whereas the analogous reaction with dibromine produces the T-shaped adducts R3PSeBr2.18 Reaction of R3PSe with dichlorine appears to be rather complicated, but preliminary studies suggest that, rather than adduct formation occurring, cleavage of the phosphorus– selenium bond occurs to produce equimolar quantities of triorganophosphorus dichloride, R3PCl2, and elemental selenium.19 These results illustrate the susceptibility of the phosphorus–selenium bond to cleavage when treated with the lighter dihalogens.We have now turned our attention to the reaction of compounds containing a carbon–selenium double bond with dihalogens, principally to investigate the types of structures exhibited upon adduct formation and also to compare the nature of such adducts with those formed by the reaction of the analogous tertiary phosphine chalcogenides with dihalogens; i.e. to compare the reaction of compounds containing a carbon– selenium double bond with those containing a phosphorus– selenium double bond with dihalogens.The reactions of selenoamides with interhalogens have been investigated far less than those with diiodine. In addition to the 2 : 1 ‘extended spoke’ adduct in Fig. 2(b) the only other reports to our knowledge concern the crystallographic studies of the IBr spoke adduct of N-methyl-1,3-thiazolidine-2-selone 4 and three intriguing products containing dications which bear the unusual –Se–Se– bridge.20 The latter show again the importance of the organic fragment of the particular selenoamide employed and how this aVects the nature of products formed.For example, the reaction of 1,3-dimethyl-4-imidazoline-2- selone, dmis, with IBr produces a dication balanced by two Br2 anions; the equivalent reaction with ICl produces the same dication balanced by a single Cl2 anion and an I3 2 anion. A further curiosity is revealed when one examines the crystalline product from the reaction of IBr with 1,3-dimethylimidazolidine- 2-selone, a selenoamide only subtly diVerent to dmis; this dication is balanced not by two Br2 anions but by a Br2 and an IBr2 2 anion (Fig. 3). The variety in structural types so far elucidated clearly show the diYculties in predicting the exact nature of products formed from reactions of selenoamides with dihalogens. These diYculties have prompted us to turn our investigations to the reactions of mbts with ICl and IBr in order to find out which (if any) of the above structural motifs are adopted by possible 1 : 1 addition products.In addition, we felt it would be useful to examine the 2 : 1 reaction of ICl with mbts in order to see if the product is isostructural with the mbts?2IBr complex described by Devillanova and co-workers in ref. 5. Apart from this single structure, reactions of selenoamides with n I–X (where X = Br or Cl; n > 1) have received virtually no attention to date. Results The compound IBr was treated with mbts in a 1 : 1 ratio and ICl in 1 : 1 and 2 : 1 ratios; in each case, we employed dichloro- Fig. 2 The ‘extended spoke’ structures of (a) mbts?2I2 and (b) mbts?2IBr.N S Se Me I I I I N S Se Me I Br I Br (a) (b) methane as the solvent and reaction times were approximately four days. (i) The 1 : 1 adduct mbts?IBr 1 is a bright orange solid isolated in 72% yield which decomposes to a black tar at 138– 139 8C. Elemental analysis, found % (calc. for C8H7BrINSSe): C, 21.9 (22.0); H, 1.4 (1.6); Br, 18.4 (18.4); I, 28.9 (29.2); N, 3.2 (3.2); S, 7.1 (7.4).Recrystallisation of 1 via the slow cooling of a solution in dichloromethane from 40 8C yielded small pale orange crystals, one of which was selected for analysis by single crystal X-ray diVraction. The structure of one molecule from the unit cell of 1 is illustrated in Fig. 4. (ii) The 1 : 1 adduct mbts?ICl 2 is a yellow solid isolated in 