摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2315–2319 2315 Two new tetranuclear Ï4-carbonato copper(II) complexes. Syntheses, crystal structure and magnetic behaviour of [(Ï4-CO3)(Ï-Br)2{Cu4- (bapa)4}]Br4 and [(Ï4-CO3)(Ï-Cl)2{Cu4(bapma)4}]Cl4?12H2O [bapa 5 bis(aminopropyl)amine and bapma 5 bis(aminopropyl)methylamine] Albert Escuer,a Evaristo Peñalba,a Ramon Vicente,*,a Xavier Solans b and Mercé Font-Bardía b a Departament de Química Inorgànica, Universitat de Barcelona, Diagonal, 647, 08028-Barcelona, Spain b Departament de Cristal.lografia i Mineralogia, Universitat de Barcelona, Martí Franqués s/n, 08028-Barcelona, Spain The syntheses, by fixation of atmospheric CO2, and the crystal structures of the new tetranuclear m4-CO3 22 compounds [(m4-CO3)(m-Br)2{Cu4(bapa)4}]Br4 1 and [(m4-CO3)(m-Cl)2{Cu4(bapma)4}]Cl4?12H2O 2, [bapa and bapma are bis(3-aminopropyl)amine and bis(3-aminopropyl)methylamine respectively] are reported. Crystallographic data for 1 space group C2/c, a = 14.928(5), b = 19.010(3), c = 17.337(4) Å, b = 92.75(4)8, U = 4914(2) Å3 and Z = 4, for 2 space group P21/n, a = 14.947(6), b = 13.047(4), c = 16.084(5) Å, b = 104.75(5)8, U = 3033(2) Å3 and Z = 2.The analogous compound [(m-CO3)(m4-Cl)2{Cu4(bapa)4}]Cl4 3 has been also prepared for comparative purposes; 1–3 show very strong antiferromagnetic coupling. According to the molecular structures, the experimental data were fitted to the expression derived from the Hamiltonian H = 22J12S1?S2 2 2J13 (S1?S3 1 S2S4) 2 2J14 (S1?S4 1 S2?S3) 2 2J34 S3?S4, which corresponds to a rectangular array of spins.The best fit parameters were for 1–3 respectively: 2J12 = 2275(14), 2390(12), 2212(8); 2J34 = 231(4), 226(7), 226(3); 2J14 = 257(10), 210(12), 272(9); 2J13 = 28(8), 22(10), 220(7) cm21; g = 2.03(1), 2.09(1) and 2.12(1). The carbonate anion is a versatile bridging ligand,1 able to generate compounds with different nuclearity including dimers,2,3 trimers,4 tetramers,5 one- 6 or two-dimensional 7 systems.The co-ordination modes described to date for the carbonate ion when it acts as a bridge in polynuclear compounds with nuclearities greater than two are summarized in Fig. 1. In spite of this general interest, there has been no report of a systematic study of procedures for the synthesis of different nuclearities. From the magnetic point of view, the unusual range of magnetic behaviour than can be obtained as a function of the coordination of the bridging carbonato ligand should be pointed out: from strongly coupled,8,9 to moderate 2a or weak 4f,6 antiferromagnetic compounds and even ferromagnetic ones.2e,4a,c,e Furthermore, the magnetochemistry of the m-carbonato ligand is poorly described for nuclearities greater than two. We have recently published the syntheses, based on the carbonate ligand generated from fixation of atmospheric CO2, and the magnetic behaviour of the trinuclear m3-CO3 22 systems [(m3- CO3){Cu3(bapma)3(ClO4)3}]ClO4,4c [(m3-CO3){Ni2(dmpn)4- (H2O)}Ni(dmpn)2(H2O)2][ClO4]4?H2O and [(m3-CO3){Ni3- (bapma)3(NCS)4}] 4d [bapma = bis(3-aminopropyl)methylamine, dmpn = 2,2-dimethylpropane-1,3-diamine]. With the aim of continuing the study of the synthetic methods and the magnetochemistry of the polynuclear derivatives of the carbonato ligand for nuclearities greater than two, this work is devoted to the tetranuclear m4-CO3 22 systems [(m4-CO3)(m-Br)2{Cu4(bapa)4}]- Br4 1 [bapa = bis(3-aminopropyl)amine] and [(m4-CO3)(m-Cl)2- {Cu4(bapma)4}]Cl4?12H2O 2.Complexes 1 and 2 are prepared by the fixation of atmospheric CO2 using copper(II) halides. The crystal structures of 1 and 2 reveal a rectangular arrangement of four copper(II) atoms with a central m4-carbonato bridge with Cl or Br atoms bridging the shorter sides of the rectangle. The tetranuclear nature of the product of the reaction between an aqueous solution of bapa with copper(II) chloride by fixation of atmospheric CO2 was suggested by Curtis et al.10 and structurally confirmed by Einstein and Willis 5a for the analogous [(m4- CO3)(m-Cl)2{Cu4(bapa)4}]Cl4 3, which has also been prepared by us in order to study its magnetic behaviour.The magnetic measurements for 1–3 show strong antiferromagnetic coupling due to the interaction of the copper atoms through four superexchange pathways. The experimental data were fitted to the expression derived from the Hamiltonian H = 22J12 S1?S2 2 2J13(S1?S3 1 S2?S4) 2 2J14(S1?S4 1 S2?S3) 2 2J34 S3?S4, which corresponds to a rectangular array of spins.Experimental Synthesis [(Ï4-CO3)(Ï-Br)2{Cu4(bapa)4}]Br4 1. To a solution of CuBr2 Fig. 1 Structurally characterized co-ordination modes of the carbonato bridge for nuclearities greater than two O C M M O O M O C M O O M M O C M O O M M O C M O O M M M O C M M O O M M O C M M O O M M O C M M O O M M M M a b c d e f g2316 J.Chem. Soc., Dalton Trans., 1997, Pages 2315–2319 (10 mmol) and bis(3-aminopropyl)amine (10 mmol) in water (50 cm3), NHEt2 (5 mmol) was added and maintained for 2 h with vigorous stirring. After three weeks blue crystals of 1, unstable when taken out of the solution at room temperature, were obtained (Found: C, 21.6; H, 5.5; N, 12.1. Calc. for C25H68- Br6Cu4N12O3: C, 22.8; H, 5.2; N, 12.7%). For this reason the structure was determined at 239 K. [(Ï4-CO3)(Ï-Cl)2{Cu4(bapma)4}]Cl4?12H2O 2.To a solution of CuCl2 (10 mmol) and bis(3-aminopropyl)methylamine (10 mmol) in water (50 cm3), NHEt2 (5 mmol) was added and maintained for 2 h with vigorous stirring. After two weeks blue crystals of 2, stable at room temperature, were obtained (Found: C, 26.1; H, 7.2; N, 12.6. Calc. for C29H100Cl6Cu4N12O15: C, 26.3; H, 7.6; N, 12.7%). [(Ï4-CO3)(Ï-Cl)2{Cu4(bapa)4}]Cl4 3. This compound was prepared as previously described,10 analytical data (C, H, N, Cl) were in agreement with the proposed formulae.Magnetic measurements Magnetic measurements were carried out on polycrystalline samples with a SQUID apparatus working in the range 2–300 K under a magnetic field of 0.3 T. Diamagnetic corrections were estimated from Pascal tables. Crystal data collection and refinement Analyses on single prismatic blue crystals of [(m4-CO3)- (m-Br)2{Cu4(bapa)4}]Br4 1 (0.1 × 0.1 × 0.2 mm) and [(m4-CO3)- (m-Cl)2{Cu4(bapma)4}]Cl4?12H2O 2 (0.1 × 0.1 × 0.2 mm) were carried out on an Enraf-Nonius CAD4 X-ray diffractometer. Intensities were collected using the w–2q scan technique with graphite-monochromatized Mo-Ka radiation (l = 0.710 69 Å).A summary of the crystallographic data is reported in Table 1. Unit-cell parameters for 1 and 2 were determined from automatic centring of 25 reflections (12 < q < 218) and refined by the least-squares method. For 1 7053 reflections were measured in the range 1.74 < q < 29.978, 2895 of which were assumed observed applying the condition I > 2 s(I).For 2 9206 reflections were measured in the range 2.04 < q < 29.978, 5707 of which were assumed observed applying the condition I > 2 s(I). For 1 and 2 three reflections were measured every 2 h as orientation and intensity control; significant intensity decay was not observed. Lorentz, polarization and absorption corrections (y scans, for compound 1 only) 11 were made. The structures of 1 and 2 were solved by direct methods, using the SHELXS computer program12 and refined by the fullmatrix least-squares method, with SHELXL 93.13 The function Table 1 Crystallographic data for [m4-CO3)(m-Br)2{Cu4(bapa)4}]Br4 1 and [(m4-CO3)(m-Cl)2{Cu4(bapma)4}]Cl4?12H2O 2 Formula M Crystal symmetry Space group a/Å b/Å c/Å b/8 U/Å3 ZT /K Dc/g cm23 m(Mo-Ka)/cm21 Ra R9 b 1 C25H68Br6Cu4N12O3 1318.53 Monoclinic C2/c 14.928(5) 19.010(3) 17.337(4) 92.75(4) 4914(2) 4 239(1) 1.782 66.24 0.0445 0.1081 2 C29H100Cl6Cu4N12O15 1324.07 Monoclinic P21/n 14.947(6) 13.047(4) 16.084(5) 104.75(3) 3033(2) 2 293(2) 1.450 17.08 0.0555 0.1347 a R(Fo) = S Fo| 2 |Fc /S|Fo|.b R9(Fo 2) = {Sw[(Fo)2 2 (Fc)2]2/Sw(Fo)2}� �� . minimized was Sw |Fo|22&;Fc|2 2, where w = [s2(I)1(0.0639P)2]21 and P = (|Fo|2 1 2|Fc|2)/3 for 1 and w = [s2(I) 1 (0.0797P)2 1 3.1803P]21, P = (|Fo|2 1 2|Fc|2)/3 for 2. Values of f, f 9 and f 0 were taken from ref. 14. The extinction coefficient was 0.0000(7) for 1 and 0.0043(4) for 2.For 1 the three O atoms of the carbonato group and for 2 the three O atoms of the carbonato group and the Cl(1) atom are disordered: an occupancy factor of 0.5 was assigned in accordance with the height of Fourier synthesis and the symmetry conditions. For 1 all the H atoms were computed and refined with an overall isotropic temperature factor using a riding model. The number of parameters refined was 237. Maximum shift/e.s.d. = 7.96, mean shift/e.s.d. = 0.92.Maximum and minimum peaks in the final difference synthesis were 0.722 and 20.616 e Å23, respectively. For 2 46 H atoms were located from a difference synthesis and refined with an overall isotropic temperature factor. The number of parameters refined was 516. Maximum shift/e.s.d. = 0.57, mean shift/e.s.d. = 0.04. Maximum and minimum peaks in final difference synthesis were 0.658 and 20.428 e Å23, respectively. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/523. Results and Discussion Syntheses As mentioned above, we have recently published the synthesis and crystal structure of the trinuclear m3-carbonato system [(m3- CO3){Cu3(bapma)3(ClO4)3}]ClO4.4c The synthetic procedure, previously described by Curtis et.al.10 for the analogous [(m3- CO3){Cu3(bapa)3(ClO4)3}]ClO4, is very similar to the one described here for the syntheses of the m4-carbonato complexes 1–3, but the starting copper(II) salt used to prepare the trinuclear compounds is the perchlorate instead of the copper(II) halide used in the preparation of the tetranuclear ones. Using the potentially tridentate base 2-[2-(2-pyridyl)ethyliminomethyl] pyridine (pip) and copper(II) nitrate, it is possible to obtain 4a another trinuclear m3-carbonato compound [(m3- CO3){Cu3(pip)3(H2O)3}][NO3]4.Consequently, the synthesis of copper(II)–carbonato derivatives with different nuclearities can be placed into two categories: using tridentate amine ligands (like bapa, bapma or pip), atmospheric CO2 or K2CO3 and copper(II) salts of poorly co-ordinative anions like nitrate or perchlorate leads to m3-CO3 22 trinuclear copper(II) derivatives. In contrast, if copper(II) halides (chloride or bromide) are used the resulting compound is a m4-carbonato tetranuclear copper(II) derivative with two bridging halide ligands.There are two published exceptions to this rule: using the bulky tridentate ligands N,N,N9,N0N0-pentaethyldiethylenetriamine (pedien) and 2,4, 4,7-tetramethyl-1,5,9-triazyclododec-1-ene (L) and copper(II) perchlorate, the dinuclear m2-CO3 22 compounds. [(m2-CO3)- {Cu2(pedien)2}][ClO4]2 2a and [(m2-CO3){Cu2(L)2}][ClO4]2?dmf (dmf = dimethylformamide)8 are obtained rather than trinuclear m3-carbonato compounds.The bulky character of pedien and L could be the reason for this anomalous results. Structures of compounds 1 and 2 The structure of these compounds is basically the same and consists of tetranuclear [(m4-CO3)(m-X)2{Cu4(triamine)4}]41 units, X = Cl or Br for compounds 2 and 1 respectively, and four isolated halide counter anions. In 2 there also exist 12 water molecules. Labelled diagrams are shown in Figs. 2 and 3 for compounds 1 and 2 respectively. The main bond lengths and angles are presented in Table 2. The structure of each tetranuclear unit consists of four copper atoms placed at the corners of a rectangle with a m4-carbonate ligand in the centre (disorderedJ. Chem. Soc., Dalton Trans., 1997, Pages 2315–2319 2317 in 1 and 2). The bridging halides are placed on the plane of the rectangle and perpendicular to the short edges. The carbonate acts as a tetradentate ligand: one oxygen atom bridges a pair of halide-bridged Cu atoms, forming a four-membered Cu]X] Cu]O ring, while the other two oxygen atoms are linked to each of the remaining two Cu atoms, forming a sixmembered Cu]X]Cu]O]C]O ring.One bapa or bapma ligand is mer co-ordinated to each copper atom making them five-coordinate. There are two different average C]O distances in the m4- carbonate ligand depending on whether the O atom bridges two Cu atoms or links to one Cu atom.In the first case the average C]O distances are 1.416(8) and 1.472(4) Å for 1 and 2 respectively. In the second case, the average C]O distances are 1.195(11) and 1.211(5) Å for 1 and 2 respectively. These values compare well with similar average C]O distances in the analogous compound [(m4CO3)(m-Cl)2{Cu4(bapa)4}]Cl4 3 5a which are 1.412(10) Å for the four- and 1.224(10) Å for the six-membered rings. As in the case of the C]O distances, the related distances and angles for 1–3 compare well, with the obvious exception of the structural parameters involving the different halides.In 1, the Cu]Br]Cu average angle is 88.32(4)8 and the average Cu]Br distance is 2.712(1) Å. In 2, the Cu]Cl]Cu average angle is 94.3(1)8 and the Cu]Cl average distance is 2.578(3) Å. In 3,5a the average Cu]Cl]Cu angle is 93.1(1)8 and the average Cu]Cl distance is 2.532(2) Å. Fig. 2 An ORTEP15 drawing of the cation [(m4-CO3)(m-Br)2- {Cu4(bapa)4}]41 of compound 1 with atom labelling scheme Fig. 3 An ORTEP drawing of the cation [(m4-CO3)(m- Cl)2{Cu4(bapma)4}]41 of compound 2 with atom labelling scheme Magnetic results Plots of cmvs. T (where cm is the molar susceptibility) for compounds 1–3 are shown in Fig. 4. For 1 the cm value of 4.0 × 1023 cm3 mol21 at room temperature increases continuously when the temperature decreases, giving a maximum of 12.9 × 1023 cm3 mol21 at 30 K, decreasing quickly close to zero at 4 K, and then increasing slightly due to the presence of a small quantity Table 2 Selected bond lengths (Å) and angles (8) for [(m4-CO3)(m-Br)2- {Cu4(bapa)4}]Br4 1 and [(m4-CO3)(m-Cl)2{Cu4(bapma)4}]Cl4?12H2O 2 Compound 1 Cu(1)]N(13) Cu(1)]N(12) Cu(1)]O(2) Cu(2)]N(21) Cu(2)]N(22) Cu(2)]O(3) C(1)]O(3) C(1)]O(2) N(13)]Cu(1)]N(11) N(11)]Cu(1)]N(12) N(11)]Cu(1)]O(1) N(13)]Cu(1)]O(2) N(12)]Cu(1)]O(2) N(13)]Cu(1)]Br(1) N(12)]Cu(1)]Br(1) O(2)]Cu(1)]Br(1) N(21)]Cu(2)]N(22) N(21)]Cu(2)]O(2) N(22)]Cu(2)]O(2) N(23)]Cu(2)]O(3) O(2)]Cu(2)]O(3) N(23)]Cu(2)]Br(1) O(2)]Cu(2)]Br(1) Cu(1)]Br(1)]Cu(2) O(3)]C(1)]O(1) O(1)]C(1)]O(2i) O(1i)]C(1)]O(2) C(1)]O(2)]Cu(2) Cu(2)]O(2)]Cu(1) 2.015(5) 2.043(5) 2.125(7) 2.001(4) 2.065(5) 2.158(12) 1.102(11) 1.416(8) 152.5(2) 94.9(2) 79.2(3) 89.3(3) 164.8(2) 103.7(2) 94.05(12) 71.4(2) 92.8(2) 94.3(3) 164.4(3) 84.5(3) 40.9(4) 107.14(14) 71.5(2) 88.32(4) 143.3(6) 107.4(5) 107.4(5) 117.3(4) 128.4(4) Cu(1)]N(11) Cu(1)]O(1) Cu(1)]Br(1) Cu(2)]N(23) Cu(2)]O(2) Cu(2)]Br(1) C(1)]O(1) N(13)]Cu(1)]N(12) N(13)]Cu(1)]O(1) N(12)]Cu(1)]O(1) N(11)]Cu(1)]O(2) O(1)]Cu(1)]O(2) N(11)]Cu(1)]Br(1) O(1)]Cu(1)]Br(1) N(21)]Cu(2)]N(23) N(23)]Cu(2)]N(22) N(23)]Cu(2)]O(2) N(21)]Cu(2)]O(3) N(22)]Cu(2)]O(3) N(21)]Cu(2)]Br(1) N(22)]Cu(2)]Br(1) O(3)]Cu(2)]Br(1) O(3i)]C(1)]O(1i) O(3)]C(1)]O(2i) O(3i)]C(1)]O(2) C(1)]O(1)]Cu(1) C(1)]O(2)]Cu(1) C(1)]O(3)]Cu(2) 2.030(5) 2.032(10) 2.6994(14) 2.025(5) 2.072(5) 2.7250(13) 1.288(10) 90.0(2) 82.9(3) 149.4(3) 92.7(3) 45.3(3) 102.89(13) 116.5(3) 151.8(2) 89.1(2) 91.2(3) 81.8(3) 154.4(3) 100.8(2) 93.5(2) 112.1(3) 143.3(6) 109.3(7) 109.3(7) 127.7(7) 114.2(4) 131.1(9) Compound 2 Cu(1)]N(3) Cu(1)]N(1) Cu(1)]O(1) Cu(2)]N(6) Cu(2)]N(4) Cu(2)]O(29) C(1)]O(1) C(1)]O(3) N(3)]Cu(1)]N(1) N(1)]Cu(1)]O(1) N(1)]Cu(1)]N(2) N(3)]Cu(1)]O(39) N(2)]Cu(1)]O(39) N(1)]Cu(1)]Cl(1) N(2)]Cu(1)]Cl(1) N(6)]Cu(2)]N(4) N(4)]Cu(2)]O(29) N(4)]Cu(2)]N(5) N(6)]Cu(2)]O(1) N(5)]Cu(2)]O(1) N(4)]Cu(2)]Cl(1) N(5)]Cu(2)]Cl(1) Cu(2)]Cl(1)]Cu(1) C(1)]O(1)]Cu(1) Cu(1)]O(1)]Cu(2) C(1)]O(3)]Cu(19) O(3)]C(1)]O(2) O(29)]C(1)]O(19) O(2)]C(1)]O(1) 1.987(4) 1.996(3) 2.047(4) 1.980(2) 1.992(4) 2.065(6) 1.472(4) 1.190(5) 155.5(2) 89.7(2) 92.98(13) 82.1(2) 153.2(2) 103.10(14) 100.53(11) 157.4(4) 82.1(2) 92.68(14) 90.3(2) 164.64(14) 97.8(2) 101.72(11) 104.82(11) 116.1(2) 129.3(2) 131.3(4) 139.3(3) 109.4(3) 109.4(3) Cu(1)]N(2) Cu(1)]O(39) Cu(1)]Cl(1) Cu(2)]N(5) Cu(2)]O(1) Cu(2)]Cl(1) C(1)]O(2) N(3)]Cu(1)]O(1) N(3)]Cu(1)]N(2) O(1)]Cu(1)]N(2) N(1)]Cu(1)]O(39) N(3)]Cu(1)]Cl(1) O(1)]Cu(1)]Cl(1) O(39)]Cu(1)]Cl(1) N(6)]Cu(2)]O(29) N(6)]Cu(2)]N(5) O(29)]Cu(2)]N(5) N(4)]Cu(2)]O(1) N(6)]Cu(2)]Cl(1) O(29)]Cu(2)]Cl(1) O(1)]Cu(2)]Cl(1) C(11)]N(1)]Cu(1) C(1)]O(1)]Cu(2) C(1)]O(2)]Cu(29) O(39)]C(1)]O(29) O(39)]C(1)]O(19) O(3)]C(1)]O(1) 2.067(3) 2.080(5) 2.376(2) 2.078(3) 2.089(4) 2.342(3) 1.232(5) 92.6(2) 91.71(13) 163.34(14) 82.9(2) 99.69(14) 62.88(13) 106.2(2) 82.8(2) 92.22(13) 150.8(2) 90.7(2) 102.77(14) 107.4(2) 62.96(13) 119.3(3) 114.5(2) 130.4(4) 139.3(3) 110.9(3) 110.9(3) Symmetry transformations used to generate equivalent atoms: i 2x 1 ��� , 2y 1 ��� , 2z.