摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 2407–2408 2407 Hydroxyethylmethacrylate as a source of ethyleneglycolate ligands. Synthesis and characterization of Nb4(,1,2- OC2H4O)2(3,1,2-OC2H4O)2(-OC2H4O)(OPri)10 Liliane G. Hubert-Pfalzgraf,*a Valérie Abada b and Jacqueline Vaissermannc a Université Claude Bernard-Lyon I, UMR-CNRS, Bâtiment 731, 43 bd du 11 Novembre 1918, 69622 - Villeurbanne Cedex, France b Laboratoire de Chimie Moléculaire, Université de Nice c Laboratoire de Chimie des Métaux de Transition, UMR-CNRS, 4 Place Jussieu, 75230 - Paris Cedex 05, France Received 1st June 1999, Accepted 28th June 1999 The reaction between niobium isopropoxide and 2- hydroxyethylmethacrylate (HEMA) at room temperature (1 :1 stoichiometry) afforded [Nb4(,1,2-OC2H4O)2- (3,1,2-OC2H4O)2(-OC2H4O)(OPri)10] as characterized by X-ray diffraction.Hybrid organic–inorganic materials have stimulated increasing research due to the diversity of their applications.1 One approach to such materials is based on the modi.cation of metal alkoxides either in processing conditions (in situ) or prior to processing with reactants and/or ligands allowing di.erential hydrolysis and/or polymerization via unsaturated moieties.2 Derivatives with vinyl or methacrylate groups are the most commonly used for access to hybrid materials of class I or class II, where organic and inorganic components are respectively weakly or covalently bonded, over a broad range of compositions and morphologies.3 2-Hydroxyethylmethacrylate (HEMA) was selected as an organic monomer with silicon 4 and zirconium alkoxides 5 for access to non-shrinking sol–gel composites.However, the di.erences in the reactivity patterns between silicon and zirconium meant that the silicon alkoxide Si(OR)4 (R = OC2H4OC(O)CH CH2) could be isolated while more complex reactions a.ording gels were observed in the case of zirconium n-propoxide and n-butoxide.We have previously shown that titanium mediated the C–O bond cleavage of HEMA giving an unusual titanium pentanuclear diolate cluster, 6 Ti5(OC2H4O)5(µ-OPri)(OPri)9. We wish to report here our investigations into HEMA and niobium isopropoxide. The reaction between niobium isopropoxide and 2-hydroxyethylmethacrylate (HEMA) was carried out in toluene at room temperature (1 : 1 stoichiometry). 1H NMR and FT-IR monitoring indicated evolution of the unsatured ligand subsequent to the substitution reactions.The absorption band at 1640 cm1 due to the .C C vibration progressively disappeared. In the 1H NMR spectra, one can notice the decrease of the multiplets attributed to the CH and CH2 groups. After work-up, a crystalline compound 1 no longer having unsaturated functionalities, as evidenced by the absence of .C C absorption bands around 1636 cm1 in the FT-IR spectrum, was isolated. Compound 1 was obtained in high and reproducible yields.† Its elemental analysis accounts for a composition corresponding roughly to two isopropoxides to one ethyleneglycolate ligand.The essential features of the 1H NMR spectra at room temperature are two septuplets at 4.85 and 4.81 ppm (integration 2 : 8) corresponding to the CH groups of the OPri ligands together with numerous peaks between 4.7 and 4.00 ppm. Low temperature spectra indicated splitting of the peak at 4.81 ppm and thus non-equivalence of the corresponding isopropoxide ligands.The molecular structure of 1 corresponds to [Nb4(µ,.1,.2- OC2H4O)2(µ3,.1,.2-OC2H4O)2(µ-OC2H4O)(OPri)10] as established by X-ray di.raction (Fig. 1).‡ The structure is based on a centrosymmetrical tetranuclear open-shell framework, the angles being 139.2(1) and 138.1(1) for Nb(1) Nb(2) Nb(3) and Nb(2) Nb(3) Nb(4) respectively. The metallic centers are of two types, Nb(1) and Nb(4) are six-coordinate while Nb(2) and Nb(3) are seven-coordinate.They are connected by ethyleneglycolate ligands derived from 2-hydroxyethylmethacrylate. The ethyleneglycolate ligands all assemble the metal cluster but display di.erent types of coordination mode namely bridging and bridging-chelating. The bridgingchelating ones are of two types assembling either two or three metals. The Nb–OR bond lengths vary from 1.84(1) to 2.196(9) Å with the ranking Nb–OPri < Nb–.2-OC2H4O < Nb–µ- OC2H4O � Nb–µ3-OC2H4O. The isopropoxide ligands are all in terminal positions, the longest bond distance being trans to µ3,.2-ethyleneglycolate ligands.The Nb–O–C angles of the alkoxide ligands vary from 135.1(10) to 166.3(13), the smallest values are observed for the equatorial bonds. The bridging diolate possesses quite large Nb–O–C angles [152.2(14) av.] as compared to the bridging-chelating ones which are more acute [114.2(8)–127.7(10)]. The central, heptacoordinated metals have a slightly distorted bipyramidal pentagonal environment [O(11)–Nb(3)–O(14) 174.7(4), O(9)–Nb(2)–O(10) 170.4(4)].The stereochemistry of the hexacoordinated metals is more severely distorted [O(4)–Nb(1)–O(3) 106.7(5), O(5)–Nb(1)– O(6) 65.9(4)]. Indeed the small bite angles of the ethyleneglycolate ligands (74.45 av.) as well as the acute intrabridge angles (65.6 av.) are more in agreement with the steric demands of the equatorial ligands in a pentagonal bipyramidal environment than with an octahedral geometry. The Nb Nb distances are quite long (av. 3.54 Å) as compared to other polynuclear niobium alkoxide derivatives which display more compact structures [e.g. 3.177(1)–2.268(1) Å for tri- or tetranuclear pinacolates].7 The formation of the tetranuclear framework can formally be seen as the assembly of two dinuclear units [Nb2- (OPri)5(OC2H4O)2(OC2H4OH)] and [Nb2(OPri)6(OC2H4O)2], in which the metals are six-coordinate. The assembly proceeds by Fig. 1 Molecular structure of [Nb4(µ,.1,.2-OC2H4O)2(µ3,.1,.2- OC2H4O)2(µ-OC2H4O)(OPri)10] showing the atom numbering scheme.Selected bond distances (Å): Nb Nb 3.54 (av.), Nb–OPri 1.84(1)– 1.91(1), Nb(4)–O(16) 2.11(1), Nb(3)–O(16) 2.11(1), Nb(4)–O(13) 2.09(1), Nb(3)–O(13) 2.12(1), Nb(3)–O(12) 2.11(1), Nb(3)–O(15) 1.92(1), Nb(2)–O(12) 2.11(1), Nb(2)–O(7) 2.196(9), Nb(3)–O(7) 2.09(1), Nb(3)–O(11) Nb(2)–O(10) 1.89(1).2408 J. Chem. Soc., Dalton Trans., 1999, 2407¡V2408deprotonation of the residual hydroxyl functionality, eliminationof one molecule of isopropanol and transformation ofthe ,£b2-diolates into 3,£b2-ligands leading to seven-coordinatemetals (Fig. 1). The structure of 1 is related to that of [Ti4(,£b2-OCH2CHCHCH2O)4(OPri)8], obtained by reacting Ti(OPri)4and 2-butene-1,4-diol,8 although the coordination numbers ofthe metals are lower, being 5 and 6.A number of tetranuclear niobium() species have beenreported. They are generally oxo-species and the structures arebased on close-packed octahedra.Typical examples are [Nb4-(-O)4(,£b2-RCO2)4(OR)8] (R = Pri, R = methacrylate,9 acetate),10 [(-BHMP)Nb2(-O)(OEt)5]2 (BHMPH3 = bis(hydroxymethyl)propionic acid) 11 and [Nb4(-O)2(3-O)2(,£b2-OCMe2-CMe2O)2(OPri)8].7 Hexacoordination was retained despite thepresence of polydentate ligands. Compound 1 corresponds toan open-shell polyhedron. The only other example of a tetranuclearopen-shell framework for pentavalent heavy Group 5metals seems to be the [M2(-O)Cl9]22 (M = Nb, Ta) anions.12Assembly into a tetrameric unit is achieved via two bridgingchloro ligands but all the metals are six-coordinate.Heptacoordinationhas been observed for pentavalent niobium and isquite common for low valent species.12,13 However, structurallycharacterized niobium alkoxide derivatives displaying heptacoordinationhave, to the best of our knowledge, not beenreported.The 1H NMR data of 1 are consistent with the retention ofthe solid state structure in solution. The formation of compound1 can be summarized by Scheme 1.The reaction between niobium isopropoxide and HEMAproceeds by transesterication geneting stable ve-memberedchelates.If this system is used for access to hybrid materialsvia polymerization of the organic and inorganic network, theformation of materials of class II will most probably be limitedto the early stages of the condensation. It is noteworthy that theuse of HEMA as a source of diolate ligands aords species withunusual coordination numbers and without oxo-ligands, bycontrast to a system using pinacol in which the assemblybetween the metals proceeds with generation of oxo-ligands.7As anticipated and despite the fact that all isopropoxide ligandsare in terminal positions and thus quite accessible, 1 is lesssusceptible to hydrolysis than niobium isopropoxide.Its poorsolubility in isopropanol however requires the use of solventsdierent from the parent alcohol such as THF or toluene.Clearsols were obtained for hydrolysis ratios in the range 1¡V5 (0.02 Min THF).Notes and references All manipulations were routinely performed under a nitrogen atmosphereusing Schlenk tubes and vacuum line techniques with dried anddistilled solvents. Nb(OPri)5 was prepared as reported in the literature.14HEMA was stored over molecular sieves. 1H NMR spectra wererecorded on solutions on a Bruker AC-200 spectrometer. Infrared spectrawere recorded with a Perkin Elmer Paraggon spectrometer as Nujolmulls between KBr plates. Analytical data were obtained from theCentre de Microanalyses du CNRS.Synthesis of Nb4(OiPr)10(OC2H4O)5 1. 0.48 ml (3.81 mmol) of 2-Scheme 1hydroxyethylmethacrylate in 10 ml of toluene were added to 1.48 g (1.9mmol) of [Nb(OiPr)5]2 in 15 ml of toluene. Evaporation of the solventafter 24 h gave a pasty compound which was dissolved in hexane¡Vtoluene (1 : 1). 1.05 g (87%) of crystals soluble in usual organic solventsexcept alcohols were obtained by crystallization at room temperature.Anal.found: C, 38.51; H, 7.43. Calc. for C40H90O20Nb4, C, 38.04; H,7.3%. IR cm1: 1324m, 1271m, 1254m, 1156s, 1133s, 1082s, 1003s, 983s,925m, 906m, 848m £hC¡VO, £hC¡VC; 632m; 594s, 534s, 486s, 461s, 442s£h(Nb¡VOR). 1H NMR (CDCl3, ppm): 4.85, 4.81 (2 : 8) (sept, J = 6 Hz,10H, CH); 4.7¡V4.00 (overlapping of peaks, CH2, 20H); 1.2 (d, J = 6 Hz,Me); 1.05 (d, J = 6 Hz, Me). Crystal data for 1: C40H90O20Nb4, M = 1262.77, triclinic, space groupP1, a = 17.938(5), b = 17.960(5), c = 9.335(5) , U = 2807(4) 3, Z = 2,(Mo-K£\) = 8.23 cm1.Intensity data were collected at 112 C on anEnraf Nonius CAD4 diractometer. The intensities of the reectionswere quite low and only a small range of £c could be used. No bettercrystals could be grown. Empirical absorption correction (DIFABS)was applied. Computations were performed by using the PC version ofCRYSTALS.15 The structure was solved by direct methods (SHELXS86) 16 and successive Fourier maps.Only niobium and oxygen atomswere anisotropically rened because of the low number of reections.Hydrogen atoms were theoretically located, they were rened isotropically.Least squares renement (2703 reections I > 2£m(I) reached convergencewith R = 0.069 and Rw = 0.080, 276 parameters. In the laststages of the renement, each reection was assigned a weight w =w[1 ( |Fo| |Fc| )/6£m(Fo)2]2 with w = 1/SrArTr(x) with 3 coecients7.67, 0.295 and 4.22 for a Chebyshev series, for which x is Fc/Fc (max).17CCDC reference number 186/1542.See http://www.rsc.org/suppdata/dt/1999/2407/ for crystallographic les in .cif format.1 H. Schmidt, J. Sol¡VGel Sci. Technol., 1994, 1, 217.2 U. Schubert, N. Husing and A. Lorenz, Chem. Mater., 1995, 7, 2010;U. Schubert, E. Arpac, W. Glaubitt, A. Helmerich and C. Chau,Chem. Mater., 1992, 4, 291; C. Sanchez, F. Ribot and B. Lebeau,J. Mater. Chem., 1999, 9, 35; U. Schubert, J. Chem. Soc., DaltonTrans., 1996, 3343; C.Sanchez and F. Ribot, New J. Chem., 1994, 18,1007; L. G. Hubert-Pfalzgraf, Coord. Chem. Rev., 1998, 178¡V180,967.3 C. Sanchez, M. In, P. Toledano and P. Griesmar, Better Ceramicsthrough Chemistry VI, Mater. Res. Soc. Proceedings, 1992, 271, 669;C. Sanchez and M. In, J. Non-Cryst. Solids, 1992, 147, 1; K. Y.Blohowick, D. R. Treadwell, B. L. Mueller, M. L. None, S. Jouppi,P. Kansal, K. W. Chew, C. L. S. Scotto, F. Babonneau, J. Kampf andR. M. Laine, Chem.Mater., 1994, 6, 2177.4 B. M. Novak and C. Davies, Macromolecules, 1991, 24, 5481;M. W. Ellsworth and B. M. Novak, Chem. Mater., 1993, 5, 839.5 R. Di Maggio, L. Fambri and A. Guerriero, Chem. Mater., 1998, 19,1777.6 N. Pajot, R. Papiernik, L. G. Hubert-Pfalzgraf, J. Vaissermann andS. Parraud, J. Chem. Soc., Chem. Commun., 1995, 1817.7 L. G. Hubert-Pfalzgraf, V. Abada and J. Vaissermann, Polyhedron,1999, 18, 845.8 N. Pajot, PhD Thesis, University of Nice, 1996; N. Pajot-Miele,R.Papiernik, L. G. Hubert-Pfalzgraf and J. Vaissermann, to bepublished.9 (a) L. G. Hubert-Pfalzgraf, V. Abada, J. Vaissermann and J. Rozire,Polyhedron, 1997, 16, 581; (b) W. A. Nugent and R. L. Harlow,J. Am. Chem. Soc., 1994, 116, 6142; (c) D. A. Brown, W. Erringtonand M. G. H. Wallbridge, J. Chem. Soc., Dalton Trans., 1993, 1067.10 N. Stenou, C. Bonhomme, C. Sanchez, J. Vaissermann and L. G.Hubert-Pfalzgraf, Inorg. Chem., 1998, 37, 901.11 J. Boyle, T. M. Alam, D. Dimos, G. J. Moore, C. D. Buchheit, H. N.Al-Shareef, E. R. Mechenbier, R. R. Bear, J. W. Ziller, Chem.Mater., 1997, 9, 3187.12 L. G. Hubert-Pfalzgraf, M. Postel and J. G. Riess, ComprehensiveCoordination Chemistry, 1987, Pergamon Press, London, ch. 34;L. G. Hubert-Pfalzgraf, Encyclopedia of Inorganic Chemistry, ed.B. King, Wiley, New York, 1994.13 D. R. Taylor, J. C. Calabrese and E. M. Larsen, Inorg. Chem., 1977,16, 721; E. Hey, F. Weller and K. Dehnicke, Z. Anorg. Allg. Chem.,1984, 514, 25.14 D. C. Bradley, R. C. Mehrotra and D. P. Gaur, Metal Alkoxides,Academic Press, London, 1978.15 D. J. Watkin, J. R. Carruthers and P. W. Betteridge, Crystals User,Chemical Crystallography Laboratory, Oxford, UK, 1988.16 G. M. Sheldrick, SHELXS 86, Program for Crystal StructureSolution, University of Gttingen, Germany, 1986.17 L. J. Pearce and D. J. Watkin, Cameron, Chemical CrystallographyLaboratory, Oxford, UK, 1992.Communication 9/04344F

ISSN:1477-9226    

DOI:10.1039/a904344f

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 2409.2410 2409 Synthesis and structure of 2,2-biphosphirenes Ngoc Hoa Tran Huy, Louis Ricard and Francois Mathey Laboratoire ¡°Heteroelements et Coordination¡± UMR CNRS 7653, DCPH, Ecole Polytechnique, 91128 Palaiseau Cedex, France Received 24th May 1999, Accepted 18th June 1999 The reaction of an excess of the transient terminal phosphinidene complex [PhP¡æW(CO)5] with selected 1,3- diynes at 110 C in toluene affords the corresponding 2,2-biphosphirene.W2(CO)10 complexes as a 1 :1 meso rac mixture; according to the X-ray crystal structure analysis of one of the rac-complexes, some delocalisation takes place within the diene sub-unit of these biphosphirenes.The phosphirene ring is now well established as one of the most interesting carbon.phosphorus heterocycles.1 Numerous syntheses of this ring are available and its rich chemistry, including its coordination chemistry with transition metals, combined with its very peculiar stereoelectronic properties 2 make it an attractive candidate for applications in homogeneous catalysis.3 In order to develop this potential, we have decided to launch a programme aiming at the incorporation of the phosphirene ring into oligomers or macrocycles.The .rst step in that direction consists in the preparation of the still unknown 2,2- biphosphirenes.4 The most versatile approach to phosphirenes is undoubtedly the [21] cyclocondensation between alkynes and electrophilic terminal phosphinidene complexes.5 Thus it was tempting to study the condensation of these phosphinidene complexes with 1,3-diynes.Unfortunately, both in our group6 and in the group of Lammertsma,7 this reaction yielded .rst a 2-alkynyl-phosphirene, and then a 1,2-dihydro-1,2-diphosphete resulting from the insertion of a second phosphinidene into the conjugatively destabilized P.C(2) bond of the initial threemembered ring (Scheme 1). However, the reaction appeared to depend sharply on the nature of the diyne substituent R1.In some cases [R1= Bu,7 But,7 SiMe3 (our work)], the insertion does not take place and the reaction apparently stops at the stage of the 2-alkynylphosphirene. This surprising observation led us to reinvestigate the condensation of [PhP¡æW(CO)5] with these diynes at higher temperature. Our and Lammertsma¡�s preliminary experiments were carried out using the CuCl-catalyzed decomposition of the appropriate 7-phosphanorbornadiene complex 1 as the generating system of [PhP¡æW(CO)5] at 60 C.In our new experiments, the phosphinidene was generated from 1 at 110 C in boiling toluene without CuCl as the catalyst. Under these more severe conditions, the reaction goes one step further (Scheme 2). Scheme 1 P R W(CO)5 R1 R1 P P R1 R1 R (OC)5W W(CO)5 R R1C¡ÕC-C¡ÕCR1 [RPW(CO)5] 60 ¡ÆC [RPW(CO)5] 60 ¡ÆC Only minor quantities of the 2-alkynyl-phosphirenes were obtained and the main products were the 2,2-biphosphirene complexes 2 and 3 obtained as meso rac-1 : 1 mixtures.¢Ó We were able to get good crystals of rac-2 and to perform their X-ray analysis (Fig.1).¢Ô The structure of the phosphirene rings of rac-2 are very similar to those already published.5 The two rings are almost coplanar with a trans-disposition: interplane angle 157.8.The C(2).C(3) bridge is very short at 1.421(5) A. This means that some conjugation takes place between the two C C double bonds.The structure of meso-3 was also obtained (C.C bridge 1.435(5) and C C 1.315(4) A) but the data are only marginally di.erent from those of rac-2 and are not detailed here. We are presently investigating the synthesis of higher oligophosphirenes. Scheme 2 Reagents and conditions: (i), (ii); toluene, 110 C, 10.12 h, 3.2 eq. of 1 and 1 eq. of R1 C C.C CR1. P CO2Me Me Me CO2Me (OC)5W Ph P Ph W(CO)5 R1 P Ph W(CO)5 R1 1 i [PhP-W(CO)5] ii meso + rac 1:1 2 R1= SiMe3 (50%) 3 R1= But (50%) Fig. 1 Crystal structure of rac-2. Signi.cant bond distances (A) and angles (): W(1).P(1) 2.484(1), W(2).P(2) 2.501(1), P(1).C(1) 1.826(4), P(1).C(2) 1.791(3), P(1).C(5) 1.822(4), P(2).C(3) 1.793(3), P(2).C(4) 1.835(4), P(2).C(11) 1.821(4), C(1).C(2) 1.327(5), C(2).C(3) 1.421(5), C(3).C(4) 1.318(5); C(2).P(1).C(1) 43.0(2), C(3).P(2).C(4) 42.6(2), C(1).C(2).P(1) 69.9(2), C(2).C(1).P(1) 67.1(2), C(3).C(4).P(2) 67.0(2), C(4).C(3).P(2) 70.4(2), C(3).C(2).P(1) 147.8(3), C(2).C(3). P(2) 144.7(3).2410 J.Chem. Soc., Dalton Trans., 1999, 2409–2410 Notes and references † Selected analytical and spectroscopic data: 2: puri.ed by chromatography on silica gel (hexane–CH2Cl2 10 : 1) meso (eluted .rst): 31P NMR (CDCl3): d 154.5, 1JP–W 257 Hz; 13C NMR (CDCl3): d 0.92 (s, SiMe3), 128.76 (pseudo-t, 2JC–P 10.0 Hz, o-Ph), 130.91 (s, p-Ph), 131.46 (pseudo-t, 3JC–P 16.4 Hz, m-Ph), 137.9 (pseudo-s, C3C3), 196.03 (pseudo-t, cis-CO); m/z (184W) 975 (M 3CO 1, 25%), 863 (M 7CO 1, 100), 779 (M 10CO 1, 90); Anal. Calc.for C32H28O10P2Si2W2: C, 36.32; H, 2.67. Found: C, 36.58; H, 2.72%. rac: 31P NMR (CDCl3): d 156.4, 1JP–W 264.7 Hz; 13C NMR (CDCl3): d 0.97 (s, SiMe3), 128.89 (pseudo-t, 2JC–P 10.4 Hz, o-Ph), 131.06 (s, p-Ph), 131.56 (pseudo-t, 3JC–P 16.6 Hz, m-Ph), 138.09 (pseudo-s, C3C3), 141.91 (pseudo-t, ipso-Ph), 195.91 (pseudo-t, 2JC–P 7.5 Hz, cis-CO), 197.54 (d, 2JC–P 33 Hz, trans-CO). 3: meso (eluted .rst): 31P NMR (CDCl3): d 138.6; 13C NMR (CDCl3): d 29.51 (s, Me), 35.30 (pseudo-s, CMe3), 111.74 (pseudo-s, C2C2), 128.91 (pseudo-t, 2JC–P 10.5 Hz, o-Ph), 131.12 (s, p-Ph), 131.57 (pseudo-t, 3JC–P 15.8 Hz, m-Ph), 137.60 (pseudo-s, C3C3), 196.27 (pseudo-t, cis-CO); m/z (184W) 942 (M 3CO, 8%), 830 (M 7CO, 36), 747 (M 10CO 1, 41), 562 (M 10CO W, 57), 292 (PhPW, 100); Anal. Calc. for C34H28O10P2W2: C, 39.79; H, 2.75. Found: C, 40.01; H, 2.81%. rac: 31P NMR (CDCl3): d 140.2, 1JP–W 250.7 Hz; 13C NMR (CDCl3): d 29.71 (s, Me), 35.76 (d, 2JC–P 3.6 Hz, CMe3), 112.03 (pseudo-t, C2C2), 129.33 (pseudo-t, 2JC–P 10.5 Hz, o-Ph), 131.55 (s, p-Ph), 132.13 (pseudo-t, 3JC–P 15.5 Hz, m-Ph), 138.09 (pseudo-s, C3C3), 148.50 (pseudo-t, 1JC–P 18 Hz, ipso-Ph), 196.41 (pseudo-t, 2JC–P 7.4 Hz, cis-CO).‡ X-Ray structure determination for rac-2: crystals suitable for X-ray di.raction were obtained from a pentane–dichloromethane solution of the compound.Data were collected with a Nonius Kappa CCD di.ractometer. The crystal structure was solved using maXus.8 While initial re.nement was performed with the latter, .nal least-squares was conducted with SHELXL 97.9 Illustrations were made using Platon.10 Crystal data. C32H28O10P2Si2W2, M = 1058.36 g mol 1, monoclinic, a = 12.0110(2), b = 17.3150(2), c = 18.9720(3) Å, ß = 104.2090(6), V = 3824.91(10) Å3, T = 150 K, space group P21/n, Z = 4, µ(Mo-Ka) = 6.207 cm 1. 8114 re.ections measured, 7801 unique (Rint = 0.021) which were used in all calculations.The .nal wR(F2) was 0.0612 (all data). CCDC reference number 186/1519. See http://www.rsc.org/suppdata/dt/1999/2409/ for crystallographic .les in .cif format. 1 Reviews: F. Mathey, Chem. Rev., 1990, 90, 997; F. Mathey and M. Regitz, Comprehensive Heterocyclic Chemistry II, A. R. Katritzky, C. W. Rees and E. F. V. Scriven (Eds.), Pergamon, Oxford, 1996, vol. I, pp. 277–304; K. B. Dillon, F. Mathey and J.F. Nixon, Phosphorus: The Carbon Copy, Wiley, Chichester, 1998, pp. 183–203. 2 Recent theoretical studies: S. M. Bachrach, J. Org. Chem., 1991, 56, 2205; M. T. Nguyen, H. Vansweevelt and L. G. Vanquickenborne, Chem. Ber., 1992, 125, 923; E. J. P. Malar, Tetrahedron, 1996, 52, 4709; A. Göller, H. Heydt and T. Clark, J. Org. Chem., 1996, 61, 5840; A. Göller and T. Clark, Chem. Commun., 1997, 1033; L. Colombet, A. Sevin and P. Chaquin, Bull. Soc. Chim. Fr., 1997, 134, 1033; W.Eisfeld and M. Regitz, J. Org. Chem., 1998, 63, 2814; T. I. Sølling, M. A. McDonald, S. B. Wild and L. Radom, J. Am. Chem. Soc., 1998, 120, 7063. 3 Till now only phosphiranes have been investigated as ligands r catalytic applications: A. Marinetti, F. Mathey and L. Ricard, Organometallics, 1993, 12, 1207; J. Liedtke, S. Loss, G. Alcaraz, V. Gramlich and H. Grützmacher, Angew. Chem., Int. Ed., 1999, 38, 1623. 4 A 1,1-biphosphirene has been described as its bis-Fe(CO)4 complex: J. Simon, U. Bergstrasser and M. Regitz, Chem. Commun., 1998, 867. 5 Initial report: A. Marinetti, F. Mathey, J. Fischer and A. Mitschler, J. Am. Chem. Soc., 1982, 104, 4484. 6 N. H. Tran Huy, L. Ricard and F. Mathey, Organometallics, 1997, 16, 4501. 7 B. Wang, K. A. Nguyen, G. N. Srinivas, C. L. Watkins, S. Menzer, A. L. Spek and K. Lammertsma, Organometallics, 1999, 18, 796. 8 S. Mackay, C. J. Gilmore, C. Edwards, M. Tremayne, N. Stuart and K. Shankland, maXus: a computer program for the solution and re.nement of crystal structures from di.raction data, University of Glasgow, Scotland, UK, Nonius BV, Delft, The Netherlands and MacScience Co. Ltd., Yokohama, Japan, 1998. 9 G. M. Sheldrick, SHELXL-97, Universität Göttingen, Germany, 1997. 10 A. L. Spek, Platon, A Multipurpose Crystallographic Tool, Utrecht University, The Netherlands, 1999. Communication 9/04150H

ISSN:1477-9226    

DOI:10.1039/a904150h

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 2411–2413 2411 Activation of manganese nitrido complexes by Brønsted and Lewis acids. Crystal structure and asymmetric alkene aziridination of a chiral salen manganese nitrido complex Chi-Ming Ho,a Tai-Chu Lau,*a Hoi-Lun Kwong a and Wing-Tak Wong b a Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Hong Kong, P.R. China. E-mail: bhtclau@cityu.edu.hk b Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R.China Received 6th May 1999, Accepted 15th June 1999 Styrene is readily converted to 2-phenylaziridine by salen manganese(V) nitrido complexes in the presence of Brønsted or Lewis acids such as F3CCO2H or BF3, the crystal structure of a chiral manganese nitrido complex that can perform asymmetric alkene aziridination has been determined. The conversion of alkenes to aziridines and amines by metal complexes has attracted much interest since Groves .rst reported that cyclooctene can be converted to a N-tri.uoroacetylated aziridine product by a manganese(.) porphyrin nitrido complex in the presence of tri.uoroacetic anhydride (TFAA).1 Subsequently a number of metal catalysts, such as Fe and Mn porphyrin complexes,2 and Cu(.,..) salts,3 were found to e.ect the conversion of alkenes into N-tosylaziridines by PhI NTs (Ts = tosyl).Recently Carreira and co-workers made use of [MnV(N)(saltmen)] 4 [saltmen = N,N-1,1,2,2-tetramethylethylenebis( salicylideneaminato)] and [MnV(N)(3-R-sal- R)2] 5 (H-3-R-sal-R = substituted salicylimine) to carry out the amination of silyl enol ethers and styrene, respectively.Very recently an asymmetric version of Carreira’s methodology was reported by Komatsu and co-workers using a chiral manganese nitrido complex in the presence of p-toluenesulfonic anhydride, pyridine and pyridine N-oxide.6 We previously reported that metal–oxo species can be activated toward the oxidation of hydrocarbons by Brønsted and Lewis acids such as tri.uoroacetic acid (TFA), boron halides and simple metal salts.7–9 We report here that this strategy also works for nitrido species; salen mangnese(.) nitrido species can be activated by acids such as TFA and BF3 to convert alkenes into aziridines.The manganese nitrido complexes shown below were investigated. Compounds 1–5 {[Mn(N)L]} were prepared using Carreira’s method 4 by treatment of [Mn(L)Cl] with ammonia and bleach.† Initial experiments were carried out with compound 1; upon adding 2 equivalents of TFA or BF3 to a solution containing 1 and styrene, 2-phenylaziridine was produced (Table 1).This is the .rst report of direct generation of the parent aziridine from an alkene using metal complexes, all previous methods produced either the N-tosyl or N-tri.uoroacetyl aziridine. Little (<2%) or no products arising from ring opening of the aziridine were detected. Lower yields of the aziridine were obtained when Al(OTf)3 (40%) or Fe(OTf)3 (35%) were employed, while weaker Lewis acids such as ZnCl2 and Cu(CF3SO3)2 were ine.ective.For the more bulky complex 2, similar yields were obtained with TFA (69%) or BF3 (56%); however, Al(OTf)3 and Fe(OTf)3 were ine.ective (yields <5%), suggesting that steric e.ects may play an important role in the aziridination reaction. Aziridination of other alkenes were also investigated using complex 1 and TFA or BF3 (Table 1).Higher yields were obtained with a- and (E)-ß-methylstyrene, however cyclooctene gave very low yields. For ß-methylstyrene, 10–20% of the E isomer was produced in addition to the Z isomer of the phenylaziridine, while the E-substrate produced solely the E product. Amination by manganese nitrido species in the presence of TFAA is believed to go through an acylimido intermediate.1 In the present system we propose that active intermediates are Mn NH for TFA and Mn NBF3 for BF3.The imido group is transferred to the alkene to produce the parent aziridine (after hydrolysis in the case of BF3). Asymmetric aziridination was investigated using the chiral compounds 3–5. In the presence of 3 equivalents of TFA, aziridination proceeded with high ee for compound 4 with the substrates styrene and (E)-ß-methylstyrene, while a very low ee was observed for (Z)-ß-methylstyrene. Compound 3 gave similar yields but lower ee (35%, 30% ee for styrene), while use of2412 J.Chem. Soc., Dalton Trans., 1999, 2411–2413 Fig. 1 Perspective view of 4(1). Selected bond lengths (Å) and angles () for both molecules: Mn(1)–O(1) 2.00(2), Mn(1)–O(2) 1.93(2), Mn(1)–N(1) 1.98(2), Mn(1)–N(2) 1.96(1), Mn(1)–N(3) 1.56(2), Mn(2)–N(6) 1.50(2), Mn(2)–O(3) 1.82(2), Mn(2)–O(4) 1.89(1), Mn(2)–N(4) 1.94(2), Mn(2)–N(5) 1.96(2); O(1)–Mn(1)–O(2) 87.0(7), O(1)–Mn(1)–N(1) 87.9(7), O(1)–Mn(1)–N(2) 150.2(6), O(1)–Mn(1)–N(3) 105.7(8), O(2)–Mn(1)–N(1) 153.9(6), O(2)–Mn(1)–N(2) 88.3(6), O(2)–Mn(1)–N(3) 103.3(9), N(1)–Mn(1)–N(2) 83.5(7), N(1)–Mn(1)–N(3) 102.7(9), N(2)–Mn(1)–N(3) 104.0(8), O(3)– Mn(2)–O(4) 80.3(6), O(3)–Mn(2)–N(4) 91.6(7), O(3)–Mn(2)–N(5) 138.9(6), O(3)–Mn(2)–N(6) 112.9(8), O(4)–Mn(2)–N(4) 155.0(6), O(4)–Mn(2)– N(5) 90.8(6), O(4)–Mn(2)–N(6) 105.0(8), N(4)–Mn(2)–N(5) 79.7(7), N(4)–Mn(2)–N(6) 99.9(8), N(5)–Mn(2)–N(6) 108.2(8).compound 5 resulted in very low yields (ca. 7%). In Komatsu’s method using Ts2O and pyridine,6 only compound 3 was found to be reactive; in the present system employing TFA to activate the nitrido complexes, however, the best result was obtained with compound 4, which is more bulky than compound 3.This .nding is consistent with a Mn N(Ts) intermediate in Komatsu’s case, and a much less bulky M NH intermediate in the present case. The structure of 4, a compound that can perform asymmetric aziridination of alkenes, has been determined by X-ray crystallography.‡ The asymmetric unit consists of two structurally similar molecules [4(1) and 4(2), both in R, R con.guration] and the structure of 4(1) is depicted in Fig. 1. Although the structure of another chiral salen manganese nitrido complex, [(R,R)-diphenyl-tert-butylmethylbis(salicylidene)ethane-1,2-diaminato] nitridomanganese, has recently been reported,11 the ability of that complex to carry out asymmetric aziridination has yet to be demonstrated. We are currently examining the e.ects of various other Lewis and Brønsted acids in order to improve the yields and ee.The mechanisms of aziridination in these systems are also under active investigation. Table 1 Aziridination of styrene derivatives with the nitrido complex 1 a 2-Phenylaziridine (% yield) Substrate BFOEt2 TFA Styrene a-Methylstyrene (E)-ß-Methylstyrene (Z)-ß-Methylstyrene Cyclooctene 63 77 88 (E) 51 (Z), 5 (E) 8 72 87 92 (E) 53 (Z), 12 (E) 8 a Conditions: complex 1, 0.3 mmol; acid, 0.6 mmol; alkene, 4.0 mmol; temperature, 78 C; solvent, MeCN (5 ml)–CH2Cl2 (10 ml).Acknowledgements Financial support from the Hong Kong Research Grants Council, the City University of Hong Kong and the University of Hong Kong are gratefully acknowledged. Notes and references † In a typical aziridination experiment, [Mn(N)L] (0.3 mmol) and alkene (4.0 mmol) in dry CH2Cl2 (10 ml) were cooled to 78 C under argon. A solution of the acid (0.3–0.9 mmol) in MeCN (5 ml) was slowly added to the mixture over 15 min.The solution was allowed to warm to room temperature and then neutralised with saturated NaHCO3 solution. The organic layer was analysed by GLC, GC-MS, and by NMR (after chromatography and isolation). The structure was con.rmed by comparison with authentic samples prepared by a literature method.10 In asymmetric reactions the aziridine product was .rst tosylated with TsCl and Et3N, the ee was then determined by chiral HPLC analysis using a commercial Whelk-O column (Regis).Compound 3: Found: C, 61.38; H, 5.27; N, 10.31. Calc. for MnN3C20H20O2: C, 61.70; H, 5.18; N, 10.79%. Compound 40.25C6H14: Found: C, 71.59; H, 8.59; N, 6.47. Calc. for MnN3C37.5H55.5O2: C, 70.90; H, 8.81; N, 6.61%. Compound 5: Found: C, 74.45; H, 8.01; N, 5.67. Calc. for MnN3C44H54O2: C, 74.24; H, 7.65; N, 5.90%. ‡ Crystal data: MnC36H52N3O20.25C6H14 4, M = 635.31, triclinic, space group P1 (no. 1), a = 10.127(1), b = 13.846(1), c = 14.428(1) Å, a = 68.40(2), ß = 83.32(2), .= 87.45(2), U = 1868.2(4) Å3, Z = 2, µ = 3.86 cm1, T = 298 K. Of 8051 re.ections, 4504 were unique with R1 = 0.069, R = 0.086, Rw = 0.099 with a goodness of .t of 2.19. Owing Table 2 Asymmetric aziridination of styrene derivatives with the nitrido complex 4 a Substrate Equiv. of TFA T/C Yield (%) ee (%) Styrene Styrene (E)-ß-Methylstyrene (E)-ß-Methylstyrene (Z)-ß-Methylstyrene 23232 40 40 78 78 78 29 36 15 20 7 b 55 81 87 91 25 a See footnote to Table 1 for conditions.b A trace amount of the (E)- aziridine product was detected by 1H NMR.J. Chem. Soc., Dalton Trans., 1999, 2411–2413 2413 to the poor quality of crystals (rapid solvent loss and weak di.raction nature), e.s.d.s on the bond lengths and angles are poor. Attempts to re.ne non-hydrogen atoms other than Mn were not successful. Re.nement of partially occupied solvent molecules also led to an unreasonable model and hence a .xed contribution of the solvent was used instead.CCDC reference no. 186/1511. See http://www.rsc.org/ suppdata/dt/1999/2411/ for crystallographic .les in .cif format. 1 J. T. Groves and T. Takahashi, J. Am. Chem. Soc., 1983, 105, 2074. 2 J.-P. Mahy, G. Bedi, P. Battioni and D. Mansuy, J. Chem. Soc., Perkin Trans. 2, 1988, 1517. 3 D. A. Evans, M. M. Faul and M. T. Bilodeau, J. Am. Chem. Soc., 1994, 116, 2742. 4 J. Du Bois, J. Hong, E. M. Carreira and M. W. Day, J. Am. Chem. Soc., 1996, 118, 915. 5 J. Du Bois, C. S. Tomooka, J. Hong, E. M. Carreira and M. W. Day, Angew. Chem., Int. Ed. Engl., 1997, 36, 1645. 6 S. Minakata, T. Ando, M. Nishimura, I. Ryu and M. Komatsu, Angew. Chem., Int. Ed., 1998, 37, 3392. 7 T. C. Lau and C. K. Mak, J. Chem. Soc., Chem. Commun., 1995, 943. 8 T. C. Lau, Z. B. Wu, Z. L. Bai and C K Mak, J. Chem. Soc., Dalton Trans., 1995, 695. 9 T. C. Lau and C. K. Mak, J. Chem. Soc., Chem. Commun., 1993, 766. 10 Y. Ittah, Y. Sasson, I. Shahak, S. Tsaroom and J. Blum, J. Org. Chem., 1978, 43, 4271. 11 A. S. Jepsen, M. Roberson, R. G. Hazell and K. A. Jorgensen, Chem. Commun., 1998, 1599. 12 H. D. Flack, Acta Crystallogr., Sect. A, 1983, 39, 876. Communication 9/03605I