77% yield which decomposes to a black tar at 165–167 8C. Elemental analysis, found % (calc.for C8H7ClINSSe): C, 24.7 (24.6); H, 1.7 (1.8); Cl, 8.8 (9.1); N, 3.6 (3.6); I, 32.2 (32.5); S, 8.2 (8.2). Recrystallisation of 2 by the same method as for 1 yielded small yellow needle crystals, one of which was selected for analysis by single crystal X-ray diVraction. The structure of one molecule from the unit cell of 2 is illustrated in Fig. 5. (iii) The reaction of mbts with two equivalents of ICl resulted in a dark purple solid 3, isolated in approximately 40% yield, which decomposed at 202 8C.Elemental analysis, found % (calc. for C8H7Cl2.9I1.1NSSe): C, 20.1 (20.4); H, 1.3 (1.5); Cl, 20.9 (21.8); I, 29.3 (29.7); N, 2.8 (3.0); S, 6.6 (6.8). Attempts to recrystallise 3 have so far failed; however, after isolation yellow crystals were produced in the dark purple filtrate by cooling to ca. 5 8C. X-Ray analysis of a single crystal showed the unit cell to contain a cationic organic species, [C8H7NSCl]1 and the anion ICl2 2, 4. No selenium is present in this material so the compound cannot be thought of as representative of the purple bulk material.An ion pair from the unit cell of 4 is illustrated in Fig. 6. Discussion Table 1 lists selected bond lengths and angles for adducts 1, 2 and 4 and compares them to those found8 for unco-ordinated mbts. Both 1 and 2 have a spoke structure based on a linear Se– I–X (X = Br or Cl) arrangement. The geometry at the selenium atom is bent. In each case, d(C–Se) has increased from the 1.817 Å seen for mbts † to 1.877(5) and 1.879(8) Å for 1 and 2 respectively. These distances are slightly beyond the normal range for carbon–selenium double bonds, but shorter than the accepted value of 1.893 Å for a truly single bond.22 It seems likely, therefore, that at least partial double-bond character is retained in the C–Se linkage.The increase in d(C–Se) is accompanied in both adducts by a reduction in d(C–N) of around 0.020 Å to 1.329(6) (1) and 1.329(10) Å (2).These values are at the lower end of the accepted scale for a C sp2–N single bond and at the top of that for a double bond. It can be postulated that upon co-ordination to the selenium atom by the interhalogen electron density moves towards the C–Se moiety away from the nitrogen atom. This eVect is even more pronounced in the T-shaped selenium-brominating agents described by Akabori and co- Fig. 3 a The CT ‘spoke’ structure of N-methyl-1,3-thiazolidine-2- selone–iodine monobromide.b Structure representing three products containing a dicationic Se–Se bridge: (i) R = CH]] CH, X, Y = Br; (ii) R = CH]] CH, X = Cl, Y = I; (iii) R = CH2CH2, X = Br, Y = IBr2. N S Se Me I Br R N N R N N Se Se Me Me Me Me + + (a) (b) X – Y – † All bond distances quoted here for mbts are averages of the distances for the two independent molecules in the unit cell reported in ref. 8. No standard deviations were given in that work, so cannot be included.J. Chem.Soc., Dalton Trans., 1999, 2219–2223 2221 workers 23 here d(C–Se) is entirely single in character at 1.95(1) to 1.99(2) Å. Hence, those molecules are best described as zwitterionic, with positive charge residing on the nitrogen atom and negative charge on the SeBr2 moiety. Adducts 1 and 2 can be thought of as being intermediate between the Akabori structure and the free mbts molecule. An interesting diVerence between adducts 1 and 2 is the change that occurs in d(C–S) on co-ordination; it shows essentially no change in 2 as compared to mbts, but for 1 decreases by 0.017 Å.It is thought that this might be a consequence of crystal packing rather than any subtle electronic eVects, this idea is supported when one examines the carbon–sulfur bond Fig. 4 An ORTEP21 drawing of one molecule of adduct 1. Fig. 5 An ORTEP drawing