(9) 2x 1 1, 2y 1 1, 2z.2318 J. Chem. Soc., Dalton Trans., 1997, Pages 2315–2319 of paramagnetic impurities. This behaviour indicates a global antiferromagnetic coupling between the copper(II) ions. Compounds 2 and 3 show similar behaviour: 3.8 × 1023 and 4.2 × 1023 cm3 mol21 at room temperature for 2 and 3 respectively, a maximum of 17.8 × 1023 cm3 mol21 at 23 K and 13.5 × 1023 cm3 mol21 at 31 K for 2 and 3 respectively, a minimum at 5 K for 2 (9 K for 3) and a slight increase due to the presence of a small quantity of paramagnetic impurities. The experimental data were fitted to the expression derived from the Hamiltonian H = 22J12 S1?S2 2 2J13 (S1?S3 1 S2?S4) 2 2J14 (S1?S4 1 S2?S3) 2 2J34 S3?S4, which corresponds to a tetrameric array of spins.16 The expression was also corrected with a r paramagnetic impurity parameter in order to fit the low-temperature data resulting in equation (1).cm = 0.37515 g2 T F(1 2 r)S10e (J12 1 J34)/2 1 (J14 1 J13) 0.69504 T 1 –––––––––––––– 2e (J12 1 J34)/2 2 (J14 1 J13) 0.69504 T 1 2e 2(J12 1 J34)/2 1 ÷(J12 2 J34)2 1 (J14 2 J13)2 0.69504 T 1 ––––––––––––– 2e 2(J12 1 J34)/2 2 ÷(J12 2 J34)2 1 (J14 2 J13)2 0.69504 T D@S5e (J12 1 J34)/2 1 (J14 1 J13) 0.69504 T 1 ––––––––––––– 3e (J12 1 J34)/2 2 (J14 1 J13) 0.69504 T 1 3e 2(J12 1 J34)/2 1 ÷(J12 2 J34)2 1 (J14 2 J13)2 0.69504 T 1 –––––––––––––– 3e 2(J12 1 J34)/2 2 ÷(J12 2 J34)2 1 (J14 2 J13)2 0.69504 T 1 –––––––––––––––––––– e 2(J12 1 J34)/2 2 (J14 1 J13) 1 ÷(J12 1 J34 2 J14 2 J13)2 1 3(J14 2 J13)2 0.69504 T 1 –––––––––––––––––––– e 2(J12 1 J34)/2 2 (J14 1 J13) 2 ÷(J12 1 J34 2 J14 2 J13)2 1 3(J14 2 J13)2 0.69504 T D1rG (1) The exchange interactions and the atom labelling scheme are illustrated in Fig. 5. The best fit parameters, using as a criterion of best fit the minimum value of R = S(cm calc 2 cm obs)2/ S(cm obs)2, were: 2J12 = 2275(14), 2J34 = 231(4), 2J14 = 257(10), Fig. 4 A plot of cm vs. T for compounds 1(h), 2(*) and 3(d). Solid lines show the best fit obtained (see text) 2J13 = 28(8) cm21, g = 2.03(1), r = 5(8) × 1024 with R = 1.7 × 1025 for 1; 2J12 = 2390(12), 2J34 = 226(7), 2J14 = 210(12), 2J13 = 22(10) cm21, g = 2.09(1), r = 1.4(5) × 1022 with R = 2 × 1025 for 2; and 2J12 = 2212(8), 2J34 = 226(3), 2J14 = 272(9), 2J13 = 220(7) cm21, g = 2.12(1), r = 5(7) × 1023 with R = 5.9 × 1024 for 3.The 2J12 and 2J34 values are reliable because they are determined by the shape of the cm vs. T curve, mainly in the high-temperature region, and the maximum of the curve respectively whereas the 2J14 and 2J13 values are slightly sensitive to the shape or the maximum of the curve and their values are poorly determined, reflecting the difficulty of including six parameters in the regression analysis. From the best fit parameters, the most efficient superexchange pathway in 1–3 is that corresponding to J12: two copper( II) atoms bridged by one O (carbonate) and one halide. The participation of the bridging halide in the superexchange pathway should be negligible because it is placed on the apical position of the square pyramidal polyhedron around the copper(II) atoms.The J12 superexchange pathway may be related to the diamagnetic dinuclear m2-carbonate compounds [(m2-CO3){Cu2- (L)2}][ClO4]2?dmf8 and [(m2-CO3){Cu2(tmpn)2Cl2}]9 (tmpn = N,N,N9,N9-tetramethylpropane-1,3-diamine), in which the two copper atoms are bridged by a doubly bidentate carbonato group: when the two copper atoms in the Cu,(carbonate),Cu plane are moved further away from the non-bridging O atoms of the carbonate, and the Cu]O]Cu angle is opened, the 2J12 coordination mode is reached.In the diamagnetic dinuclear compounds, the Cu]O distances are short and the Cu]O]Cu angles are close to 1808: 176.6(2)8 for [(m2-CO3){Cu2(L)2}][ClO4]2?dmf8 and 170.268 for [(m2-CO3){Cu2(tmpn)2Cl2}],9 adequate for a good Cu]O]Cu orbital overlap.2a In compounds 1, 2 and 3 the Cu]O distances are also short, but the Cu(1)]O(2)]Cu(2) angles are 128.4(4)8, 129.3(2)8 and 124.0(4)8 respectively, and the overlap should diminish.For this reason, an antiferromagnetic coupling may be predicted, but with a 2J value lower than that found in [(m2-CO3)- {Cu2(L)2}][ClO4]2?dmf8 or [(m2-CO3){Cu2(tmpn)2Cl2}].9 The 2J12 values of 2275(14), 2390(12) and 2212(8) cm21 for 1, 2 and 3 respectively are as expected.The superexchange pathway corresponding to J34, two copper(II) atoms bridged by a syn–syn carboxylato group, may also be predicted to be antiferromagnetic by analogy with copper acetate derivatives and related complexes,17–19 but the value of the coupling constant should be lower due to the decreasing number of carboxylate bridges from four to one.20 The 2J34 values are 231(4), 226(7) and 226(3) cm21 for 1, 2 and 3 respectively.The sign of the superexchange pathway corresponding to J13, two copper(II) atoms bridged by a syn–anti carboxylato group, is difficult to Fig. 5 Exchange interactions and atom labelling scheme for the four operative exchange pathways in compounds 1–3 O C O O Cu Cu Cu Cu O C O O Cu Cu Cu Cu O C O O Cu Cu Cu Cu O C O O Cu Cu Cu Cu J 34 J 12 J 13 J 14 Cu O Cu C O O O C Cu Cu O OJ. Chem. Soc., Dalton Trans., 1997, Pages 2315–2319 2319 predict but the value should be low:21,22 2J13 = 28(8) for 1, 122(10) for 2 and 220(7) cm21 for 3.The superexchange pathway corresponding to J14, two copper(II) atoms bridged by an anti–anti carboxylato group, has been measured for the dinuclear carbonato compound [(m2-CO3){Cu2(bipy)4}][PF6]2?2dmf (bipy = 4,49-bipyridine),2g which displays antiferromagnetic coupling with a 2J value of 2140.5 cm21. The 2J14 values of 257(10), 210(12) and 272(9) cm21 for 1, 2 and 3 respectively, taking into account the structural differences and the certain indeterminacy of 2J14, are in accordance with this value.Conclusion From the synthetic point of view, the strategy to achieve trinuclear m3-carbonato–copper(II) derivates is to use copper(II) salts of poorly co-ordinative anions such as nitrate or perchlorate, tridentate amines (e.g. bapa, bapma or pip) and atmospheric CO2 or K2CO3. In contrast, if the starting salt is a copper(II) halide (chloride or bromide), with the same reagents and method, the resulting compound is a m4-carbonato tetranuclear copper(II) derivative with two bridging halides.In this work we have shown two examples of m4-carbonato tetranuclear copper(II) compounds. The magnetic behaviour of these compounds has been magnetically studied by using the expression derived from thn H = 22J12 S1?S2 2 2J13 (S1?S3 1 S2?S4) 2 2J14 (S1?S4 1 S2?S3) 2 2J34 S3?S4, which corresponds to a tetrameric array of spins.The values of 2J12 and 2J34 can be determined with precision but 2J14 and 2J13 are sensitive to the shape or the maximum of the curve (cm vs. T) and their values are poorly determined. Acknowledgements This work was supported financially by the Comisión Interministerial de Ciencia y Tecnología (PB93/0772 grant). E. P. thanks Comissió Interdepartamental de Recerca i Tecnologia (Generalitat de Catalunya) for a doctoral fellowship. References 1 D. A. Palmer and R.V. Eldik, Chem. Rev., 1983, 83, 651. 