ISSN:1477-9226    

DOI:10.1039/a903605i

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTONCOMMUNICATIONJ. Chem. Soc., Dalton Trans., 1999, 2415¡V2416 2415Crystal structure and ferromagnetic behaviour of a noveltetranuclear copper(II) complex with an open cubane-like Cu4O4frameworkXiang Shi Tan,a Yuki Fujii,*a Ryoji Nukada,b Masahiro Mikuriya b and Yoshiharu Nakano aa Department of Chemistry, Faculty of Science, Ibaraki University, 2-1-1 Bunkyo,Mito 310-8512, Japanb Department of Chemistry, School of Science, Kwansei Gakuin University, Uegahara,Nishinomiya 662-8501, JapanReceived 4th May 1999, Accepted 22nd June 1999The novel tetranuclear copper(II) complex [Cu4(hpda)4]-[ClO4]4H2O (Hhpda N-(2-hydroxyethyl)-1,3-propanediamine)with an open cubane-like Cu4O4 framework hasbeen obtained and characterized by X-ray crystallographyand magnetic measurements, exhibiting strongly ferromagneticexchange interaction.Over the years multinuclear copper() complexes have beenreceiving much attention, much of which stems from magnetostructuralcorrelations in copper() complexes.The exibilityof the coordination sphere around Cu(), in combination withsteric and crystal packing forces, leads to its tremendous structuraldiversity. Small changes in structure can have far reachingeects on the magnetic properties of these systems.1 Anotherreason for interest in multinuclear copper() complexes is thegrowing awareness of the involvement of cluster compounds atthe active sites of biomolecules. Up to now several kinds oftetranuclear copper() complexes have been studied, most ofwhich show antiferromagnetic coupling.2 We have been studyingsome copper() complexes which catalyze the hydrolysisof phage DNA or peptides.3 Recently, during our study ofthe hydrolytic cleavage of peptides promoted by the copper()[N-(2-hydroxyethyl)-1,3-propanediamine] complex, a noveltetranuclear copper() complex with an open cubane-likeCu4O4 framework has been isolated and characterized by X-raycrystallography and magnetic measurements, which showsstrongly ferromagnetic interactions via single-oxygen bridgedcopper() ions.We present here the crystal structure andmagnetic behaviour of this compound.The copper()¡Vhpda complex was isolated as its perchloratesalt {[Cu4(hpda)4][ClO4]4H2O 1} in 60% yield from the reactionsolution ( H2O¡VMeOH) of copper() perchlorate hexahydrate(2 mmol) and N-(2-hydroxyethyl)-1,3-propanediamine (Hhpda)(2 mmol) at pH 8. Blue crystals were grown by slow evaporationof an ethanol¡Vwater solution of this compound.The crystalstructure of [Cu4(hpda)4][ClO4]4H2O 1 (Fig. 1) exhibits anopen cubane-like Cu4O4 core structure arrangement of fourcopper() ions and four bridging oxygens from deprotonatedN-(2-hydroxyethyl)-1,3-propanediamine and the four Cu()ions form a tetrahedral conguration. This structure is dierentfrom all other cubane-like Cu4O4 core structures in whichtwo neighbouring Cu() atoms are dibridged with oxygenatoms or acetates.2 Each hpda acts as a tridentate ligand to onecopper atom leading to a ve-membered ring and a sixmemberedring.Each Cu() atom is found in a slightly distortedsquare-planar N2O2 coordination environment. The dihedralangle between the two square planes of Cu() atoms bridgedwith single oxygen is nearly perpendicular (95.08 for Cu1 andCu2, 96.57 for Cu1 and Cu3, and 82.58 for Cu3 and Cu4),respectively, while the other kind of dihedral angles betweentwo square planes of copper() atoms without an oxygen bridgeare 37.91 for Cu1 and Cu4 and 38.19 for Cu2 and Cu3,respectively. The bridged Cu Cu separation is in the rangefrom 3.15(1) (Cu1 Cu2) to 3.22(1) (Cu1 Cu3), whilethe unbridged Cu Cu separation is 3.41(1) (Cu1 Cu4) or3.38(1) (Cu2 Cu3), respectively.The magnetic properties of the complex have been investigateddown to 5 K (Fig. 2). The magnetic exchange interactionfor this tetranuclear complex can be described as in Fig. 3 withJ (J = J12 = J13 = J34 = J24) for bridged Cu() atoms and J(J = J14 = J23) for unbridged Cu() atoms.The magnetic susceptibilitydata for the complex was least-squares tted to theHeisenberg¡Vvan Vleck equation 2f and the tting parameterswere found to be J = 44.9 cm1, J = 16.3 cm1 , g = 2.06,£l = 5.1 ¡Ñ 104 (for the molar fraction of mononuclear Cu()ions) and N£\ (temperature independent magnetic susceptibility)taken as 240 ¡Ñ 106 emu mol1. The solid lines in Fig. 2represent a least-squares t to the theoretical equation, whichcan be seen to be good (R = £U(£qcalc £qobs)2/£U(£qobs)2 = 0.043).Fig. 1 An ORTEP4 representation of the cation in [Cu4(hpda)4]-[ClO4]4H2O 1 with 30% probability ellipsoids. H atoms have been omittedfor clarity. Selected bond distances () and angles (): Cu(1)¡VO(1)1.957(8), Cu(1)¡VO(2) 1.957(8), Cu(1)¡VN(1) 1.99(1), Cu(1)¡VN(2) 2.00(1),Cu(2)¡VO(2) 1.935(9), Cu(2)¡VO(4) 1.994(8), Cu(2)¡VN(3) 1.96(1), Cu(2)¡VN(4) 2.04(1), Cu(3)¡VO(1) 1.979(8), Cu(3)¡VO(3) 1.923(9), Cu(3)¡VN(5)1.97(1), Cu(3)¡VN(6) 2.02(1), Cu(4)¡VO(3) 1.966(8), Cu(4)¡VO(4) 1.960(8),Cu(4)¡VN(7) 1.98(1), Cu(4)¡VN(8) 2.00(1), Cu(1) Cu(2) 3.15(1),Cu(1) Cu(3) 3.22(1), Cu(1) Cu(4) 3.41(1), Cu(2) Cu(3)3.38(1), Cu(2) Cu(4) 3.22(1), Cu(3) Cu(4) 3.19(1), Cu(1)¡VO(2)¡VCu(2) 108.0(4), Cu(1)¡VO(1)¡VCu(3) 110.1(4), Cu(3)¡VO(3)¡VCu(4)110.0(4), Cu(2)¡VO(4)¡VCu(4) 108.9(4).2416 J.Chem. Soc., Dalton Trans., 1999, 2415¡V2416The results show the presence of both strongly ferromagnetic(between bridged Cu() atoms) and weakly antiferromagnetic(between unbridged Cu() atoms) interactions, which aredierent from those of other dioxygen-bridged tetranuclearcopper() complexes with antiferromagnetic spin coupling.2c,dThe magnetic behaviour of this compound is similar to that ofanother tetranuclear Cu() complex2e in which each copperatom is strictly ve-co-ordinate and the magnetic exchangeinteraction is relatively weak.The ferromagnetic intratetramerinteraction could be attributed to the orthogonality of themagnetic orbitals of square-planar copper() atoms (dx2 y2orbitals) and bridging oxygen atom (p orbitals).Eects for themagnetic exchange mechanism study of this complex by performinga quantum calculation to nd the relationship betweenenergy gaps of two singly occupied orbitals of Cu() atoms andsome structural factors is underway.Fig. 2 Plots of molar susceptibility (£qm/emu mol1) and eective magneticmoment (eff /B) versus temperature of a powdered sample of[Cu4(hpda)4][ClO4]4H2O. The solid lines represent the best t of thedata.Fig. 3 Schematic representation of the magnetic coupling model in[Cu4(hpda)4][ClO4]4H2O.AcknowledgementsThe support of this work by a JSPS (Japan Society for thePromotion of Science) postdoctoral fellowship to X. S. Tan(No. P97370) and by a Grant-in-Aid for Science Research (No.09440224) from the Ministry of Education, Science, Sport andCulture of Japan is gratefully acknowledged.Notes and references Crystal data for C20H54N8O21Cl4Cu4, M = 1138.68, monoclinic,space group P21/n, a = 19.458(5), b = 11.518(3), c = 19.846(4) ,£] = 109.15(1), U = 4201(1) 3, £f = 0.71069 , Z = 4, Dc = 1.800 g cm3,(Mo-K£\) = 2.335 mm1, T = 296.2 K. 12453 Reections measured,6935 unique (Rint = 0.075), 3092 observed (I > 2.00£m(I )). Crystal structuresolution was by direct methods with (SIR92) 5 and was expandedusing Fourier techniques with DIRDIF94.6 Full-matrix least-squaresrenement was carried out on F with most non-hydrogen atoms anisotropic,while several oxygen atoms of disordered perchlorates wererened isotropically.Hydrogen atoms were included but not rened.Final R and Rw values on observed data are 0.068 and 0.071. CCDCreference number 186/1528. See http://www.rsc.org/suppdata/dt/1999/2415/ for crystallographic les in .cif format. Magnetic susceptibility measurements were measured on a QuantumDesign MPMS-5S SQUID susceptometer with a powdered sample ofthe copper tetramer.Measurements were made in the temperatureregion 5¡V300 K and at external eld strengths of 0.5 T. Fig. 2 shows theplots of molar susceptibility (£qm/emu mol1) and eective magneticmoment (eff/B) versus temperature. The magnetic data were analysedusing the Heisenberg Hamiltonian and the magnetic susceptibility canthen be expressed as:2h£qm =2Ng2£]2kTAB(1 £l) Ng2£]2KT£l N£\A = 2exp(2J/kT) exp[4J 2J)/kT] 5exp[4J 2J)/kT]B = 1 6exp(2J/kT) exp[(4J 4J)/kT] 3exp[(4J 2J)/kT] 5exp[(4J 2J)/kT]where £l is the (molar) fraction of mononuclear copper() ions and theother symbols have their usual meanings.1 W.E. Hateld, in Magnetostructural Correlations in ExchangeCoupled Systems, eds. R. D. Willett, D. Gatteschi and O. Kahn,Reidel, Dordrecht, The Netherlands, 1985, p. 555.2 (a) P. V. Bernhardt and L. A. Jones, Chem. Commun., 1997, 655; (b) S.S. Tandon, L. K. Thompson and D. O. Miller, J. Chem. Soc., Chem.Commun., 1995, 1907; (c) L.P. Wu, T. Kuroda-Sowa, M. Maekawa,Y. Suenaga and M. Munakata, J. Chem. Soc., Dalton Trans., 1996,2179; (d ) J. Reim, K. Griesar, W. Haase and B. Krebs, J. Chem. Soc.,Dalton Trans., 1995, 2649; (e) L. Walz, H. Paulus and W. Haase,J. Chem. Soc., Dalton Trams., 1983, 657; ( f ) S. Teipel, K. Griesar,W. Haase and B. Krebs, Inorg. Chem., 1994, 33, 456; ( g) G. Kolks,S. J. Lippard, J. V. Waszczak and H. R. Lilienthal, J. Am. Chem. Soc.,1982, 104, 717; (h) H. Zhang, D. Fu, F. Ji, G. Wang, K. Yu andT. Yao, J. Chem. Soc., Dalton Trans., 1996, 3799; (h) I. S. T. Trey,N. N. Murthy, S. T. Weintraub, L. K. Thompson and K. D. Karlin,Inorg. Chem., 1997, 36, 956.3 (a) T. Itoh, H. Hisada, T. Sumiya, M. Hosono, Y. Usui and Y. Fujii,Chem. Commun., 1997, 677; (b) X. S. Tan, Y. Fujii, T. Sato,Y. Nakano and M. Yashiro, Chem. Commun., 1999, 881.4 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge NationalLaboratory, Oak Ridge, TN, 1976.5 A. Altomare, M. C. Burla, M. Camalli, M. Cascarano, C.Giacovazzo, A. Guagliardi and G. Polidori, J. Appl. Crystallogr.,1994, 27, 435.6 P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Boseman, R.de Gelder, R. Israel and J. M. M. Smits, The DIRDIF-94 programsystem, Technical Report of the Crystallography Laboratory,University of Nijmegen, 1994.Communication 9/03524I