of one molecule of adduct 2. Table 1 Selected bond lengths (Å) and angles (8) for adducts 1, 2 and 4. A comparison with the average of those found for mbts 8 mbtsa 1 2 4 Se(1)–I(1) I(1)–Br(1) I(1)–Cl(1) C(2)–Se(1) C(2)–S(3) N(1)–C(2) N(1)–C(10) C(2)–Cl(1) I(1)–Cl(2) I(1)–Cl(3) Se(1)–I(1)–Br(1) Se(1)–I(1)–Cl(1) N(1)–C(2)–Se(1) S(3)–C(2)–Se(1) N(1)–C(2)–Cl(1) N(1)–C(2)–S(3) S(3)–C(2)–Cl(1) C(2)–Se(1)–I(1) C(10)–N(1)–C(2) Cl(2)–I(1)–Cl(3) ——— 1.817 1.723 1.349 1.443 ——— —— 127.3 122.1 — 110.5 —— 121.9 2.6360(8) 2.8137(8) — 1.877(5) 1.706(5) 1.329(6) 1.464(6) ——— 177.09(2) — 121.9(4) 124.8(2) — 113.2(4) — 99.14(1) 122.3(4) 2.6186(10) — 2.691(2) 1.879(2) 1.722(8) 1.329(10) 1.470(10) ——— — 178.76(5) 122.1(6) 124.8(5) — 113.1(6) — 100.6(3) 122.6(7) ———— 1.696(8) 1.294(10) 1.464(9) 1.673(8) 2.559(2) 2.502(2) ———— 123.1(6) 116.0(6) 121.0(5) — 122.6(7) 179.19(8) a The value reported here is an average of the bond lengths found for each of the two crystallographically independent molecules in the unit cell in ref. 8. No standard deviations were given in that work. length obtained by Devillanova and co-workers 4 for mbts?2I2.Three crystallographically discrete molecules are present in the unit cell; 4 one of which has a d(C–S) higher than that of mbts, one lower and one similar. It would appear, therefore, that although carbon–selenium and carbon–nitrogen bond lengths can be usefully invoked when attempting to describe such adducts, carbon–sulfur bond lengths are not a reliable tool. Both adducts 1 and 2 were obtained in high yield and elemental analyses found correspond well to calculated values.However, considerable structural variation has been encountered with such systems, as outlined in the Introduction, and it is appreciated that there is a small possibility that the structures described do not correspond to that of the bulk material. However, the ‘spoke’ structures of 1 and 2 are in keeping with those observed for similar materials 4,7 which exhibit a diiodine spoke. We feel confident, therefore, that the structures reported herein are indeed representative of the bulk material.The dark purple solid of stoichiometry C8H7Cl2.9I1.1NSSeI 3 obtained as the insoluble product from the 2 : 1 reaction with ICl can be rationalised if halogen scrambling has occurred. This is a phenomenon we have previously reported for the product of the reaction of triphenylphosphine with iodine monobromide, Ph3PI1.29Br0.71. Alternatively, this material may consist of several minor products in addition to the bulk ‘mbts? ICl3’; this could be an equally valid explanation of the relatively poor chlorine analysis.Powder diVraction has shown that no elemental selenium is present in 3 but, so far, recrystallisation attempts have failed and NMR and infrared techniques have been unhelpful in characterising this material. An interesting feature of the additional product, 4, is that the selenium atom in mbts is replaced by a chlorine atom; the short d(C–N) bond length of 1.294(10) Å indicates a carbon–nitrogen double bond and d(C–S) also decreases to 1.696(8) Å.This may imply that the positive charge of the organic cation, although located mostly on the nitrogen atom, is at least partially distributed round the heterocyclic ring. This reaction would therefore seem at first glance to not be analogous to that undergone between mbts and two equivalents of IBr which forms the product in Fig. 2(b). However, the stoichiometry of the reaction leading to 3 and 4 seems to imply that other products may well form in the 2 : 1 ICl reaction.It is conceivable that the 2 : 1 adduct ‘[mbts–I]1 [ICl2]2’ is one of these, or that it could be obtained if reaction conditions (such as solvent or reaction time) were adjusted. Prima facie, it would seem that mbts forms an