2 (a) J. Sletten, H. Hope, M. Julve, O. Kahn, M. Verdaguer and A. Dworkin, Inorg. Chem., 1988, 27, 542; (b) Z. Tyeklar, P. P. Partha, R. Jacobson, A. Farooq, K. D. Karlin and J. Zubieta, J. Am. Chem. Soc., 1989 111, 388; (c) N. Kitajima, T. Koda, S. Hashimoto, T. Kitagawa and Y. Moro-oka, J. Am. Chem. Soc., 1991, 113, 5664; (d) N. Kitajima, S. Hikichi, M. Tanaka and Y. Moro-oka, J. Am. Chem. Soc., 1993, 115, 5496; (e) A. L. Brenk, K. A. Byriel, D.P. Fairlie, L. R. Gahan, G. R. Hanson, C. J. Hawkins, A. Jones, C. H. L. Kennard, B. Moubaraki and K. S. Murray, Inorg. Chem., 1994, 33, 3549; ( f ) T. N. Sorrell, W. E. Allen and P. S. White, Inorg. Chem., 1995, 34, 952; (g) P. E. Kruger, G. D. Fallon, B. Moubaraki, K. J. Berry and K. S. Murray, Inorg. Chem., 1995, 34, 4808; (h) A. L. Rheingold, B. S. Haggerty and S. Trofimenko, Angew. Chem., Int. Ed. Engl., 1994, 33, 1983. 3 R. Kempe, J. Sieler, D. Walther, J. Reinhold and K.Z. Rommel, Z. Anorg. Allg. Chem., 1993, 619, 1105; H. Harada, M. Kodera, G. VucKovic, N. Matsumoto and S. Kida, Inorg. Chem., 1991, 30, 1190; N. Arulsamy, P. A. Goodson, D. J. Hodgson, G. Glerup and K. Michelsen, Inorg. Chim. Acta, 1994, 216, 21; L. Spiccia, G. D. Fallon, A. Markiewicz, K. S. Murray and H. Riesen, Inorg. Chem., 1992, 31, 1066. 4 (a) G. Kolks, S. J. Lippard and J. V. Waszczak, J. Am. Chem. Soc., 1980, 102, 4832; (b) C. Bazzicalupi, A. Bencini, A.Bianchi, V. Fusi, P. Paoletti and B. Valtancoli, J. Chem. Soc., Chem. Commun., 1995, 1555; (c) A. Escuer, R. Vicente, E. Peñalba, X. Solans and M. Font- Bardía, Inorg. Chem., 1996, 35, 248; (d) A. Escuer, R. Vicente, S. B. Kumar, X. Solans and M. Font-Bardía, Inorg. Chem., 1996, 35, 3094; (e) C. Bazzicalupi, A. Bencini, A. Bianchi, F. Corana, V. Fusi, C. Giorgi, P. Paoli, P. Paoletti, B. Valtancoli and C. Zanchini, Inorg. Chem. 1996, 35, 5540; ( f ) A. Escuer, R. Vicente, S. B.Kumar, X. Solans and M. Font-Bardía, J. Chem. Soc., Dalton Trans., 1997, 403. 5 (a) F. W. B. Einstein and A. C. Willis, Inorg. Chem., 1981, 20, 609; (b) R. Alvarez, J. L. Atwood, E. Carmona, P. J. Perez, M. L. Poveda and R. D. Rogers, Inorg. Chem., 1991, 30, 1493. 6 J. Sletten, Acta Chem. Scand., Ser. A, 1984, 38, 491; D. Y. Jeter, D. J. Hodgson and W. E. Hatfield, Inorg Chem., 1972, 11, 185. 7 P. C. Healy and A. H. White, J. Chem. Soc., Dalton Trans., 1972, 1913; P. D. Brotherton and A. H. White, J. Chem. Soc., Dalton Trans., 1973, 2338; A.K. Gregson and P. C. Healy, Inorg. Chem., 1978, 17, 2969. 8 A. R. Davis, F. W. B. Einstein, N. F. Curtis and J. W. L. Martin, J. Am. Chem. Soc., 1978, 100, 6258. 9 M. R. Churchill, G. Davies and M. El-Sayed, Inorg. Chem., 1979, 18, 2299. 10 N. F. Curtis, R. W. Hay and Y. M. Curtis, J. Chem. Soc. A, 1968, 182. 11 A. C. T. North, D. C. Phillips and F. C. Matthews, Acta Crystallogr., Sect. A, 1968, 24, 351. 12 G. M. Sheldrick, Acta. Crystallogr., Sect. A, 1990, 46, 467. 13 G. M. Sheldrick, SHELXL 93, University of Göttingen, 1993. 14 International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4, pp. 99–110 and 149. 15 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 16 W. E. Hatfield and G. W. Inman, Inorg. Chem., 1969, 8, 1376. 17 P. de Meester, S. R. Fletcher and A. C. Skapsky, J. Chem. Soc., Dalton Trans., 1973, 2575. 18 H. U. Gudel, A. Stebler and A. Furrer, Inorg. Chem., 1979, 18, 1021. 19 B. Chiari, O. Piovesana, T. Tarantelli and P. F. Zanazzi, Inorg. Chem., 1993, 32, 4834. 20 A. Neels, H. Stoeckli-Evans, A. Escuer and R. Vicente, unpublished work. 21 E. Colacio, J. M. Dominguez-Vera, R. Kivekäs, J. M. Moreno, A. Romerosa and J. Ruiz, Inorg. Chim. Acta, 1993, 212, 115. 22 R. L. Carlin, K. Kopinga, O. Kahn and M. Verdaguer, Inorg. Chem., 1986, 25, 1786. Received 18th February 1997; Paper 7/01138E

ISSN:1477-9226    

DOI:10.1039/a701138e

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2321–2326 2321 Polymeric silver(I) complexes of the multinucleating ligand 4,7-dihydro-5-methyl-7-oxo[1,2,4]triazolo[1,5-a]pyrimidine. Analogous hydrogen-bonded structures in the crystal and vapour phases of the ligand Jorge A. R. Navarro,a M. Angustias Romero,a Juan M. Salas,*,†,a René Faure b and Xavier Solans c a Departamento de Química Inorgánica, Universidad de Granada, Av. de Fuentenueva S/N, 18071 Granada, Spain b Laboratoire de Chimie Analytique II, LICAS, Université Claude Bernard, Lyon-1, 69622 Villeurbanne, France c Departamento de Cristalografía, Mineralogía y Depositos Minerales, Universidad de Barcelona, Barcelona, Spain X-Ray crystallography showed that the crystal structure of Hmtpo (4,7-dihydro-5-methyl-7-oxo[1,2,4]triazolo- [1,5-a]pyrimidine) is built up of hydrogen-bonded polymeric chains, whereas mass spectroscopy and solution 15N NMR spectroscopy suggested the existence of a dimeric structure comprising eight-membered ? ? ?H]N]C]N ? ? ?H]N]C]N rings in less condensed phases.On the other hand, the reaction between the silver(I) salts AgX (X = NO3, ClO4 or ��� SO4) and Hmtpo yielded polymeric complexes. The compounds have been structurally characterised by IR spectroscopy and X-ray crystallography. The X-ray results show that the compounds containing the Hmtpo derivative in its neutral form comprise infinite one-dimensional chains, in which the ligand bridges the metal centres through N(1) and N(3) donor atoms.The presence of an additional soft and bulky ligand such as triphenylphosphine in [{AgX(m-Hmtpo-k2N1,N3)(PPh3)}n] (X = NO3 or ClO4) partially changes the tendency to form polymeric complexes, lengthening the Ag]N(1) bond distance by 0.35 Å. Finally, deprotonation of Hmtpo results in an additional available coordination position at N(4), the ligand bridging three metal centres in [{Ag3(m3-mtpo-k4N1,N3,N4,O7)2(HSO4)(H2O)2]?H2O}n].The new co-ordination mode results in the formation of eight-membered Ag]N]C]N]Ag]N]C]N rings, which give rise to short intermetallic contacts of 3.078(1) Å. The structures of free Hmtpo in the solid state and the postulated vapour-phase structure are compared to those of linear co-ordinated silver(I) complexes. Hydrogen bonding plays a fundamental role in several chemical and biochemical processes. Its highly selective and directional nature makes it ideal for the construction and stabilisation of large non-covalently linked molecular and supramolecular architectures.1 Indeed, the biological world is replete with examples of such systems: nucleic acids and protein tertiary structures.2 Some authors have extensively studied the replacement of hydrogen bonds by metal entities of appropriate geometry [e.g.AgI, trans-(H3N)2PtII, AuI, etc.] in models of biological interest, such as nucleobase Watson–Crick and Hoogstein pairs,3,4 triplets 5 and quartets,6 or materials of technological interest,7 concluding that the basic structures are preserved, but the strength of interaction is changed.At the same time, the tendency of AgI to build polymeric complexes with the help of ligands containing multiple donor positions makes this ion suitable for building supramolecular co-ordination compounds.8,9 We are currently involved in a detailed study of the coordination chemistry of the polydentate 4,7-dihydro-5-methyl- 7-oxo[1,2,4]triazolo[1,5-a]pyrimidine (Hmtpo), which has a great versatility as a ligand forming either mono-10 or polynuclear metal complexes.11,12 At the same time, this derivative is well known as a stabilising agent for photographic silver halide emulsions.13,14 Its behaviour has been related to the stability and high insolubility of the compounds formed in its reactions with silver salts as a result of its multidentate co-ordination to the metal centres,15 e.g.pKsp = 9.7 for [{Ag(m3-mtpo-N1,N3, N4,O7)}2n].16 † E-Mail: jsalas@goliat.ugr.es In this paper we present results concerning the preparation and structural characterisation by IR spectroscopy and X-ray crystallography of a series of silver(I) complexes formed upon reaction of AgI and Hmtpo in acidic aqueous or ethanolic media.The hydrogen-bonded polymeric crystal structure of free Hmtpo, as well as its postulated vapour-phase dimer structure, from mass spectroscopy, comprising