ISSN:1477-9226    

DOI:10.1039/a903524i

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2417–2426 2417 Dinuclear oxomolybdenum(V) complexes which show strong electrochemical interactions across bis-phenolate bridging ligands: a combined spectroelectrochemical and computational study Nicholas C. Harden, Elizabeth R. Humphrey, John C. Je.ery, Siu-Ming Lee, Massimo Marcaccio, Jon A. McCleverty,* Leigh H. Rees and Michael D. Ward * School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK BS8 1TS. E-mail: mike.ward@bristol.ac.uk; jon.mccleverty@bristol.ac.uk Received 13th May 1999, Accepted 3rd June 1999 A UV/VIS/NIR spectroelectrochemical study has been carried out on a series of dinuclear complexes of the type [{Mo(TpMe,Me)(O)Cl}2{µ-OO}], where ‘OO’ denotes a bis-phenolate bridging ligand and TpMe,Me is tris(3,5- dimethylpyrazolyl)hydroborate.The bridging ligands are 1,4-[O(C6H4)nO]2 (n = 1 1, 2 2, 3 3 or 4 4), 1,4- [O(C6H3Me2)2O]2 5, 1,3-[O(C6H4)O]2 6 and 1,4-[OC6H4XC6H4O]2 (X = CH2 7, S 8 or SO2 9).Thus 1–4 have oligophenylene spacers; in 5 the biphenyl bridge is twisted by the presence of the Me substituents, in contrast to 2 which has a normal biphenyl spacer; 6 has a meta-substituted phenylene bridge in contrast to the para-substituted analogue 1; and 7–9 have single-atom spacers between the two phenyl rings. All complexes undergo two one-electron oxidations and two one-electron reductions, apart from 6 whose oxidation is irreversible.The e.ects of the di.erent spacer groups on the electrochemical interactions in the complexes were examined by voltammetric determination of the redox splittings, the thioether spacer of 8 proving particularly e.ective at transmitting electronic interactions compared to the SO2 bridge of 9. UV/VIS/NIR Spectroelectrochemical studies on the mono- and di-oxidised complexes showed the presence of intense, low-energy phenolate.MoVI charge-transfer bands; for example for [4]2, .max = 1033 nm (e = 50 000 dm3 mol1 cm1).The assignments of these as LMCT transitions were con.rmed by spectroelectrochemical studies on mononuclear model complexes [Mo(TpMe,Me)(O)Cl(OC6H4R)] (R = H 10 or OMe 11) and by molecular orbital (ZINDO) calculations. Experimental and computational evidence indicate that the large separation between the two oxidations of 1–4 is ascribable in part to a near-planar bridging ligand conformation. The reduced forms of 1 and 6 were also examined by spectroelectrochemistry; whereas [1] [MoIVMoV state] shows low-energy intervalence charge-transfer transitions across the para-substituted bridge, no such transitions are detectable across the meta-substituted bridge of [6].Introduction We are interested in the study of electronic and magnetic metal– metal interactions across bridging ligands in polynuclear complexes, 1 with a view to the development of e.ective molecular wires,2 an area of considerable current interest.1–3 We recently prepared a series of dinuclear complexes [{Mo(TpMe,Me)(O)- Cl}2(µ-OO)] [TpMe,Me is tris(3,5-dimethylpyrazolyl)hydroborate] in which two oxomolybdenum(.) fragments are linked to the termini of various bis-phenolate bridging ligands (‘OO’) which were chosen to allow the systematic study of the e.ects of length, conformation, and substitution pattern of the bridging ligand on the magnetic and electrochemical interactions between the paramagnetic and redox-active termini (see complexes 1–6).The mononuclear complex building-block on which these dinuclear complexes are based is [Mo(O)(TpMe,Me)Cl(OPh)], which was .rst described by Enemark and co-workers 6 in 1987. Its most signi.cant property for the purposes of this work is that it undergoes chemically reversible one-electron oxidation and reduction processes, which are formally MoV–MoVI and MoIV–MoV couples respectively. The dinuclear complexes are therefore expected to undergo two one-electron oxidations [to give the MoV–MoVI and MoVI 2 states] and two one-electron reductions [to give the MoV–MoIV and MoIV 2 states], and this was generally true with all redox processes for 2–5 being chemically fully reversible.For 1 only the .rst oxidation is reversible, and for 6 there are no reversible oxidations; however both complexes undergo the expected two reversible reductions. Although dinuclear complexes in which a strong electronic interaction between the metals allows access to a mixed-valence state are common,2 those in which oxidation and reduction processes allow access to two di.erent mixed-valence states are relatively rare.7,8 The work we describe here was prompted by an interesting feature of the electrochemical behaviour of these complexes: viz.for complexes 1–5, in which there is an all-para linkage pattern across the bridging ligands, the redox potential separation between the two oxidations is much larger than the separation between the two reductions.4 In 2 for example the two oxidations are 480 mV apart whereas the two reductions are almost O Mo O Mo n O Mo O Mo 1 n = 1 2 n = 2 3 n = 3 4 n = 4 5 O Mo O Mo O Mo O Mo X 6 7 X = CH2 8 X = S 9 X = SO2 R O Mo 10 R = H 11 R = OMe Mo = {Mo(TpMe,Me)OCl}+2418 J.Chem. Soc., Dalton Trans., 1999, 2417¡V2426Table 1 Characterisation data for the new complexes aElemental analytical data b (%)Complex Colour Yield (%) C H N FAB-MSc m/z788a99a11PurpleBlackBlackRedRedBlue38313823276448.2 (47.5)44.9 (45.6)48.7 (49.0)44.8 (44.4)46.1 (46.7)46.6 (46.4)5.0 (5.0)4.8 (4.7)4.9 (4.7)4.5 (4.6)4.4 (4.5)5.1 (5.1)15.2 (15.5)14.8 (15.2)12.6 (12.7)14.5 (14.8)11.8 (12.1)14.3 (14.8)108911076631138695569a The IR spectra of all complexes (as KBr discs) showed £hB¡VH in the range 2540¡V2560 cm1 and £hMoO in the range 945¡V955 cm1.b Calculated values inparentheses. c Matrix: 3-nitrobenzyl alcohol.coincident and cannot be resolved by cyclic or square-wave voltammetry.Thus the oxidised MoV¡VMoVI mixed-valence statesare much more stable with respect to disproportionation thanare the reduced MoV¡VMoIV mixed-valence states, and the extentof electronic delocalisation across the bridging ligand is substantiallydierent in the two dierent mixed-valence states.This suggested to us that whereas the reductions are metallocalisedand the interactions between them over these distancesare therefore weak, the two oxidations could have someligand-centred character, such that the doubly oxidised formcould be expressed either as MoVI¡VL2¡VMoVI (metal-basedoxidations) or MoV¡VL¡VMoV (ligand-based oxidations, to givea bridging quinone); see Scheme 1.A contribution from theligand-oxidised form would account for the strong electrochemicalinteraction between the two MoV¡VMoVI couplesbecause the positive charges would be much closer together,and this is also consistent with the ability of para-substituteddihydroxypolyphenyls to give quinones on oxidation.9¡V12 We 13¡V16and others 17 have recently described examples of ligandcentredredox processes involving the formation of bridgingquinone-type ligands; spectroelectrochemical studies were generallyessential to ascertain the nature of the redox processesconcerned.A spectroelectrochemical study of these complexestherefore appeared highly desirable.In this paper we describe the results of a detailed electrochemical,spectroelectrochemical and computational study of aseries of nine such dinuclear complexes with various bridgingligands, carried out in order to clarify the nature of theirelectrochemical processes.The results were dramatic, with theoxidised forms of the complexes showing very intense newelectronic transitions in the near-infrared (NIR) region of thespectrum. In addition to the previously reported complexes 1¡V6with oligophenylene bridges, we describe also the new dinuclearcomplexes 7¡V9 which were prepared in order to extend ourunderstanding of the eects of dierent bridging groups onmetal¡Vmetal electronic interactions.Complex 7 contains asaturated CH2 spacer between the two phenolate termini, and 8and 9 contain respectively thioether (S) or sulfone (SO2)spacers. The presence of single-atom spacers of this type willdisrupt both the planarity and delocalisation across the bridgingligand, and makes it impossible for the bridging ligands toform a quinonoidal structure on oxidation; comparison of theelectrochemical and spectroelectrochemical properties of thesecomplexes with their fully conjugated analogues is therefore ofinterest. The crystal structures of dinuclear 8 and its mononuclearanalogue 8a are included.Two mononuclear com-Scheme 1 Extreme canonical forms of the doubly oxidised complexes:metal-centred oxidations to give two molybdenum() centres (left), orligand-centred oxidations to give a bridging quinone (right).O OMoVIMoVIO OMoVMoVn nplexes [Mo(TpMe,Me)(O)Cl(OC6H4R)] (R = H 10, OMe 11)were also examined, to assist with interpretation of the spectraof their dinuclear counterparts 1¡V9.In addition, we have performed molecular orbital calculationson some of the complexes to resolve the abovementionedquestion of ligand-centred or metal-centredoxidation, and consequently assignment of the strong NIRtransitions that occur in the mono- and di-oxidised forms ofthese complexes.Results and discussion(i) Syntheses of new complexes 7¡V9 and the crystal structures of 8and 8aThe new complexes were all prepared in the same general wayas the previously reported 1¡V6, by reaction of the appropriatebis-phenol bridging ligands with an excess of [Mo(TpMe,Me)-(O)Cl2] in toluene at reux in the presence of Et3N.4 The bisphenolsused for 7¡V9 are all commercially available.In everycase the dinuclear complex was the main product and the rstto elute from a silica column; traces of the mononuclearanalogues, in which one phenol site is co-ordinated and theother pendant, are more polar and eluted after the dinuclearcomplexes. These were generally present in small amounts andthe only ones isolated and characterised were 8a and 9a, themononuclear counterparts of 8 and 9. Characterisation datafor all new complexes are collected in Table 1.The crystal structures of 8a and 8 are shown in Figs. 1 and 2respectively and are fairly self-explanatory; see Tables 2 and 3for the bond lengths and angles.In each case the co-ordinationgeometries and metrical parameters of the metal centres areunremarkable and comparable to those of the previouslydetermined structures in this series.4,5,18 The Mo¡VO and Mo¡VCl distances in both structures are (as usual) rendered ratherinaccurate by the occurrence of disorder between the O and Clatoms; only the major component of the disorder is shown inthe Figures. The C¡VS¡VC angles in the thiodiphenol ligands are102.78(14) and 103.4(2) for 8a and 8 respectively, which arestatistically identical.This shows that there is no signicantsteric interaction between the two metal complex units indinuclear 8 which, if it occurred, would be expected to increaseFig. 1 Crystal structure of complex 8a.J. Chem. Soc., Dalton Trans., 1999, 2417.2426 2419 the C.S.C angle. The two phenyl rings in the ligands are approaching orthogonality in each case, with angles between their mean planes of 82.9 in 8a and 77.4 in 8.This implies that it is not possible in this conformation for a ¥�-symmetry orbital (d or p) on the S atom to interact with both phenyl ¥� systems simultaneously; this point is signi.cant for discussion of the electrochemical data (below). (ii) Electrochemical studies on the new dinuclear complexes 7.9 Electrochemical data are summarised in Table 4; the data for 1.6 are included for comparison with the new complexes. The mononuclear complexes 8a and 9a show the expected chemically reversible one-electron MoV.MoVI and MoIV.MoV Table 2 Selected bond lengths (A) and angles () for complex 8aa Mo(1).O(1 ) Mo(1).O(1) Mo(1).O(41) Mo(1).N(37) O(1 ).Mo(1).O(41) O(1).Mo(1).O(41) O(1 ).Mo(1).N(37) O(1).Mo(1).N(37) O(41).Mo(1).N(37) O(1 ).Mo(1).Cl(1 ) O(41).Mo(1).Cl(1 ) N(37).Mo(1).Cl(1 ) O(1 ).Mo(1).N(17) O(1).Mo(1).N(17) O(41).Mo(1).N(17) N(37).Mo(1).N(17) 1.720(6) 1.847(10) 1.962(2) 2.168(3) 101.7(3) 96.2(5) 89.7(3) 90.4(5) 164.68(9) 101.9(3) 93.4(2) 94.3(2) 84.8(3) 167.5(4) 86.41(9) 84.35(10) Mo(1).N(27) Mo(1).N(17) Mo(1).Cl(1) Mo(1).Cl(1 ) O(1).Mo(1).Cl(1) O(41).Mo(1).Cl(1) N(37).Mo(1).Cl(1) N(17).Mo(1).Cl(1) O(1 ).Mo(1).N(27) O(1).Mo(1).N(27) O(41).Mo(1).N(27) N(37).Mo(1).N(27) Cl(1 ).Mo(1).N(27) N(17).Mo(1).N(27) Cl(1).Mo(1).N(27) Cl(1 ).Mo(1).N(17) 2.268(3) 2.221(3) 2.242(2) 2.214(4) 98.9(5) 99.04(9) 93.60(10) 92.79(10) 163.8(3) 86.6(5) 85.88(9) 80.68(10) 91.8(2) 81.35(9) 172.14(10) 173.1(2) a The bond distances and angles involving the disordered atoms O(1)/ O(1 ) and Cl(1)/Cl(1 ) should be treated with caution as they are likely to be considerably less reliable than the others.couples. Comparison with the parent mononuclear complex [Mo(TpMe,Me)(O)Cl(OPh)] 104 shows how the MoV.MoVI redox potentials re.ect the electron-donating e.ect of the thioether substituent (shift towards more negative potentials because the electron-rich metal is easier to oxidise and harder to reduce) and the electron withdrawing e.ect of the sulfone (shift towards more positive potentials because the electron-poor metal centre is harder to oxidise and easier to reduce).The MoIV.MoV redox potentials in contrast appear to be much less sensitive to the e.ects of substituents on the phenolate ligand, consistent with the poor delocalisation of the negative charges of the mixedvalence states [1].[6] across the bridging ligands that is apparent from electrochemical data. The dinuclear complex 7 shows the same general behaviour as that of 1.4,4 with two MoV.MoVI couples separated by 120 mV but two MoIV.MoV couples essentially coincident giving a single double-intensity wave in the voltammogram.Compared to complex 2 (two phenylene spacers) where this redox separation is 480 mV, the greatly reduced redox separation for 7 is clearly ascribable to the saturated CH2 spacer. This breaks the conjugation across the bridging ligand, and thereby prevents delocalisation of charge beyond each individual phenyl ring Fig. 2 Crystal structure of complex 8. Table 3 Selected bond lengths (A) and angles () for complex 8a Mo(1).O(1 ) Mo(1).O(1) Mo(1).O(141) Mo(1).Cl(1) Mo(1).N(131) Mo(1).N(111) Mo(1).Cl(1 ) Mo(1).N(121) O(1 ).Mo(1).O(141) O(1).Mo(1).O(141) O(1).Mo(1).Cl(1) O(141).Mo(1).Cl(1) O(1 ).Mo(1).N(131) O(1).Mo(1).N(131) O(141).Mo(1).N(131) Cl(1).Mo(1).N(131) O(1 ).Mo(1).N(111) O(1).Mo(1).N(111) O(141).Mo(1).N(111) Cl(1).Mo(1).N(111) N(131).Mo(1).N(111) O(1 ).Mo(1).Cl(1 ) O(141).Mo(1).Cl(1 ) N(131).Mo(1).Cl(1 ) N(111).Mo(1).Cl(1 ) O(1 ).Mo(1).N(121) O(1).Mo(1).N(121) O(141).Mo(1).N(121) Cl(1).Mo(1).N(121) N(131).Mo(1).N(121) N(111).Mo(1).N(121) Cl(1 ).Mo(1).N(121) 1.810(14) 1.83(2) 1.945(3) 2.165(6) 2.187(3) 2.220(3) 2.242(5) 2.254(3) 100.1(5) 98.5(6) 101.2(6) 93.1(2) 86.9(5) 88.2(6) 168.55(12) 94.6(2) 88.1(5) 163.4(6) 88.16(12) 93.6(2) 83.01(12) 102.0(5) 94.8(2) 92.6(2) 168.8(2) 164.8(4) 86.3(6) 87.21(12) 172.4(2) 83.95(12) 78.81(13) 90.5(2) Mo(2).O(2) Mo(2).O(2 ) Mo(2).O(241) Mo(2).N(221) Mo(2).N(211) Mo(2).Cl(2 ) Mo(2).N(231) Mo(2).Cl(2) O(2).Mo(2).O(241) O(2 ).Mo(2).O(241) O(2).Mo(2).N(221) O(2 ).Mo(2).N(221) O(241).Mo(2).N(221) O(2).Mo(2).N(211) O(2 ).Mo(2).N(211) O(241).Mo(2).N(211) N(221).Mo(2).N(211) O(2 ).Mo(2).Cl(2 ) O(241).Mo(2).Cl(2 ) N(221).Mo(2).Cl(2 ) N(211).Mo(2).Cl(2 ) O(2).Mo(2).N(231) O(2 ).Mo(2).N(231) O(241).Mo(2).N(231) N(221).Mo(2).N(231) N(211).Mo(2).N(231) Cl(2 ).Mo(2).N(231) O(2).Mo(2).Cl(2) O(241).Mo(2).Cl(2) N(221).Mo(2).Cl(2) N(211).Mo(2).Cl(2) N(231).Mo(2).Cl(2) 1.716(10) 1.825(13) 1.947(3) 2.180(3) 2.209(3) 2.211(5) 2.250(3) 2.273(4) 98.9(4) 98.7(5) 88.2(4) 88.6(5) 168.25(12) 88.8(3) 165.1(5) 86.78(12) 84.01(12) 99.5(5) 94.4(2) 93.4(2) 93.8(2) 165.5(3) 87.4(5) 88.08(12) 83.01(13) 78.90(12) 172.1(2) 102.8(3) 92.56(14) 94.98(14) 168.33(14) 89.43(14) a The bond distances and angles involving the disordered atoms O(1)/O(1 ) and Cl(1)/Cl(1 ) should be treated with caution as they are likely to be considerably less reliable than the others.2420 J.Chem. Soc., Dalton Trans., 1999, 2417–2426 which becomes e.ectively electronically isolated from its neighbour. A similar e.ect wihis ligand has been observed before.19 For complex 8, where the CH2 spacer is replaced by S, the separation between the two MoV–MoVI couples has increased to 430 mV, and is therefore almost restored to the value observed for the fully conjugated complex 2 despite the increased length of the bridge and presence of a formally saturated, tetrahedral spacer [Fig. 3(a)]. The marked contrast with the behaviour of 7 shows that the thioether S atom of 8 is clearly playing a signi.- cant role in facilitating electronic delocalisation across the bridging ligand. Although the only other studies of metal– metal interactions across a diaryl thioether bridging ligand of this sort showed the interactions to be rather weak,19,20 we note that a disul.de bridge between two pyridyl rings has recently been shown to be very e.ective at transmitting electronic interactions, because of overlap of relatively extended p-symmetry (p or d) orbitals on the sulfur atoms with the p systems of the phenyl rings.21 We suggest that a similar e.ect is operative in complex 8; this would require a signi.cant conformational change from that observed in the crystal structure, in which the two phenyl rings of the bridging ligand are nearly orthogonal.We note that for 8 the strong electronic interaction cannot be ascribed to formation of a quinone structure by ligand-centred oxidation (cf. Scheme 1). For complex 9 the electron-withdrawing sulfone group in the bridging ligand shifts the redox processes towards more positive potentials compared to those of 7 and 8, but the main di.erence between 9 and 8 is that the redox splitting between the MoV–MoVI couples has decreased from 430 mV in 8 to just 80 mV in 9, even less than the coupling across the CH2 spacer of 7, despite the through-bond separation between the metal centres being unchanged [Fig. 3(b)]. Oxidation of the sulfur atom to the 6 oxidation state will result in considerable contraction of its orbitals, such that any overlap with the p system of the phenyl rings will be reduced. In addition, whereas a p(p) orbital on the thioether S atom in 8 might be available to interact with the phenyl p systems if the S atom were sp2 hybridised, the necessary sp3 hybridisation of the tetrahedral sulfone S atom in 9 makes this impossible.Whichever explanation is more appropriate it is clear that oxidation of the thioether to a sulfone has almost completely removed its ability to act as conduit for p-electron delocalisation, which constitutes an interesting (albeit irreversible) switching e.ect. A similar e.ect has been observed before, but more weakly: the e.ect is much more dramatic with complex 9.19 Table 4 Electrochemical data a E/V vs.Fc–Fc Complex MoIV–MoV couple MoV–MoVI couple .E1/2/mV 12345678 8a 9 9a 10 11 1.19, 1.44 1.13 b 1.16 b 1.16 b 1.21 b 1.20, 1.40 1.23 b 1.16 b 1.16 1.07 b 1.02 1.21 1.28 0.26, 1.25 c 0.44, 0.92 0.56, 0.74 0.61 b 0.55, 0.78 0.58 c 0.60, 0.72 0.45, 0.88 0.48 0.88, 0.96 0.91 0.68 0.44 990 480 180 d 230 — 120 430 — 80 ——— a All measurements made in CH2Cl2 containing 0.1–0.2 M Bu4NPF6 as base electrolyte using a Pt-bead working electrode.Data for complexes 1–6 are reproduced from ref. 4. b Two coincident one-electron couples. c Irreversible process. d Redox separation is too small to measure. (iii) Spectroelectrochemical studies on mononuclear complexes 10 and 11 Before studying the spectroelectrochemical properties of the dinuclear complexes we .rst need to understand the electronic spectra of the mononuclear components in their accessible oxidation states (4, 5, 6).Accordingly we performed spectroelectrochemical studies on the mononuclear oxomolybdenum( .) complexes 10 and 11 (the studies on 10 were brie.y reported earlier).14 Both complexes undergo chemically reversible one-electron oxidation and reduction processes, giving formally molybdenum(..) and -(..) species respectively. Their electrochemical properties are summarised in Table 4, and the results of the UV/VIS/NIR spectroelectrochemical study are in Table 5. In the electronic spectrum of complex 10 the lowest-energy feature at 520 nm we ascribed to a phenolate.MoV LMCT process; the higher-energy transitions at 340 and 266 nm are probably Cl(p).Mo(dxy) LMCT and ligand-centred p ..p* processes respectively.4 On one-electron oxidation, formally a metal-centred process generating MoVI, the phenolate-to-MoV LMCT band is replaced by two more intense bands at 475 and 681 nm. Since metal-centred oxidation will both lower the energy of the metal d(p) orbitals and increase their electronaccepting ability, we might expect the phenolate.Mo LMCT at 520 nm to become red-shifted and to increase in intensity.On this basis the 681 nm transition is assigned to a phenolate. MoVI LMCT transition. The additional new transition at 475 nm is also likely to be an LMCT band of some sort. We note that the three d(p) orbitals are non-degenerate, with the d(xy) orbital lying below d(xz) and d(yz) (which are raised in energy by interaction with the p-donor oxo-ligand);4 two phenolate.d(p) LMCT transitions might therefore be expected.The behaviour of complex 11 is similar to that of 10, with the e.ect of the substituents on the phenolate being clear: the phenolate.MoV LMCT is red-shifted to 593 nm in 11, because the .lled ligand-based orbitals are raised nearer to the metal orbitals by the electron-donor substituent. On oxidation to the molybdenum(..) state these are again replaced by two intense Fig. 3 Cyclic voltammograms of complex 8 (a) and 9 (b).J. Chem. Soc., Dalton Trans., 1999, 2417�C2426 2421 Table 5 Summary of spectroelectrochemical data (CH2Cl2, 243 K) Complex ¦Ëmax/nm (103 ¦Å/dm3 mol1 cm1) 1[ 1] [1] [1]2 2[ 2] [2]2 3[ 3] [3]2 4[ 4] [4]2 5[ 5] [5]2 6[ 6] [6]2 7[ 7] [7]2 8[ 8] [8]2 9[ 9] [9]2 8a 9a 10 [10] 11 [11] [11] 660 (5.1) a 817 (12) b ¡Ö1700 (sh) c 800 (0.3) d 614 (6.7) a 1096 (50) b 1017 (48) b 592 (5.4) a 1131 (25) b 1015 (62) b 586 (5.2) a 1047 (24) b 1033 (50) b 570 (5.9) a 1245 (19) b 832 (32) b 544 (3.3) a 627 (1.5) a 860 (0.1) d 533 (4.8) a 733 (20) b 771 (37) b 578 (4.2) a ¡Ö1200 (sh) b ¡Ö1200 (sh) b 497 (5.2) a 695 (12) b 699 (24) b 570 (2.3) a 489 (2.5) a 520 (1.8) a 681 (13) b 593 (3.1) a 724 (9.6) b 830 (0.5) d 397 (7.8) 700 (sh) 1127 (2.1) c 383 (7.7) 389 (14.5) 643 (15) 599 (11) 373 (16) 600 (9.8) 567 (sh) 380 (sh) 562 (7.7) 548 (9.0) 364 (14) 580 (10) 479 (11) 352 (10) 360 (6.8) 430 (sh) 358 (13) 595 (12) 595 (22) 361 (12) 900 (8.2) b 900 (15) b 348 (19) 485 (9.2) 486 (sh) 362 (6.8) 325 (sh) 340 (6.2) 475 (5.4) b 369 (6.3) 554 (7.0) b 369 (3.2) 266 (15) 566 (18) b 746 (2.7) a 300 (7.7) 272 (33.1) 475 (10) 475 (12) 297 (31) 374 (13) 357 (17) 311 (33) 310 (20) 302 (17) 262 (sh) 357 (14) 266 (19) 280 (15) 372 (4.5) 264 (23) 520 (sh) 515 (13) 260 (29) 595 (7.4) 600 (10) 267 (30) 348 (18) 350 (18) 260 (19) 263 (21) 266 (9.8) 359 (6.8) 268 (11) 352 (8.0) 294 (11) 307 (11) 430 (4.3) 311 (14) 353 (15) 273 (16) 277 (21) 283 (17) 286 (10) 351 (14) 354 (16) 360 (sh) ¡Ö300 (sh) 260 (21) 272 (10) 290 (sh) 265 (19) 260 (17) 260 (24) a Phenolate¡úMoV LMCT.b Phenolate¡úMoVI LMCT. c MoIV¡úMoV IVCT. d Molybdenum() d�Cd transition. new transitions (Fig. 4). The fact that both new transitions are red-shifted compared to the two analogous transitions of [10], an obvious eect arising from the electron-donating substituents on the phenolate ligand, conrms that both of these transitions have phenolate¡úMoVI LMCT character (see also the ZINDO calculations below).On reduction of these mononuclear complexes to the molybdenum( ) state the phenolate¡úMoV LMCT band completely disappears such that the complexes are essentially transparent above about 500 nm (Fig. 4). The only exception to this is a weak d�Cd transition at about 800 nm, arising from a transition between the lled d(xy) level and the empty d(xz) and d(yz) levels. Such low-energy d�Cd transitions have been observed for complexes of RuIII in which a distorted pseudo-octahedral geometry splits the®t2g¡� orbital set.22 (iv) Reductions of dinuclear complexes 1 and 6 The dinuclear complexes 1 and 6 contain two {MoV(TpMe,Me)- (O)Cl} fragments, linked by the deprotonated dianion of 1,4- Fig. 4 Electronic spectra of complex 11 (i), [11] (ii) and [11] (iii). dihydroxybenzene and 1,3-dihydroxybenzene, respectively: accordingly they dier only in the substitution pattern of the bridging ligand, and this has been shown to result in signicant dierences between their electrochemical and magnetic properties.4,5 The electronic spectra of complexes 1, [1] and [1]2 are shown in Fig. 5. In the MoV 2 state the spectrum of 1 shows the expected LMCT transition at 660 nm arising from the bridging ligand, directly analogous to the phenolate¡úMoV LMCT bands of mononuclear 7�C9. The expected higher-energy LMCT and ¦� ¡ú ¦�* transitions are also apparent, and overall there is an obvious correspondence between the spectra of dinuclear 1 and mononuclear 10.On one-electron reduction to the MoVMoIV form the 660 nm LMCT transition approximately halves in intensity and is red-shifted to 746 nm. This intensity reduction is consistent with the presence of one molybdenum() Fig. 5 Electronic spectra of complex 1 (i), [1] (ii) and [1]2 (iii). Inset is an expansion of the near-IR region of the spectrum of [1] with the IVCT bands labelled *.2422 J.Chem. Soc., Dalton Trans., 1999, 2417¡V2426centre in the complex instead of two, and the red-shift of thisLMCT band at the remaining molybdenum() site occursbecause reduction of the other metal to MoIV will raise theorbitals of the bridging ligand in energy. In addition, newtransitions are apparent at 1127 and ca. 1700 nm, the latter ofwhich is very broad and extends completely across the NIRregion out to 3000 nm. From our studies on 10 and 11 weknow that mononuclear molybdenum() and molybdenum()centres of this type have no transitions in this region, so weascribe these to MoIV¡÷MoV intervalence charge-transfer(IVCT) bands.This assignment is conrmed by the fact thatthey completely disappear following the second reduction to theMoIV2 state in [1]2. The observation of a transition ascribableto a localised molybdenum() site in the mixed valence state(at 746 nm) means that [1] could be classied as a class IImixed valence species, although the presence of the IVCTbands shows that there is a signicant interaction between themetal centres.The presence of two identiable IVCT bands maybe related to the substantial splitting of the d(£k) orbital set oneach metal, such that the electron which originates from a lledd(xy) orbital on the molybdenum() centre could transfereither to the half-empty d(xy) level or the completely emptyd(xz)/d(yz) level on the molybdenum() centre.Comparison with the spectra of complex 6, [6] and [6]2(Fig. 6) is interesting as the eect of the substitution pattern onthe bridging ligand becomes apparent. In the spectrum of 6 thelowest-energy LMCT transition (bridging ligand to metal) is at544 nm; this is similar to the position of the phenolate¡÷MoVLMCT in 10, because the meta-substitution pattern of thebridging ligand results in each donor atom of the bridging ligandbehaving more like an electronically isolated phenolatethan was the case for 1, where this transition is at 660 nm.Reduction to [6] [the mixed-valence MoVMoIV state] againresults in an approximate halving of the intensity of this LMCTband coupled to a red-shift to 627 nm, consistent (as for [1])with the presence of localised molybdenum() and -() centres.Fig. 6 Electronic spectra of complex 6 (i), [6] (ii) and [6]2 (iii).Fig. 7 Electronic spectra of complex 1 (i) and [1] (ii).However, in this case the additional low-energy IVCT bands,which were such a striking feature of the spectrum of [1],are completely absent, suggesting that the meta-substitutionpattern has substantially attenuated the metal¡Vmetal electroniccoupling.The 200 mV separation between the two MoV¡VMoIVcouples of 6 does suggest that the electronic interactionbetween the metal centres is still signicant.2 However it is possiblethat this redox splitting is largely ascribable to a throughspaceCoulombic eect because the metals are so closetogether,4 such that there is little contribution to the stability ofthe mixed-valence state arising from delocalisation across thebridging ligand: this would account for the lack of IVCT bands.It has been pointed out before that dinuclear complexes withstrong electrochemical interactions (i.e.large E1/2 values) canstill have very weak IVCT features in their electronic spectra ifthe relative orientations of the metal fragments and the bridgingligand preclude ecient orbital overlap.15 The mostappropriate description of [6] is therefore (at most) weaklycoupled class II, in obvious contrast to [1].This dependence ofthe nature of the mixed-valence state on the substitution patternof the bridging ligand has been noted before, in dinuclearMoIIMoI complexes with ortho-, meta- and para-[HNC6H4-NH]2 as bridging ligands.16(v) Oxidations of the dinuclear complexes 1¡V5 and 7¡V9Although complex 1 undergoes two oxidation processes with avery large separation of 990 mV between them, only the rst ischemically reversible; the spectrum of [1] (together with thatof 1) is in Fig. 7. Attempts to study the spectral behaviour of[1]2 proved, as expected, unsuccessful because the irreversibilityof this process clearly results in decomposition of the complex.Mono-oxidation of the complex has resulted in replacementof the lowest-energy MLCT transition of 1 at 660 nm bytwo more intense new transitions, one at lower energy (817 nm)and one at higher energy (566 nm). This behaviour is similar tothat of the mononuclear complexes 10 and 11 (compare withthe spectrum of [11] in Fig. 4), and suggests that the rstoxidation of 1 is in fact metal-centred to give a MoV¡VMoVIspecies. Whether this is class II or class III is not obvious: thelarge separation between the oxidation potentials suggests classIII behaviour, but there is no evidence for a new IVCT transitionin the near-IR region out to 3000 nm.Complexes 2¡V4 behave similarly to one another on oxidation.The rst oxidation results in the appearance of an intense newtransition in the near-IR region which, after the second oxidation,moves to slightly higher energy (Table 5, Fig. 8). For thefully oxidised complexes [2]2, [3]2 and [4]2 the absorptionmaxima are at almost identical positions (1017, 1015 and 1033nm respectively) and have very high intensities (ca. 50 000 dm3mol1 cm1). Complex 5 behaves generally similarly, althoughthe eect of the methyl substituents on the bridging ligand,which force it to adopt a twisted conformation with the twohalves near-orthogonal, is clear by comparison with the spectraof 2.In particular the principal low-energy transition in theFig. 8 Electronic spectra of complex 3 (i), [3] (ii) and [3]2 (iii).J. Chem. Soc., Dalton Trans., 1999, 2417¡V2426 2423spectrum of the fully oxidised form [5]2 is at higher energythan that of [2]2 (832 nm, compared to 1017 nm), consistentwith the fact that decoupling the £k systems of the two phenylrings should make each terminus behave more like an electronicallyisolated phenolate (cf.the spectrum of [10], £fmax =681 nm). The natures of these electronic transitions for complexes1¡V5 will be discussed later. Complex 6 undergoes noreversible oxidations.Oxidation of complex 7 to [7] results in a strong transitionappearing at 733 nm, which is not very dierent from thatobserved for the mononuclear phenolate complex [10](although more intense). For this reason, and because of theobvious fact that ligand-centred oxidations to give a quinonoidalstructure are not possible for 7, we ascribe this to asimple phenolate¡÷Mo LMCT transition as seen for the mononuclearcomplexes. On further oxidation to [7]2 this transitionapproximately doubles in intensity whilst only changing inenergy slightly, consistent with sequential oxidation of twoequivalent but electronically near-independent chromophoresgiving rst one and then two equivalelisedphenolate¡÷MoVI LMCT transitions.Similar behaviour wasobserved during oxidation of 9 to [9] and then [9]2. The contrastof these with the behaviour of the more strongly coupledcomplexes 1¡V5, in which (i) the LMCT transitions in the oxidisedforms are in the near-IR region and (ii) the singly- anddoubly-oxidised forms can give quite dierent spectra, is obvious.In [8] the LMCT transition is at lower energy than thoseof [7] and [9], and also has a marked low-energy shoulder atabout 1200 nm; it appears that the strong electronic couplingbetween the metals that arises from participation of thethioether bridging group in delocalisation also results in theLMCT transition in the mixed-valence state being red-shifted.Further oxidation of [8] to [8]2 results in no change in theposition of this band but an approximate doubling in intensity.This behaviour is again consistent with the two LMCT bandsbehaving independently of one another, despite the strongredox separation between the MoV¡VMoVI couples of thiscomplex.Reductions of representative complexes to the MoVMoIVand nally the MoIV2 states were uninteresting, showing onlythe same evolution of spectra that occurred for the mononuclearcomplexes, viz.collapse of the phenolate¡÷MoV LMCTtransition and the appearance of a weak d¡Vd transition associatedwith the molybdenum() centres. No evidence for IVCTtransitions in the reduced mixed-valence states was foundexcept for [1] as detailed earlier.(vi) Molecular orbital calculations, and the nature of the oxidisedforms of complexes 1¡V5 and 7¡V9The intense, low-energy transitions of the oxidised formsof 1¡V5 could be consistent with the presence of a highlydelocalised £k system such as those found in extendedquinones.9¡V12 This agrees with our suggestion that ligandcentredoxidations could have occurred to give a dinuclearmolybdenum() complex with a bridging neutral quinone ineach case (Scheme 1), which was prompted by the electrochemicalresults.For example the delocalised £k systems ofnickel dithiolene complexes in some oxidation states give comparablenear-IR transitions.23 However two features of thesespectra behaviour are inconsistent with this idea. First free di-,10ter-,11 and tetra-phenobenzoquinones 12 have their £k¡V£k* absorptionsat 394, 534 and 630 nm respectively, showing the expecteddrop in energy as the quinonoidal £k systems lengthen: in contrastthe absorption maxima of [2]2¡V[4]2 are essentiallyindependent of the length of the bridging ligand.Secondly, theonly free semiquinone radical anions of this type that have beenspectroscopically characterised have their absorption maximaat much lower energy than that of the corresponding quinone.10,24,25 For example, the absorption maximum of the parabiphenosemiquinoneradical anion (£fmax 800 nm, £` 7500 dm3mol1 cm1) doubles in energy and becomes much more intenseon further oxidation to para-biphenoquinone (£fmax 394 nm, £`45 000 dm3 mol1 cm1).10 In contrast, oxidation of [2] to [2]2only causes the NIR transition to move from 1096 to 1017 nmwith a much less signicant change in intensity, and 3 and 4show similar behaviour.The alternative explanation for these strong NIR transitionsis that, by analogy with the mononuclear complexes [10] and[11], and with the dinuclear complexes [7]2¡V[9]2 where abridging quinone cannot be formed, they are phenolate-to-MoVI LMCT processes, albeit at lower energy and having greaterintensity than was seen for the mononuclear complexes.Wesaw earlier in [10] and [11] that an electron-donating substituenton the phenolate lowers the energy and raises the intensityof the LMCT bands, and the double negative charge on thebridging ligands of 1¡V5 means that each phenolate terminuseectively has a good electron-donor substituent (anotherphenolate anion) attached to it, which could account for thelow energies of these bands. The much greater intensities ofthese bands for the dinuclear complexes compared to themononuclear complexes can be ascribed partially (although notwholly) to the presence of two chromophores rather than one.In order to clarify the nature of these strong low-energy transitionswe therefore performed molecular orbital calculations onsome of these oxidised complexes (10 as a representative mononuclearcomplex, and 2 as a representative dinuclear complex)using the ZINDO method.To start with we performed calculations on the mononuclearcomplex 10 in its oxidised and reduced forms.In the molybdenum() form [10] the HOMO is phenolate-based, and theLUMO is largely metal-based (dxy), such that the lowest-energytransition is predicted to be phenolate¡÷MoVI LMCT. The calculatedabsorption maximum for this transition (690 nm) agreesvery closely with what we observed (681 nm). The higher-energytransition in [10] at 475 nm also, as expected, has LMCT character,from the phenolate HOMO to the higher-energy metald(£k) orbitals (dxz and dyz, which are close together).Its calculatedwavelength of 430 nm agrees reasonably well with what weobserved. In the reduced form [10] the low-lying d(xy) orbitalis predicted to be doubly occupied giving a low-spin diamagneticconguration, and the lowest-energy transition is predictedto be the weak d¡Vd transition that we detected at about800 nm (calculated, 1200 nm). In fact, because of the low concentrationsused for the spectroelectrochemical experiments (inorder to keep the strong £k¡V£k* transitions on-scale), we did notdetect these weak d¡Vd transitions in our rst experiments, andonly found them by repeating the reductions with more concentratedsamples after the ZINDO calculations predicted thatthey should be present.In short the calculations on [10] and[10] show no surprises and the predicted electronic transitionsare in good agreement with what we observed. Although theagreement between calculated and actual absolute energies forthe electronic transitions is variable, qualitatively the number,nature and relative positions of the principal transitions arewell accounted for.Calculations on the oxidised dinuclear complex [2]2 arecomplicated by the fact that the results depend on the bridgingligand conformation.At room temperature in solution abiphenyl spacer is expected to have free rotation about the centralinterannular C¡VC bond; the optimum dihedral angle, whichminimises steric repulsion between the H2/H6 protons onadjacent rings yet still maintains as much conjugation in the £ksystems as possible, is about 32 in solution.26 To gain some ideaof the importance of bridging ligand conformation we performedthe calculations under three conditions: (i) with thebridging ligand constrained to be planar; (ii) with the bridgingligand twisted at the intermediate angle of 32 which waspredicted by a molecular mechanics energy minimisationusing standard MM2 parameters and (iii) with the bridging2424 J.Chem. Soc., Dalton Trans., 1999, 2417–2426 ligand constrained to have a 90 twist between the two phenyl rings. Irrespective of bridging ligand conformation, the calculations showed that complex [2]2 is a MoVI 2 species, following metal-centred oxidation. The strong near-IR band is an LMCT transition from the HOMO, based on the bridging ligand, to the metal-centred degenerate pair of LUMOs (sum and di.erence combinations of the dxy orbitals on each metal); the orbitals involved are depicted in Fig. 9. The low energy of these transitions compared to those of the mononuclear molybdenum( ..) complexes arises because the bridging-ligand centred HOMO is relatively high in energy because of its double negative charge. As the bridging ligand is twisted the ZINDO calculations predict that the energy of this transition should increase and its intensity decrease, exactly as we observed by comparison of [2]2 and [5]2 (Fig. 10). Although the absolute energies of these transitions are somewhat overestimated by the ZINDO calculation (by ca. 20%), the di.erence that is calculated on changing the conformation of the bridging ligand agrees very well with what we observe. Thus the energy di.erence between the predicted absorption maxima with torsion angles of 32 (.calc = 805) and 90 (.calc = 690 nm) is 2070 cm1; the shift we actually observe between [2]2 (.obs = 1017) and [5]2 (.obs = 832 nm) is 2190 cm1.The low energies and high intensities of these near-IR transitions for [2]2–[4]2 compared to those of mononuclear [10] are therefore consistent with the bridging ligands adopting conformations that are only moderately twisted, such that there is still substantial p overlap between the phenyl rings. Decoupling of the two termini would result in spectra closer to that observed for [5]2 with a 90 twist. It appears therefore that the large redox separations between the two oxidations, which imply substantial delocalisation across the HOMO of the bridging ligand in the oxidised mixedvalence state, are facilitated by a near-planar conformation of the bridging ligand in the oxidised forms of the complex.It is tempting to suggest in turn that the very small redox separ- Fig. 9 The HOMO (bottom) and LUMO (top) of complex [2]2 calculated by the ZINDO method. Only the metal ions and the bridging ligand are shown for clarity; the other atoms make no signi.cant contribution to either orbital.A torsion angle of 32 between the phenyl rings has been assumed in this calculation (see text). Fig. 10 Predicted LMCT transitions in complex [2]2 from the ZINDO calculations, with twist angles of (i) 0, (ii) 32 and (iii) 90 between the two phenyl rings. ations between the reductions could arise because a more highly twisted conformation of the bridging ligand in the reduced mixed-valence state prevents delocalisation across it.This however does not account for the properties of 1 in which the bridging ligand is a single phenyl ring with no conformational .exibility, where the redox splitting between the oxidations is still much larger than it is between the reductions. The interplay of molecular orbital properties, redox properties and ligand conformations is clearly complex and is an interesting target for future, more sophisticated, computational studies. (vii) Comments on the intense near-IR transitions The strong absorbance in the near-infrared region exhibited by the singly and doubly oxidised forms of many of these complexes is of special interest as such NIR dyes have a variety of potential applications.These include optical data storage devices, in which reading and writing of information is performed by diode lasers in the NIR region of the spectrum, Q-switching of lasers, whereby continuous low-energy output of such lasers in the NIR region is converted into very short, intense bursts, and photodynamic therapy, which takes advantage of the relative transparency of living tissue to NIR radiation.27 If the NIR absorbance is not permanent but may be switched on by a redox change, then the material is electrochromic and of additional interest in the area of electrooptical switching if the absorbance maximum is close to the energy of the laser source used for optical information transfer. 14,15,28 We are currently attempting to exploit the properties of these complexes in some of these areas. Experimental The complexes 1–6,4 10,14 and [Mo(TpMe,Me)(O)Cl2] 6 were prepared according to the published methods.The ligands 4,4 - dihydroxydiphenylmethane (for 7), 4,4 -thiodiphenol (for 8 and 8a) and 4,4 -sulfonyldiphenol (for 9 and 9a) were purchased from Aldrich and used as received. Spectroelectrochemical measurements were performed at 30 C in CH2Cl2, using a home-built OTTLE (optically transparent thin layer electrode) cell mounted in the sample compartment of a Perkin-Elmer Lambda 19 UV/VIS/NIR spectrometer; the details have been published elsewhere.13 For all redox interconversions studied clean isosbestic points were observed except where explicitly stated otherwise, and the chemical reversibility of these processes was established by returning to the starting state and checking that the spectrum had not changed.ZINDO Calculations were performed on a CAChe workstation.29 Preparations Complexes 7–9 were prepared according to the usual method.4 A mixture of the appropriate bridging ligand, 2.2 equivalents of [Mo(TpMe,Me)(O)Cl2] and dry Et3N (0.5 cm3, excess) was heated to re.ux in dry toluene under N2 for 8 h.After removal of the solvent in vacuo the solid residue was puri.ed by column chromatography on silica using CH2Cl2 as eluent; the desired dinuclear complex was in every case the .rst intensely coloured band to elute. Following chromatographic isolation of 8 and 9, their mononuclear analogues 8a and 9a were also isolated; these are slower-running fractions due to the polarity arising from their pendant hydroxyl groups. Yield and characterisation data are summarised in Table 1.Complex 11 was prepared from a mixture of [Mo- (TpMe,Me)(O)Cl2] (0.20 g, 0.41 mmol) and 4-methoxyphenol (0.062 g, 0.50 mmol) in dry toluene (20 cm3) containing dry Et3N (0.5 cm3). The mixture was heated to 100 C with stirring for 3 h under N2 then cooled and the solvent removed in vacuo.The resulting solid was puri.ed by column chromatography on silica gel using CH2Cl2–hexane (1 : 1, v/v), with the obvi-J. Chem. Soc., Dalton Trans., 1999, 2417¡V2426 2425Table 6 Crystallographic data for complexes 8a and 8a8a 8CH2Cl20.5C6H14FormulaMSystem, space groupa/b/c/£\/£]/£^/U/3ZDc/g cm3/mm1Crystal size/mmReections collected:total, independent, RintData, restraints, parametersFinal R1, wR2 aLargest residuals/e 3C27H31BClMoN6O3S661.84Monoclinic, P21/c13.581(2)17.475(3)12.663(1)104.772(7)2905.9(7)41.5130.6550.45 ¡Ñ 0.2 ¡Ñ 0.229491, 6675, 0.02546675, 0, 3900.0459, 0.10430.571, 1.008C46H61B2Cl4Mo2N12O4S1233.43Triclinic, P110.8807(12)15.5555(13)16.969(3)80.708(10)79.243(14)76.397(7)2721.7(6)21.5050.7490.4 ¡Ñ 0.3 ¡Ñ 0.328471, 12324, 0.032312321, 3, 6960.0507, 0.16480.784, 1.511a Structure was rened on Fo2 using all data; the values of R1 is given for comparison with older renements based on Fo with a typical threshold ofF 4£m(F).ous principal dark coloured fraction being collected ineach case.Yield and characterisation data are summarised inTable 1.X-Ray crystallographyCrystals of complexes 8a and 8CH2Cl20.5C6H14 were grownby slow diusion of hexane in to concentrated CH2Cl2 solutionsof the complexes. Suitable crystals were mounted on aSiemens SMART diractometer in a stream of cold N2 at100 C. A detailed experimental description of the methodsused for data collection and integration using the SMART systemhas been published.30 Data were collected to 2£cmax = 55 at100 C using graphite-monochromatised Mo-K£\ X-radiation(£f 0.71073 ), and after integration of the data and mergingof equivalent reections were absorption-corrected usingSADABS.31 Details of the crystal parameters, data collectionand renement are summarised in Table 6.The structures weresolved by conventional or direct methods, and rened bythe full-matrix least-squares method using all F2 data, using theSHELX suite of programs.32 All non-hydrogen atoms wererened with anisotropic thermal parameters; hydrogen atomswere included in calculated positions and rened with isotropicthermal parameters riding on those of the parent atom.In both structures disorder between the oxo and chloride ligandsattached to each metal site was observed.For complex 8athese atoms were rened with site occupancies of 50% for thetwo components. For 8CH2Cl20.5C6H14 the extent of disorderappeared to be slightly dierent at Mo(1) and Mo(2).ThusO(1) and Cl(1) [attached to Mo(1)] were rened with site occupanciesof 44 and 56% for their two orientations; for O(2) andCl(2) [attached to Mo(2)] the site occupancies were 59 and 41%.The unit cell of this structure also contains a hexane moleculeastride an inversion centre, such that three carbon atoms arepresent in the asymmetric unit.CCDC reference number 186/1491.See http://www.rsc.org/suppdata/dt/1999/2417/ for crystallogrpahicles in .cif format.AcknowledgementsThe following agencies are thanked for nancial support:EPSRC (UK), the Croucher foundation (Hong Kong), and theEuropean Community TMR Network programme (contractno.EC-CHRX-CT96-0047).References1 J. A. McCleverty and M. D. Ward, Acc. Chem. Res., 1998, 31, 842.2 M. D. Ward, Chem. Soc. Rev., 1995, 121; Chem. Ind. (London), 1996,568.3 Some representative recent examples: J.-M. Tour, M. Kozaki andJ. M.Seminario, J. Am. Chem. Soc., 1998, 120, 8486; S. Anderson,R. T. Aplin, T. D. W. Claridge, T. Goodson, A. C. Maciel,G. Rumbles, J. F. Ryan and H. L. Anderson, J. Chem. Soc., PerkinTrans. 1, 1998, 2383; A. P. H. J. Schenning, R. E. Martin, M. Ito,F. Diederich, C. Boudon, J.-P. Gisselbrecht and M. Gross, Chem.Commun., 1998, 1013; A. Harriman and R. Ziessel, Coord. Chem.Rev., 1998, 171, 331; I. Jestin, P. Frere, P. Blanchard and J. Roncali,Angew. Chem., Int. Ed. Engl., 1998, 37, 942; R.D. Adams,T. Barnard, A. Rawlett and J.-M. Tour, Eur. J. Inorg. Chem., 1998,429; S. N. Yaliraki and M. A. Ratner, J. Chem. Phys., 1998, 109,5036; B. W. Jiang, S. W. Yang, S. L. Bailey, L. G. Hermans, R. A.Niver, M. A. Bolcar and W. E. Jones, Coord. Chem. Rev., 1998, 171,365; L. Jaquinod, O. Siri, R. G. Khoury and K. M. Smith, Chem.Commun., 1998, 1261.4 V. A. Ung, D. A. Bardwell, J. C. Jeery, J. P. Maher, J. A.McCleverty, M. D. Ward and A. Williamson, Inorg. Chem., 1996,35, 5290.5 V.A. Ung, A. M. W. Cargill Thompson, D. A. Bardwell,D. Gatteschi, J. C. Jeery, J. A. McCleverty, F. Totti and M. D.Ward, Inorg. Chem., 1997, 36, 3447.6 W. E. Cleland, Jr., K. M. Barhhart, K. Yamanouchi, D. Collison,F. E. Mabbs, R. B. Ortega and J. H. Enemark, Inorg. Chem., 1987,26, 1017.7 W. Bruns, W. Kaim, E. Waldhr and M. Krejcik, Inorg. Chem., 1995,34, 663; M. Ketterle, J. Fiedler and W. Kaim, Chem. Commun., 1998,1701.8 A. Wlodarczyk, G. A. Doyle, J. P. Maher, J.A. McCleverty andM. D. Ward, Chem. Commun., 1997, 769.9 K. Takahashi, A. Gunji, K. Yamagi and M. Miki, J. Org. Chem.,1996, 61, 4784; K. Takahashi, T. Suzuki, K. Akiyama, Y. Ikegamiand Y. Fukazawa, J. Am. Chem. Soc., 1991, 113, 4576.10 W. J. Detroit and H. Hart, J. Am. Chem. Soc., 1952, 74, 5215;O. B. Lantratova, A. I. Prokof¡¦ev, I. V. Khudyakov, V. A. Kuzminand I. F. Pokrovskaya, Nouv. J. Chim., 1982, 6, 365.11 R. West, J. A. Jorgensen, K. L. Stearley and J. C. Calabrese, J.Chem.Soc., Chem. Commun., 1991, 1234; P. Boldt, D. Bruhnke, F. Gerson,M. Scholz, P. G. Jones and F. Br, Helv. Chim. Acta, 1993, 76,1739.12 A. Rebmann, J. Zhou, P. Schuler, H. B. Stegmann and A. Rieker,J. Chem. Res. (M), 1996, 1765.13 S.-M. Lee, R. Kowallick, M. Marcaccio, J. A. McCleverty andM. D. Ward, J. Chem. Soc., Dalton Trans., 1998, 3443.14 S.-M. Lee, M. Marcaccio, J. A. McCleverty and M. D. Ward, Chem.Mater., 1998, 10, 3272.15 A. M. Barthram, R. L. Cleary, R. Kowallick and M.D. Ward,Chem. Commun., 1998, 2695.2426 J. Chem. Soc., Dalton Trans., 1999, 2417–2426 16 A. M. Barthram, R. L. Cleary, J. C. Je.ery, S. M. Couchman and M. D. Ward, Inorg. Chim. Acta, 1998, 267, 1; L. F. Joulié, E. Schatz, M. D. Ward, F. Weber and L. J. Yellowlees, J. Chem. Soc., Dalton Trans., 1994, 799. 17 T. E. Keyes, R. J. Forster, P. M. Jayaweera, C. G. Coates, J. J. McGarvey and J. G. Vos, Inorg. Chem., 1998, 37, 5925. 18 V. A. Ung, S. M. Couchman, J. C. Je.ery, J. A. McCleverty, M. D. Ward, F. Totti and D. Gatteschi, Inorg. Chem., 1999, 38, 365. 19 S. M. Charsley, C. J. Jones, J. A. McCleverty, B. D. Neaves and S. J. Reynolds, J. Chem. Soc., Dalton Trans., 1998, 301. 20 H. Fischer, G. Tom and H. Taube, J. Am. Chem. Soc., 1976, 98, 5512. 21 I. de S. Moreira and D. W. Franco, Inorg. Chem., 1994, 33, 1607; J. Chem. Soc., Chem. Commun., 1992, 450. 22 D. A. Bardwell, D. Black, J. C. Je.ery, E. Schatz and M. D. Ward, J. Chem. Soc., Dalton Trans., 1993, 2321; G. K. Lahiri, S. Bhattacharya, B. K. Ghosh and A. Chakravorty, Inorg. Chem., 1987, 26, 4324. 23 U. T. Mueller-Westerhof, B. Vance and D. I. Yoon, Tetrahedron, 1991, 47, 909; F. Bigoli, P. Deplano, M. L. Mercuri, M. A. Pellinghelli, G. Pintus, E. F. Trogu, G. Zonnedda, H. H. Wang and J. M. Williams, Inorg. Chim. Acta, 1998, 273, 175; H. Shiozaki, H. Kakazumi, Y. Nakado and T. Kitao, Chem. Lett., 1987, 2393; J. A. McCleverty, Prog. Inorg. Chem., 1968, 1049. 24 J. Mayer and R. Krasiunkianis, J. Chem. Soc., Faraday Trans., 1991, 2943; P. S. Rao and E. Hayon, J. Phys. Chem., 1973, 77, 2274; R. H. Schuler, G. N. R. Tripathi, M. F. Prebenda and D. M. Chipman, J. Phys. Chem., 1983, 87, 5357. 25 E. A. Braude, J. Chem. Soc., 1945, 490; A. Kuboyama, S. Matsuzaki, H. Takagi and H. Arano, Bull. Chem. Soc. Jpn., 1974, 47, 1604. 26 V. J. Eaton and D. Steele, J. Chem. Soc., Faraday Trans. 2, 1973, 1601. 27 M. Emmelius, G. Pawlowski and H. W. Vollmann, Angew. Chem., Int. Ed. Engl., 1989, 28, 1445; J. Fabian and R. Zahradnik, Angew. Chem., Int. Ed. Engl., 1989, 28, 677; J. Fabian, H. Nakazumi and M. Matsuoka, Chem. Rev., 1992, 92, 1197. 28 M. D. Ward, Chem. Ind., 1997, 640; K. Yoshida, N. Oga, M. Kadota, Y. Ogasahara and Y. Kubo, J. Chem. Soc., Chem. Commun., 1992, 1114; Y. Kubo, J. Chem. Soc., Perkin Trans. 1, 1994, 2521. 29 ZINDO version 4.0.2 in the CAChe system, Oxford Molecular, Oxford, 1998. 30 P. L. Jones, A. J. Amoroso, J. C. Je.ery, J. A. McCleverty, E. Psillakis, L. H. Rees and M. D. Ward, Inorg. Chem., 1997, 36, 10. 31 SADABS, A program for absorption corrections using the Siemens SMART di.ractometer system, G. M. Sheldrick, University of Göttingen, 1996. 32 SHELXTL 5.03 program system, Siemens Analytical X-Ray Instruments, Madison, WI, 1995. Paper 9/03841H