extended spoke with two equivalents of I2 or IBr but not (at least not to the same extent) with ICl. Obviously this is somewhat speculative, and we plan to examine the sensitive system of mbts and ICl further.Conclusion The direct reaction of mbts with equimolar quantities of IBr and ICl results in the quantitative formation of 1 : 1 adducts which exhibit the molecular ‘spoke’ structure. An increase of d(C–Se) is observed (accompanied by a reduction in d(C–N)), but the double bond character of the carbon–selenium bond is essentially preserved. These two new adducts are therefore Fig. 6 An ORTEP drawing of the ion pair in the unit cell of adduct 4.2222 J. Chem. Soc., Dalton Trans., 1999, 2219–2223 Table 2 Crystal data and structure refinement for adducts 1, 2 and 4 1 2 4 Empirical formula MT /K Crystal system Space group a/Å b/Å c/Å b/8 V/Å3 Z Dc/mg m23 m/mm21 Reflections collected/unique [Rint] Final R1, wR2 indices [I > 2s(I)] (all data) C8H7BrINSSe 434.98 173(2) Orthorhombic P212121 6.9764(13) 9.1423(19) 17.817(5) 1136.4(4) 4 2.542 9.676 6711/2494 [0.0368] 0.0251, 0.0543 0.0276, 0.0550 C8H7ClINSSe 390.52 150(2) Orthorhombic Pnma 9.0950(2) 6.74600(10) 17.9527(4) 1101.49(4) 4 2.355 6.597 6175/1362 [0.0561] 0.0466, 0.0912 0.0646, 0.0977 C8H7Cl3INS 382.46 203(2) Monoclinic P21 7.844(2) 7.8546(10) 10.058(2) 92.860(10) 618.9(2) 2 2.052 3.365 1252/1174 [0.0260] 0.0301, 0.0728 0.0327, 0.0747 isostructural with the IBr complex of N-methyl-1,3-thiazolidine- 2-selone.4 It should be of interest to extend the range of selenoamides under investigation to establish whether this is the only structural motif available for such products.In addition, although previous workers have described the mbts?2IBr complex which consists of an ‘extended spoke’ arrangement (Fig. 2(b)), we have shown that the analogous reaction with ICl appears to be more complicated; a variety of products form, including the as yet unidentified material, 3, and the ionic compound 4. This is the first report to our knowledge which has shown that oxidation of the selenium atom in a selenoamide can occur by using two equivalents of an interhalogen. In addition, our studies and reports by other workers appear to suggest that this oxidation does not take place if only one equivalent of interhalogen is used.Therefore, whilst we do not dismiss the possibility that a 2: 1 ‘extended spoke’ adduct of mbts and ICl can form in a manner analogous to that with IBr, it seems fair to conclude that this is not necessarily the preferred reaction pathway for the mbts–ICl system. Our results lead us to suggest that subtle diVerences in acceptor abilities of IBr and ICl are of more importance for reactions involving two equivalents of interhalogen than for the corresponding equimolar reactions.Experimental Compounds 1–4 are moisture sensitive. Therefore, strictly anaerobic and anhydrous conditions must be observed for their successful synthesis. Any subsequent manipulation of the complexes was carried out inside a Vacuum Atmospheres HE-493 glove-box. The compound mbts was obtained commercially (Aldrich) and used as received.Dichloromethane (BDH) was dried over calcium hydride and refluxed in an inert atmosphere (N2) for at least two hours prior to use. The synthesis of mbts?IBr is typical: mbts (0.5 g, 2.19 mmol) was dissolved in dichloromethane (ca. 100 cm3) and subsequently iodine monobromide (Aldrich, 0.45 g, 2.19 mmol) added. After ca. 4 d the resultant orange solid was isolated using standard Schlenk techniques and dried in vacuo. It was then transferred to predried argon-filled ampoules that were flame-sealed. Elemental analyses were performed by the analytical laboratory of this department and are listed in the Results section.X-Ray crystallography The X-ray experiments for