eight-membered H]N]C]N? ? ?H]N]C]N? ? ? rings, are also reported and compared to the similar structures found in linearly coordinated silver(I) complexes.Experimental Reactants and methods The compound Hmtpo was obtained from Aldrich Chem. Co. and used as received. Crystals suitable for X-ray analysis were obtained by recrystallisation from MeOH. The other chemical reagents and solvents were supplied by commercial sources. All experiments were performed in air. Preparations [{Ag(NO3)(Ï-Hmtpo-Í2N1,N3)}n] 1.The addition of an acidic solution of Hmtpo (1 mmol in ca. 20 cm3 of HNO3, 4.5 mol N N N N H Me O 1 2 3 4 5 6 7 8 3a2322 J. Chem. Soc., Dalton Trans., 1997, Pages 2321–2326 dm23) to another one of AgNO3 (1 mmol in ca. 20 cm3 of HNO3, 4.5 mol dm23) gave a colourless solution that yielded, after 1 week, a precipitate of colourless crystals of 1. The crystals were rinsed with water and air dried. Yield 18% [Found (Calc. for C6H6AgN5O4): C, 22.7 (22.5); H, 1.9 (1.9); Ag, 31.7 (32.9); N, 21.8 (21.9)%].IR data (selected bands, cm21): 650m, 820m, 1250s, 1380vs, 1570vs, 1625s, 1700vs, 2890s and 3000s. [{Ag(ClO4)(Ï-Hmtpo-Í2N1,N3)}n] 2. A similar procedure to the previous one resulted in the immediate formation of a white microcrystalline precipitate of complex 2. Yield 70% [Found (Calc. for C6H6AgClN4O5): C, 20.2 (20.1); H, 1.7 (1.7); N, 16.1 (15.7)%]. IR data (selected bands, cm21): 625s, 920m, 1110vs, 1190s, 1570s, 1635vs, 1700vs and 3080m.[{Ag(NO3)(Ï-Hmtpo-Í2N1,N3)(PPh3)}n] 3. An ethanol solution of Hmtpo (2 mmol in ca. 50 cm3) was added to another one containing PPh3 (2 mmol) and AgNO3 (2 mmol) in ethanol (80 cm3), forming a turbid solution. The subsequent careful addition of concentrated HNO3 (2 cm3) resulted in the formation of a clear solution; after some hours plate-like crystals of complex 3 were formed. Yield 81% [Found (Calc. for C24H21Ag- N5O4P): C, 49.1 (49.5); H, 3.6 (3.6); Ag, 19.1 (18.5); N, 12.5 (12.0)%].IR data (selected bands, cm21): 830w, 1270s, 1420s, 1570vs, 1640s, 1710vs and 3080m. [{Ag(ClO4)(Ï-Hmtpo-Í2N1,N3)(PPh3)}n] 4. Following the same procedure as for compound 3, but using AgClO4 instead of AgNO3 and without addition of acid, crystals suitable for X-ray diffraction were obtained. Yield 71% [Found (Calc. for C24H21AgClN4O5P): C, 46.1 (46.5); H, 3.4 (3.4); N, 9.0 (9.0)%]. IR data (selected bands, cm21): 620s, 925m, 1040s, 1100vs, 1130s, 1570vs, 1640s, 1710vs and 3080m.[{[H2mtpo][Ag(SO4)(Ï-Hmtpo-Í2N1,N3)]?H2O}n] 5. This compound was obtained by diffusion, through a sinteredglass membrane, of an acidic solution of Ag2SO4 (1 mmol in ca. 120 cm3 H2SO4, 6 mol dm23) into another one containing Hmtpo (2 mmol in ca. 120 cm3 H2SO4, 6 mol dm23). After some days, plate crystals of 5 were obtained. Yield 18% [Found (Calc. for C12H15AgN8O7S): C, 27.3 (27.5); H, 2.8 (2.9); Ag, 20.5 (20.6); N, 21.4 (21.4)%]. IR data (selected bands, cm21): 420w, 450w, 600s, 900m, 1190vs, 1410s, 1575vs, 1620vs, 1665vs, 1700vs, 1725vs, 2890s, 3160s and 3480m.[{[Ag3(Ï3-mtpo-Í4N1,N3,N4,O7)2(HSO4)(H2O)2]?H2O}n] 6. The addition with stirring of an acidic solution of Hmtpo (1 mmol in ca. 40 cm3 of H2SO4, 6 mol dm23) to another one of Ag2SO4 (1 mmol in ca. 50 cm3 H2SO4, 6 mol dm23) gives a clear solution from which crystals of complex 6 suitable for X-ray analysis separated after some days. Yield 63% [Found (Calc. for C12H17Ag3N8O9S): C, 18.8 (18.6); H, 2.1 (2.2); Ag, 41.8 (41.9); N, 14.5 (14.7)%]).IR data (selected bands, cm21): 435w, 595w, 620s, 960m, 1110vs, 1140 (sh), 1195m, 1515s, 1570s, 1630s, 1695vs, 2800m and 3440s. [H2mtpo]Cl?H2O 7. This compound was prepared by dissolving Hmtpo (2 mmol) in concentrated HCl (ca. 5 cm3). From the resulting clear solution it was pe to collect, after 1 week, chunky colourless crystals of 7 [Found (Calc. for C6H9ClN4O2): C, 35.1 (35.2); H, 4.4 (4.4); N, 27.2 (27.4)%]. IR data (selected bands, cm21): 1410s, 1600m, 1665vs, 1725vs, 3165s and 3480m. Instrumentation Microanalyses of C, H and N were performed with a Fisons- Instruments EA-1008 microanalyser at the Instrumentation Centre of the University of Granada, whereas the silver content was determined thermogravimetrically by means of Mettler TA-3000 equipment provided with a Mettler TG-50 thermobalance, at a heating rate of 20 K min-1 and using an atmosphere of pure air (100 cm3 min21).Infrared spectra were recorded in the range 4000–180 cm21 on a Perkin-Elmer 983G spectrophotometer, using KBr and polyethylene pellets. Mass spectra by chemical ionisation were performed with Fisons Platform-II equipment, using direct sample injection and a potential of 36 eV (ca. 5.76 × 10218 J) and methane as reactant gas. Crystallography Relevant crystallographic data and details of the refinement are presented in Table 1. A crystal of compound 1 was mounted on a Philips PW-1100, 4 on a Nonius CAD-4 and 6 and Hmtpo on a Stoe-Siemens AED-2 diffractometer.The intensity data were corrected for Lorentz-polarisation effects and empirically (y scans) for absorption (with the exception of Hmtpo). The structures were solved by direct methods in the case of Hmtpo, and by heavy-atom and Fourier methods in the other cases, applying the SHELXTL PLUS17 (compounds 1, 6 and Hmtpo) and SDP18 programs (4). Full-matrix least-squares refinements were performed with anisotropic thermal parameters for nonhydrogen atoms.The hydrogen atoms of the organic ligands were idealised and those of water and hydrogensulfate groups refined with fixed O]H distances (0.85 Å). In the case of compounds 6 and Hmtpo, the last sets of refinements were made on F2 applying the SHELXL 93 program package.19 Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/507. Results Crystal and vapour-phase structures of Hmtpo A view of the crystal structure of Hmtpo is presented in Fig. 1 and the most relevant interatomic parameters are summarised in Table 2. The structure is built of one-dimensional infinite polymers, supported by strong hydrogen bonds formed between N(4)]H and O(7) groups from adjacent Hmtpo moieties, such that the H(4) ? ? ? O(7) separation is 1.80 Å [N(4) ? ? ? O(7) is 2.630(2) Å and the N(4)]H? ? ? O(7) angle is 1638].The geometry of the Hmtpo rings, which are planar to ±0.01 Å, does not differ significantly from that of the unco-ordinated Hmtpo in [Pd(tu)4]Cl2?2Hmtpo?2H2O21 (tu = thiourea). An examination of the derived interatomic parameters reveals that each of the N(1)]C(2), N(3)]C(3A), C(5)]C(6) and C(7)]O(7) bonds has significant double-bond character, which is in accord with the presence of the N(4)]H tautomer in the solid state.The chemical ionisation mass spectrum of free Hmtpo presents a high-intensity peak with m/z 301 corresponding to 2M 1 1. This result points to the existence of a dimeric structure in the vapour phase of Hmtpo. A feasible structure may be such that it contains H]N]C]N? ? ?H]N]C]N? ? ? rings (see Fig. 2). Analogous structures are also found for similar compounds such as 8-azaxanthine 22 in the solid state.The formation of dimeric structures in the vapour phase is reasonable, since the less-condensed matter may favour interactions of lower multiplicity 23 than those of the polymer found in the solid state (see Fig. 2). On the other hand, 15N NMR studies for Hmtpo, reported by Kleinpeter et al.,24 show the N(3) and N(4) signals broadened by proton exchange. A dimeric structure in solution similar to that postulated in the vapour phase may facilitate such N(3), N(4) proton transfer. Silver complexes The reaction of AgX (X = NO3 or ClO4) with Hmtpo in 1 : 1 molar ratio in strongly acidic aqueous media yields polymericJ.Chem. Soc., Dalton Trans., 1997, Pages 2321–2326 2323 Table 1 Crystal data and details of refinement for compounds 1, 4, 6 and Hmpto studied by X-ray crystallography * Formula M Space group a/Å b/Å c/Å b/8 U/Å3 Crystal dimensions Dm/g cm23 Dc/g cm23 F(000) m(Mo-Ka)/mm21 h kl 2qmax/8 Maximum, minimum transmission Maximum feature in DF map/e Å23 No.parameters