ISSN:1477-9226    

DOI:10.1039/a903841h

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTONFULL PAPERJ. Chem. Soc., Dalton Trans., 1999, 2427¡V2432 2427Complexation of aluminium(III) with 3-hydroxy-2(1H)-pyridinone.Solution state study and crystal structure of tris(3-hydroxy-2(1H)-pyridinonato)aluminium(III)Valerio B. Di Marco,a G. Giorgio Bombi,*a Andrea Tapparo,b Annie K. Powell c andChristopher E. Anson ca Universit degli Studi di Padova, Dipartimento di Chimica Inorganica,Metallorganica ed Analitica, via Marzolo 1, 35131 Padova, Italy. E-mail: g.g.bombi@unipd.itb Universit degli Studi di Sassari, Dipartimento di Chimica, via Vienna 2, 07100 Sassari, Italyc School of Chemical Sciences, University of East Anglia, Norwich, UK NR4 7TJReceived 15th April 1999, Accepted 11th June 1999The formation of complexes between aluminium() and 3-hydroxy-2(1H)-pyridinone (HL) in aqueous 0.6 m (Na)Clat 25 C has been investigated by means of potentiometric titrations.The following complex stability constantshave been evaluated (pKa = 8.590 ¡Ó 0.008): log £]AlL = 8.59 ¡Ó 0.01, log £]AlL2 = 16.34 ¡Ó 0.03, log £]AlL3 = 23.11 ¡Ó 0.05,log £]AlL3H1 = 13.85 ¡Ó 0.04.The qualitative and quantitative results obtained have been conrmed in part by UVspectrophotometry and 1H NMR spectroscopy. Some potentiometric titrations were executed at 37 C as well, andthe following stability constants were obtained (pKa = 8.452 ¡Ó 0.004): log £]AlL = 8.19 ¡Ó 0.02, log £]AlL2 = 16.03 ¡Ó 0.04,log £]AlL3 = 21.77 ¡Ó 0.08, and log £]AlL3H1 = 13.0 ¡Ó 0.2.Crystals of the complex AlL3 were obtained and analysed byX-ray diraction. The neutral species is an octahedral six-co-ordinate complex with the ligand chelating in abidentate fashion through the pyridinone oxygen and the deprotonated hydroxylic group.IntroductionOver the last 20¡V30 years the mainstay of aluminium (and iron)chelation therapy has been Desferal (desferrioxamine mesylate).1 Despite its good prognosis the general use of Desferal isrestricted because of its several drawbacks and toxic sideeects.1,2 For this reason, a number of chelators have beentested in vitro and in animals for the replacement of Desferalwith a more suitable chelating drug;1¡V4 these studies necessarilyhave to be accompanied by accurate chemical investigations,in order to determine the thermodynamic and kinetic propertiesof likely compounds of the metal under physiologicalconditions.Hydroxypyridinones have been extensively tested, and sometimesalso used, as alternatives to Desferal.1,2 For somecompounds of this class, especially for 1,2-dialkyl-3-hydroxy-4(1H)-pyridinones, much thermodynamic data for aluminiumcomplexes in aqueous solutions have been collected,5,6 whereasfor other ligands, like 3-hydroxy-2(1H)-pyridinones, whichare not used to the same extent as the 3-hydroxy-4(1H)-pyridinones,1,7 these studies are less systematic.7In the present study the stability constants for aluminiumcomplexes of 3-hydroxy-2(1H)-pyridinone, hereafter namedHL, have been determined.The thermodynamic properties ofits aluminium complexes in aqueous solutions have not yet beenexamined. The study has been conducted at 25 C, in order toallow the direct comparison with thermodynamic data for otherhydroxypyridinones evaluated at this temperature, and at 37 Cto investigate how the stability constants vary with temperatureunder physiological conditions. The results obtained frompotentiometric measurements at 25 C have been checked usingtwo independent techniques, UV spectrophotometry and NMRspectroscopy; in the case of the complex AlL3, solid-state data(elemental analysis and X-ray diraction) were also obtained.N HO HOHLExperimentalApparatus, reagents and measurement methods were similarto those reported previously,8 and the following summaryindicates where details dier.ApparatusPotentiometric measurements were performed with a RadiometerABU93 Triburette apparatus equipped with 1, 5 and10 mL burettes and with two independent potentiometricchannels. The UV spectra were recorded with a Perkin-ElmerLambda 5 instrument and 1H NMR spectra with Bruker 200AC and AM 400 spectrometers.ReagentsAll analyte concentrations were expressed in the molality scale(mol kg1 of water).For the potentiometric titrations, standardsolutions of HCl (ca. 0.1 m), AlCl3 (ca. 0.05 m), NaOH (ca.0.1 m) and ligand were used; 3-hydroxy-2(1H)-pyridinone(Acros, nominal purity 98%) was used as received to prepare a0.009 m (0.01 m HCl) working solution.Solutions for UV and1H NMR measurements were prepared by dissolving in water(H2O and D2O, respectively) the correct amounts of the ligandand/or AlCl3.Potentiometric measurementsThe measurements were carried out in a 200 mL water-jacketedcell, and duplicate potentiometric measurements obtainedby using an Ag¡VAgCl¡V3 M KCl reference electrode (BDH309/1030/06) and two dierent glass electrodes (RadiometerpHG201 and BDH 309/1015/02); titrations were executed at25.00 ¡Ó 0.05 and at 37.00 ¡Ó 0.05 C in aqueous 0.6 m (Na)Cl.Titrations of the ligand in the absence of AlIII wereperformed to determine its acid¡Vbase properties and to checkits exact titre.Ligand concentrations ranged from 1.90 ¡Ñ 104to 2.21 ¡Ñ 103 m; the pH range was from 2.5 to 11.In the titrations in the presence of both ligand and AlIII,concentrations ranged from 2.82 ¡Ñ 104 to 2.78 ¡Ñ 103 m for the2428 J. Chem. Soc., Dalton Trans., 1999, 2427.2432 ligand and from 1.68 ¡¿ 10 4 to 1.29 ¡¿ 10 3 m for the metal; the ligand : metal ratio varied from 8: 1 to 1 : 2; the pH range was from 2.5 to 11.The potentiometric study of aqueous solutions containing aluminium and HL has been partially complicated by the low water solubility of the neutral AlL3 complex, which precipitates at pH . 4.5.6.5, depending on the initial aluminium and ligand concentrations, and redissolves at pH > 9. To avoid the presence of solid, titrations had to be stopped at acidic or slightly acidic pH values; otherwise they had to be performed at a concentration of aluminium lower than the solubility of AlL3 (ca. 2 ¡¿ 10 4 m). The ligand protonation constants and the metal.ligand complex stability constants were calculated using the computer program PITMAP.9 The values of the formation constants of aluminium hydroxo-complexes at 25 C and in 0.6 M NaCl have been taken from the literature 10 and were held constant during data optimisation.UV measurements Spectra were collected at various pH values at 25 C for solutions containing aluminium (ca. 10 2 m), ligand (ca. 10 3 m) and 0.6 m (Na)Cl; the concentrations of AlIII and ligand and the pH interval were chosen so that only two absorbing species, AlL and HL (charges omitted), were present in solution at signi.cant concentrations, as predicted from the equilibrium constants previously obtained from potentiometric data; under these conditions only the equilibrium (1) needs to be HL Al AlL H K = [AlL][H]/[HL][Al] (1) considered.The absorbance di.erence between AlL and HL is su.ciently large in the wavelength range 200.325 nm to allow the value of K to be determined by .tting the experimental points (absorbances vs. pH at a given wavelength) by the theoretical equation obtained by combining the above mass-law expression with the mass balance equations for the metal and the ligand; the only unknown parameters of the equation are the equilibrium constant K and the absorption coe.cients of HL and AlL. 1H NMR measurements Spectra were obtained for D2O solutions containing the ligand alone (10 2 m) and for these also containing aluminium (3 ¡¿ 10 3 m) at various pH values at 25 C. Only the spectrum at the neutral pH value was obtained with a 400 MHz instrument (instead of 200 MHz) in order to allow the detection of the species AlL3; in this case, after the addition of the ligand and the metal and the adjustment of the pH value, a brown precipitate was formed; the NMR spectrum of this solution was collected after .ltration and a subsequent small addition of D2O in order to prevent further precipitation during the measurement.In all cases the pH readings were corrected by adding 0.41 pH units 11 to allow for isotopic and solvent e.ects caused by the substitution of normal water (calibration environment) with heavy water (measurement environment). Preparation of solid AlL3 The compound HL (3 mmol), 3 mmol of KOH (Fluka) and 1 mmol of Al(NO3)3 9H2O (Prolabo) were dissolved in 50 mL of water at 60 C (pH . 4) under moderate stirring. The hazel-brown powder obtained from the solution was washed with water and dried under vacuum (269 mg, 75%). Elemental analysis (expected value): C, 48.52 (50.43%); H, 3.58 (3.39%); N, 11.59 (11.76%). From this raw material useful crystals for XRD analysis could not be obtained. The crystallisation of AlL3 was therefore performed in a di.erent way.Compound HL (3 mmol) and 1 mmol of AlCl3 6H2O were dissolved in 50 mL water at room temperature; this acidic solution (pH . 2) was brought to pH . 10 using NaOH. The slow neutralisation of this clear, brown solution by atmospheric CO2 (about one month, room temperature) gave the complex in the form of brown crystals. No elemental analysis could be done on these crystals due to their small quantity. Crystal analysis Crystal data were collected on a Rigaku/MSC Raxis II imaging plate system (Mo-K¥á, ¥ë = 0.71073 A) on a single crystal of ca. 0.3 ¡¿ 0.3 ¡¿ 0.3 mm in size. Some experimental details are reported in Table 4. CCDC reference number 186/1514. See http://www.rsc.org/suppdata/dt/1999/2427/ for crystallographic .les in .cif format. Results and discussion Potentiometric results As a check of the accuracy of the whole experimental system the pKw value for water in 0.6 m (Na)Cl was computed from HCl NaOH titrations at 25 C.The value obtained from seven experiments (pKw = 13.714 ¡¾ 0.002) compares well with the literature value 12 in 0.6 M NaCl at 25 C (13.727 ¡¾ 0.001). A value for pKw has also been obtained at 37 C from twelve experiments (13.352 ¡¾ 0.002), which is in a good agreement with the calculated value, 13.355, obtained from tabulated values of pKw and .H0 at 25 C13 by applying the van¡�t Ho. equation. The pKa values of free HL at the two investigated temperatures are given in Table 1, together with other thermodynamic parameters; the deprotonation occurs at the phenolic oxygen.14 Reasonable similar pKa values are reported in the literature [8.694 ¡¾ 0.007 in 0.1 M KCl at 25 C,14 9.00 ¡¾ 0.01 at 20 C (ionic strength not speci.ed),15 8.66 ¡¾ 0.01 at 25 C and ionic strength 0.1 M 16].The deprotonation of the oxy-group, i.e. of the species H2L , has occasionally been detected (pKa about 0.1.0.2 14,15); the deprotonation of the species L at the pyridinic nitrogen, which has a signi.cant amidic character, is not measurable in water 14 (pKa > 13).In the present study of metal.ligand complexes, the interpretation of potentiometric data was started by plotting n. L,M vs. log[L] curves. If predominantly mononuclear AlLn complexes are formed in solution the quantity n. L,M is the average number of L co-ordinated per Al3 ,17 and the n. L,M curves are coincident. This was found in the present case (Fig. 1), with a limiting value of n.L,M larger than 2, even if, at low n. L,M values, some small di.erences of the curves could support the existence of other, protonated or polynuclear, species. It was noticed that these di.erences are not correlated to modi.cations either of aluminium and ligand concentration or of their ratio, i.e. they seem to be only due to experimental uncertainties. In any case, the experimental low-pH data were carefully reanalysed, see later. The complete computer treatment of experimental titration data gives the stoichiometries and stability constants of the aluminium.ligand complexes reported in Table 2.Table 1 Acidic properties of HL in aqueous 0.6 m NaCl at 25 and 37 C; .G = 49.03 ¡¾ 0.05 kJ mol 1, .H = 20 ¡¾ 2 kJ mol 1, .S = 97 ¡¾ 6 J mol 1 at 25 C 25 C 37 C pKa n pKa n 8.590 ¡¾ 0.008 22 8.452 ¡¾ 0.004 24 a n is the number of titrations from which the data were obtained; the reported uncertainty is the standard deviation of the mean calculated from the n results.J. Chem.Soc., Dalton Trans., 1999, 2427�C2432 2429 The logarithmic distribution diagram of most important aluminium species at concentrations typical for the potentiometric measurements is in Fig. 2 (25 C). The main aluminium complexes in solution are AlL, AlL2 and AlL3. An estimate of the solubility product of AlL3 was evaluated from the pAl and pL values obtained from the distribution diagram at the pH value corresponding to the observed start of AlL3 precipitation: pKs (AlL3) = 26.58 ¡À 0.07 (mean of 5 values, 25 C).At an initial aluminium concentration about 2 ¡Á 10 4 m or lower and at ligand : metal ratio 3 : 1 alkaline pH values could be reached without the occurrence of AlL3 or Al(OH)3 precipitation. Under these conditions another species could be detected in solution, AlL3H 1, which is the deprotonation product of AlL3 at the pyridinic nitrogen, with a pKa of 9.26 at 25 C (log ¦Â1,3,0 log ¦Â1,3, 1); this value is reasonable, because for this species there can be a signicant resonance formula which delocalises the positive charge from the nitrogen to the ortho-oxygen.In fact, the pKa of AlL3 is a compromise of the value typical of a pyridinic proton (pKa ¡Ö 5) and that of an amidic proton (pKa > 13). Other possible deprotonation products, like AlLH 1, AlL2H 1, AlL3H 2 and AlL3H 3, could not be detected: in the rst two cases the attachment of another ligand to the metal centre is favoured, whereas formation of last two species is likely to occur only at more alkaline pH values, where however only Al(OH)4 was found to exist.A careful investigation of the experimental low-pH data was Fig. 1 Experimental data from the AlIII�CHL system (25 C) plotted as n¡¥ L,M vs. log [L] curves at various ligand and metal concentrations. also executed, in order to verify whether the observed small dierences in the starting parts of the n¡¥ L,M curves were due to the presence of polynuclear or deprotonated species. No complexes except AlL could be detected.The increase of the temperature (from 25 to 37 C) causes a decrease of the stability constants of all complexes. The H and S values could be obtained from the Van¡�t Ho equation; they are however very imprecise (and not reported in Table 2), because of the small dierence between the two investigated temperatures. UV results The UV spectra for solutions containing known concentrations of aluminium and ligand at various pH values are given in Fig. 3, and the value obtained for log K (reaction (1), see Experimental section) was: 0.00 ¡À 0.05. This value has to be compared with the potentiometric one at 25 C [0.00 ¡À 0.02, obtained by combining pKa (Table 1) with log ¦Â1,1,0 (Table 2)]; the excellent agreement suggests the absence of any bias in the results. 1H NMR results The 1H NMR spectra of D2O solutions containing aluminium and ligand, at various pH values at 25 C, are reported in Fig. 4. In addition to the strong signals of the ¡°free¡± ligand at ¦Ä 7.1�C7.2 and 6.4�C6.55, at pH 2.5 and 2.9 two new groups of peaks at ¦Ä 6.95�C7.1 and at 6.7�C6.85 are observed. These signals (labelled with ¡°1¡± and ¡°2¡± respectively) can be attributed to the pyridinic protons of two (and probably not more than two) complexes, which should be AlL and AlL2 according to the potentiometric data. There are two reasons to attribute peaks ¡°1¡± to AlL and peaks ¡°2¡± to AlL2.(1) In the spectrum at pH 2.9 signal ¡°2¡± becomes more intense with respect to signal ¡°1&as predicted Table 2 Results of potentiometric study of complex formation between Al3 and HL in aqueous 0.6 m NaCl at 25 and 37 C (reactions: m Al3 lL hH AlmLlHh 3m l h 25 C 37 C m,l,h log ¦Â n log ¦Â n 1,1,0 1,2,0 1,3,0 1,3, 1 8.59 ¡À 0.01 16.34 ¡À 0.03 23.11 ¡À 0.05 13.85 ¡À 0.04 26 24 20 6 8.19 ¡À 0.02 16.03 ¡À 0.04 21.77 ¡À 0.08 13.0 ¡À 0.2 9 10 46 Fig. 2 Logarithmic distribution diagram of most important aluminium species in the presence of HL (aqueous 0.6 m NaCl, T = 25 C, [Al]0 = 2 ¡Á 10 4 m, [HL]0 = 10 3 m; pKs of amorphous Al(OH)3 = 10.8, pKs of AlL3 = 26.58).2430 J. Chem. Soc., Dalton Trans., 1999, 2427.2432 by potentiometric results. (2) The peaks labelled with ¡°1¡± are narrow, whereas those labelled with ¡°2¡± are broader; this fact is likely to be caused by the presence of isomers (for AlL there is Fig. 3 The UV spectra for solutions containing aluminium and HL (aqueous 0.6 m NaCl, 25 C, [Al]0 = 9.95 ¡¿ 10 3 m, [HL]0 = 1.80 ¡¿ 10 3 m, pH 1.25, 1.64, 2.00, 2.36, 2.77, 3.11, 3.50 and 3.89); cell length = 0.1 cm. Calculations were performed at ¥ë = 206, 227, 247, 268.5, 300 and 323 nm. Fig. 4 The 1H NMR spectra in D2O, 0.6 m NaCl at 25 C of a solution containing aluminium and HL ([Al]0 = 3 ¡¿ 10 3 m, [HL]0 = 10 2 m, pH 2.5, 2.9 and 6.8 from top to bottom). only one isomer, whereas for AlL2 there can be up to 8 isomers simultaneously present in solution), which are identical in potentiometric titrations, but can be (and in fact they are) di.erent in the NMR analysis.It is also probable that these isomers interchange ligand molecules with slower rates than before, because the peaks of the ¡°free¡± ligand at pH 2.9 are slightly broader than the corresponding ones at pH 2.5. The integration of the signals gives the relative amount of ¡°free¡± and complexed ligand; the values obtained are reported in Table 3 together with the corresponding values calculated from the potentiometric results.The agreement between the two sets of data is reasonably good; the di.erences can be attributed to isotopic and solvent e.ects introduced by using D2O instead of H2O. The analysis of the spectrum at pH 6.8 suggests the presence of only one complex, the signal pattern of which is di.erent from those of AlL and AlL2. According to the potentiometric data this complex should be AlL3.Crystal structure analysis The structure of the complex AlL3 is shown in Fig. 5. Bond distances and interbond angles are reported in Table 5. Initial re.nement with Al(1), O(1) and O(2) anisotropic, and the six atoms of the ring as isotropic carbons, resulted in a lower thermal parameter for atom N(2) than for C(5) (U = 0.0424 and 0.0581 A3). Atoms C(1) and C(6) have very similar thermal parameters, as do C(3) and C(4). Accordingly, the nitrogen atom in the ring is identi.ed as N(2).An attempt to re.ne N(2) and C(5) as partially disordered nitrogen and carbon atoms found no signi.cant evidence for disorder. This is entirely consistent with O(1) being the ketonic oxygen of the parent ligand, with C.O and O.Al distances of 1.285(6) and 1.915(3) A, respectively, and O(2) being derived from the hydroxyl oxygen, with C.O and O.Al distances of 1.317(6) and 1.899(3) A, respectively. The six ring atoms were then re.ned anisotropically.It should be noted that the partial ketonic character of the C(1).O(1) bond was also suggested by comparing the pKa values of AlL3, HL and pyridinic protons (see potentiometric results). Although the acentric space group chosen, R3c, is racemic, with alternate molecules of opposite handedness in each stack (parallel to the c axis), it is a polar space group, and here it is to the polarity of the structure to which the Flack asymmetry parameter refers.With only one aluminium atom as a ¡°heavy¡± atom in the molecule, it was likely Fig. 5 Crystal structure of AlL3. Table 3 Percentages of ¡°free¡± and complexed ligand pH From NMR data From potentiometric results 2.5 2.9 ¡°Free¡± ligand Complexed ligand ¡°Free¡± ligand Complexed ligand 73.7 26.3 66.7 33.3 HL AlL 2AlL2 HL AlL 2AlL2 71.3 28.7 62.1 37.9J. Chem. Soc., Dalton Trans., 1999, 2427–2432 2431 that this structure would prove to be a borderline case as to whether the polarity could be determined reliably.This was indeed the case; the .nal value for ., 0.44(0.51), di.ers from 1 by just under 3s. Inverting the structure inevitably results in a value for . greater than unity. While the polarity of the structure has not quite been established, that chosen is much the more likely. The possible presence of twinning was investigated using the appropriate TWIN and BASF command lines in SHELXTL.18 From an initial value of 0.5, BASF re.ned to zero, suggesting that no twinning was present.The model was further tested with reference to the structure of the analogous iron complex reported by Scarrow et al.,16 in which they assumed complete disorder of the ligands, selecting the space group R3c. The present structure was therefore tested in that space group, but the thermal parameters for some of the atoms became unreasonable. Therefore, in contrast to Scarrow et al., we believe that our aluminium complex crystallises in R3c, with no detectable disorder in the ligand.Conclusion The ligand HL forms very stable complexes with aluminium, and can inhibit the formation of hydroxo-complexes of the metal and the precipitation of Al(OH)3 even at neutral and alkaline pH values. Its high a.nity towards aluminium is due to the signi.cant acidity of the phenolic group and to the high partial negative charge of the chelating oxygens (almost 1). The speciation is relatively simple because only AlLn complexes (n = 1, 2 or 3) and a deprotonation product of AlL3 are formed in aqueous solution.Data obtained at 37 C show a slight reduction of complex stability constants with respect to corresponding values at 25 C; the enthalpic and entropic properties of the complexes cannot however be evaluated from our data, because the temperature interval examined is too narrow. The accuracy of the formation constant values obtained from potentiometric data at 25 C is substantiated by the agreement with the result obtained from UV spectrophotometry regarding AlL and, in some degree, from 1H NMR spectroscopy regarding AlL and AlL2; this agreement indirectly con.rms the whole speciation model. The crystal structure of tris(3-hydroxy-2(1H)-pyridinonato)- aluminium(...) (AlL3) is in agreement with the solution state .ndings; AlL3 crystallises in space group R3c, with no detectable disorder in the ligand.Fig. 6 Aluminium complexation strength, reported as pAl vs.pH, of HL and other similar ligands at 25 C (A = 3-hydroxy-N-methyl- 2-pyridinone in 0.1 M KCl,7 B = 1-hydroxy-2-pyridinone in 0.1 M KCl,20 C = 3-hydroxy-2-methyl-4(1H)-pyridinone in 0.6 M NaCl,6 D = catechol in 0.6 M NaCl 21). As a .nal comment, a comparison between the complexation strength of HL and other hydroxypyridinones can be made. The relative a.nities of the di.erent ligands have been compared by means of pAl plots 19 (pAl = log[Al3 ]) vs. pH at a given ligand and metal concentration (Fig. 6): the greater the value of pAl, the more stable are the corresponding aluminium complexes.Strictly speaking, pAl values reported in Fig. 6 cannot be directly compared, because corresponding thermodynamic data were obtained at di.erent ionic strengths; however, di.erences introduced by changing an ionic medium are usually small and, for our present purpose, negligible. The pAl curves suggest that HL forms weaker complexes than do the other hydroxypyridinones. 1-Hydroxy-2-pyridinone is a stronger aluminium chelator because of the greater acidity of the phenolic group.For 3-hydroxy-N-methyl-2-pyridinone and for 3-hydroxy-2-methyl-4(1H)-pyridinone the higher complexation strength arises from the greater stabilisation of a positive charge on the pyridinic nitrogen, due to the methyl group (inductive stabilising e.ect) and to the larger distance from the positive metal centre (minor inductive destabilising e.ect) respectively.16 Therefore a higher negative charge on the chelating oxygens is allowed, for both ligands.In the case of 3-hydroxy-2-methyl-4(1H)-pyridinone, this “chemical” result veri.es medical tests, which showed that derivatives of 3-hydroxy-4(1H)-pyridinones can be better therapeutic agents against aluminium overload than other hydroxypyridinones. Table 4 Crystal data for AlL3 Empirical formula Formula weight T/K Crystal system Space group a,b/Å c/Å C15H12AlN3O6 357.26 296 ± 2 Rhombohedral R3c 9.6840 ± 0.0014 29.523 ± 0.006 V/Å3 Z Independent re.ections Rint Final R1, wR2 [I > 2s(I)] (all data) 2397.7 ± 0.7 6 705 0.0474 0.0468, 0.1098 0.0434, 0.1211 Table 5 Bond distances (Å) and angles ( ) in AlL3 Al(1)–O(21) Al(1)–O(22) Al(1)–O(1) O(1)–C(1) C(1)–N(2) N(2)–C(3) C(4)–C(5) C(3)–H(3) C(5)–H(5) O(21)–Al(1)–O(2) O(2)–Al(1)–O(22) O(2)–Al(1)–O(11) O(21)–Al(1)–O(1) O(22)–Al(1)–O(1) O(21)–Al(1)–O(12) O(22)–Al(1)–O(11) O(1)–Al(1)–O(12) C(6)–O(2)–Al(1) O(1)–C(1)–C(6) C(3)–N(2)–C(1) C(3)–C(4)–C(5) O(2)–C(6)–C(5) C(5)–C(6)–C(1) N(2)–C(3)–H(3) C(5)–C(4)–H(4) C(4)–C(5)–H(5) 1.899(3) 1.899(3) 1.915(3) 1.285(6) 1.362(6) 1.295(9) 1.538(10) 0.93 0.93 91.40(15) 91.40(15) 170.47(11) 97.08(10) 170.47(10) 170.47(11) 84.08(9) 88.14(14) 112.6(3) 118.0(4) 121.3(5) 122.8(5) 125.8(5) 120.1(5) 119.5(3) 118.6(3) 123.5(3) Al(1)–O(2) Al(1)–O(11) Al(1)–O(12) O(2)–C(6) C(1)–C(6) C(3)–C(4) C(5)–C(6) C(4)–H(4) O(21)–Al(1)–O(21) O(21)–Al(1)–O(11) O(22)–Al(1)–O(11) O(2)–Al(1)–O(1) O(11)–Al(1)–O(1) O(2)–Al(1)–O(12) O(11)–Al(1)–O(12) C(1)–O(1)–Al(1) O(1)–C(1)–N(2) N(2)–C(1)–C(6) C(4)–C(3)–N(2) C(6)–C(5)–C(4) O(2)–C(6)–C(1) C(4)–C(3)–H(3) C(3)–C(4)–H(4) C(6)–C(5)–H(5) 1.899(3) 1.915(3) 1.915(3) 1.317(6) 1.412(5) 1.294(11) 1.355(6) 0.93 91.40(15) 84.08(9) 97.08(10) 84.08(9) 88.14(14) 97.09(10) 88.14(14) 111.1(3) 120.5(4) 121.4(5) 121.1(6) 113.0(5) 114.1(4) 119.5(4) 118.6(4) 123.5 Symmetry transformations used to generate equivalent atoms: 1 x y 1, x 1, z; 2 y 1, x y, z.2432 J.Chem. Soc., Dalton Trans., 1999, 2427–2432 Acknowledgements We would like to thank a referee for helpful comments concerning the crystal structure analysis, Sigrid Wocadlo for X-ray data collection and Italian Consiglio Nazionale delle Ricerche for .nancial support in the framework of the Cooperation Project with Magyar Tudomànyos Akadémia. We also thank the European Science Foundation for a provision of a fellowship to A. T.in 1993, when the collaboration between University of Padova and University of East Anglia began. References 1 G. J. Kontoghiorghes, Analyst (London), 1995, 120, 845. 2 G. J. Kontoghiorghes, Toxicol. Lett., 1995, 80, 1. 3 L. Gra., G. Muller and D. Burnel, Vet. Human Toxicol., 1995, 37, 455. 4 R. A. Yokel, A. K. Datta and E. G. Jackson, J. Pharmol. Exp. Ther., 1991, 257, 100. 5 E. T. Clarke and A. E. Martell, Inorg. Chim. Acta, 1992, 191, 57. 6 D. J. Clevette, W. O. Nelson, A. Nordin, C. Orvig and S. Sjöberg, Inorg. Chem., 1989, 28, 2079. 7 E. T. Clarke and A. E. Martell, Inorg. Chim. Acta, 1992, 196, 185. 8 V. B. Di Marco, A. Tapparo and G. G. Bombi, Ann. Chim. (Rome), 1999, 89, 397. 9 V. B. Di Marco, Ph.D. Thesis, University of Padova, 1998. 10 L. O. Öhman, Inorg. Chem., 1988, 27, 2565. 11 A. K. Covington, M. Paabo, R. A. Robinson and R. G. Bates, Anal. Chem., 1968, 40, 700. 12 S. Sjöberg, Y. Hägglund, A. Nordin and N. Ingri, Marine Chem., 1983, 13, 35. 13 R. C. Weast, D. R. Lide, M. J. Astle and W. H. Beyer (Editors), Handbook of Chemistry and Physics, 70th edn., CRC Press Inc., Boca Raton, FL, 1990. 14 K. E. Curtis and G. F. Atkinson, Can. J. Chem., 1972, 50, 1649. 15 E. Spinner and J. C. B. White, J. Chem. Soc. B, 1966, 991. 16 R. C. Scarrow, P. E. Riley, K. Abu-Dari, D. L. White and K. N. Raymond, Inorg. Chem., 1985, 24, 954. 17 F. J. C. Rossotti and H. Rossotti, The Determination of Stability Constants and Other Equilibrium Constants in Solution, McGraw- Hill Book Company Inc., New York, Toronto, London, 1961. 18 G. M. Sheldrick, SHELXTL PLUS, Siemens Analytical Instruments, Madison, WI, 1990. 19 T. Kiss and E. Farkas, Perspect. Bioinorg. Chem., 1996, 3, 199. 20 Y. J. Lin and A. E. Martell, Inorg. Chim. Acta, 1993, 214, 103. 21 L. O. Öhman and S. Sjöberg, Acta Chem. Scand., 1983, 37, 875. Paper 9/02997D