adducts 1 and 2 were carried out on Station 9.8 at the Daresbury Laboratory on a Siemens SMART CCD diVractometer using silicon 111 monochromated synchrotron radiation of wavelength 0.68620 Å. DiVraction measurement employed w rotation with narrow frames.An absorption correction using an empirical ellipsoidal method was applied. The X-ray diVraction experiment for adduct 4 was carried out at 203 K on a Nonius MACH 3 4-circle diVractometer using graphite monochromated Mo-Ka radiation. The w–2q scan technique was used to collect 1252 reflections with 2q £ 508. Three standard reflections were measured every 3 h and showed no significant decay. The intensities were corrected for Lorentz-polarisation eVects. An absorption correction using the y-scan method was applied.The SHELXL 97 suite of programs24 was used to solve the structures by direct methods and refined them using full-matrix least-squares. Crystallographic data are summarised in Table 2. CCDC reference number 186/1465. Acknowledgements Two of us (P. D. B. and W. I. C.) are grateful to the EPSRC for research studentships. We also wish to thank Daresbury Laboratories (station 9.8) for use of their single crystal X-ray diVraction facility.References 1 F. Cristiani, F. A. Devillanova, A. Diaz and G. Verani, J. Chem. Soc., Perkin Trans. 2, 1984, 1383. 2 M. Cau, F. Cristiani, F. A. Devillanova and G. Verani, J. Chem. Soc., Perkin Trans. 2, 1985, 749. 3 F. Cristiani, F. Demartin, F. A. Devillanova, F. Isaia, G. Saba and G. Verani, J. Chem. Soc., Dalton Trans., 1992, 3553. 4 F. Cristiani, F. A. Devillanova, F. Isaia, V. Lippolis and G. Verani, Inorg. Chem., 1994, 33, 6315. 5 F. Demartin, P. Deplano, F. A. Devillanova, F.Isaia, V. Lippolis and G. Verani, Inorg. Chem., 1993, 32, 3694. 6 F. Demartin, F. A. Devillanova, F. Isaia, V. Lippolis and G. Verani, Inorg. Chim. Acta, 1997, 255, 203. 7 F. Bigoli, A. M. Pellinghelli, P. Deplano, F. A. Devillanova, V. Lipolis, M. L. Mercuri and E. F. Trogu, Gazz. Chim. Ital., 1994, 124, 445. 8 S. Husebye, S. V. Lindeman and M. D. Rudd, Acta Crystallogr., Sect. C, 1997, 53, 809. 9 J. S. Rutherford and C. Calvo, Z. Kristallogr., 1969, 128, 229. 10 H. M. K. K. Pathirana, T. J. Weiss, J. H. Reibenspies, R. A. Zingaro and E. A. Meyers, Z. Kristallogr., 1994, 209, 697. 11 H. Hope, Acta Crystallogr., 1965, 18, 259. 12 T. Srikrishnan, Acta Crystallogr., Sect. C, 1988, 44, 290. 13 J. Nakayama, A. Mizumura, I. Akiyama, T. Nishio and I. IIda, Chem. Lett., 1994, 77. 14 S. M. Godfrey, C. A. McAuliVe, R. G. Pritchard and S. Sarwar, J. Chem. Soc., Dalton Trans., 1997, 3501. 15 S. M. Godfrey, C. A. McAuliVe, R. G. Pritchard and S. Sarwar, J. Chem. Soc., Dalton Trans., 1997, 1031. 16 C. Knobler and J. D. McCullough, Inorg. Chem., 1968, 7, 365.J. Chem. Soc., Dalton Trans., 1999, 2219–2223 2223 17 S. M. Godfrey, S. L. Jackson, C. A. McAuliVe and R. G. Pritchard, J. Chem. Soc., Dalton Trans., 1997, 4499. 18 S. M. Godfrey, S. L. Jackson, C. A. McAuliVe and R. G. Pritchard, J. Chem. Soc., Dalton Trans., 1998, 4201. 19 S. M. Godfrey, S. L. Jackson, C. A. McAuliVe and R. G. Pritchard, unpublished results. 20 F. Bigoli, F. Demartin, P. Deplano, F. A. Devillanova, F. Isaia, V. Lippolis, M. L. Mercuri, M. A. Pellinghelli and E. F. Trogu, Inorg. Chem., 1996, 35, 3194. 21 C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 22 Handbook of Chemistry and Physics, ed. D. R. Lide, CRC Press, Boca Raton, FL, 76th edn., 1995, ch. 9, part 10. 23 M. Miura, Y. Takanohashi, Y. Habata and S. Akabori, J. Chem. Soc., Perkin Trans. 1, 1995, 1719; Tetrahedron Lett., 1994, 35, 8213. 24 G. M. Sheldrick, SHELXTL 97, Programs for crystal structure analysis (release 97-2), Göttingen, 1998. Paper 9/02188D

ISSN:1477-9226    

DOI:10.1039/a902188d

出版商:RSC    

年代:1999

数据来源: RSC