refined No. reflections measured No. reflections independent No. reflections observed RR 9 wR2(F2, all) Weighting scheme Goodness of fit 1 C6H6AgN5O4 320.0 P21/c 12.205(3) 8.269(3) 9.858(3) 109.03(3) 940.5(9) 0.3 × 0.08 × 0.08 2.33 2.26 624 2.1 215 to 15 0–7 0–13 62 83, 62 0.4 175 3156 (0.05) 3060 965 [I > 2.5s(I)] 0.054 0.054 — 1/[s2(Fo) 1 0.005Fo 2] 1.18 4 C24H21AgClN4O5P 619.7 P21/c 16.489(3) 8.064(2) 25.462(8) 132.92(2) 2479(2) 0.5 × 0.5 × 0.35 — 1.661 1248 1.0 21 to 16 21 to 18 218 to 17 60 100, 98 0.69 389 7377 (0.05) 7222 5685 [I > 3s(I)] 0.031 0.031 — 1/[s2(Fo)] 1.10 6 C12H17Ag3N8O9S 773.0 P21/c 11.972(2) 13.455(3) 13.672(3) 112.30(3) 2037.6(7) 0.8 × 0.5 × 0.5 2.52 2.517 1496 3.0 28 to 8 210 to 10 0–13 60 87, 52 1.56 322 6866 (0.07) 6613 6613 0.058 — 0.193 1/[s2(Fo 2) 1 (0.1P)2] 1.26 Hmpto C6H6N4O 150.15 P21/n 3.9119(8) 14.711(2) 11.711(3) 85.670(8) 672.0(2) 1 × 0.5 × 0.1 — 1.484 312 0.11 25 to 5 217 to 17 0–21 65 — 0.246 101 9525 (0.04) 2890 2890 0.062 — 0.178 1/[s2(Fo 2) 1 (0.1P)2] 1.05 * Details in common: monoclinic; Z = 4, colourless, 293 K, l(Mo-Ka) 0.710 73 Å, R = ||Fo| 2 |Fc||/S|Fo|; R9 = (||Fo| 2 |Fc||w)� �� /S|Fo|w� �� ; wR2 = [Sw[(Fo 2 2 Fc 2)2]/S(wFo 4)]� �� ; P = (Fo 2 1 2Fc 2)/3.complexes of formula [{AgX(m-Hmtpo-k2N1,N3)}n] (X = NO3 1 or ClO4 2) in which the Hmtpo ligand shows a bidentate bridging mode via N(1), N(3).The additional presence of PPh3 gives also rise to the formation of [{AgX(m-Hmtpo-k2N1,N3)(PPh3)}n] with Hmtpo coordinated in the same way but with weaker Ag]N(1) bonds. Fig. 1 An ORTEP20 view of the one-dimensional chain in the crystal structure of Hmtpo Table 2 Bond distances (Å) and angles (8) for Hmpto N(1)]C(2) C(2)]N(3) C(3A)]N(8) N(4)]C(5) C(5)]C(5) C(7)]O(7) N(4) ? ? ? O(7I) C(2)]N(1)]N(8) C(3A)]N(3)]C(2) N(3)]C(3A)]N(4) C(5)]N(4)]C(3A) N(4)]C(5)]C(51) C(5)]C(6)]C(7) O(7)]C(7)]C(6) C(3A)]N(8)]C(7) C(7)]N(8)]N(1) 1.243(3) 1.382(3) 1.320(2) 1.230(2) 1.524(3) 1.200(2) 2.630(2) 100.2(2) 105.3(2) 131.2(2) 121.8(2) 117.8(2) 124.8(2) 130.0(2) 120.9(2) 127.1(2) N(1)]N(8) N(3)]C(3A) C(3A)]N(4) C(5)]C(6) C(6)]C(7) C(7)]N(8) N(1)]C(2)]N(3) N(3)]C(3A)]N(8) N(8)]C(3A)]N(4) N(4)]C(5)]C(6) C(6)]C(5)]C(51) O(7)]C(7)]N(8) N(8)]C(7)]C(6) C(3A)]N(8)]N(1) 1.406(2) 1.283(2) 1.381(3) 1.323(3) 1.456(3) 1.349(2) 115.6(2) 107.0(2) 121.8(2) 116.4(2) 125.7(2) 115.7(2) 114.3(2) 112.0(2) Symmetry relation: I x 2 1, y, z 1 1.Structure of [{Ag(NO3)(Ï-Hmtpo-Í2N1,N3)}n] 1. A view of the polymeric structure of compound 1 is presented in Fig. 3 and the most relevant interatomic parameters are summarised in Table 3. The structure of the complex comprises infinite chains, as a result of the nearly linear co-ordination shown by the Ag atom and the Hmtpo ligand in a N(1), N(3) bidentate bridging mode. The weaker interactions with the oxygen atoms O(1) [2.412(9) Å] and O(7) [2.691(9) Å] from the nitrate group and Hmtpo, respectively, make the effective co-ordination number 212.The Ag]N and Ag]O bond distances are comparable to those found in other complexes with similar environments.3,25 The geometry of Hmtpo appears almost unaltered after coordination, compared to that of free Hmtpo (see above). With respect to the geometry of the nitrate group, O(1) co-ordination to Ag results in a lengthening of the N]O(1) bond by ª0.04(1) &Ar[{Ag(ClO4)(Ï-Hmtpo-Í2N1,N3)(PPh3)}n] 4. This compound is also built of infinite Hmtpo N(1), N(3)-bridged Fig. 2 Structure conversion from solid-state hydrogen-bonded polymers to vapour-phase dimers N N N N N N N N O H O Me H Me N N N N N N N N O Me O Me H H less condensed state solid-state polymer vapour-phase dimer2324 J. Chem. Soc., Dalton Trans., 1997, Pages 2321–2326 chains (see Fig. 4) but the addition of the bulky and soft ligand PPh3 nearly displaces N(1) from the co-ordination environment of Ag, lengthening the Ag]N(1) bond distance by 0.35 Å, compared to the previous structure (see Tables 3 and 4). This displacement is a consequence of the preference of the soft acid AgI for a ligand such as PPh3 which is softer than Hmtpo.The silver atoms are placed in a distorted-tetrahedral N2PO environment. Nitrogen N(3) from Hmtpo and P from PPh3 appear strongly bonded to Ag, whereas N(1) and O(4) interact weakly. The Ag]P separation is normal.26 Regarding the geometry of the perchlorate group, the lengthening of the Cl]O(1) bond, as a consequence of its involvement in a hydrogen bond [N(4) ? ? ? O(1), 2.864 Å], is noteworthy, whereas the weak O(4) ? ? ? Ag interaction does not result in an appreciable modi- fication of the C(l)]O(4) distance.Fig. 3 View of the polymeric [{Ag(NO3)(m-Hmtpo-N1,N3)}n] chains in compound 1 Table 3 Selected bond distances (Å) and angles (8) for compound 1 Ag]N(1) Ag]N(3I) N]O(1) N]O(3) N(4) ? ? ? O(1II) N(3I)]Ag]N(1) O(7)]Ag]N(1) O(7)]Ag]N(3I) 2.253(8) 2.154(8) 1.28(1) 1.25(1) 2.760 150.8(3) 70.1(3) 105.3(3) Ag]O(7) Ag]O(1) N]O(2) O(1)]Ag]N(1) O(1)]Ag]N(3I) O(1)]Ag]O(7) 2.691(9) 2.412(9) 1.23(1) 82.3(3) 126.6(3) 98.9(3) Symmetry relations: I x 2 ��� , 2y 1 ��� , z 2 ��� ; II 2x 1 1, 2y, 2z 1 1.Table 4 Selected bond distances (Å) and angles (8) for compound 4 Ag]P Ag]N(3) Cl]O(1) Cl]O(3) N(4) ? ? ? O(1) P]Ag]N(3) P]Ag]N(1I) P]Ag]O(4) 2.3603(7) 2.217(2) 1.451(3) 1.395(3) 2.864 154.81(6) 108.22(6) 107.82(7) Ag]N(1I) Ag]O(4) Cl]O(2) Cl]O(4) N(3)]Ag]N(1I) N(3)]Ag]O(4) O(4)]Ag]N(1I) 2.597(2) 2.728(3) 1.419(3) 1.380(2) 82.7(1) 96.8(1) 75.9(1) Symmetry relation: I 2x, y 2 ��� , 2z 1 ��� .IR spectroscopy and thermal studies for compounds [{AgX- (Ï-Hmtpo-Í2N1,N3)}n] and [{AgX(Ï-Hmtpo-Í2N1,N3)(PPh3)}n] (X 5 NO3ClO4) Thermogravimetry has been shown to be of poor structural value. The compounds are thermally stable up to 150–300 8C, when pyrolysis commences. This process is very violent in the complexes containing the ClO4 2 anion.The IR spectra of compounds 1–4 present only small changes when compared to free Hmtpo, the only appreciable change above 600 cm21 being due to the concurrence of PPh3, NO3 2 and ClO4 2 characteristic bands. The absorption bands assigned to vibrations of the nitrate group, n3 (1380, 1250), n2 (820), n4 (650 cm21) for compound 1, n3 (1420, 1270), n2 (830 cm21) for 3, can be related to the presence of monoco-ordinated nitrate groups in both complexes.In 2 the original Td symmetry of the perchlorate group is preserved with n3, n1 and n4 appearing at 1120, 920 and 625 cm21, respectively. In the case of compound 4 the clear splitting of the perchlorate vibration mode n3 (1130, 1100, 1040 cm21) and n1 and n4 appearing at 925 and 620 cm21, respectively, are in accord with the loosening of the original Td geometry (see Table 4).Reactivity of Ag2SO4 towards Hmtpo The Hmtpo compound behaves very variably towards Ag2SO4. Thus, its reaction in neutral or basic media yields [{Ag(m3-mtpok4N1, N3,N4,O7)}2n] as reported by Smith and Luss.16 In strongly acidic aqueous media and depending on the silver to Hmtpo ratio, the reaction gives alternatively [{[H2mtpo][Ag(SO4)- (m-Hmtpo-k2N1,N3)]?H2O}n] 5 and [{[Ag3(m3-mtpo-k4N1,N3, N4,O7)2(HSO4)(H2O)2]?H2O}n] 6. The structure of 5 will be discussed on the basis of the IR data, whereas in the case of 6 it was possible to solve its structure by crystallography. Structure of compound 6.A perspective view of the asymmetric unit of the complex is shown in Fig. 5 and the most relevant interatomic parameters are summarised in Table 5. The crystal structure comprises infinite cationic [{Ag3(m3-mtpok4N1, N3,N4,O7)2}n]n1 chains and hydrogensulfate anions and water molecules weakly interacting with the silver atoms. The cationic chains contain dimeric [Ag(mtpo)]2 units, displaying Ag2N4C2 rings, which give rise to short Ag ? ? ? Ag contacts of 3.078(1) Å.The polymeric structure is generated by a third silver nucleus linearly bridging the N(1) atoms of adjacent dimeric [Ag(mtpo)]2 units. The co-ordination geometry about the metal centres is nearly linear (N2) with weak Ag ? ? ? O interactions from mtpo, HSO4 2 and water molecules also