ISSN:1477-9226    

DOI:10.1039/a902997d

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2433–2440 2433 Experimental and theoretical studies of a triazole ligand and complexes formed with the lanthanides Michael G. B. Drew,*a Michael J. Hudson,a Peter B. Iveson,a Charles Madic b and Mark L. Russell a a Department of Chemistry, University of Reading, Whiteknights, Reading, UK RG6 6AD. E-mail: m.g.b.drew@reading.ac.uk b Commissariat à l’Energie Atomique, Direction du Cycle du Combustible, B.P. 171, 30207, Bagnols-sur-Cèze, Cedex, France Received 9th March 1999, Accepted 9th June 1999 The crystal structure of 2DBTZPH2O [DBTZP = 2,6-bis(5-butyl-1,2,4-triazol-3-yl)pyridine] has been determined and shows a dimeric structure in which two ligands, with di.erent protonation patterns, form four hydrogen bonds with an enclosed water molecule.Several crystal structures have been determined of lanthanide complexes with the corresponding 5-methyl derivative (DMTZP) which cover the lanthanide series.Four di.erent structural types are reported: LaIII forms [La(DMTZP)(NO3)(H2O)5][NO3)2; NdIII, SmIII and TbIII in the .rst part of the lanthanide series form [M(DMTZP)(NO3)3(H2O)] which is crystallographically disordered over a two-fold axis, HoIII forms [Ho(DMTZP)(NO3)3(H2O)], with one monodentate nitrate giving nine co-ordination, while ErIII and YbIII form [M(DMTZP)(NO3)3] complexes which are also nine-co-ordinate. Introduction One possible future scenario in nuclear reprocessing is the conversion or transmutation of the long-lived minor actinides, such as americium, into short-lived isotopes by irradiation with neutrons.1,2 In order to achieve this transmutation it is necessary to separate the trivalent minor actinides from the trivalent lanthanides by solvent extraction, otherwise the lanthanides absorb neutrons e.ectively and hence prevent neutron capture by the transmutable actinides.3 For many years we have been designing and testing ligands for the co-extraction of lanthanides and actinides from nuclear waste and their subsequent separation.4,5 Various oligoamines have been shown selectively to extract actinides in preference to the lanthanides from nitric acid solutions into an organic phase. Particularly useful have been tridentate planar ligands such as 2,2:6,2-terpyridine and 2,4,6-tris(4-tert-butyl-2- pyridyl)-1,3,5-triazine 6 and tetradentate ligands such as tris- [(2-pyridyl)methyl]amine and tris[(2-pyrazinyl)methyl]amine.7 Recently, the triazole ligands 2,6-bis(5-butyl-1,2,4-triazol-3-yl)- pyridine, DBTZP, and 2,6-bis(5-methyl-1,2,4-triazol-3-yl)- pyridine, DMTZP, have been found to have good extraction properties.However, they have remarkable separation properties in synergistic combination with 2-bromohexanoic acid.8 Thus, at concentrations between 0.003 and 0.03 M, DMTZP was able to extract from an aqueous phase containing 0.05 M HNO3 and 0.1 M NH4NO3 into para.nic diluent TPH (hydrogenated tetrapropene) giving AmIII/EuIII separation factors between 41 and 68.The compound DBTZP is an even better extractant and was found to extract from an aqueous phase containing 0.1 M HNO3 and 0.1 M NH4NO3 into TPH to give AmIII/EuIII separation factors up to 150 at low ligand concentrations between 0.014 and 0.055 M.8 We have, therefore, initiated experimental and theoretical studies of these ligands in order to establish why they have these remarkable properties.We wished to establish the stoichiometries of the metal complexes extracted at low acid concentrations with a view to understanding the processes involved and hence to establish the best possible ligands for the An/Ln separations. We have adopted a theoretical and experimental approach to the identi- .cation of these species. Quantum mechanical methods, were used to investigate the conformational preferences of the ligand; in addition we attempted preparation of solid complexes in order to provide evidence for the typical species involved in this type of extraction.Experimental Valeryl chloride (98%), lanthanum nitrate hexahydrate (99.999%), neodymium nitrate hexahydrate (99.9%), samarium nitrate hexahydrate (99.9%), terbium nitrate pentahydrate (99.9%), holmium nitrate pentahydrate (99.9%) and ytterbium nitrate pentahydrate (99.9%) were purchased from Aldrich; DMF (GPR, BDH) was dried over calcium hydride under nitrogen and then distilled under reduced pressure, acetonitrile was dried and stored over 3Å molecular sieves.The NMR spectra were run using a JEOL JNM-EX 400 spectrometer. Microanalyses were carried out by Medac Ltd., Brunel Science Centre and mass spectra were run on a VG autospec machine. Uncorrected melting points were obtained on a Stuart melting point apparatus. Preparation of ligands The ligand DMTZP was prepared according to the literature method.9 The synthesis of DBTZP has not been described in detail previously and we therefore report here the details.The synthetic route is outlined in Scheme 1. Pyridine-2,6- dicarboxamide was prepared from dimethyl pyridine-2,6-2434 J. Chem. Soc., Dalton Trans., 1999, 2433–2440 Scheme 1 dicarboxylate as described previously.10 Its conversion into 2,6-dicyanopyridine was e.ected using a Vilsmeier complex as dehydrating agent.11 The preparation of pyridine-2,6- dicarbohydrazide imide was carried out by treating the cyanide with hydrazine hydrate in the absence of solvent.12 The dicarbohydrazide imide was then converted into DBTZP as follows: 1 g (0.00518 mol) of it was initially suspended in DMF (20 cm3) under a nitrogen atmosphere.After the addition of 2 g of anhydrous sodium hydrogencarbonate the solution was cooled in an ice-bath and valeryl chloride (1.28 cm3, 0.01076 mol dissolved in 12 cm3 DMF) added dropwise with vigorous stirring. The cold solution was stirred for 1 h and during this time the dicarbohydrazide imide gradually dissolved and a yellow solid began to precipitate.After this time the solid divaleryl derivative was .ltered o., washed with a large amount of water and then dried thoroughly under vacuum over calcium chloride. Yield 0.97 g, 52%, mp 186–188 C. Found: C, 55.66; H, 7.48; N, 28.15. C17H27N7O2 requires C, 56.49; H, 7.53; N, 27.13%. 1H NMR (DMSO): d 0.93 (6 H, t), 1.33 (4 H, sex), 1.56 (4 H, qt), 2.19 (1 H, m), 2.61 (1 H, m), 6.95 (4 H, s), 7.84–7.89 (1 H, m), 8.03–8.11 (2 H, m) and 9.77 (2 H, m).Mass spectrum (CI): m/z 362 (MH, 5), 344 (MH H2O, 22) and 326 (M 2H2O, 100%). The most abundant fragment ion indicates that the dicarbohydrazide imide loses two water molecules and cyclises to form 2,6-di(5-butyl-1,2,4-triazol-3-yl) pyridine DBTZP under the conditions used to obtain the mass spectrum. The .nal product DBTZP was formed on heating the divaleryl derivative at 225 C for 1 h in a nitrogen atmosphere.The dark brown solid residue obtained on cooling was dissolved in ethyl acetate–methanol (1 : 2) and then passed through a short silica gel column to remove decomposition products. The solvents were then removed and a white precipitate was obtained in 32% yield, mp 120–125 C. Found: C, 59.64: H, 7.01, N, 28.78. C17H23N7H2O requires C, 59.45; H, 7.34; N, 28.55%. 1H NMR (CDCl3): d 0.80 (6 H, t), 1.32 (4 H, sex), 1.73 (4 H, qt), 2.86 (4 H, t), 7.75–7.87 (1 H, m) and 8.01–8.19 (2 H, m).Crystals suitable for a single crystal X-ray analysis were obtained on dissolution in DMSO and very slow evaporation of the solvent at room temperature. Preparation of metal complexes of DMTZP The salt La(NO3)36H2O (0.060 g, 0.14 mmol) dissolved in 0.5 cm3 CH3CN was added to a vigorously stirred solution of DMTZP (0.030 g, 0.14 mmol) in 0.5 cm3 CH3CN at ca. 50 C. After slow evaporation of almost all the solvent over a period of two weeks crystals suitable for structure determination were obtained.Yield 9 mg, 20% [La(DMTZP)(NO3)(H2O)5][NO3]2 1. Found: C, 20.20; H, 3.34; N, 20.97. C11H21LaN10O14 requires C, 20.13; H, 3.22; N, 21.34%. An additional water molecule was found in the lattice of the crystal used for the structure determination. A solution containing Nd(NO3)36H2O (0.030 g, 0.07 mmol) in 0.5 cm3 CH3CN was added to a stirred solution of DMTZP (0.015 g, 0.07 mmol) in 1 cm3 CH3CN at ca. 50 C. Good quality crystals were formed after standing overnight at room temperature: [Nd(DMTZP)(NO3)3(H2O)]CH3CN2H2O 2a (12 mg, 26%).Found: C, 22.41; H, 2.40; N, 24.12. C13H20- N11NdO12 requires C, 23.40; H, 3.02; N, 23.11%. The corresponding isomorphous complexes of Sm 2b (22%) and Tb 2c (46%) were obtained in the same way. Found: C, 22.25; H, 2.38; N, 23.94. C13H20N11O12Sm requires C, 23.21; H, 3.00; N, 22.90%. Found: C, 23.00; H, 2.46; N, 22.97. C13H20N11O12Tb requires C, 22.92; H, 2.96; N, 22.60%. The salt Ho(NO3)35H2O (0.0305 g, 0.07 mmol) in 1 cm3 CH3CN was added slowly with stirring to DMTZP (0.015 g, 0.07 mmol) in 1 cm3 CH3CN at ca. 50 C. Crystals suitable forJ. Chem. Soc., Dalton Trans., 1999, 2433–2440 2435 X-ray analysis were formed after slow evaporation and standing at room temperature for three days. Yield 13 mg (29%) [Ho- (DMTZP)(NO3)3(H2O)]2H2O 3. The sample sent for analysis indicated the presence of two additional water molecules rather the acetonitrile found in the crystal structure.Found: C, 20.42; H, 2.52; N, 21.93. C11H17HoN10O12 requires C, 20.44; H, 2.65; N, 21.67%. A solution containing Yb(NO3)35H2O (0.062 g 0.14 mmol) in 2 cm3 CH3CN was added to a stirred solution containing DMTZP (0.030 g, 0.14 mmol) in 3 cm3 CH3CN at ca. 50 C. Crystals suitable for X-ray crystallography appeared after only 2 min at room temperature: [Yb(DMTZP)(NO3)3]CH3CN 4, yield 19 mg, 21%. Found: C, 24.00; H, 2.21; N, 23.61. C13H14N11O9Yb requires C, 24.35; H, 2.20; N, 24.01%.Crystallography The structure of the DBTZP as a demihydrate, 2DBTZPH2O, was determined together with those of 6 metal complexes of DMTZP, viz [La(DMTZP)(NO3)(H2O)5][NO3]2H2O 1, [M(DMTZP)(NO3)3(H2O)]CH3CN2H2O (M = Nd 2a, Sm 2b or Tb 2c) [Ho(DMTZP)(NO3)3(H2O)]CH3CN 3, and [Yb(DMTZP)(NO3)3]CH3CN 4. Crystal data are given in Table 1 together with re.nement details. Data for all 7 crystals were collected with Mo-Ka radiation using the MARresearch Image Plate System.The crystals were positioned at 70 mm from the Image Plate. Ninety .ve frames were measured at 2 intervals with a counting time of 2 min. Data analysis was carried out with the XDS program.13 Default re.nement details are described here while di.erences for speci.c structures are included below. Structures were solved using direct methods with the SHELXS 86 program.14 All non-hydrogen atoms were re.ned anisotropically. Hydrogen atoms on the carbon atoms and nitrogen atoms were included in calculated positions and given thermal parameters equivalent to 1.2 times those of the atom to which they were attached.Hydrogen atoms on water molecules were not included. An empirical absorption correction was made for all lanthanide structures using the DIFABS program.15 All structures were re.ned on F 2 till convergence using SHELXL.16 All calculations were carried out on a Silicon Graphics R4000 Workstation at the University of Reading. In the structure of 2DBTZPH2O the ligand has crystallographic C2 symmetry.A hydrogen atom found in a Fourierdi .erence map bonded to N(4) was included with 50% occupancy. Hydrogen atoms bonded to the water molecule or to any other nitrogen atom were not located and not included. The butyl chain was disordered and two sites with constrained dimensions were re.ned for the outermost three carbon atoms. The structure of complex 1 showed some disorder. Two positions were re.ned for each of the methyl groups C(100) and C(300) each with 50% occupancy. The dipositive cation contained only one nitrate.One further ordered nitrate was located in the asymmetric unit while a second was disordered over two sets of positions both close to two-fold axes and were each re.ned with 50% occupancy. The structures of 2a–2c were isomorphous and the metal atoms located on crystallographic two-fold axes. Initially the moiety containing the metal was determined as [M(DMTZP)(NO3)4] but this formulation was subsequently ruled out from unreasonable intramolecular contacts and high thermal parameters for two symmetry related nitrates.A successful structural model was found with a metal complex formulated as [M(DMTZP)(NO3)3(H2O)] with one nitrate and the water molecule disordered over the two-fold axis. This model was consistent with the presence of an acetonitrile solvent molecule also with 50% occupancy that was hydrogen bonded to the disordered water molecule.For 2a, the R value was 0.0611 for the disordered model and 0.0714 for the tetranitrate model, thus con.rming the accuracy of our disordered treatment. There was an additional water molecule in the asymmetric unit given full occupancy. The structures of 3 and 4 were re.ned with the default methodology. Both contained a solvent acetonitrile molecule in the asymmetric unit. Relevant bond lengths in each structure are shown in Table 2. Hydrogen bonds lengths are shown in Table 3.CCDC reference number 186/1507. See http://www.rsc.org/suppdata/dt/1999/2433/ for crystallographic .les in .cif format. Discussion The crystal structure of 2DBTZPH2O is shown in Fig. 1 together with the atomic numbering scheme. The ligand has crystallographic two-fold symmetry and the water molecule which occupies a crystallographic 222 position is also positioned on this axis. The N(4) atoms are mutually cis with the central pyridine nitrogen atom and all four N(4) atoms are 2.94(1) Å from the oxygen atom.The arrangement of the four N(4) nitrogen atoms around the oxygen atom is distorted tetrahedral with angles ranging from 107–112. It seems unlikely that all four would be protonated with hydrogen atoms directed at the water molecule particularly as the latter has two hydrogen atoms of its own that can also form hydrogen bonds. A possible scenario therefore is for the oxygen atom to participate in two acceptor hydrogen bonds and two donor hydrogen bonds.This would be consistent with the fact that two of the .ve-membered rings (possibly in the same molecule but not necessarily so) would have their hydrogen atoms located on N(1) or N(2) rather than N(4). However, the Fourier-di.erence map gives no indication that N(1) or N(2) is protonated, indeed the evidence suggests that N(4) is the only atom protonated. However due to the poor quality of the data this result is not de.nitive. In this structure the two N(4)–C–C–N (py) torsion angles are cis.Quantum mechanics calculations (see below) in the absence of a water molecule show that the order of energies for this conformation, with N(4) atoms cis to the central pyridine nitrogen atom, with proton positions is N(1) < N(4) < N(2). Thus, the results suggest that the scenario proposed above with the protons positioned on N(1) and N(4) in the two ligands is reasonable. These calculations were carried out in the absence of the water molecule and it can easily be envisaged how the con.guration with N(4) protonated can be stabilised by the inclusion of a water molecule and the formation of hydrogen bonds.Of course, the same could be said for the con.guration with N(1) or N(2) protonated but here the stabilisation would come from the donating hydrogen bond to N(4) from the water molecule. As is apparent from Fig. 1, the Fig 1 The structure of 2DBTZPH2O with the atomic numbering scheme.Hydrogen atoms bonded to nitrogen and oxygen are not shown apart from those on N(4) (see text). Ellipsoids at 30% probability.2436 J. Chem. Soc., Dalton Trans., 1999, 2433–2440 hemihydrate structure is stabilised by the butyl chains which encapsulate the dimer. However these chains are disordered and two sets of positions were re.ned for each with occupancy factors of x and 1 x respectively; x re.ned to 0.40(1). The compound DBTZP can potentially bond to a metal in many di.erent ways depending on the conformation of the ligand and which nitrogen atoms co-ordinate.We were unable to prepare any crystals of metal complexes containing this ligand due to solubility problems but instead formed many complexes with the methyl analogue DMTZP and report here the structures of six. In all cases, the ligand co-ordinates to a metal via the two N(4) atoms together with the central pyridine nitrogen atom to form a tridentate chelate. This co-ordination mode was also observed in the corresponding complexes with molecular formulae Fe(DMTZP)2(NO3)24H2O and Ni(DMTZP)2Cl23H2O.9 Co-ordination through the other triazole nitrogen atom is also possible.In bis(2,2-bipyridyl)- (3-methyl-5-pyridin-2-yl-1,2,4-triazole)ruthenium hexa.uorophosphate tetrahydrate the Ru is bound to the N(2) triazole atom.17 The authors suggest that this is the most favoured mode of co-ordination because of steric hindrance caused by the methyl group in the 5 position. Our own structural and molecular modelling studies suggest, however, that this steric hindrance is not a signi.cant factor.The hydrogen atoms, present on N(4) in the “free” ligand, are then to be found on N(1) as shown by Fourier-di.erence maps and established by the pattern of intermolecular hydrogen bonds in all six structures. While these structures contain the DMTZP ligand, there seems no reason why the bonding pattern should be any di.erent in DBTZP. This was con.rmed by modelling studies where the methyl groups of the DBTZP ligand in the crystal structures were replaced by butyl groups and the resulting structures energy-minimised by molecular mechanics.It was found that these butyl groups did not cause any steric crowding and no adjustment of the co-ordination sphere was required. The structure of the [La(DMTZP)(NO3)(H2O)5]2 cation in complex 1 is shown together with the atomic numbering scheme in Fig. 2. Note that in this structure and the other lanthanide complexes the atoms in the .ve-membered rings are numbered N(n1), N(n2), C(n3), N(n4) and C(n5), where n represents the ring number 1 or 3.The central pyridine has a ring number n = 2 and the nitrogen atom is numbered N(21). In 1 the metal atom is bound to the three nitrogen atoms of the DMTZP ligand with distances La–N(14) 2.713(18), La–N(21) 2.774(12), La–N(34) 2.724(17) Å. The remaining distances in the coordination sphere showed La–O (nitrate) distances of 2.60(2) and 2.72(2) Å and La–O (water) distances of 2.563(15)–2.641 (15) Å.The co-ordination number is therefore 10, which is common for lanthanum with predominantly monodentate ligands although higher co-ordination numbers such as 11 and 12 are often found in co-ordination spheres with polydentate ligands. However this cation has an unexpected stoichiometry especially in comparison with that found for the other lanthanides in that only one of the nitrates is bound to the metal.We have carried out extensive structural studies of complexes of the lanthanide elements with a variety of terdentate ligands with nitrate anions and the vast majority of these complexes show the metal bonded to three nitrates to form a neutral species; occasionally cations with two nitrates are found but never before a dication with one nitrate. Search of the Cambridge Crystallographic Database con.rmed that this type of compound is most unusual. This could be due to some special properties of the DMTZP ligand but this seems unlikely because of the other structures presented here.However we have often found in our studies of series of complexes with identical ligands across the lanthanide elements that lanthanum is very often the odd one out producing unique structures, no doubt because of its size and closed shell, although in this case we have been unable to prepare crystals of complexes with the adjacent elements Ce and Pr which might have provided equivalent stoichiometries.The structures of complexes 2a–2c are isomorphous containing [M(DMTZP)(NO3)3(H2O)]CH3CN2H2O. That of 2b (M = Sm) is shown in Fig. 3. The metal atom is bonded to the three nitrogen atoms of the DMTZP ligand, six oxygen atoms from three nitrates and one water molecule making a coordination number of 10. The structure contains a two-fold axis and there is therefore disorder between one nitrate anion O(21), O(22), N(23), O(24) and the water molecule O(200).The dimensions for the three structures are compared in Table 2 and show consistent values with di.erences only due to the decrease in metal size (Nd > Sm > Tb). This result can be compared to the dimensions obtained for nitrogen donor tridentate planar ligands containing three six-membered rings. We have analysed complexes of 2,2:6,2 terpyridine in the Cambridge Crystallographic Database. There were 262 examples of metals bonded to terpyridine.We plotted the di.erence . between the average M–N bond length for the two outer M–N bond lengths and the central bond against the central M–N bond length. We found a good correlation (though 3 outliers were rejected) with r 2 = 0.620. The linear equation is . = 0.163 (M–N) 0.421 thus signifying that below 2.58 Å the outer M–N distance was greater than the inner M–N distance and above 2.58 Å the central M–N distances were the greater. Fig. 2 The structure of complex 1 with the atomic numbering scheme.Ellipsoids at 30% probability. Hydrogen atoms on the water molecules could not be located. Fig. 3 The structure of complex 2b with the atomic numbering scheme. Details as in Fig. 2.J. Chem. Soc., Dalton Trans., 1999, 2433.2440 2437 In all the present triazole structures the outer M.N distances are less than the central M.N distance, while the opposite is the case for the aforementioned nickel and iron structures. It would appear that there are considerable similarities between the bonding pattern in the triazoles and the terpyridines.Though there are not enough examples of the triazoles to be conclusive, it would appear that the change in sign for . (di.erences in bond lengths) occurs at a smaller bond length than in terpyridine. There is a signi.cant amount of intermolecular hydrogen bonding in the isomorphous lattices. The solvent acetonitrile has 50% occupancy and forms a hydrogen bond to O(200) at 2.74(3) (Nd), 2.71(4) (Sm) and 2.78(4) A (Tb).The water molecule forms two donating hydrogen bonds to N(12) and O(34) (2.97, 2.89, Nd; 3.00, 2.88, Sm; 3.00, 2.88 A, Tb) while forming an accepting hydrogen bond from N(11) (2.73(2), Nd; 2.74(2), Sm; and 2.74(2) A, Tb). Extensive intermolecular hydrogen bonding was also observed in the corresponding FeII/ DMTZP complex involving triazole NH, nitrate anions and water molecules. The authors suggested that N.H OH2 hydrogen bonding would increase the acidity of the NH groups which would increase the acidity of the co-ordinating nitrogen atoms and as a result favour the singlet state of FeII.9 The opposite may also be the case because N H2O intermolecular hydrogen bonding is possible and this would result in a decrease in the electron density on the co-ordinating triazole nitrogen atoms.Intermolecular hydrogen bonding involving water molecules, anions and unco-ordinated triazole N atoms was also suggested as a signi.cant factor in the stabilisation of the another Fe/triazole complex.18 The structure of complex 3 is shown in Fig. 4 and is very similar to the type 2 structures (though not isomorphous) except that one of the nitrate anions is monodentate with the Ho O(61) distance 3.76 A. Monodentate nitrates are not common but as is apparent from the Cambridge Crystallographic Database have been observed before in a few lanthanide structures. This structure also shows hydrogen atoms on N(n1) as con.rmed by a similar hydrogen bond pattern to type 2 in that N(11) is hydrogen bonded to a nitrate oxygen O(64) at 2.87(2) A and N(31) to an acetonitrile nitrogen atom at 2.89(2) A.The water molecule O(100) which is co-ordinated to the metal is also hydrogen bonded to O(64) and N(32) in two other molecules. The .nal complex in the series 4 is shown in Fig. 5 and shows a nine-co-ordinate structure with the terdentate ligand and three nitrate ligands bonded to the metal.Hydrogen bonds are also formed here from N(11) to an acetonitrile ligand at 2.91(2) A and N(31) to a nitrate O(62) at 2.87(2) A.¢Ó Fig. 4 The structure of complex 3 with the atomic numbering scheme. Details as in Fig. 2. It is interesting that in both complexes 3 and 4 intermolecular hydrogen bonds are formed to give polymeric one-dimensional chains. In 3 the N(n1).H donor hydrogen bond is formed with a nitrate oxygen O(64) that is not bonded to the metal, while in 4 the bond is formed to O(62), an oxygen atom that is bonded to the metal.In all the other cases the N(n1).H donor hydrogen bond is formed to solvent. Clearly the presence of these hydrogen bond interactions can facilitate the extraction process by forming complex agglomerates. Theoretical structural analysis of DMTZP Our purpose here was to study the energies of the possible structures of the DMTZP ligand. There are three possible conformations for DMTZP which can be characterised by the N(4).C.C.N (py) torsion angles as tt (trans,trans), ct (cis,trans) and cc (cis,cis).In addition there is one hydrogen atom which can theoretically be attached in each .ve-membered ring to any one of the three nitrogen atoms N(1), N(2) or N(4). We made the assumption that the position of the hydrogen atom was equivalent in each of the two .ve-membered rings and this gave nine di.erent possible structures for the DMTZP ligand which are denoted as 1-cc, 1-ct, 1-tt, 2-cc, 2-ct, 2-tt and 4-cc, 4-ct, 4-tt, the number indicating the nitrogen atom to which the proton is attached.If asymmetric models were considered, another 12 possible structures would need to be studied. We have analysed these 9 structures for DMTZP using the GAUSSIAN 94 program.19 Starting models were built using the CERIUS 2 software 20 and the three rings were made approximately coplanar but no symmetry was imposed. Structures were then optimised using the 6-31G** basis set.Results are summarised in Table 4. The lowest energy structure by quite a margin (>6.0 kcal mol 1) was 2-tt. Here the two N(2) atoms are bound to a hydrogen atom while N(1) and N(4) are not, and the structure is stabilised by interactions between the protons and the central nitrogen N(21) of the pyridine ring. A similar stabilisation from intramolecular hydrogen bonds was also found in our study of the terpyridine ligand.5 For the latter (in which no nitrogen atoms are protonated) the trans, trans conformation was favoured but for the diprotonated terpyridine cation (in which the two nitrogen atoms in the outer pyridine rings were protonated) the cis, cis conformation had the lowest energy because Fig. 5 The structure of complex 4 with the atomic numbering scheme. Ellipsoids at 30% probability. ¢Ó The structure of the corresponding erbium complex was found to be isomorphous but the data were not of su.cient quality to report: a = 16.123(17), b = 8.211(11), c = 16.625(14) A, ¥â = 101.69(1), monoclinic, space group P21/n, Z = 4.2438 J. Chem.Soc., Dalton Trans., 1999, 2433–2440 Table 1 Crystal data and structure re.nement for the structures 2DBTZPH2O [LaL(NO3)(H2O)5]- [NO3]2H2O 1 [NdL(NO3)3(H2O)] CH3CN2H2O 2a [SmL(NO3)3(H2O)] CH3CN2H2O 2b [TbL(NO3)3(H2O)] CH3CN2H2O 2c [HoL(NO3)3(H2O)] CH3CN 3 [YbL(NO3)3]CH3- CN 4 Empirical formula Formula weight Crystal system, space group a/Å b/Å c/Å a/ ß/ ./ V/Å3 Z, Dc/Mg m 3 µ/mm 1 Re.ections collected Unique re.ections/R(int) Data/restraints/parameters Final R1, wR2 [I > 2s(I )] (all data) Largest di.erence peak and hole/e Å 3 C34H48N14O 668.86 Orthorhombic, Fddd 11.324(14) 22.00(3) 31.39(4) 7820 8, 1.136 0.073 3114 1209/0.0949 1209/12/112 0.1215, 0.3668 0.1890, 0.4110 0.269, 0.214 C11H23LaN10O15 674.30 Triclinic, P1� 9.830(12) 11.254(14) 13.787(17) 73.96(1) 79.89(1) 67.60(1) 1351 2, 1.658 1.662 3412 3412 3412/12/325 0.1172, 0.3176 0.1263, 0.3220 2.752, 1.544 C13H20N11NdO12 666.64 Monoclinic, C2/c 9.326(9) 29.71(3) 9.895(11) 113.03(1) 2523 4, 1.876 2.135 4158 2293/0.0395 2293/0/162 0.0611, 0.1555 0.0669, 0.1584 1.448, 1.443 C13H20N11O12Sm 672.75 Monoclinic, C2/c 9.353(12) 29.59(3) 9.889(12) 112.95(1) 2521 4, 1.773 2.407 4050 2221/0.0448 2221/0/162 0.0647, 0.1859 0.0759, 0.1914 1.207, 0.970 C13H20N11O12Tb 681.32 Monoclinic, C2/c 9.354(12) 29.40(3) 9.836(12) 112.52(1) 2499 4, 1.811 2.908 3846 2190/0.0353 2190/0/163 0.0618, 0.1668 0.0671, 0.1721 2.767, 1.679 C13H16HoN11O10 651.30 Triclinic, P1� 8.563(9) 11.095(14) 13.346(16) 96.98(1) 98.06(1) 114.60(1) 1118 2, 1.934 3.612 3873 3873 3873/0/320 0.0281, 0.0800 0.0315, 0.0826 1.160, 1.219 C13H14N11O9Yb 641.39 Monoclinic, P21/n 16.102(18) 8.179(10) 16.571(19) 101.69(1) 1244 4, 1.993 4.448 6452 3898/0.0291 3898/0/334 0.0447, 0.1230 0.0614, 0.1344 2.085, 1.573J.Chem. Soc., Dalton Trans., 1999, 2433–2440 2439 of intramolecular hydrogen bonds between the two outer nitrogen atoms and the central nitrogen atom.The other energies listed in Table 4, together with the N(4)–C–C–N(py) torsion angles, show that the presence of the hydrogen atom on N(4) or N(2) ortho to the bridge to the central pyridine ring destabilises the structure when it is adjacent to a C–H bond on the central pyridine ring and torsion angles of 30–40 are found as the rings twist to reduce the steric interactions.Clearly this low energy 2-tt con.guration with N(2) bound to a hydrogen atom is not compatible with metal co-ordination. Although it is of course possible for the two .ve-membered rings to rotate to form the 2-cc con.guration, this would lead to close N–H and C–H contacts. Not surprisingly this con- Table 2 Dimensions (bond lengths in Å, angles in ) in the metal coordination spheres of complexes 1, 2a–2c, 3 and 4 1 La(1)–O(100) La(1)–O(200) La(1)–O(300) La(1)–O(400) La(1)–O(500) 2.563(15) 2.584(15) 2.641(15) 2.586(17) 2.573(17) La(1)–O(51) La(1)–O(52) La(1)–N(14) La(1)–N(34) La(1)–N(21) 2.60(2) 2.72(2) 2.713(18) 2.724(17) 2.774(12) 2a–2c M(1)–O(200) M(1)–O(31) M(1)–O(32) M(1)–O(21) M(1)–O(22) M(1)–N(14) M(1)–N(21) Nd 2.44(2) 2.496(9) 2.568(9) 2.577(15) 2.591(15) 2.629(7) 2.697(9) Sm 2.44(2) 2.470(10) 2.525(10) 2.57(2) 2.588(19) 2.594(10) 2.687(12) Tb 2.38(3) 2.428(9) 2.505(10) 2.540(18) 2.549(18) 2.582(9) 2.626(11) 3 Ho(1)–O(100) Ho(1)–O(51) Ho(1)–O(52) Ho(1)–O(41) Ho(1)–O(42) 2.364(4) 2.458(5) 2.406(4) 2.427(4) 2.455(4) Ho(1)–O(62) Ho(1)–N(14) Ho(1)–N(34) Ho(1)–N(21) 2.392(4) 2.460(4) 2.462(5) 2.518(4) 4 Yb(1)–O(41) Yb(1)–O(42) Yb(1)–O(51) Yb(1)–O(52) Yb(1)–O(61) 2.356(6) 2.433(7) 2.372(7) 2.360(6) 2.451(7) Yb(1)–O(62) Yb(1)–N(14) Yb(1)–N(34) Yb(1)–N(21) 2.407(6) 2.433(7) 2.414(7) 2.479(7) .guration is not observed and for all the metal complexes reported here the 1-cc con.guration is found.This not only presents a tridentate donor set to the metal for binding, but also because the hydrogen atom is positioned on N(1) rather than N(2) there are no close H H contacts with the pyridine ring.In the unco-ordinated ligand all three conformations 1-tt, 1-ct and 1-cc have relatively low energies because of this lack of H H contacts which is con.rmed by the close coplanarity of the three rings so that the torsion angles are all less than 10.0 from planarity. In the (DBTZP)2 hydrate (Fig. 1) the two independent ligands also have the cis, cis conformation found in the metal Table 3 Hydrogen bonds (Å) in the structures 2DBTPZH2O N(14A) O(100) 2.94 N(14B) O(100) 2.94 1 N(11) O(621) N(11) O(612) N(31) O(71) N(31) O(72) O(100) O(700) O(100) O(443) 2.93 3.04 2.81 3.09 2.70 2.78 O(200) O(414) O(200) O(415) O(300) N(121) O(400) O(424) O(400) N(326) 2.74 2.85 2.88 2.90 3.24 Symmetry relations: 1 x, 1 y, 1 z; 2 x, 1 y, z; 3 x, y 1, z; 4 x 1, y, z; 5 x, 1 y, z; 6 1 x, y, 1 z. 2a–2c N(11)–O(1001) N(12)–O(1002) N(100)–O(200) O(100)–O(34) Nd 2.73 2.97 2.74 2.89 Sm 2.74 3.00 2.71 2.88 Tb 2.74 3.00 2.78 2.88 Symmetry relations: 1 x, y, 3– 2 z; 2 x, 1 y, 1– 2 z. 3 O(100) O(644) O(100) N(321) 2.73 2.80 N(11) O(643) N(31) N(1002) 2.87 2.89 Symmetry relations: 1 x, y, z; 2 x, y, z; 3 1 x, 1 y, 1 z; 4 x 1, y, z. 4 N(11) N(1001) 2.91 N(31) O(622) 2.87 Symmetry relations: 1 1– 2 y ½, 1– 2 z; 2 1– 2 x, y 1– 2, z 1– 2.2440 J. Chem. Soc., Dalton Trans., 1999, 2433–2440 complexes. The positions of the protons were not established unequivocally but as detailed above it seems likely that one ligand has the structure 4-cc while the other could also be 4-cc but more likely is 1-cc. As is apparent from Table 4 neither structure (4-cc or 1-cc) has a particularly low energy compared to other con.gurations, but given the presence of the water molecule it is easy to see why these particular con.gurations are favoured in the crystal structure.We have previously shown how the presence of a water molecule in the cavity can stabilise a tridentate planar ligand in the cis, cis conformation.5 Conclusion We have shown that DMTZP (and by analogy DBTZP) forms a consistent series of structures across the lanthanide series with variations in stoichiometry due to the decreasing size of the metals across the series.Lanthanum as is often the case provides the only inconsistency. The reasons for the exceptional extraction properties of this ligand remain unclear. It has been suggested that the basicity of the heterocyclic nitrogen ligand has a big in.uence on the AmIII/LnIII separations.6 A pKa (base) value of 3.40 has been determined for 3-methyl-5-(pyridin-2- yl)-1,2,4-triazole 17 which indicates that this type of ligand has a lower basicity than, for example, pyridine (5.25) 21 and bipyridine (4.45).22 Heterocyclic nitrogen ligands with lower basicities have been shown to give better AmIII/LnIII separations.6 It is also clear that the addition of a weak acid, 2-bromohexanoic acid, is crucial to the ligands extraction performance.8 Therefore, although the solid Ln/DMTZP complexes isolated in this work are likely to give a good indication of the type of species which may be extracting, future work will include solution studies with and without 2-bromohexanoic acid, to establish better the nature of the extracting species in solution.Acknowledgements We are grateful for the .nancial support by the European Union Nuclear Fission Safety Programme Task 2 (Contract Table 4 Results from quantum mechanics calculations on DMTZP. Geometry optimisation was carried out using the 6-31G** basis set; energies in au (= 627.509 kcal mol 1) Structure Energy N(4)–C–C–N (py) torsion angle/ H on N(1) H on N(2) H on N(4) 1-cc 1-ct 1-tt 2-cc 2-ct 2-tt 4-cc 4-ct 4-tt 804.11510 804.11644 804.11763 804.10797 804.12327 804.13301 804.11348 804.10453 804.08451 6.4, 6.4 1.1, 179.8 179.4, 179.7 46.7, 46.7 33.9, 177.6 180.0, 180.0 0.0, 0.0 2.9, 153.9 141.3, 141.3 F141-CT-96-0010).We would also like to thank the EPSRC and the University of Reading for funding of the image-plate system. The use of the Origin 2000 at the University of Reading High Performance Computer Centre (HPCC) is gratefully acknowledged.References 1 J. Tommasi, M. Delpech, J. P. Grouiller and A. Zaetta, Nucl. Technol., 1995, 111, 133. 2 M. Salvatores, A. Zaetta, C. Girard, M. Delpech, I. Slessarev and J. Tommasi, Int. J. Appl. Radiat. Isot., 1995, 46, 681. 3 Z. Kolarik, Separation of Actinides and Long-lived Fission Products from High-level Radioactive Wastes (a review), Kernforschungszentrum, Karlsruhe, 1991. 4 G. Y. S. Chan, M. G. B. Drew, M. J. Hudson, P.B. Iveson, J.-O. Liljenzin, M. Ska° lberg, L. Spjuth and C. Madic, J. Chem. Soc., Dalton Trans., 1997, 649. 5 M. G. B. Drew, M. J. Hudson, P. B. Iveson, M. L. Russell, J.-O. Liljenzin, M. Ska° lberg, L. Spjuth and C. Madic, J. Chem. Soc., Dalton Trans., 1998, 2973. 6 P.-Y. Cordier, C. Hill, P. Baron, C. Madic, M. J. Hudson and J.-O. Liljenzin, J. Alloys Compds, 1998, 271, 738. 7 R. Wietzke, M. Mazzanti, J. M. Latour, J. Pecaut, P.-Y. Cordier and C. Madic, Inorg. Chem., 1998, 37, 6690. 8 Z. Kolarik, U. Müllich and F. Gassner, Ion Exch. Solvent Extr., 1999, 17, 23. 9 K. H. Sugiyarto, D. C. Craig, A. D. Rae and H. A. Goodwin, Aust. J. Chem., 1993, 46, 1269. 10 H. Meyer, Monatsh. Chem., 1903, 24, 207. 11 O. I. Gorbyleva, M. I. Evstratova and L. N. Yakhontov, Chem. Heterocycl. Compd. (Engl. Transl.), 1983, 1133. 12 F. H. Case, J. Heterocycl. Chem., 1971, 8, 1043. 13 W. Kabsch, J. Appl. Crystallogr., 1988, 21, 916. 14 SHELXS 86, G. M. Sheldrick, Acta Crystallogr. Sect. A, 1990, 46, 467. 15 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158. 16 SHELXL, G. M. Sheldrick, program for crystal structure re.nement, University of Göttingen, 1993. 17 B. E. Buchanan, J. G. Vos, M. Kaneko, W. J. M. Van der Putten, J. M. Kelly, R. Hage, R. A. G. de Graa., R. Prins, J. G. Haasnoot and J. Reedijk, J. Chem. Soc., Dalton Trans., 1990, 2425. 18 R. A. G. de Graaf, J. G. Haasnoot, A. M. Van der Kraan, P. de Vaal and J. Reedijk, Inorg. Chem., 1984, 23, 2905. 19 GAUSSIAN 94 (Revision A.1), M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheesman, T. A. Keith, G. A. Peterson, J. A. Montogomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresham, J. Cioslowski, B. B. Stefanov, A. Nanayakkara, M. Challalcombe, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez and J. A. Pople, Gaussian, Inc., Pittsburgh, PA, 1995. 20 CERIUS 2 software, Molecular Simulations Inc., San Diego, CA, 1997. 21 A. G. Boulton and A. McKillop, in Comprehensive Heterocyclic Chemistry, eds. A. R. Katritsky and C. W. Rees, Pergamon, Oxford, 1984, vol. 5. 22 K. Nakamoto, J. Phys. Chem., 1960, 64, 1420. Paper 9/01842E

ISSN:1477-9226    

DOI:10.1039/a901842e

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON PERSPECTIVE J. Chem. Soc., Dalton Trans., 1998, Pages 2437–2443 2437 Structural direction by the dominant metal Michael A. Beswick, Marta E. G. Mosquera and Dominic S. Wright * Chemistry Department, University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW Assessment of the structures of a number of heterometallic alkali metal/p block metal complexes suggests that the p block metals have a dominant role in dictating the structures of these species, since generally greater covalency of the metal–ligand interactions leads to more geometrically rigid metal co-ordination. 1 Introduction We have recently reported the development of a general synthetic strategy for the preparation of a variety of heterometallic alkali metal/p block metal cage complexes involving the stepwise metallation reactions of primary amines and phosphines (REH2; E = N or P) with organoalkali metal reagents, producing [(REH)M]n (M = alkali metal), followed by their deprotonation by various p block metal reagents 1–3 such as Sb(NMe2)3 4 (Scheme 1).Our principal aims in these Scheme 1 R E H H R E M H R E M Y [R¢M] [Y] M= alkali metal, Y= p block source studies have been the preparation of a broad range of species containing a variety of mixed-metal stoichiometries and the investigation of the dependence of the cage structures and mixed-metal stoichiometries on the reaction system employed. A large number of these species have now been synthesized and structurally characterised, containing a broad spectrum of Group 13, 14 and 15/alkali metal compositions, and we are now in an appropriate position to assess the central factors governing the structures of these species.This assessment is of primary importance to us since the imido and phosphinidene p block metal anion fragments of these cages are novel ligand systems and can be used as robust synthons in the targeted design of heterobimetallic complexes.5 The purposes of this perspective are (i) to highlight the fact that it is the p block metal–ligand frameworks (not the alkali metal–ligand frameworks) which largely control the structures of heterometallic p block metal/alkali metal cage compounds of this type, (ii) to clarify the issues concerned in thermodynamic and kinetic control of p block metal/alkali metal cage compounds in general and (iii) to address the issue of whether ‘ring-stacking’ and ‘ring-laddering’ models 6 are appropriate in the prediction or interpretation of structural influences in systems in which metal valence and covalency provide the fundamental structural influences.Dr. Michael A. Beswick was born in Warrington, Cheshire in 1964. He obtained his first degree at Hatfield Polytechnic in 1990 and his Ph.D. at Cambridge University in 1992, under the supervision of Professor the Lord Lewis. After a period of research at the University of Murcia in Spain, with Professor J. Vicente, he returned to Cambridge where he is now a postdoctoral researcher in inorganic chemistry. His principal interests concern cluster and cage compounds of transition and main group metals.Dr. Marta E. G. Mosquera was born in Astorga (León, Spain) in 1969. She obtained her first degree in 1992 at the University of Oviedo. Her Ph.D. research, under the supervision of Professor V. Riera and Dr. J. Ruiz at the University of Oviedo, concerned the chemistry of ruthenium–diphosphinomethanide complexes.She joined the Wright group in Cambridge as a postdoctoral researcher in 1997. Her research focuses on the chemistry of Groups 14 and 15. Dr. Michael A. Beswick Dr. Marta E. G. Mosquera Dr. Dominic S. Wright Dr. Dominic S. Wright was born in Gosport, Hampshire in 1964. He obtained his first degree at Strathclyde University in 1986 and his Ph.D. at Cambridge in 1989, under the supervision of Dr. R. Snaith. After a college research fellowship with Gonville and Caius College, Cambridge, he was appointed to his current position as a lecturer in inorganic chemistry at Cambridge University.He was the recipient of the 1993 RSC Meldola Medal. Current research interests include synthetic and structural studies of p block metal metallocene compounds, metallacyclic p block metal– ligand systems, and heterometallic complexes containing novel metalbased ligand arrangements.2438 J. Chem. Soc., Dalton Trans., 1998, Pages 2437–2443 Fig. 1 Structures of [(Me2N)2Sb3(NCy)4Li] 1, [{Sb2(NCy)4}2Li4] 2 and [{Sb(NCy)3}2Li6]?2Me2NH 3 (top) and imido anion units (bottom) 2 Structural Influences in p Block Metal/Alkali Metal Cages Clearly the outcome of the reactions producing any mixed p block metal/alkali metal cage complex will be highly dependent on the thermodynamic balance between the p block metal– ligand and alkali metal–ligand bond energies.In the case of imido SbIII/Li complexes, all the evidence illustrates that Sb]N bonding dominates the reactions involved.This is witnessed particularly by the formation of alternative imido anions in which the Sb–N frameworks of the antimony precursors are conserved. This point is illustrated in Fig. 1 which depicts the alternative imidoantimony(III) anions formed by the reactions of dimethylamidoantimony(III) reagents with various primary amido or phosphido lithium precursors [Li(REH); E = N or P] and the structures of the heterobimetallic cages resulting. For example, in the reaction of Li1[Sb(HNR)4]2 with Sb(NMe2)3 (1 : 2 equivalents) the (10e) antimony centre of the [Sb(HNR)4]2 anion is preserved in the resulting [(Me2N)2Sb3(NR)4]2 monoanion (e.g.in Li[Sb3(NMe2)2(NR)4] 13b) and in the reaction of the dimer [{Sb(NMe2)(m-NCy)}2] with [(CyNH)Li]n (1:2 equivalents) the Sb2N2 unit is maintained in [{Sb2(NCy)4}2Li4] 2, containing the dianion [Sb2(NCy)4]22.3a The dominance of the antimony(III) frameworks over the outcome of these reactions is also emphasised by the formation of similar complexes of the type [{Sb(ER)3}2Li6],3b, f,g containing [Sb(ER)3]32 trianions (e.g.[{Sb(NCy)3}2Li6]?2Me2NH 3,3b Fig. 1), from a broad range of Li(REH) with Sb(NMe2)3 (3 : 1 equivalents), and by the fact that even where the same organic groups are present the outcome of the reactions is dictated by the reaction sequence [e.g., as in the case of 1, 2 and 3, all of which contain CyN groups (Cy = C6H11)]. Studies of the reactions of heterobimetallic SbIII/Li complexes with metal salts stress the fact that it is the imido antimony(III) monoanion, dianion and trianion units of the cages which are the robust chemical entities.5 Most dramatically, all six of the Li1 cations of the N6Li6 core of [{Sb- (NCy)3}2Li6]?2Me2NH 3 are substituted in the transmetallation reaction with [PbCp2] (Cp = C5H5), giving the heterobimetallic complex [{Sb(NCy)3}2Pb3] 4 (Fig. 2).5a In the reaction of 3 with [KOBut], cleavage of the N6Li6 core occurs (the weaker N]Li bonds being replaced by stronger O]Li interactions), giving the trimetallic cage [{Sb(NCy)3}2Li6]?3KOBut 5 (Fig. 3).5c It should be noted that the lability of the Li]N frameworks is in fact a general feature of all of the imido SbIII/alkali metal cages shown in Fig. 1,5 in which the various imido antimony(III) anions are readily transferred (intact) to a range of main group and transition metal ions, e.g. the reactions of [{Sb2(NCy)4}2- Li4] 2 with Group 11 salts give [{Sb2(NCy)4}2M4] (M = Cu 6 or Ag 7).5b Further evidence of the integrity of the [Sb(ER)3]32 trianions of the [{Sb(ER)3}2Li6] (E = N or P) cages and of the lability of Fig. 2 Conversion of compound 3 into the lead complex [{Sb- (NCy)3}2Pb3] 4J. Chem. Soc., Dalton Trans., 1998, Pages 2437–2443 2439 their E6Li6 cores comes from variable-temperature 7Li NMR studies of the Me2NH-solvated phosphinidene system [{Sb- (PCy)3}2Li6]?6Me2NH 8 in which a binomial septet is observed even at 290 8C (Fig. 4).3e Semiempirical MO calculations suggest that the six Li1 cations are involved in a dynamic ‘carousel’ process by which they are coupled to the six equivalent P centres of the two intact [Sb(PCy)3]32 trianions of the core. Fig. 3 Cage expansion of compound 3 into the trimetallic [{Sb- (NCy)3}2Li6]?3KOBut 5 Fig. 4 Structure of the cage [{Sb(PCy)3}2Li6]?6Me2NH 8 (top), the 7Li NMR spectrum of 8 (298–208 K) and the associated ‘carousel’ process involved (bottom) The dominance of Sb]N bonding over Li]N bonding in these systems allows direct control of the nature of the imidoantimony(III) anions formed and clearly these units will have a direct bearing on the ultimate structures adopted by the heterobimetallic SbIII/alkali metal cages.Although it cannot be taken for granted that the more covalent p block metal– nitrogen bonds will necessarily be stronger than the ionic alkali metal–nitrogen interactions in heterometallic p block metal/ alkali metal cages in general, what is certain is that even where there is a closer match in bond energies than appears to be present in the antimony(III) systems the more covalent p block metal–ligand bonding will always exert the greatest influence over the structures adopted, since such bonding imparts directionality in the surrounding ligand framework.These more rigid geometric requirements will dominate the ionic and largely non-directional alkali metal–ligand interactions and the alkali metals will have generally a minor role in dictating the structure. One consequence of the greater structural influence of the p block metal framework is that the alkali metal–nitrogen frameworks of heterobimetallic imido complexes should be modified at the expense of the more rigid bonding demands of the p block metal.As the diVerence in the metal–ligand bond energies increases greater distortion of the alkali metal–ligand cores is anticipated.Some evidence for this is seen in the structure of the sodium complex [{Sb(NCy)4}2Na4] 9 (Fig. 5).7 In contrast to the lithium analogue (2 in Fig. 1) which has a tetrahedral arrangement of the four Li1 cations at its centre,3a the four Na1 cations of 9 are distorted into a square-planar arrangement. This occurs as a consequence of the strain induced by the complexation of the larger Na1 cations by the [Sb2(NCy)4]22 dianions, the weaker and more flexible Na]N core being modified as a result.It is noticeable here that distortion of the imidoantimony(III) dianions only occurs at the m-N centres and that the pyramidal geometries of the antimony(III) centres are very similar in 2 and 9. There is emerging evidence that the p block metal– heteroatom frameworks have a dominant role over the structures of heterometallic cage complexes in general. In the reactions of primary amidolithiums [Li(RNH)] with Sn(NMe2)2 only the imido tin(II) cubanes [Sn(NR)]4 are isolated.8 For this reason alternative stepwise metallation procedures have to be employed in order to build the desired mixed SnII/alkali metal arrangements.Using the reactions of Li(REH) (E = N or P) with [Sn(NR)]4 9 (employing the cubane as the base) we showed that heterobimetallic systems are accessible. The fragmentation Fig. 5 Structure of [{Sb(NCy)4}2Na4] 92440 J. Chem. Soc., Dalton Trans., 1998, Pages 2437–2443 of the imido tin(II) cubane arrangement of the precursor in these reactions exhibit a dependency on the acidity of the primary amido or phosphido lithium.Thus, all four of the ButN groups of [Sn(NBut)]4 9c are replaced in the reaction with Li(CyPH) (4 : 6 monomer equivalents), giving the metallacyclic cage complex [{Sn2(m-PCy)}2(m-PCy)2(Li?thf)4] 10 (Fig. 6), whereas the reaction of the less acidic Li(C10H7NH) with [Sn(NBut)]4 gives [Li(thf)4][Sn3(NBut)(NC10H7)3] 11 (Fig. 7), in which only three of the ButN groups are eliminated.2a The pattern of reactivity observed for [Sn(NBut)]4 and the structures of the products formed strongly suggest that the products are templated by the comparatively thermodynamically robust imido tin(II) cubane.Similar reactivity is observed for the imidoaluminium cubane [MeAl(NMes)]4 (Mes = 2,4,6-Me3- C6H2),10 the reaction with Li(CyPH) giving [{AlMe(m-PCy)}2- (m-PCy)2(Li?thf)4] 12 (the aluminium analogue of 10).1 Although the direct reactions of Sn(NMe2)2 with primary amido lithiums has been unsuccessful in the preparation of heterobimetallic complexes, we have recently shown that the polynuclear dimethylamido reagent [{Sn(NMes)2}- {Sn(m-NMe2)}2] 138 is more well behaved in this respect.The reaction of the latter with Li(2-MeOC6H4NH) gives the ‘pseudo-ladder’ [{Sn(MesNH)(m-NC6H4OMe-2)}2(Li?2thf)2] 14 (composed of a central [Sn(MesNH)(m-NC6H4OMe-2)}2]22 dianion complex associated with two thf-solvated Li1 cations) (Fig. 8).2b The latter appears to result from the deprotonation of the primary amido lithium by the MesN groups of 13 followed by elimination of Sn(NMe2)2 (Scheme 2).It is highly significant that no remnant of any N]Li framework (beyond that of a monomer) is preserved in 14. Indeed, the structure, which can be regarded as a co-complex between two Li(MesNH) mono- Fig. 6 Structure of [{Sn(m-PCy)}2(m-PCy)2](Li?thf)4] 10 Fig. 7 Structure of [(Li(thf)4][Sn3(ButN)(C10H7N)3] 11 mers and two SnNC6H4OMe-2 monomers, illustrates from a thermodynamic standpoint that the primary amido lithium precursor is dissembled by lithium solvation and as a result of the preference for Sn]N bonding.The Z-shaped profile of the ladder core of 14 arises directing from the typical pyramidal geometry of the tin(II) centres (N]Sn]N ca. 908). This geometry contrasts with the far flatter ladder arrangements typical of amidolithium ladders,6,11 such as [{[Li(C4H4N)]2?tmen}2] 12 and stresses the dominance of Sn]N bonding and tin(II) valence over the structure of 14.The nature of the reaction producing compound 14 obviously has a profound eVect on the stoichiometry of the product since one Sn is eliminated, leading to the observed 2 : 2 ratio of Sn: Li. As with the related imido SbIII/alkali metal cages, the ultimate structures of the heterobimetallic SnII/alkali metal cage adopted is thermodynamically controlled by the relative metal–ligand bond energies involved and by the key influence of tin(II) valence.However, comparison of the structures of the complexes formed by the reactions of primary amido and phosphinidene compounds with [Sn(NBut)]4 10 and 11 2a and [{Sn(NMes)2}{Sn(m-NMe2)}2]2b provides good evidence for our emerging belief that the type and stoichiometry of the basic anion system produced can be influenced by the reaction employed. Another important factor dictating the structures of these heterometallic species is Lewis base solvation.This factor is of Fig. 8 Structure of [{Sn(MesNH)(m-NC6H4OMe-2)}2(Li?2thf)2] 14 Scheme 2 (i) 12[Li(2-MeOC6H4NH)], thf, 2Sn(NMe2)2 N Sn N Sn N Sn N R R Me Me Me Me Sn N Sn N Li N Li N R' R' R R thf thf thf thf H H 3 Sn(NMe2)2 + 2 RNH2 (i)J. Chem. Soc., Dalton Trans., 1998, Pages 2437–2443 2441 course in common with the organo and metalloorganic alkali metal complexes, whose structures and association states are well known to be drastically modified by co-ordination of the metal centres.5,11,13 However, the key diVerence between the latter and mixed p block metal/alkali metal complexes is that the higher solvation energies for the more electropositive alkali metals and the closed-shell configurations of p block metals will lead to the preferential or exclusive solvation of the alkali metal cations. This will diminish the competition for the ligand electron density by the alkali metal cations and will have the result of strengthening the control of the p block metal ligand framework over the cage structure of the complexes. Semiempirical PM3 calculations on models of the heterobimetallic ‘pseudo-ladder’ complex [{Sn(MesNH)(m-NC6H4OMe-2)}2- (Li?thf)2] 142b illustrate that the centralised Sn2N2 open-ladder arrangement is therefore strongly influenced by solvation of Fig. 9 Semiempirical PM3 calculations of models of compound 14; heats of formation (DHf) in kcal mol21, cal = 4.184 J Fig. 10 Structure of [{Bi2(NBut)4}(Li?thf)2] 15 Li1.The Sn2N2 open ladder [(LiNH2){Sn(m-NH)}2(LiNH2)] (akin to 14) is only marginally more favourable than the cubane [{Sn(m-NH)}2{Li(m-NH2)}2] and the Li2N2 open ladder [(SnNH){Li(m-NH2)}2(SnNH)]. However, the eVect of monosolvation of Li1 by H2O in these uncomplexed species gives a marked preference for the Sn2N2 open ladder structure (A?2H2O) over the cubane (B?2H2O) or Li2N2-centred ladder (C?2H2O) (Fig. 9). Notably, there is no thermodynamic preference for further solvation of the tin centres of the Li2N2 open ladder, so that the bisolvated Sn2N2 open ladder [{(H2O)2LiNH2}{Sn(m-NH)}2{(H2O)2LiNH2}] A?H2O (Fig. 9) is preferred by 40.5 kcal mol21 to the preservation of the monosolvated Li2N2 open ladder. The balance between the relative energies of the Bi]N and Li]N bonds and lithium solvation appears to underlie the structure of the heterobimetallic BiIII/Li cubane [{Bi2(NBut)4}(Li?thf)2] 15 (Fig. 10),3c whose arrangement is similar to the monosolvated calculational model B?2H2O (Fig. 9). Presumably, the expected closer energies of the metal–nitrogen bonds leads to greater competition for the nitrogen electron density by Bi and Li. This results in a greater influence of the Li1 cations over the Bi]N framework of the [Bi2(NBut)4]22 dianion and in a lower solvation energy for Li1. The monosolvated cubane is now preferred to the bis-solvated open ladder structure. A recent study also illustrates that the electronegativity of the organic substituents can have a strong influence on the structure of p block metal/alkali metal cages.The reaction of the terminal NMe2 substituents of [{Sb(NMe2)(m-NCy)2}2SbK] 16, containing a [{Sb(NMe2)(m-NCy)2}2Sb]2 monoanion and having a similar structure to the Li1 complex 1 (Fig. 1), with CyNH2 gives [{Sb(CyNH)(m-NCy)2}2SbK] 17 in which the spiro structure of 16 is retained.3g However, the reaction of 16 with ButOH gives K[{Sb(m-NCy)}3(m3-NCy)]?h6-C6H5Me 18 in which the antimony(III) anion has rearranged into a nido- Fig. 11 Conversion of the spiro [{Sb(NMe2)(m-NCy)2}2Sb]2 anion of compound 16 into the nido anion of K[{Sb(m-NCy)}3(m3-NCy)(OBut)? h6-C6H5Me 182442 J. Chem. Soc., Dalton Trans., 1998, Pages 2437–2443 type structure (Fig. 11).3g The reason for this transformation is that the greater electronegativity of the alkoxide substituents increases the Lewis acidity of the antimony(III) centres, the nido arrangement maximising their co-ordination numbers.This result also reiterates the previous conclusion that the p block metal frameworks provide one of the greatest influences over the structures of such cages. 3 Conclusions and General Remarks On the basis of the cyclic ladder structure of the primary amido lithium complex [(ButNH)Li]8 19,14 it was suggested recently that the structure of one such species [{Sb(NCH2CH2Ph)3}2- Li6?2thf] 20,3b whose Sb2N6Li6 core can be regarded as being constructed from the capping of a hexameric imidolithium stack by two antimony(III) centres, is templated by metallation of a rigid hexameric primary amido lithium precursor [(RNH)Li]6 by Sb(NMe2)3 (Fig. 12). The idea that the structures of the cage complexes [{Sb- (NR)3}2Li6] are ‘directed’ by the common hexameric structure of a cyclic primary amido lithium precursor 6 assumes that the N6Li6 units of these species are thermodynamically robust enough to template the eventual cage arrangement and that this unit is sustained during metallation by Sb(NMe2)3.In eVect, the mechanism and the structure of the product are dominated by a single thermodynamic factor. Although we agree that thermodynamic considerations generally play the greatest role in dictating the outcomes of the variety of reactions discussed above and the structures of the heterometallic complexes formed, our conclusion is that structural direction by the primary amido lithium complexes is unlikely and that the bonding demands of the p block metals dominate the kinetics and thermodynamics involved. In this regard, it is noteworthy that the infinite ladder structure of the primary phosphido lithium complex [(CyPH)Li?thf]• 21 (which has previously been structurally characterised) 15 has no bearing on the structure of [{Sb(PCy)3}2Li6]?6Me2NH 8 formed in its reaction with Sb(NMe2)3 3e and that the reaction of the cyclic ladder [(ButNH)Li]8 itself with Sb(NMe2)3 gives [{Sb(NBut)3}2Li6] 22, containing the expected Sb2N6Li6 core (Fig. 13).3f In complexes of the type [{Sb(ER)3}2Li6] 3b,e,f (E = N or P) the eight electron, pyramidal antimony(III) centres have the greatest influence on the molecular architecture of the core (not the ionically bonded, flexible E6Li6 framework) (Fig. 14). Their overall structures are constrained by the rigid geometry of the [Sb(ER)3]32 trianions and the appearance of a E6Li6 cyclic ladder motif, which simply maximises ionic interactions between the chemically robust anion units, has no necessary mechanistic significance.In a general sense, the nature of the p block metal anion units formed in an individual reaction system obviously has a primary role in dictating the ultimate structure of the heterometallic cage formed with alkali metal cations. The structure adopted relies mainly on the interplay between the p block metal–ligand and alkali metal–ligand bond energies, on the diVerent (ionic and covalent) bonding requirements of the alkali and p block metals and on the presence of Lewis base solvation.Assessment of these structures shows the geometric rigidity of the p block metal frameworks, which results from greater covalency and the requirements of metal valence, is a predominant structural factor. Since the alkali metal–ligand Fig. 12 Proposed structural direction of compound 20 by the supposed cyclic ladder [(PhCH2CH2NH)Li]6 precursor NH Li HN Li NH Li NH Li HN Li NH Li N Li N Li N Li N Li N Li N Li Sb Sb 2 Sb(NMe2)3 –6 Me2NH frameworks present in these complexes are almost entirely ionic in nature, it is clear that the alkali metal cations will exert a lesser influence.The dominance of the p block metal frameworks is reinforced by preferential Lewis base solvation of the alkali metal cations. Bearing in mind the complicated factors governing the formation and structures of these heterometallic cage arrangements, no one global theory is appropriate in their general rationalisation or prediction.In this context, although the ‘ring-stacking’ and ‘ring-laddering’ models have been of immense value in the prediction of the structures of a large range of metalloorganic and organoalkali metal complexes,6 it should be noted that all these systems are dominated by ionic interactions. In mixed p block/alkali metal arrangements, in which there is a large disparity between the character and bonding demands of the metals, it should not be expected that related or similar structural arrangements will be adopted because (i) the p block metal valence generally places large demands on structure, (ii) the geometries of the p block metal centres will not be modified significantly by non-directional alkali metal–ligand interactions and (iii) the alkali metal–ligand frameworks are generally the weakest and the most readily solvated and are therefore subject to breakdown and distortion.A key point here is that the formulation of the ‘ring-stacking’ and ‘ring-laddering’ models deliberately ignores whether the alkali metal–ligand bonds are ionic or covalent. Indeed, in the analysis of ring, stack or ladder options consideration of ionicity or covalency is largely irrelevant since the structures and the detailed variations in metal–ligand bond lengths within them can be rationalised equivalently either by assuming overlap between the metal and ligand orbitals or that the most favourable ionic interactions occur by the alignment of the ligand lone pairs towards the Li1 cations.7 It is precisely this point, however, which will lead to the breakdown of these models as predictive tools in heterometallic p block/alkali metal systems where the directionality and rigidity of the p block metal–ligand bonding outweights the propensity for the alignment of the ligand lone pairs towards the alkali metal cations.Thus, it is not just the relative strengths of the alkali metal–ligand and p block metal–ligand bonds which aVect the outcome of the conflict between the two metals for ligand electron density and the resulting dominance of either metal over the structure, but unfavourable distortion and electronic rearrangement of the p block metal also provide potent contributions to the thermodynamic balance.Fig. 13 Reaction of [(ButNH)Li]8 with Sb(NMe2)3 and the formation of [{Sb(NBut)3}2Li6] 22 Fig. 14 An ‘ionic’ formulation (a) in which the Sb31 ions reside in the N6Li6 ‘bed’ 6 and a ‘covalent’ formulation (b) in which the [Sb(NR)3]32 anions are associated by six Li1 cations N Li N Li N Li Li N Li N Li N Sb Sb N Li N Li N Li Li N Li N Li N .... Sb Sb (b) (a)J. Chem. Soc., Dalton Trans., 1998, Pages 2437–2443 2443 4 Acknowledgements We gratefully acknowledge the EPSRC (postdoctoral research grant for M. A. B., 1994–1997), the Leverhulme Trust (postdoctoral research grant for M. A. B., 1997–2000), the Royal Society (D.S. W.), the NuYeld Foundation (D. S. W.) and the Spanish Government (M. E. G. M.) for financial support. 5 References 1 R. E. Allan, M. A. Beswick, P. R. Raithby, A. Steiner and D. S. Wright, J. Chem. Soc., Dalton. Trans., 1996, 4135. 2 (a) R. E. Allan, M. A. Beswick, N. L. Cromhout, M. A. Paver, P. R. Raithby, A. Steiner and D. S. Wright, Chem. Commun., 1996, 1501; (b) R. E. Allan, M. A. Beswick, N. Feeder, M. Kranz, M. E. L. G. Mosquera, P. R. Raithby and D.S. Wright, Inorg. Chem., 1998, 37, 2602. 3 (a) R. A. Alton, D. Barr, A. J. Edwards, M. A. Paver, M.-A. Rennie, C. A. Russell, P. R. Raithby and D. S. Wright, J. Chem. Soc., Chem. Commun., 1994, 1481; (b) A. J. Edwards, M. A. Paver, M.-A. Rennie, C. A. Russell, P. R. Raithby and D. S. Wright, Angew. Chem., Int. Ed. Engl., 1994, 106, 1334; Angew. Chem., Int. Ed. Engl., 1994, 33, 1277; (c) D. Barr, M. A. Beswick, A. J. Edwards, J. R. Galsworthy, M. A. Paver, M.-A. Rennie, C. A.Russell, P. R. Raithby, K. L. Verhorevoort and D. S. Wright, Inorg. Chim. Acta, 1996, 248, 9; (d ) M. A. Paver, C. A. Russell and D. S. Wright, Angew. Chem., 1995, 107, 1077; Angew. Chem., Int. Ed. Engl., 1995, 34, 1545; (e) M. A. Beswick, J. M. Goodman, C. N. Harmer, A. D. Hopkins, M. A. Paver, P. R. Raithby, A. E. H. Wheatley and D. S. Wright, Chem. Commun., 1997, 1879; ( f ) M. A. Beswick, N. Choi, C. N. Harmer, A. D. Hopkins, M. McPartlin, P. R. Raithby, A. Steiner, M.Tombul and D. S. Wright, Inorg. Chem., 1998, 37, 2177; ( g) A. Bashall, M. A. Beswick, C. N. Harmer, A. D. Hopkins, M. McPartlin and D. S. Wright, Chem. Commun., 1998, 261. 4 A. Kiennemann, G. Levy, F. Schue and C. Tanielian, J. Organomet. Chem., 1972, 143, 35; F. Ando, T. Hayashi, K. Ohashi and J. Kotetsu, J. Nucl. Chem., 1991, 15, 2011; K. Moedritzer, Inorg. Chem., 1964, 3, 609; W. Clegg, N. A. Compton, R. J. Errington, G. A. Fisher, M. E. Green, D. C. R. Hockless and N.C. Norman, Inorg. Chem., 1991, 30, 4680; M. M. Olmstead and P. P. Power, Inorg. Chem., 1984, 23, 413. 5 (a) M. A. Beswick, C. N. Harmer, M. A. Paver, P. R. Raithby, A. Steiner and D. S. Wright, Inorg. Chem., 1997, 36, 1740; (b) D. Barr, A. J. Edwards, S. Pullen, M. A. Paver, P. R. Raithby, M.-A. Rennie, C. A. Russell and D. S. Wright, Angew. Chem., 1994, 106, 1960; Angew. Chem., Int. Ed. Engl., 1994, 33, 1875; (c) A. J. Edwards, M. A. Paver, M.-A. Rennie, C. A. Russell, P. R.Raithby and D. S. Wright, Angew. Chem., 1995, 107, 1088; Angew. Chem., Int. Ed. Engl., 1995, 34, 1012. 6 K. Gregory, P. von R. Schleyer and R. Snaith, Adv. Inorg. Chem., 1991, 37, 47; R. E. Mulvey, Chem. Rev., 1991, 20, 167. 7 M. A. Beswick, N. Choi, C. N. Harmer, A. Hopkins, M. A. Paver, P. R. Raithby, M. McPartlin and D. S. Wright, J. Chem. Soc., Dalton. Trans., 1998, 517. 8 R. E. Allen, G. R. Coggan, P. R. Raithby, A. E. H. Wheatley and D. S. Wright, Inorg. Chem., 1997, 36, 5202. 9 (a) R. E. Allan, M. A. Beswick, M. A. Paver, P. R. Raithby, M.-A. Rennie and D. S. Wright, J. Chem. Soc., Dalton. Trans., 1995, 1994; (b) M. Veith and G. Schlemmer, Chem. Ber., 1982, 115, 2141; (c) M. Veith and O. Recktenwald, Z. Naturforsch., Teil B, 1983, 38, 1054; (d ) H. Chen, R. A. Bartlett, H. V. R. Dias, M. M. Olmstead and P. P. Power, Inorg. Chem., 1991, 30, 3390. 10 P. P. Power and K. M. Waggoner, J. Am. Chem. Soc., 1991, 113, 3385. 11 M. A. Beswick and D. S. Wright, Comprehensive Organometallic Chemistry, 1995, vol. 1, ch. 1. 12 D. R. Armstrong, D. Barr, W. Clegg, S. M. Hodgson, R. E. Mulvey, D. Reed, R. Snaith and D. S. Wright, J. Am. Chem. Soc., 1989, 111, 4719. 13 W. N. Setzer and P. v. R. Schleyer, Adv. Organomet. Chem., 1985, 24, 353; C. Schade and P. v. R. Schleyer, Adv. Organomet. Chem., 1987, 27, 169. 14 N. D. R. Barnett, W. Clegg, L. Horsburgh, D. M. Linsay, Q.-Y. Liu, F. M. McKenzie, R. E. Mulvey and P. G. Williard, Chem. Commun., 1996, 2321. 15 E. Hey-Hawkins and S. Kurz, Phosphorus, Sulfur, Silicon Relat. Elem., 1994, 90, 281. Received 26th January 1998; Paper 8/00687CJ. Chem. Soc., Dalton Trans., 1998, Pages 2437–2443 2443 4 Acknowledgements We gratefully acknowledge the EPSRC (postdoctoral research grant for M. A. B., 1994–1997), the Leverhulme Trust (postdoctoral research grant for M. A. B., 1997–2000), the Royal Society (D. S. W.), the NuYeld Foundation (D. S. W.) and the Spanish Government (M. E.G. M.) for financial support. 5 References 1 R. E. Allan, M. A. Beswick, P. R. Raithby, A. Steiner and D. S. Wright, J. Chem. Soc., Dalton. Trans., 1996, 4135. 2 (a) R. E. Allan, M. A. Beswick, N. L. Cromhout, M. A. Paver, P. R. Raithby, A. Steiner and D. S. Wright, Chem. Commun., 1996, 1501; (b) R. E. Allan, M. A. Beswick, N. Feeder, M. Kranz, M. E. L. G. Mosquera, P. R. Raithby and D. S. Wright, Inorg. Chem., 1998, 37, 2602. 3 (a) R. A. Alton, D. Barr, A. J. Edwards, M. A. Paver, M.-A.Rennie, C. A. Russell, P. R. Raithby and D. S. Wright, J. Chem. Soc., Chem. Commun., 1994, 1481; (b) A. J. Edwards, M. A. Paver, M.-A. Rennie, C. A. Russell, P. R. Raithby and D. S. Wright, Angew. Chem., Int. Ed. Engl., 1994, 106, 1334; Angew. Chem., Int. Ed. Engl., 1994, 33, 1277; (c) D. Barr, M. A. Beswick, A. J. Edwards, J. R. Galsworthy, M. A. Paver, M.-A. Rennie, C. A. Russell, P. R. Raithby, K. L. Verhorevoort and D. S. Wright, Inorg. Chim. Acta, 1996, 248, 9; (d ) M.A. Paver, C. A. Russell and D. S. Wright, Angew. Chem., 1995, 107, 1077; Angew. Chem., Int. Ed. Engl., 1995, 34, 1545; (e) M. A. Beswick, J. M. Goodman, C. N. Harmer, A. D. Hopkins, M. A. Paver, P. R. Raithby, A. E. H. Wheatley and D. S. Wright, Chem. Commun., 1997, 1879; ( f ) M. A. Beswick, N. Choi, C. N. Harmer, A. D. Hopkins, M. McPartlin, P. R. Raithby, A. Steiner, M. Tombul and D. S. Wright, Inorg. Chem., 1998, 37, 2177; ( g) A. Bashall, M. A. Beswick, C. N. Harmer, A. D.Hopkins, M. McPartlin and D. S. Wright, Chem. Commun., 1998, 261. 4 A. Kiennemann, G. Levy, F. Schue and C. Tanielian, J. Organomet. Chem., 1972, 143, 35; F. Ando, T. Hayashi, K. Ohashi and J. Kotetsu, J. Nucl. Chem., 1991, 15, 2011; K. Moedritzer, Inorg. Chem., 1964, 3, 609; W. Clegg, N. A. Compton, R. J. Errington, G. A. Fisher, M. E. Green, D. C. R. Hockless and N. C. Norman, Inorg. Chem., 1991, 30, 4680; M. M. Olmstead and P. P. Power, Inorg. Chem., 1984, 23, 413. 5 (a) M. A. Beswick, C. N. Harmer, M. A. Paver, P. R. Raithby, A. Steiner and D. S. Wright, Inorg. Chem., 1997, 36, 1740; (b) D. Barr, A. J. Edwards, S. Pullen, M. A. Paver, P. R. Raithby, M.-A. Rennie, C. A. Russell and D. S. Wright, Angew. Chem., 1994, 106, 1960; Angew. Chem., Int. Ed. Engl., 1994, 33, 1875; (c) A. J. Edwards, M. A. Paver, M.-A. Rennie, C. A. Russell, P. R. Raithby and D. S. Wright, Angew. Chem., 1995, 107, 1088; Angew. Chem., Int. Ed. Engl., 1995, 34, 1012. 6 K. Gregory, P. von R. Schleyer and R. Snaith, Adv. Inorg. Chem., 1991, 37, 47; R. E. Mulvey, Chem. Rev., 1991, 20, 167. 7 M. A. Beswick, N. Choi, C. N. Harmer, A. Hopkins, M. A. Paver, P. R. Raithby, M. McPartlin and D. S. Wright, J. Chem. Soc., Dalton. Trans., 1998, 517. 8 R. E. Allen, G. R. Coggan, P. R. Raithby, A. E. H. Wheatley and D. S. Wright, Inorg. Chem., 1997, 36, 5202. 9 (a) R. E. Allan, M. A. Beswick, M. A. Paver, P. R. Raithby, M.-A. Rennie and D. S. Wright, J. Chem. Soc., Dalton. Trans., 1995, 1994; (b) M. Veith and G. Schlemmer, Chem. Ber., 1982, 115, 2141; (c) M. Veith and O. Recktenwald, Z. Naturforsch., Teil B, 1983, 38, 1054; (d ) H. Chen, R. A. Bartlett, H. V. R. Dias, M. M. Olmstead and P. P. Power, Inorg. Chem., 1991, 30, 3390. 10 P. P. Power and K. M. Waggoner, J. Am. Chem. Soc., 1991, 113, 3385. 11 M. A. Beswick and D. S. Wright, Comprehensive Organometallic Chemistry, 1995, vol. 1, ch. 1. 12 D. R. Armstrong, D. Barr, W. Clegg, S. M. Hodgson, R. E. Mulvey, D. Reed, R. Snaith and D. S. Wright, J. Am. Chem. Soc., 1989, 111, 4719. 13 W. N. Setzer and P. v. R. Schleyer, Adv. Organomet. Chem., 1985, 24, 353; C. Schade and P. v. R. Schleyer, Adv. Organomet. Chem., 1987, 27, 169. 14 N. D. R. Barnett, W. Clegg, L. Horsburgh, D. M. Linsay, Q.-Y. Liu, F. M. McKenzie, R. E. Mulvey and P. G. Williard, Chem. Commun., 1996, 2321. 15 E. Hey-Hawkins and S. Kurz, Phosphorus, Sulfur, Silicon Relat. Elem., 1994, 90, 281. Received 26th January 1998; Paper 8/00687C