being present. Fig. 4 Perspective of loosely polymeric [{Ag(ClO4)(m-Hmtpo-N1, N3)(PPh3)}n] chains in compound 4J.Chem. Soc., Dalton Trans., 1997, Pages 2321–2326 2325 In the crystal, the chains associate in pairs supported by p–p interactions between the planar mtpo rings (mean separation 3.22 Å). Also, an intercatena Ag ? ? ? Ag contact of 3.268(1) Å is noted. Finally, the double chains are associated by means of weaker stacking interactions, with an interplanar separation of 3.20 Å but with lower overlap between the p rings than in the previous association.The coexistence of two kinds of short Ag ? ? ? Ag contacts in this structure is of note. The shorter one, with separation 3.078(1) Å, is supported by two bridging mtpo, acting in a N(3), N(4) bidentate mode. The unsupported one shows an intermetallic separation of 3.268(1) Å. The existence of direct Ag ? ? ? Ag bonding interactions, in compounds displaying intermetallic distances in the range 2.655–3.377 Å, is a matter of current controversy.27 However, our ab initio molecular orbital studies 27a on the dimer [{Ag(NO3)L}2] (L = 5,7- dimethyl[1,2,4]triazolo [1,5a]pyrimidine), which displays an intermetallic separation of 3.058(1) Å, show the stabilising nature of these interactions.The fact that compound 6 displays also a short Ag ? ? ? Ag contact without bridging ligands points to the existence of a direct intermetallic interaction. A similar conclusion has been made in the case of other unsupported silver polynuclear compounds.9 However, it should be noted that even if there is not a bridging ligand, other interactions contribute to the stabilisation of these associations such as hydrogen bonding in [{[Ag(NH3)2]2(SO4)}n],28 stacking inter- Fig. 5 An ORTEP view of the asymmetric unit of compound 6. The thermal ellipsoids are drawn at the 25% probability level Table 5 Selected bond distances (Å) and angles (8) for compound 6 Ag(2)]Ag(1I) Ag(1)]Ag(3) Ag(1)]N(3) Ag(1)]N(4b) Ag(1)]O(1) Ag(1)]O(1w) Ag(2)]O(7) S]O(1) S]O(2) O(1w) ? ? ? O(3) O(1w) ? ? ? O(4IV) O(2w) ? ? ? O(7I) O(2w) ? ? ? O(3wV) Ag(1)]Ag(3)]Ag(2I) N(3)]Ag(1)]N(4b) N(1)]Ag(2)]N(1bII) N(4)]Ag(3)]N(3b) Ag(1)]N(3)]C(3a) 3.268(1) 3.078(1) 2.176(5) 2.159(5) 2.689(5) 2.718(6) 2.698(5) 1.444(6) 1.455(8) 2.831 2.976 2.755 2.837 76.8(1) 162.8(2) 175.7(2) 161.6(2) 129.3(4) Ag(2)]O(7bII) Ag(2)]N(1) Ag(2)]N(1bII) Ag(3)]N(4) Ag(3)]N(3b) Ag(3)]O(3w) Ag(3)]O(1III) S]O(3) S]O(4) O(4) ? ? ? O(2w) O(3w) ? ? ? O(2III) O(3w) ? ? ? O(7bV) Ag(1)]N(4b)]C(3ab) Ag(3)]N(4)]C(3a) Ag(3)]N(3b)]C(3ab) N(4)]C(3a)]N(3) N(4b)]C(3ab)]N(3b) 2.628(5) 2.178(5) 2.202(5) 2.186(6) 2.154(5) 2.882(6) 2.746(5) 1.446(5) 1.555(7) 2.528 2.858 2.725 119.0(4) 118.5(4) 129.8(4) 129.2(6) 128.3(5) Symmetry relations: I 2x, 12y, 2z; II x, 1 1 y, z; III 2x, 2y, 2z; IV x, ��� 2 y, ��� 1 z; V 2x, ��� 1 y, ��� 2 z.actions between aromatic rings in our case, etc. The final result may be the sum of the whole set of interactions. Another interesting feature of compound 6 is that it represents one of the few examples of X-ray characterised hydrogensulfate groups.27b,29 The location of the acidic proton at oxygen O(4) is responsible for the lengthening of the S]O bond by 0.1 Å, which results in a C3v geometry for the anion (see Table 5).Hydrogen bonding appears to be especially important in thvery strong hydrogen-bond interaction between the hydrogensulfate group and solvation water O(2w) is noted, such that H? ? ? O(2w) is 1.71 Å [O(4) ? ? ? O(2w) 2.528 Å and O(4)]H? ? ? O(2w) is 1438].Thermal studies and IR spectroscopy. Thermogravimetric curves reveal that the dehydration processes take place in the temperature ranges 110–140 and 45–130 8C for compounds 5 and 6, respectively. A thermal stability zone follows up to 200 and 300 oC, respectively, temperatures at which a pyrolitic process starts which is finished at 700 oC, leaving metallic silver as final residue.In order to establish the nature of the Hmtpo ligands in compound 5 the chlorohydrate of Hmtpo was prepared, giving [H2mtpo]Cl?H2O 7. The IR spectrum 5, apart from the anions bands, can be considered the sum of those of 1 1 7. From this result a similar polymeric structure to that found in 1 is proposed for 5 in which the ligand acts in bidentate N(1), N(3) bridging mode. The SO4 22 bands (assigned Td symmetry) are as follows: n3 at 1190, n1 900, n4 600 cm21 and n2 450, 420 cm21.The splitting of the n2 band suggests a C2v geometry for the sulfate group, consistent with a possible bidentate behaviour,30 although such a geometry would require a splitting of n3 and n4. The IR spectrum of compound 6 shows a broad band in the 2900–2000 cm21 range, corresponding to the presence of the acidic hydrogensulfate proton, this region being similar to that of KHSO4. With respect to the characteristic bands of the Hmtpo ligand, they differ considerably from those found for [{Ag(m3-mtpo-k4N1,N3,N4,O7)]}2n]16 and other complexes containing Hmtpo in its monoanionic form;11 these are very similar, however, to those containing the ligand in its neutral form.10 It appears that the higher strength of the silver–ligand interactions in 6, compared to the similarly co-ordinated [{Ag(m3- mtpo-k4N1,N3,N4,O7)}2n],16 is responsible for a major charge localisation in the molecule, resulting in a shift of the bands to higher frequency, similar to the protonation effect.The sulfate bands are consistent with the C3v symmetry found in the solid state. The activation of the n1 vibration mode centred at 960 cm21, together with the splitting of n4 into two bands at 620 and 595 cm21 and n3 , n2 appearing, respectively, at 1110 and 435 cm21, is in accord with the X-ray results. Discussion The hydrogen-bonded structures, found in the solid and vapour phases of free Hmpto are similar to those of the nearly linear co-ordinated silver(I) complexes.However, there are some significant differences: in the case of the silver polymeric systems, the involvement of the exocyclic O(7) donor atom in the coordination is minimal, in agreement with the soft nature of the AgI ion. On the other hand, the tendency of the ligand to display eight-membered A]N]C]N]A]N]C]N rings (A = H or Ag) is shown to occur both in the vapour phase of free Hmpto and in the silver complexes containing Hmtpo in its monoanionic form, namely 6 and [{Ag(m3-mtpo-k4N1,N3, N4,O7)}2n].16 These kind of structures may be considered the result of a formal replacement of the hydrogen atom of a hydrogen bond by a metal atom with a linear co-ordination geometry.This replacement appears to have a marked effect on the strength of the association but not on the geometry of the2326 J. Chem. Soc., Dalton Trans., 1997, Pages 2321–2326 system.6 The formation of eight-membered Ag]N]C]N]Ag] N]C]N rings is also interesting from a theoretical point of view, since they give rise to short intermetallic contacts of 3.078(1) Å for 6 and 3.187 Å for [{Ag(m3-mtpo-k4N1,N3,N4, O7)}2n] 16 which suggest the possibility of direct M]M bonding interactions.6 Similar eight-membered rings are also found in the binuclear compound [Pt2(m-mtpo-k2N3,N4)4]11a which displays a very short M]M separation of 2.744(2) Å, the M]M interaction being suggested, from ab initio molecular orbital calculations, to be of bonding nature.Acknowledgements The authors thank Dirección General de Investigación Científica y Técnica for financial support (Grant No. PB94-0807- CO2–01), also Dr. M. Quirós for his helpful discussions and suggestions. References 1 D. S. Lawrence, T. Jiang and M. Levett, Chem. Rev., 1995, 95, 2229; D. Philp and J. F. Stoddart, Angew. Chem., Int. Ed. Engl., 1996, 35, 1154. 2 W. Saenger, Principles of Nucleic Acid Structure, Springer, New York, 1984; D.Voet and J. G. Voet, Biochemistry, Wiley, New York, 1990. 3 S. Menzer, M. Sabat and B. Lippert, J. Am. Chem. Soc., 1992, 114, 4644. 4 O. Krizanovic, M. Sabat, R. Beyerle-Pfnür and B. Lippert, J. Am. Chem. Soc., 1993, 115, 5538. 5 I. Dieter-Wurm, M. Sabat and B. Lippert, J. Am. Chem. Soc., 1992, 114, 357. 