ISSN:1477-9226    

DOI:10.1039/a800687c

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2441–2449 2441 The .rst systematic stability study of mononuclear and dinuclear iron(II) and iron(III) complexes incorporating a dinucleating macrocyclic ligand in aqueous solution † Zheng Wang, Arthur E. Martell,* Ramunas J. Motekaitis and Joseph Reibenspies Department of Chemistry, Texas A&M University, College Station, Texas 77842-3012 Received 16th October 1998, Accepted 3rd June 1999 The dinucleating 24-membered hexaazadiphenol macrocyclic ligand 15,31-dimethyl-3,11,19,27,33,35-hexaazapentacyclo[ 27.3.1.1. 5,91. 13,171. 21,25]-hexatriaconta-5,7,9(33),13,15,17(34),21,23,25(35),29,31,1(36)-dodecaene-34,36- diol ([24]RBPyBC), prepared by the NaBH4 reduction of the Schi. base obtained from the [2 2] condensation between 2,6-diformylpyridine and 2,6-bis(aminomethyl)-p-cresol, forms a variety of anionic and cationic species in aqueous solution. The structure of ([24]RBPyBC)4HCl6CH3OH was determined by X-ray crystallographic methods.The ligand maintains dinuclear integrity for both iron(..,..) and iron(..., ...) states, while facilitating the formation of bridging µ-phenolate diiron cores. Potentiometric equilibrium studies indicate that a variety of protonated, mononuclear and dinuclear iron(..) and iron(...) complexes form through p[H] 2 to 11 in aqueous solution. The protonation constants of the ligand and all associated stability constants of the 1 : 1, 1 : 2 [ligand:iron(..) or iron(...)], and 1:1:1 [ligand : iron(..) : iron(...)] complexes were determined in KCl supporting electrolyte (0.100 M) at 25.0 C.The mechanisms of the formation of dinuclear iron(..), iron(...) and the mixed-valence iron(..,...) complexes are described. Introduction Dinuclear iron centers have been found in hemerythrin, methane monooxygenase, and the B2 subunits of ribonucleotide reductase.1 These proteins have elicited interest because of their widespread occurrence and the diverse nature of their functions, including reversible O2 binding, alkane hydroxylation, and DNA biosynthesis.2 During the last decade, synthetic structural models for these proteins using several types of ligand have appeared in the literature 3 in recognition of the role played by dinuclear iron centers in metalloproteins.The synthetic dinuclear iron complexes of a large body of facially capped tridentate or tetradentate ligands,4 alkoxo-bridging polypodal ligands 5 and a few dinucleating macrocyclic ligands 6 have contributed much to our understanding of the behavior of coupled diiron systems.In recent years, two 20-membered tetraazadiphenol macrocyclic ligands (see Fig. 1, H2LI and H2LII) were used to study diiron as well as other dinuclear transition metal (M2) complexes, in which LIM2M2, LIIM2Fe3, and LIIFe3- (OH)2Fe3LII species were successfully prepared.7 However, the dinuclear species containing two Fe(...) ions within a single macrocycle could not be obtained.The tripositivelycharged centers Fe3, Fe3 cannot be held together in the 20-membered macrocycle because of the strong coulombic repulsion between the Fe(...) centers that would be imposed in such a structure. In order to study the various oxidation states of the dinuclear iron site in a preorganized arrangement, specially designed dinucleating macrocyclic ligands need to be developed. Recently, we have widened the scope of the available dinucleating ligands by designing larger macrocycles containing more donor groups which are known to have special a.nity for ferrous and ferric centers.8 Such ligands are the 24-membered † Supplementary data available: UV-visible spectra of [24]RBPyBC.For direct electronic access see http://www.rsc.org/suppdata/dt/1999/2441/, otherwise available from BLDSC (No. SUP 57573, 1 pp.) or the RSC library. See Instructions for Authors, 1999, Issue 1 (http://www.rsc.org/ dalton).hexaazadiphenol and 30-membered octaazadiphenol macrocycles (See Fig. 1, H2LIII, H2LIV, H2LV and H2LVI).9 As part of the continuing studies of the new series of dinucleating macrocyclic ligands 10 and their homonuclear and heteronuclear transition metal complexes, we report here the X-ray crystal structure of one such macrocyclic ligand, [24]RBPyBC (hereafter H2LIV). In contrast to tetraimine Schi. base ligands (H2LI, H2LIII, H2LV), one advantage of the corresponding tetraamine ligands (H2LII, H2LVI) is that they can be studied in aqueous solution, the natural medium of enzymes. Moreover, the dinuclear metal models incorporating the more .exible polyamine ligands may allow metal–metal spatial distances and coordination geometry to vary from one intermediate to the next.Regarding the di.erent coordination chemistries of these ligands, the pairs of enlarged 24-membered macrocycles H2LIII and H2LIV along with the 30-membered analogs H2LV and H2LVI, provide two sets of macrocyclic ligands that closely parallel the 20- membered systems H2LI and H2LII.The stepwise stability constants of mononuclear and dinuclear complexes formed by iron(..) and iron(...) with [24]RBPyBC from p[H] 2 to 11 (where p[H] represents log[H]) were determined and discussed in this paper. This constitutes a major addition to the work reported on dinuclear iron(..) and iron(...) complexes in aqueous solution.6 Results and discussion H2LIV4HCl In our previously published procedure,9 the ligand was recrystallized from methanolic solution containing 32% HCl as an approximate hexahydrochloride salt in which the HCl content was not quite reproducible because the pyridine nitrogens of the ligand are di.cult to protonate completely.In order to obtain the ligand sample with a reproducible chemical composition for titration studies, a methanolic solution containing 5% HCl was employed to prepare the ligand as a tetrahydrochloride salt.Drying in vacuo followed by reexposure to the atmosphere gave a solid of composition2442 J. Chem. Soc., Dalton Trans., 1999, 2441–2449 Fig. 1 Polyazadiphenol dinucleating macrocyclic ligands. N N CH3 N N CH3 OH N N N OH N N N NH HN CH3 HN CH3 NH HN CH3 OH N N HN CH3 OH NH CH3 N N N N N N N N OH CH3 OH CH3 N NH N HN CH3 NH OH H2LIV [24]RBPyBC OH H2LI [20]BPrBC H2LV [30]BBPyBC H2LVI [30]RBBPyBC H2LII [20]RBPrBC H2LIII [24]BPyBC OH OH CH3 OH NH HN CH3 OH N N H2LIV4HCl1/3CH3OH5/3H2O by elemental analysis (F.W. = 725), which agrees with the results found by potentiometric titration (F.W. = 722).A single crystal suitable for X-ray crystallography with the composition H2LIV4HCl6CH3OH, 1, was obtained by recrystallization from methanol. Fig. 2 shows the structure and the atom-numbering scheme of the macrocyclic tetracation H6LIV 4, together with the associated four chloride ions and the six methanol molecules which are involved in a complex hydrogen-bonded network.Selected interatomic distances and angles are given in Table 1. The X-ray crystallographic analysis of 1 (see Fig. 2) shows that all four amino nitrogens of the macrocycle are protonated but not the two pyridyl nitrogens, which were fully protonated in the previously determined structure of the heptahydrobromide salt of this ligand.9 The H6LIV 4 cation adopts a parallelogram arrangement with two phenolic oxygen atoms and two pyridyl nitrogen atoms oriented toward the center of the macrocycle and the aromatic groups at the farther corners.The four amino nitrogens lie on a perfect plane of the inherent crystal symmetry. The two pyridines are inclined equally to this N4 plane, with a dihedral angle of 38.4. The two aromatic phenolic rings are also inclined to the N4 plane, with a dihedral angle of 29.2. The macrocycle is shaped by internal hydrogen bonding so that the ligand molecule adopts a central symmetry in the space group P1� .Though a hydrogen atom associated with O(1) was not observed in the crystal structure analysis, the short distance between O(1) and Cl(2) was strongly suggestive of hydrogen bonding [O(1) Cl(2), 3.02(1) Å].11 As is indicated in Table 1, N(1) and N(3) are hydrogen bonded to Cl(1) [N(1) Cl(1), 3.20(1); N(3) Cl(1), 3.07(1) Å], and also to N(2) [N(1) J. Chem. Soc., Dalton Trans., 1999, 2441–2449 2443 N(2), 2.65(1); N(3) N(2), 2.75(1) ring;].Cl(2) is hydrogen bonded to the oxygen atoms of two methanol molecules [O(3) Cl(2), 3.14(1); O(4) Cl(2), 3.07(1) Å]. The O(2) of the methanol is solely involved in the hydrogen bonding to O(4) [O(2) O(4), 2.74(1) Å] outside of the H6LIV 4 macrocyclic cavity. The structure, therefore, could be described as [(H6LIV 4)(Cl)4](CH3OH)6. On the other hand, the structure of the heptahydrobromide salt of the ligand was determined crystallographically 9 as [(H8LIV 6)(Br)6H3O]Br.It is interesting to see that the ligand adopts various symmetries when the protonation and the solvation are changed. Fig. 2 Molecular structure of [24]RBPyBC4HCl6CH3OH (1). Ellipsoids are drawn at the 50% probability level. Table 1 Selected interatomic distances (Å) and angles () for H2LIV 4HCl6CH3OHa O1 Cl2 N3 Cl1 N3 N2 O4 Cl2 O1 Cl1 O(1)–C(15) O(2)–C(17) O(3)–C(18) O(4)–C(19) N(1)–C(2) N(1)–C(1) N(2)–C(3) N(2)–C(7) N(3)–C(8) N(3)–C(9) C(1)–C(14) b C(2)–C(3) C(3)–C(4) C(2)–N(1)–C(1) C(3)–N(2)–C(7) C(8)–N(3)–C(9) C(14) b–C(1)–N(1) N(1)–C(2)–C(3) N(2)–C(3)–C(4) N(2)–C(3)–C(2) C(4)–C(3)–C(2) C(5)–C(4)–C(3) C(4)–C(5)–C(6) C(7)–C(6)–C(5) N(2)–C(7)–C(6) N(2)–C(7)–C(8) C(6)–C(7)–C(8) C(7)–C(8)–N(3) 3.02(1) 3.07(1) 2.75(1) 3.07(1) 3.36(1) 1.368(7) 1.379(8) 1.383(8) 1.374(8) 1.476(7) 1.518(7) 1.317(7) 1.350(7) 1.502(7) 1.504(7) 1.477(8) 1.500(8) 1.396(8) 115.3(4) 118.3(5) 115.2(4) 109.6(5) 110.8(5) 122.1(6) 117.0(5) 120.7(6) 118.9(6) 119.5(5) 118.4(6) 122.7(6) 114.7(5) 122.5(6) 110.2(5) N1 Cl1 N1 N2 O3 Cl2 O1 N2 O2 O4 C(4)–C(5) C(5)–C(6) C(6)–C(7) C(7)–C(8) C(9)–C(10) C(10)–C(15) C(10)–C(11) C(11)–C(12) C(12)–C(13) C(12)–C(16) C(13)–C(14) C(14)–C(15) C(14)–C(1) b N(3)–C(9)–C(10) C(15)–C(10)–C(11) C(15)–C(10)–C(9) C(11)–C(10)–C(9) C(10)–C(11)–C(12) C(13)–C(12)–C(11) C(13)–C(12)–C(16) C(11)–C(12)–C(16) C(12)–C(13)–C(14) C(13)–C(14)–C(15) C(13)–C(14)–C(1) b C(15)–C(14)–C(1) b O(1)–C(15)–C(10) O(1)–C(15)–C(14) C(10)–C(15)–C(14) 3.20(1) 2.65(1) 3.14(1) 3.21(1) 2.74(1) 1.359(9) 1.382(9) 1.368(8) 1.501(8) 1.506(7) 1.381(8) 1.391(8) 1.400(8) 1.381(9) 1.492(8) 1.392(8) 1.415(7) 1.477(8) 109.6(4) 118.3(5) 120.4(5) 121.0(6) 122.9(6) 116.5(6) 122.1(5) 121.3(6) 123.4(5) 117.5(6) 123.2(5) 119.2(5) 122.8(5) 116.0(5) 121.2(6) a Numbers in parentheses are standard deviations in the last signi.cant digit.b Symmetry transformation used to generate equivalent atoms: x 1, y 1, z 1.Protonation constants of the ligand The potentiometric curve for the ligand H2LIV4HCl shown in Fig. 3 features a steeply sloping region from a = 0 to a = 2, where a is moles of base added per mole of ligand present in the experimental solution. This indicates two almost non-overlapping protonation equilibria. A smooth bu.er region from a = 2 to almost a = 4 indicates two overlapping protonation equilibria. In this region, the neutral ligand remains in homogeneous supersaturated solution at 103 M levels.Above p[H] 10, precipitation of the neutral ligand occurred. Insolubility is indicated by a sudden discontinuity in p[H] readings, which can be detected before visual observation of the presence of the insoluble material. Such data were not used in the equilibrium calculations. Instead, the experiments were repeated several times in order to achieve supersaturation to the maximum extent possible.Above a = 4, a very low concentration (1.10 × 104 M) was studied spectrophotometrically and the data were analyzed by considering the variability of absorbance at 298 nm with p[H]. The combined results from both potentiometric and spectroscopic analyses for the protonation constants for this ligand are listed in Table 2. From a microscopic point of view, the values of the .rst and second protonation constants are essentially the phenolic protonations, while the third, fourth, .fth, and sixth ones should correspond to the protonations of the four aliphatic nitrogens.The pyridine nitrogens were found to be too weakly basic to become protonated under these experimental conditions. The stepwise protonation scheme is shown in Scheme 1 (only one microspecies is shown in all cases). At p[H] < 3, the ligand exists in the fully protonated form, Fig. 3 Potentiometric equilibrium curves for LIV–Fe(..) systems in argon at 25.00 ± 0.05 C and µ = 0.100 M (KCl) :TL = 2.212 × 103 M; TFe(II) = 2.120 × 103 M (1: 1 Fe2–LIV); TFe(II) = 4.240 × 103 M (2: 1 Fe2–LIV) [a = moles of standard KOH added per mole of ligand present]. Table 2 Successive protonation constants of [24]RBPyBC, HBED,a and C-BISBAMPb c logKi H i [24]RBPyBCd HBEDf i C-BISBAMPg 123456 12.1 e 11.3 e 9.18 8.92 6.65 4.52 12.6 11.0 8.44 4.72 2.53 1.7 1234 9.11 8.32 7.12 3.72 a HBED = N,N-di(2-hydroxybenzyl)ethylenediamine-N,N-diacetic acid.b C-BISBAMP = 3,8,16,21,27,28-hexaazatricyclo[21.3.1.110.14]- octacosa-1(26),10(28),11,13,23(27),24-hexaene. c Ki H = [HiLi 2]/[H]- [Hi 1Li 3]. d This work (µ = 0.100 M (KCl), 25.0 C), Standard deviation = ±0.04. e This work, UV-visible measurement, estimated error = ±0.1. f Reference 12(a,b) (µ = 0.100 M (KNO3), T = 25 C). g Reference 12(c) (µ = 0.0100 M (NaClO4), T = 25 C).2444 J. Chem. Soc., Dalton Trans., 1999, 2441–2449 Scheme 1 Stepwise protonation diagram of LIV 2. NH NH CH3 O- N N HN CH3 O- NH +H+ +H+ LIV 2- p[H]>12 HLIV - p[H] 11.6 ~~ H2LIV p[H] 10.5 ~~ + H3LIV + p[H] 9.0 ~~ NH HN CH3 O- N N HN CH3 OH NH NH HN CH3 OH N N HN CH3 OH NH NH HN CH3 OH N N HN CH3 OH NH2 H5LIV 3+ p[H] 5.7 ~~ + H4LIV 2+ p[H] 7.8 ~~ NH H2N+ CH3 OH N N H2N CH3 OH NH2 NH H2N+ CH3 OH N N HN CH3 OH NH2 + + +H+ H6LIV 4+ p[H]<3 NH2 H2N+ CH3 OH N N H2N CH3 OH NH2 + + +H+ +H+ +H+ + H6LIV 4.As p[H] is increased, the macrocycle loses its protons from amino nitrogens to become H5LIV 3, H4LIV 2 and H3LIV species respectively. The neutral ligand H2LIV reaches its maximum concentration (88%) at p[H] 10.5. Under more alkaline conditions, the two phenol groups .nally deprotonate to form the free ligand dianion LIV 2 (p[H] > 12).To our knowledge, there are no examples of protonation constant studies of polyazadiphenol macrocyclic ligands in the literature.8 Therefore acyclic ligands containing combinations of similar functional groups, HBED12a,b and C-BISBAMP,12c are included in Table 2 for comparison.HBED is a well-known bis(o-hydroxybenzyl) ligand which has a very high stability constant with Fe(...) and with other highly charged metal ions. The .rst two protonation constants of [24]RBPyBC and HBED are fairly close. Since there are two .-amino groups adjacent to each phenolate in [24]RBPyBC exhibiting electron-withdrawing e.ects, instead of one .-amino group as in HBED, it is reasonable that the .rst protonation constant of [24]RBPyBC (log K1 H = 12.1) is 0.5 log units lower than that of the ligand HBED (log K1 = 12.6). Since the two phenol groups of [24]RBPyBC are somewhat more separated than those of HBED, the di.erence in the .rst two protonation constants (log K1 H log K2 H = 0.8) of [24]RBPyBC is smaller than that (log K1 H log K2 H = 1.6) of HBED.In addition, the increase in absorbance around 300 nm that occurs in the conversion of one species to the next less protonated form is an indication of the participation of phenolate groups.12a,b HBED has been reported to have absorptions at .= 294 nm with the following extinction coe.cients for the three highest pH species: eL4 = 8300, eHL3 = 4000, eH2L2 = 650 M1 cm1. In this work, [24]RBPyBC has absorptions at . = 298 nm with the following extinction coef- .cients for the three highest pH species: eLIV 2 = 9000, eHLIV =J. Chem. Soc., Dalton Trans., 1999, 2441¡V2449 24454900, £`H2LIV = 1200 M1 cm1.The increases in absorptivitiesper protonation step for HBED and [24]RBPyBC are fairlyparallel, indicating similar protonation patterns of phenolatesin both ligands. As shown in Table 2, the log values of theprotonation constants of [24]RBPyBC are also compared withthose of C-BISBAMP which also has the 24-membered ring.The main dierence between these ligands is the presence of thecresol groups in the bridges between the two BAMP moieties,so that the successive protonation constants of aliphatic nitrogensof [24]RBPyBC are fairly close to the corresponding onesof C-BISBAMP.The small variations can be ascribed topossible hydrogen bonding between phenolic oxygens andprotonated nitrogens. The greater rigidity of [24]RBPyBCrelative to that of C-BISBAMP is also expected to contribute toobserved dierences in the protonation constants.Fig. 4 Species distribution diagram for the LIV¡VFe() system as afunction of p[H] (Fe = Fe2, TFe(II) = 2TLIV = 4.00 ¡Ñ 103 M).Onlymajor species are shown: LIVH4 and LIVFe2H2 (1%) are omitted.Table 3 Overall and stepwise stability constants for the LIV¡VFe()system [ = 0.10 M (KCl), 25.0 C]StoichiometryL Fe H Log £] a Stepwise quotient K Log Ka11111111111222012301115.3226.0035.2440.1025.2031.2215.29[LIVFe]/[LIV][Fe][LIVFeH]/[LIVFe][H] b[LIVFeH2]/[LIVFeH][H] b[LIVFeH3]/[LIVFeH2][H] b[LIVFe2]/[LIVFe][Fe][LIVFe2H]/[LIVFe2][H] b[LIVFe2]/[LIVFe2(OH)][H] b,c15.3210.689.244.869.886.029.91a Estimated error = ¡Ó0.06.b H = H. c OH = OH.Stability of mononuclear and dinuclear iron(II) complexesThe potentiometric data obtained for solutions containingH2LIV4HCl and ferrous ion are illustrated in Fig. 3. The inectionsat a = 4.0 and a = 6.0 indicate the formation of themononuclear and dinuclear complexes, respectively. The p[H]titration curves were employed to calculate 1 :1 and 1 :2 ligand:metal binding constants, together with constants involvingprotonated, deprotonated, and hydroxo-bridged species shownin Table 3.Four mononuclear and three dinuclear complexeswere identied with fairly high stability constants for theferrous ion-ligand system. The species distribution diagram ofthe system H6LIV4¡V2FeII is shown in Fig. 4. When p[H] < 5, theligand exists as various protonated species in solution. Betweenp[H] 5 and 7, the mononuclear ferrous complex forms andreaches the maximum concentration (72%) at p[H] 5.7.Theconversion of the 1 : 1 into 1: 2 complexes occurs aboutp[H] > 7, when a second ferrous ion enters the same macrocycleto form dinuclear ferrous complexes (maximum concentration94% at p[H] 8.1). Finally, the hydroxo-bridged species [FeII2-(-OH)LIV] dominates when p[H] > 10.Stability of mononuclear and dinuclear iron(III) complexesPotentiometric equilibrium curves having 1 : 1 and 1 : 2 molarratios of ligand to ferric ion are shown in Fig. 5. For the 1 : 1system the strong inection at a = 4 indicates the formation ofthe mononuclear ferric complex, [FeIIIH2LIV]3.For the 1 : 2 systema strong inection occurs at a = 7 and 8, indicating that 2mol of hydrogen ions were neutralized in addition to the 6 molreleased from the ligand. This observation is evidence for theformation of the -hydroxo and -oxo bridges between twoferric ions in the dinuclear species even under fairly acidic conditions.This result is also consistent with the spectroscopicstudies in aqueous solution. The overall and stepwise stabilityconstants for the ligand¡VFe() system are included in Table 4.Four mononuclear and ve dinuclear complexes were identiedwith very high stability constants.The species distribution diagram of the system H6LIV4¡V2FeIII is shown in Fig. 6. It is seen that the mononuclear[FeIIIH2LIV]3 complex predominates from p[H] 2 to 3. Then theother ferric ion coordinates to the macrocycle to form thedinuclear ferric complex [FeIII2LIV]4 and reaches a maximumconcentration (27%) at p[H] 3.1.Between p[H] 3.5 and 7, thestable -hydroxo bridged diferric complex [FeIII2(-OH)LIV]3dominates. Above p[H] > 7, the -oxo bridged diferric complex[FeIII2(-O)LIV]2 and its further hydrolytic species become themain components in aqueous solution.Stability of mixed-valence dinuclear iron(II, III) complexesThe pH prole for the 1:1:1 solutions of the ligand with Fe3Table 4 Overall and stepwise stability constants for the LIV¡VFe() and the LIV¡VFe()¡VFe() systems [ = 0.10 M (KCl), 25.0 C], H = H,OH = OHStoichiometryL Fe3 Fe2 H Log £]a Stepwise quotient K Log Ka11111111111111112222211100000000011101210123401232.0241.0847.9922.0644.941.9934.6525.6415.3736.5630.8921.60[LIVFe]/[LIV][Fe][LIVFeH]/[LIVFe][H] b[LIVFeH2]/[LIVFeH][H] b[LIVFe]/[LIVFe(OH)][H] b,c[LIVFe2]/[LIVFe][Fe][LIVFe2]/[LIVFe2(-OH)][H] b,c[LIVFe2(-OH)]/[LIVFe2(-O)][H] b[LIVFe2(-O)]/[LIVFe2(-O)(OH)][H] b,c[LIVFe2(-O)(OH)]/[LIVFe2(-O)(OH)2][H] b,c[LIVFe3Fe2]/[LIVFe3][Fe2][LIVFe3Fe2]/[LIVFe3Fe2(-OH)][H] b,c[LIVFe3Fe2(-OH)]/[LIVFe3Fe2(OH)2][H] b,c32.029.066.919.9612.892.927.349.0110.274.545.679.29a Estimated error = ¡Ó0.06 or less.b H = H. c OH = OH.2446 J. Chem. Soc., Dalton Trans., 1999, 2441–2449 and Fe2 (Fig. 5) shows an in.ection at a = 4 indicative of the initial formation of the mononuclear [FeIIIH2LIV]3 complex and an in.ection at a = 6 indicative of the formation of the mixed-valence [FeIIIFeIILIV]3 complex.In addition, the µ-hydroxo bridged mixed-valence species, [FeIIIFeII(µ-OH)- LIV]2, and the corresponding dihydroxo species [FeIIIFeII(OH)2- LIV], are also identi.ed and the stability constants for these species are included in Table 4. From a coordination point of view, the ligand (Fig. 2) contains six nitrogens able to act as donor atoms in complexes, but they are arranged as two subunits separated by two phenolic bridging donor groups. It is expected that a mononuclear complex [FeIIIH2LIV]3 will be formed by the coordination of the ferric ion to one of the subunits (Scheme 2).Because of the low .exibility of the aromatic rings in the macrocycle, the amino nitrogens in the other subunit remain protonated in acidic solution. When the p[H] is raised, the amino groups deprotonate and .nally the ferrous ion coordinates the donor groups on the other side of the macrocycle to form the mixed-valence complex. Finally the µ-hydroxo bridged species and further hydrolytic mixed-valence species are subsequently formed in alkaline solution. The stability of the mixed-valence complex formed from dinuclear iron(...) and dinuclear iron(..) complexes is indicated by its comproportionation constant for the following equilibrium.13 [FeIII 2LIV]4 [FeII 2LIV]2 2[FeIIIFeIILIV]3 (1) Kcom = ([FeIIIFeIILIV]3)2/[FeIII 2LIV]4[FeII 2LIV]2 (2) Fig. 5 Potentiometric equilibrium curves for LIV–Fe(..., ..) systems in argon at 25.00 ± 0.05 C and µ = 0.100 M (KCl) :TL = 2.212 × 103 M, TFe(III) = 2.201 × 103 M (1: 1 Fe3–LIV); TFe(III) = 4.402 × 103 M (2: 1 Fe3–LIV); TFe(III) = 1.966 × 103 M, TFe(II) = 2.120 × 103 M (1:1:1 Fe3–Fe2–LIV) [a = moles of standard KOH added per mole of ligand present].Fig. 6 Species distribution diagram for the LIV–Fe(...) system as a function of p[H] (Fe = Fe3, TFe(III) = 2TLIV = 4.00 × 103 M). Only major species are shown; LIVFeH, LIVFe and LIVFeH1 which are minor species (1%) are omitted.From the stability constants of dinuclear ferrous, ferric and mixed-valence complexes listed in Table 3 and Table 4, the comproportionation constant (Kcom = 1.8 × 104) is calculated for equilibrium (1) in aqueous solution. The magnitude of Kcom indicates that a mixture of single valence complexes is less stable than the mixed-valence diiron complexes of the polypodal ligands containing phenolate bridging groups. For example, Kcom = 4 × 106 for the [FeIIFeIII(BBPPNOL)(µ-OAc)2] complex [BBPPNOL = N,N-bis(2-hydroxybenzyl)-N,N-bis(2-pyridylmethyl- 2-hydroxy)-1,3-propanediamine] and Kcom = 8 × 109 for the [FeIIFeIII(BBPMP)(µ-OAc)2] complex (BBPMP = 2,6-bis- {[(2-hydroxybenzyl)(2-pyridylmethyl)amino]methyl}-4-methylphenol). 13 Macrocyclic e.ects and coulombic interactions might be the most probable factors in the stabilization of these mixed-valence complexes. Summary and perspectives We have synthesized and characterized a 24-membered hexaazadiphenol macrocyclic ligand [24]RBPyBC.A single-crystal structure was obtained for the ligand with the formula [(H6LIV 4)(Cl)4]6CH3OH. The protonation constants of the ligand and stability constants of mononuclear FeII and FeIII complexes, and stability constants of dinuclear FeII 2, FeIII 2, and FeIIFeIII complexes have been determined by potentiometric and spectroscopic titration in aqueous solution. This is the .rst systematic study of both diferrous and diferric model compounds having high stabilities in water.The results have provided useful information about the formation of the diiron complexes in aqueous solution at various pH values and their quantitative stabilities. The high stabilities of these complexes also raise interest in future work on dinuclear complexes of other transition metals with this remarkable ligand, including heterobimetallic species such as FeIIICoII, FeIIINiII, FeIIICuII, FeIIIZnII, and FeIIIMnII, by the method used for the preparation of the mixed-valence FeIIIFeII species.The dinuclear iron(..) complex of the ligand has been found to have catalytic properties for the hydroxylation of alkanes with molecular oxygen as an oxidant and H2S as a two-electron reductant. The diiron complex thus serves as a functional model for MMO.14 Some of this research is in progress in this laboratory and will be the subject of future reports. Experimental Materials The synthesis and puri.cation of the dinucleating macrocyclic ligand [24]RBPyBC was based in part on a previously published method.9 FeCl36H2O was purchased from Aldrich Chemical Co.and was used without further puri.cation. Light green crystalline FeCl2 was prepared under nitrogen by the direct reaction of concentrated hydrochloric acid with 99.9% iron chips. The stock solutions of iron(..) and iron(...) were prepared from crystalline FeCl2 and analytical grade FeCl3 in the presence of 0.0100 M hydrochloric acid.The concentrations of all above stock solutions were quanti.ed by cation exchange techniques (Dowex 50W X8 cation exchange resin 20–50 mesh, hydrogen form). Solvents were appropriately puri.ed, dried, and degassed. Where anaerobic conditions were required, an argon glove-box and standard Schlenk techniques were employed. Physical measurements Elemental analyses were measured by Galbraith Laboratories, Inc., Knoxville, TN. NMR spectra were measured with a Varian XL200 FT spectrometer.Chemical shifts are reported as d(in ppm) relative to external tetramethylsilane or internal solvent. Mass spectra (FAB) were obtained with a VG analytical 70s high resolution double focusing magnetic sectorJ. Chem. Soc., Dalton Trans., 1999, 2441¡V2449 2447Scheme 2 Mixed-valence diiron(, ) complexes formed with H6LIV4.N NNH H2NCH3OCH3O NH H2NNH2 H2NCH3OHN NH2NCH3OH NH2N NNH HNCH3OCH3O NH HNN NNH H2NCH3OCH3O NH HNN NNH HNCH3OCH3O NH HNN NNH HNCH3OCH3O NH HN++ H+Fe2LIV3+ Fe2(OH)LIV2+H2FeLIV3+++++FeLIV++H6LIV4++Fe3+HFeLIV2+-H+-H++Fe2+HFe2+OFe3+ Fe2+ Fe3+Fe3+ Fe3+Fe3+spectrometer, and by electrospray ionization with a Vestec 201ESI quadrupole mass spectrometer at the Mass SpectrometryApplications Laboratory, Texas A&M University.Electronic spectra were recorded at 25.0 C with a Perkin-Elmer 553 Fast-Scan spectrophotometer equipped with1.000 ¡Ó 0.001 cm matched quartz cells.The solutions were generally104 M. Stability constants were calculated from spectraldata with the help of short programs written in Basic utilizingmass balance and equilibrium constant equations by minimizingthe least-squares absorbances t to the observed absorbancesat a prominent wavelength over a series of samples.Preparation of ligand for potentiometric titrationThe 2 2 condensation of 2,6-diformylpyridine with 2,6-bis(aminomethyl)-p-cresol, followed by hydrogenation withNaBH4, was used to synthesize the hexaazadiphenol macrocyclicligand.9 The free ligand H2LIV (2.2 g, 4.0 mmol) was dissolvedin 60 mL 5% HCl methanolic solution and then ltered.The ltrate was stored at 4 C for 24 h and a white soliddeposited.The product was collected by ltration, washed withcold methanol, and dried for 12 h at 65 C under vacuum. 1.8 gproduct of H2LIV4HCl1/3CH3OH5/3H2O was obtained(F.W. = 725, Yield = 62%). The purity of the sample and theHCl content were determined by potentiometric titration andelemental analysis.The CH3OH content was checked by recordingthe 1H NMR spectrum in D2O. Anal. Calc. for C32.33Cl4-H46.67N6O4: C, 53.55; H, 6.49; N, 11.59; Cl, 19.55. Found: C,53.50; H, 6.49; N, 11.57; Cl, 19.53. 1H NMR (D2O), £_: 2.32 (s,CH3, 6H), 4.38 (s, CH2, 8H), 4.57 (s, CH2, 8H), 7.32 (s, aryl incresol, 4H), 7.51 (d, aryl in pyridine, J = 8.0 Hz, 4H), and 7.94(t, aryl in pyridine, J = 8.0 Hz, 2H). Mass spectrum (FAB):m/z 539 ([H2LIVH]).Isolation of crystalline ligand H2LIV4HCl6CH3OH, 1In order to obtain a crystalline sample, the above solid product(0.30 g, 0.41 mmol) was redissolved in 50 mL methanol and the2448 J.Chem. Soc., Dalton Trans., 1999, 2441–2449 solution was .ltered. The .ltrate was heated to 60C to reduce the volume by half and allowed to evaporate at room temperature for 3 days to a.ord colorless single crystals of the ligand as a tetrahydrochloride hexamethanol solvate, H2LIV4HCl 6CH3OH 1, which was suitable for X-ray di.raction study.Potentiometric determinations A Corning Model 350 pH meter .tted with a blue-glass electrode and a calomel reference electrode was calibrated with standard dilute strong acid at 0.10 M ionic strength to read hydrogen concentration directly so that the measured quantity was log[H], designated as p[H]. Hydrogen ion activities (pH) were not employed in this research. Potentiometric p[H] measurements and computation of the protonation constants and the stability constants of the iron complexes were carried out by procedures described in detail elsewhere.15 The p[H] measurements were made at 25.00 ± 0.05 C and ionic strength 0.10 M adjusted with KCl. Typical concentrations of experimental solutions were 2.20 × 103 M ligand and 0.100 M KOH as titrant.Typical initial solution volumes were 50.0 mL. The range of accurate p[H] measurement was considered to be 2–12. For the ligand the .rst and second protonation constants were determined spectrophotometrically. The third, fourth, .fth, and sixth protonation constants were determined by the direct titration.The stoichiometry of LIV–Fe(..) and LIV–Fe(...) systems were 1 : 1 and 1 : 2, with a slight (ca. 2%) excess of the ligand. The ternary system containing LIV, Fe(..), and Fe(...) was studied at the molar ratio of 1:1:1. All systems were investigated under anaerobic conditions; oxygen and carbon dioxide were excluded from the reaction mixture by maintaining a slight positive pressure of puri.ed argon gas in the reaction cell.Each titration was repeated at least 2 times and over 80 points were collected per titration. Computations were all carried out with the program BEST.15 The log Kw de.ned as log([H][OH]), was found to be 13.78 at the ionic strength employed and was maintained .xed during re.nements. The preliminary 1 : 1 stability constants were calculated from the equilibrium data of the 1 : 1 systems. The formation constants of the 1 : 2 complexes were then calculated from 1: 2 titration data with the inclusion of the preliminary constants from the 1: 1 systems.A more detailed re.nement of the constants of the 1 : 1 system was then carried out while including the formation constants of the binuclear complexes obtained from the 1: 2 systems. The procedure was repeated until the di.erences between the calculated and observed values of log [H] were minimized for the potentiometric data of both the 1 : 1 and 1: 2 complexes.Similar procedures were also followed for the calculations of the 1:1:1 ternary systems. Species distributions were calculated from the equilibrium constants with the help of program SPE15 and plotted with SPEPLOT.15 Determination of high protonation constants Because of the extremely high pKa’s of the phenolic groups and low solubility of the ligand containing hydrophobic aromatic rings, the values for two protonation constants had to be determined from the analysis of UV-visible spectral measurements made as a function of the amount of incremental alkali needed to raise the p[H] to about 13.A series of solutions containing appropriate concentrations of KOH and KCl ([KOH] [KCl] = 0.100 M), and with each 1.10 × 104 M in ligand concentration, were measured between 260 and 360 nm, with matched 1.000 cm quartz cells and a thermostat set at 25.0 C. In addition, several solutions were prepared with measured higher concentrations of KOH in order to help determine the ultimate molar absorbance of the totally deprotonated ligand. This was necessary because the protonation constants are too high to carry out the extrapolation to complete dissociation with measurements limited to an ionic strength of 0.100 M.The calculations involved the least-squares minimization of calculated versus observed absorbances through the variation of the .rst and second protonation constants as well as the second extinction coe.cient corresponding to fully protonated phenolic groups.From the appropriate simultaneous equations for mass balance and total absorbance: the elimination of [LIV] gives: TLIV = [LIV](1 K1[H] K1K2[H]2) (3) A = [LIV](eLIV eHLIVK1[H] eH2LIVK1K2[H]2) (4) A = TLIV (eLIV eHLIVK1[H] eH2LIVK1K2[H]2)/ (1 K1[H] K1K2[H]2) (5) where eLIV, eHLIV, and eH2LIV are the extinction coe.cients of LIV 2, HLIV , and H2LIV, respectively, and K1 and K2 are the two stepwise protonation constants leading to the HLIV and H2LIV species from the fully deprotonated ligand L2.The wavelength chosen is near 300 nm, the characteristic wavelength of the phenolate absorbance maximum. X-Ray structure analysis Crystal data for complex 1 are given in Table 5. A colorless parallelepiped (0.42 × 0.31 × 0.14 mm) of 1 was mounted on a glass .ber with epoxy cement at room temperature. Preliminary examination and data collection were performed on a Rigaku AFC-5R X-ray di.ractometer (Mo-Ka .= 0.71073 Å radiation). Cell parameters were calculated from the least-squares .t of the angles for 25 re.ections. Data were collected with 3.6 = 2. = 50 at 293 K. Three control re.ections collected every 97 re.ections showed no signi.cant trends. Lorentz and polarization corrections were applied to 4201 re.ections. A semiempirical absorption correction was applied. A total of 3936 unique re.ections was obtained. The structure was solved by direct methods.16 Full-matrix least-squares anisotropic re.nements17 for all non-hydrogen atoms yielded R = 0.0772, wR(F2) = 0.1498, and GOF = 1.017 at convergence.Hydrogen atoms were placed in idealized positions with isotropic thermal parameters .xed at 0.08 Å2. Neutral atom scattering factors and anomalous scattering correction terms were taken from ref. 18. Positional parameters and the packing diagram of 1 are given in the Supplementary Material. CCDC no. 186/1487.Acknowledgements This research was supported by the Robert A. Welch Foundation through Grant A-259. The crystallographic Table 5 Summary of crystallographic data for complex 1 Formula Formula weight Space group a/Å b/Å c/Å a/ ß/ ./ V/Å3 Z Dc/g cm3 µ/mm1 ./Å T/K R(F) a wR(F2) b GOF(F2) c C38H66N6O8Cl4 876.76 Triclinic, P1� 9.2906(11) 9.4416(13) 14.332(2) 76.417(11) 73.912(10) 71.765(10) 1132.1(3) 1 1.286 0.315 0.71073 193(2) 0.0772 0.1498 1.017 a R(F) = S Fo| |Fc /SFo.b wR(F2) = {[Sw(Fo 2 Fc 2)2]/[Sw(Fo 2)2]}. �� . c GOF(F2) = Sw(Fo 2 Fc 2)2/(ND NP), ND = number of data, NP = number of parameters.J. Chem. Soc., Dalton Trans., 1999, 2441–2449 2449 computing system in the Crystal and Molecular Structure Laboratory of the Department of Chemistry, Texas A&M University, were purchased from funds provided by the National Science Foundation (Grant CHE-8513273). We thank Dr Abraham Clear.eld, Texas A&M University, for use of the AFC5R X-ray di.ractometer and thank Dr Lloyd W.Sumner for his assistance with the mass spectral analyses. References 1 (a) J. B. Vincent, G. L. Olivier-Lilley and B. A. Averill, Chem. Rev., 1990, 90, 1447; (b) J. D. Lipscomb, Annu. Rev., Microbiol., 1994, 48, 371. 2 (a) R. H. Holm, P. Kennepohl and E. I. Solomon, Chem. Rev., 1996, 96, 2239; (b) A. L. Feig and S. J. Lippard, Chem. Rev., 1994, 94, 759; (c) K. D. Karlin, Science, 1993, 261, 701. 3 (a) A. Stassinopoulos, S.Mukerjee and J. P. Caradonna, Mechanistic Bioinorganic Chemistry, Plenum Press, New York, 1995, p. 84; (b) V. McKee, Adv. Inorg. Chem., 1993, 40, 323. 4 W. H. Armstrong, A. Spool, G. C. Papaefthymiou, R. B. Frankel and S. J. Lippard, J. Am. Chem. Soc., 1984, 106, 3653; (b) K. Wieghardt, K. Pohl and W. Gebert, Angew. Chem., Int. Ed. Engl., 1983, 22, 727; (c) S. Menage, Y. Zhang, M. P. Hendrich and L. Que, Jr., J. Am. Chem. Soc., 1992, 114, 7786; (d) N. Kitajima, H. Fukui and H.Moro-oka, J. Chem. Soc., Chem. Commun., 1988, 485. 5 (a) A. S. Borovik and L. Que, Jr., J. Am. Chem. Soc., 1998, 110, 2345; (b) V. D. Campbell, E. J. Parsons and W. T. Pennington, Inorg. Chem., 1993, 32, 1773; (c) M. Suzuki, A. Uehara, H. Oshio, K. Endo, M. Yanaga, S. Kida and K. Saito, Bull. Chem. Soc. Jpn., 1987, 60, 3547. 6 C. L. Spiro, S. L. Lambert, T. J. Smith, E. N. Duesler, R. R. Gagne and D. N. Hendrickson, Inorg. Chem., 1981, 20, 1229; (b) H. S. Mountford, D. B.MacQueen, A. Li, J. W. Otvos, M. Calvin, R. B. Frankel, L. O. Spreer, Inorg. Chem., 1994, 33, 1748; (c) R. J. Motekaitis, W. B. Utley and A. E. Martell, Inorg. Chim. Acta, 1993, 212, 15. 7 (a) S. K. Mandal, L. K. Thompson, K. Nag, J. P. Charland and E. J. Gabe, Inorg. Chem., 1987, 26, 1391; (b) R. Das, K. K. Nanda, K. Venkatsubramanian, P. Paul and K. Nag, J. Chem. Soc., Dalton Trans., 1992, 1253; (b) K. K. Nanda, S. K. Dutta, S. Baitalik, K. Venkatsubramanian and K. Nag, J. Chem.Soc., Dalton Trans., 1995, 1239; (d ) S. Dutta, R. Werner, S. Mohanta Florke, K. K. Nanda, W. Haase and K. Nag, Inorg. Chem., 1996, 35, 2292; (e) K. K. Nanda, L. K. Thompson, J. N. Bridson and K. Nag, J. Chem. Soc., Chem. Commun., 1994, 1337. 8 R. M. Smith, A. E. Martell and R. J. Motekaitis, Critical Stability Constants Database, Version 4, NIST, Gaithersburg, MD, USA, 1993. 9 Z. Wang, J. Reibenspies and A. E. Martell, Inorg. Chem., 1997, 36, 629. 10 The complexity of the ligands discussed here requires that nomenclature now in use be revised (refer to N.F. Curtis, Coord. Chem. Rev., 1968, 3, 3 and J. C. Dabrowiak, P. H. Merrell and D. H. Busch, Inorg. Chem., 1982, 11, 1979; and compare reference 7 and reference 9). In order to represent these and more complicated ligands by convenient abbreviations we are recommending a new abbreviation system based in part on the starting materials of bis(primary amines) and dialdehydes used for preparation of macrocyclic ligands.In this system the internal ring size of the macrocyclic ligand is indicated by a number in brackets. In the absence of any unsaturated Schi. base bonds the heading “R” is adopted to indicate that all Schi. base bonds are reduced. Substituents, heteroatoms and azomethine linkages may be indicated with or without positions depending on the information that needs to be conveyed. For example the abbreviation for ligand 20,41-dimethyl-3,16,24,27,43,44,46,47-octaazaheptacyclo- [37.3.1.1.5,91.10,141.18,221.26.301.31,35]-octatetraconta-5,7,9(43)12,12, 14(44),18,20,22(45),26,28,30(46)31,33,35(47)39,41,1(48)-octadecaene- 45,48-diol (see Fig. 1) then becomes [30]RBBPyBC (B = bis, BPy = bipyridine, and C = cresol). The abbreviation for ligand 15,31-dimethyl-3,11,19,27,33,35-hexaazapentacyclo- [27.3.1.1.5,91.13,171.21,25]-hexatriconta-3,5,7,9(33),10,13,15,17(34),19, 21,23,25(35),26,29,31,1(36)-hexacaene-34,36-diol becomes [24]- 1,6,13,18-tetraSb-BPyBC (Sb = Schi. base). These represent relatively complex abbreviations and often could be shortened further, for example, [24]BPyBC for [24]-1,6,13,18-tetraSb-BPyBC. Since the subject of this paper deals almost exclu with metal complexes of 15,31-dimethyl-3,11,19,27,33,35-hexaazapentacyclo- [27.3.1.1. 5,91. 13,171. 21,25]-hexatriaconta-5,7,9(33),13,15,17(34),21,23, 25(35),29,31,1(36)-dodecaene-34,36-diol, the short abbreviation ([24]RBPYBC or the dianion, LIV 2) is used. Our system is designed to use the simplest abbreviation that contains the necessary structural information in the context of the discussion that is at hand. While these abbreviations are still more cumbersome than we might like, they are short enough to use in tabulated entries and one can derive from them much pertinent structural information. 11 G. C. Pimentel and A. L. McClellan, The Hydrogen Bond, Reinhold, New York, 1960, p. 290. 12 (a) F. L’Eplattenier, I. Murase and A. E. Martell, J. Am. Chem. Soc., 1967, 89, 837; (b) R. J. Motekaitis, A. E. Martell and M. J. Welch, Inorg. Chem., 1990, 29, 1463; (c) M. G. Basallote and A. E. Martell, Inorg. Chem., 1988, 27, 4219. 13 M. Suzuki, H. Oshio, A. Uehara, K. Endo, M. Yanaga, S. Kida and K. Saito, Bull. Chem. Soc. Jpn., 1988, 61, 3907. 14 Z. Wang, A. E. Martell and R. J. Motekaitis, Chem. Commun., 1998, 1523. 15 A. E. Martell and R. J. Motekaitis, The Determination and Use of Stability Constants, VCH Publishers, New York, 2nd edn., 1992. 16 G. M. Sheldrick, SHELXS 86, Program for Crystal Structure Solutions, University of Göttingen, Germany, 1986. 17 G. M. Sheldrick, SHELXS 93, Program for Crystal Structure Solutions, University of Göttingen, Germany, 1993. 18 T. Hahn and D. Reidel, International Tables for X-ray Crystallography, Vol. C, distributed by Kluwer Academic Publishers, Dordrecht, 1992. Paper 8/08051H

ISSN:1477-9226    

DOI:10.1039/a808051h

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1998, Pages 2445–2446 2445 Elemental silicon and solid SiO give the same products as SiO2 upon reaction with alkali-metal glycolates Wolfgang Donhärl, Ines Elhofer, Petra Wiede and Ulrich Schubert * Institut für Anorganische Chemie, Technische Universität Wien, Getreidemarkt 9, A-1060 Wien, Austria Treatment of Si, SiO and SiO2 with lithium or sodium ethylene glycolate gave five-co-ordinate silicon ethylene glycolate derivatives in quantitative yield: Li[Si(OCH2CH2O)2- OCH2CH2OH] in the reactions with lithium glycolate and dimeric Na2[Si2(OCH2CH2O)5] with sodium glycolate; reaction of the latter compound with hot methanol resulted in an exchange of the monodentate glycolate group and the formation of Na[Si(OCH2CH2O)2OMe]. Amorphous, solid SiO is technically prepared from Si and SiO2 at high temperatures and is used for making antireflection layers by CVD.Great eVorts have been directed towards the structural and physical characterization of solid SiO.The results are sometimes controversial (possibly also due to the use of ill-defined and diVerently prepared samples), and no clearcut structural model has emerged from these studies.1,2 However it is unambiguous that solid SiO is not just a homogeneous mixture of finely divided silicon and SiO2 phases. The reactivity of solid SiO has only been tested in rather straightforward reactions. By 1907 Potter had already reacted SiO with aqueous and anhydrous HF.3 The products were similar to those expected for a mixture of Si and SiO2.However, solid SiO is stable up to at least 900 8C, and disproportionation into SiO2 and silicon phases is only observed at higher temperatures. In all the other known reactions, SiO was used as a reductant, with the concomitant formation of SiIV compounds.3–6 One of the few straightforward reactions of SiO2 leading to molecular compounds is its reaction with alkali-metal hydroxide and ethylene glycol by which Laine and co-workers obtained monomeric and dimeric five-co-ordinate complexes of composition M[Si(OCH2CH2O)2OCH2CH2OH] and M2[Si2(OCH2CH2O) 5] (M = Li, Na, K or Cs) with two chelating and one monodentate glycolate ligand per silicon.7,8 To compare the reactivity of solid SiO with that of SiO2, we reacted SiO powder † with a solution of lithium or sodium ethylene glycolate in ethylene glycol at T > 140 8C.‡ The glycolate was prepared by reacting one to three molar equivalents of the alkali-metal (relative to SiO) with the glycol.Depending on the temperature, the brown solid SiO dissolved within several hours † Merck Patinal, particle size <0.044 mm. Elemental analysis of the SiO as delivered gave a stoichiometry of SiO1.101. ‡ All manipulations were carried out under an atmosphere of dry and oxygen-free argon, using standard Schlenk tube techniques and dried solvents; SiO, Si (Merck, particle size <0.15 mm) and SiO2 (FO Optipur, Merck) were used as received.Lithium (0.57 g) (or 1.86 g of Na) was added to 80 ml of freshly distilled ethylene glycol and stirred at room temperature until all of the metal was dissolved. Silicon (0.652 g) (or 1.0 g of SiO, or 1.388 g of SiO2) was added and the mixture heated to T > 140 8C until all the solid had disappeared. The clear yellow solution was allowed to cool overnight, and a white precipitate was formed. The solution was concentrated to about 30 ml.The white solid was filtered oV, washed four times with 50 ml of dry, distilled ethanol, and then dried in vacuo at room temperature. (for example, within 4 h at 160 8C), while a slight gas evolution was observed. When the amount of solvent was less than 70 ml g21 SiO, a colorless microcrystalline precipitate of 1 (M = Li) or 2 (M = Na) was quantitatively formed during the reaction; in less concentrated solutions the solids were obtained on cooling. The same reactions were observed when lithium or sodium was directly added to a suspension of SiO in ethylene glycol.The MAS 29Si NMR spectra of the precipitates showed only one peak at about d 2101.5. This proves that only one siliconcontaining product was formed. The signal was in the typical range for five-co-ordinate silicate species. Solid SiO did not react with NaOR (R = Me, Et, Bu, Pri or But) when refluxed in the corresponding alcohol for 1 d. A suitable crystal of 1 was investigated by an X-ray structure analysis.§ The structure contains the monomeric five-coordinate glycolato silicate anion with the trigonal-bipyramidally co-ordinated silicon atom bonded to two chelating and one monodentate glycolate ligands.The square-pyramidally coordinated lithium cation is bridging two silicate anions, leading to a layered crystal structure (Fig. 1). It has contacts to the OH oxygen of the pendant glycolate ligand (apex of the square pyramid) and to the oxygen atoms of the chelating ligands.The basic features of the structure of the silicate anion are the same as those reported for the corresponding potassium 8 and sodium derivatives.9 We got the same results when elemental silicon was similarly treated. As in the case of SiO, gas evolution was observed. While the reaction of elemental silicon with alkali-metal glycolates has not previously been investigated, reactions of Si with monoalcohols in the presence of metal alkoxides are known to give tetraalkoxysilanes.10 Thus, the outcome of the reaction of solid SiO or elemental Si with alkali-metal glycolates in ethylene glycol is the same as for SiO2 under the same conditions (except the hydrogen Si O O O O O HO Si O O O O O Si O O O O O Si O O O O MeO Li+ 2Na+ Na+ – 2– – 1 2 3 § Crystal data for 1: orthorhombic, space group P212121, a = 798.9(2), b = 877.0(2), c = 1336.2(2) pm, U = 936.2(3) × 106 pm3, T = 303 K, Dc = 1.534 g cm23 for Z = 4, F(000) = 456, m = 0.250 mm21, R1 = 0.0263 for all 1734 reflections, wR2 = 0.0532.2446 J.Chem. Soc., Dalton Trans., 1998, Pages 2445–2446 evolution). The powder X-ray diVraction (XRD) spectra of the solids obtained in the reaction of Si, SiO or SiO2 with lithium glycolate in ethylene glycol were identical, independent of the source of silicon. They were also identical with the XRD profile calculated from the single-crystal structure analysis of 1, proving that 1 is the only (crystalline) reaction product.The XRD patterns and TGA profiles of the samples obtained from Si, SiO and SiO2 with sodium glycolate were also identical to each other, but diVerent to the lithium-containing samples. They had the same appearance as that reported for Li2[Si2(OCH2CH2O)5].8 The products formed with sodium glycolate therefore appear to be the dimeric silicates 2, in which Fig. 1 Crystal structure of compound 1. The hydrogen atoms have been omitted for clarity. The dashed lines represent hydrogen bridges and the dotted lines Li]O bonds.Selected bond lengths (pm) and angles (8): Si]O (eq) 167.0(1)–170.5(1), Si]O (ax) 174(1), 174.2(1), Li]O (of OH) 198.1(3), Li]O (of glycolate) 198.8(3)–221.3(3); O (ax)]Si]O (ax) 165.53(5), O (of OH)]Li]O (glycolate) 105.4(1)–122.6(1), O (glycolate)] Li]O (glycolate) 67.19(9)–147.6(1) Fig. 2 Crystal structure of compound 3. The hydrogen atoms have been omitted for clarity. The dashed lines represent hydrogen bridges and the dotted lines Na]O bonds.Selected bond lengths (pm) and angles (8): Si]O (eq) 166.1(3)–169.4(3), Si]O (ax) 173.4(3)–176.2(3), Na]O 232.1–244.5(3); O (ax)]Si]O (ax) 170.3(2), 172.9(2), O]Na]O (trans) 141.6(1)–160.2(1), O]Na]O (cis) 59.9(1)–126.2(1) one glycolate ligand bridges two Si(OCH2CH2O)2 entities. This agrees with the observation of Laine and co-workers that the dimeric compound is preferentially formed from SiO2 when sodium glycolate is used instead of the lithium glycolate. It is known that the pendant glycolate group can be exchanged by other alkoxide moieties.8 Dissolving 2 in hot methanol resulted in the formation of the methoxy derivative 3 (washing with alcohol at room temperature does not result in an exchange of the alkoxide groups, as shown by XRD powder spectra).The structure of the silicate anion of 3, as determined by a single-crystal structure analysis ¶ is very similar to that of 1. The two crystallographically independent silicate anions have a rather similar trigonal-bipyramidal geometry. Both independent sodium cations are six-co-ordinate (strongly distorted octahedral geometry) and bridge the silicate anions.This results in a layered crystal structure (Fig. 2). The main diVerence between 3 and 1 is that there is an interaction of the cation in 3 with the silicon-bonded oxygen atom of the monodentate ligand. The results presented here suggest that the reactivity of SiO is a combination of that of silica and silicon.However, this does not imply that SiO is an intimate mixture of Si and SiO2. If this was the case one would expect reactions typical of elemental silicon. When a suspension of elemental silicon in glycol was heated in the presence of highly dispersed elemental copper, a mixture of alkoxysilanes was obtained as expected for Müller– Rochow type reactions.11 Contrary to this, solid SiO did not react under the same conditions. This result excludes the presence of a distinct silicon phase.However, it does not exclude silicon-rich regions in SiO. Acknowledgements This work was supported by the Fonds zur Förderung der wissenschaftlichen Forschung (FWF). We thank Merck GmbH for the gift of SiO. References 1 H. R. Philipp, J. Phys. Chem. Solids, 1971, 32, 1935. 2 R. J. Temkin, J. Non-Cryst. Solids, 1975, 17, 215. 3 H. N. Potter, Trans. Electrochem. Soc., 1907, 12, 191, 215, 223. 4 A. Weiss and A. Weiss, Z. Anorg.Allg. Chem., 1954, 276, 95. 5 E. Zintl, W. Bräuning, H. L. Grube, W. Krings and M. Morawietz, Z. Anorg. Allg. Chem., 1940, 245, 1. 6 E. G. Rochow, Comprehensive Inorganic Chemistry, Pergamon, New York, 1973, p. 1353. 7 R. M. Laine, K. Y. Blohowiak, T. R. Robinson, M. L. Hoppe, P. Nardi, J. Kampf and J. Uhm, Nature (London), 1991, 353, 642; B. Herreros, S. W. Carr and J. Klinowski, Science, 1994, 263, 1585. 8 K. Y. Blohowiak, D. R. Treadwell, B. L. Mueller, M. L. Hoppe, S. Jouppi, P. Kansal, K. W. Chew, C. L. Scotto, F. Babonneau, J. Krampf and R. M. Laine, Chem. Mater., 1994, 6, 2177. 9 G. J. Gainsford, T. Kemmitt and N. B. Milestone, Acta. Crystallogr., Sect. C, 1995, 51, 8. 10 See, for example, W. Joch, A. Lenz and W. Rogler, Ger. Pat., 2,354,683, 1973; R. D. Yarwood, UK Pat. 2,140,814, 1984. 11 W. Simmler, in Houben-Weyl, Methoden der Organischen Chemie, Georg Thieme, Stuttgart, 1963, vol. VI/2, p. 100. Received 15th May 1998; Communication 8/03672A ¶ Crystal data for 3: monoclinic, space group P21/n, a = 877.8(2), b = 1521.2(2), c = 1393.2(3) pm, b = 96.80(1)8, U = 1847.3(6) × 106 pm3, T = 301 K, Dc = 1.454 g cm23 for Z = 8, F(000) = 848, m = 0.283 mm21, R1 = 0.0589 for 1882 reflections with I > 2s(I), wR2 = 0.1253. CCDC reference number 186/1057. See http://www.rsc.org/suppdata/ dt/1998/2445/ for crystallographic files in .cif format.

ISSN:1477-9226    

DOI:10.1039/a803672a

出版商:RSC    

年代:1998

数据来源: RSC