6 A. Schreiber, M. S. Lüth, A. Erxleben, E. C. Fusch and B. Lippert, J. Am. Chem. Soc., 1996, 118, 4124. 7 J. Barberá, A. Elduque, R. Giménez, L. A. Oro and J. L. Serrano, Angew.Chem., Int. Ed. Engl., 1996, 35, 2832. 8 G. Smith, D. E. Lynch and C. H. L. Kennard, Inorg. Chem., 1996, 35, 2711; C. M. Hartshorn and P. J. Steel, Inorg. Chem., 1996, 35, 6902; L. Carlucci, G. Ciani, D. M. Proserpio and A. Sironi, J. Chem. Soc., Chem. Commun., 1994, 2755; Angew. Chem., Int. Ed. Engl., 1995, 34, 1895. 9 M. Quirós, Acta Crystallogr., Sect. C, 1994, 50, 1236. 10 E. J. Dirks, J. G. Haasnoot, A. J. Kinneging and J. Reedijk, Inorg. Chem., 1987, 26, 1902; J.A. R. Navarro, M. A. Romero, J. M. Salas, J. Molina and E. R. T. Tiekink, Inorg. Chim. Acta, submitted for publication; J. Salas, J. A. R. Navarro, M. A. Romero, J. M. Salas and M. Quirós, An. Quim. Int. Ed., 1997, 93, 55. 11 (a) J. A. R. Navarro, M. A. Romero, J. M. Salas, M. Quirós, J. El Bahraoui and J. Molina, Inorg. Chem., 1996, 35, 7829; (b) J. A. R. Navarro, M. A. Romero and J. M. Salas, J. Chem. Soc., Dalton Trans., 1997, 1001. 12 J. A. R. Navarro, M. A. Romero, J.M. Salas and M. Quirós, Inorg. Chem., in the press. 13 G. Fischer, J. Inf. Rec. Mater., 1992, 20, 43. 14 G. Fischer, Adv. Heterocycl. Chem., 1995, 57, 81. 15 G. Fischer, J. Inf. Rec. Mater., 1992, 16, 91. 16 D. L. Smith and H. R. Luss, Photogr. Sci. Eng., 1976, 20, 184. 17 G. M. Sheldrick, SHELXTL PLUS, Program package for the solution of crystal structures. Release 34, Siemens Analytical X-Ray Instruments Inc., Madison, WI, 1989. 18 SDP, Structure Determination Package; B. A. Frenz & Associates Inc., College Station, TX, 1982. 19 G. M. Sheldrick, SHELXL 93, University of Göttingen, 1993. 20 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 21 J. M. Salas, M. A. Romero, J. A. Rodríguez and R. Faure, J. Chem. Crystallogr., 1996, 26, 847. 22 H. C. Mez and J. Donahue, Z. Kristallogr., 1969, 130, 376. 23 J. A. Dobado and J. Molina Molina, J. Phys. Chem., 1993, 97, 7499; 1994, 98, 1819. 24 E. Kleinpeter, St. Thomas and G. Fischer, J. Mol. Struct., 1995, 355, 273. 25 J. M. Salas, M. P. Sánchez, E. Colacio and R. Faure, J. Crystallogr. Spectrosc. Res., 1990, 20, 133. 26 T. S. A. Hor, S. P. Neo, C. S. Tan, T. C. W. Mak, K. W. P. Lesung and R.-J. Wang, Inorg. Chem., 1992, 31, 4510; S. P. Neo, Z.-Y. Zhou, T. C. W. Mak and T. S. A. Hor, Inorg. Chem., 1995, 34, 520. 27 (a) M. A. Romero, J. M. Salas, M. Quirós, M. P. Sánchez, J. Molina, J. El Bahraoui and R. Faure, J. Mol. Struct., 1995, 354, 189; (b) J. M. Salas, M. A. Romero, A. Rahmani and M. Quirós, An. Quim. Int. Ed., 1996, 92, 249 and refs. therein. 28 U. Zachwieja and H. Jacobs, Z. Kristallogr., 1992, 201, 207. 29 M. Y. Antipin, G. G. Aleksandrov, Y. T. Struckov, Y. A. Belousov, V. N. Babin and N. S. Kochetkova, Inorg. Chim. Acta, 1983, 68, 228; J. M. Malin, E. O. Schlemper and R. K. Murmann, Inorg. Chem., 1977, 16, 615; R. D. Rogers, A. H. Bond, W. G. Ipple, A. N. Rollins and R. F. Henry, Inorg. Chem., 1991, 30, 2671. 30 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Wiley-Interscience, New York, 1977. Received 7th February 1997; Paper 7/00888K

ISSN:1477-9226    

DOI:10.1039/a700888k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2327–2330 2327 Electron transfer between Fe(CN)6 32 and iodide promoted by supercomplexation with a polyammonium macrocycle Fernando Pina,*,† ,a A. Jorge Parola,a André Saint-Maurice,a M. Francesca Manfrin,b Luca Moggi,*,b Teresa Indelli c and Franco Scandola *,c a Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2825 Monte de Caparica, Portugal b Dipartimento di Chimica G. Ciamician, Università di Bologna, via Selmi 2, 40126 Bologna, Italy c Dipartimento di Chimica dell’ Università, Centro di Fotoreattività e Catalisi CNR, 44100 Ferrara, Italy Some new properties promoted by the formation of a supercomplex between iron hexacyanometallates and the polyazamacrocycle [32]aneN8 (1,5,9,13,17,21,25,29-octaazacyclodotriacontane) are described.In the presence of the polyazamacrocycle, thermal and photoinduced electron transfer from iodide to Fe(CN)6 32 were observed in moderately acidic media.The thermal reaction is slow (kobs = 8.9 × 1024 s21, at 25 8C) and proceeds to an equilibrium (K = 7 M22, at 25 8C). The reaction is almost isoergonic, with favorable enthalpy and unfavorable entropy changes (DG8 = 24.8 kJ mol21, DH8 = 2160 kJ mol21, DS8 = 20.54 kJ mol21 K21). A photoinduced electron-transfer process, leading to additional iodide oxidation, was observed upon flash irradiation of equilibrated solutions. Following the photoinduced process, the system reverts to the thermal equilibrium in the dark.The promoting role of the macrocycle is thermodynamic for the thermal process (anodic shift in the FeII/III potential upon supercomplex formation) and kinetic for the photoinduced process [formation of ion-paired species between hexacyanoferrate(III) and iodide upon supercomplex formation]. The thermal reaction is reversible in basic media (where the macrocycle deprotonates and supercomplex formation is prevented), providing an example of on/off switching by pH changes of an electron-transfer reaction.The thermal and photochemical reactivity, as well as the redox, spectroscopic and photophysical properties of co-ordination compounds can be greatly modified by their inclusion into supramolecular structures (supercomplexes) involving appropriate macrocyclic receptors.1–12 In these structures the macrocyclic receptor is bound by non-covalent interactions to the transition-metal complex, and thus can be viewed as a secondsphere co-ordination ligand.3 Several examples of this chemistry have been described for the class of supercomplexes formed between metal cyanides and polyazamacrocycles of general type [n]aneNmHm m1 (fully protonated form).For example, for the large macrocycle [32]aneN8H8 81 ([32]aneN8 = 1,5,9,13,17,21,25,29-octaazacyclodotriacontane), supercomplexes with metal cyanides of type M(CN)6 32 (M = CoIII,4 CrIII 5 or FeIII 6) and M(CN)6 42 (M = FeII 6 or RuII 6), M(CN)5- (H2O)22 and M(CN)5Br32 (M = CoIII 4) and M(bipy)(CN4)22- (M = RuII, bipy = 2,29-bipyridine) 7 have been studied.In all cases, the main driving force for the formation of the supramolecular structure is the coloumbic attraction between the negatively charged co-ordination compound and the positively charged macrocycle. However, the supercomplex is not a simple ion-pair because hydrogen bonds between the protonated nitrogens of the macrocycle and the nitrogens of the cyanide ligands seem to play an important structural role.7 As usual in supramolecular chemistry, the physical chemical characteristics of the supercomplexes are not the simple addition of the properties of each component, and the study of the new properties is one of the interesting aims in the investigation of supercomplex formation.Among the new properties induced by supercomplex formation, of particular interest is the change in redox potential of the metal-based redox couple (Scheme 1).The shift in reduction potential upon supercomplex formation is always in the anodic † E-Mail: fjp@dq.fct.unl.pt direction (in Scheme 1, Kred > Kox) 6,8 and the effect can be quite substantial.6,7 On this basis, one can think of using the macrocycle as a ‘switch’ for redox reactions involving metal cyanides. For instance, by choosing a reaction partner S such that E8M < E8S < E8M?h, switching between Sox and Sred could be obtained, in principle, by addition or removal of the macrocycle [equation (1)].An indirect, but easier way to achieve reversible switching would be to operate in the presence of macrocycle and switch on or off its supercomplexing ability by changes in pH [equation (2)]. In this article, we wish to present a study of the thermal redox reaction between Fe(CN)6 32 and I2, promoted by [32]aneN8- Mred Mox • Mox Mred • K red K ox E M• o E M o + e– – e– – e– + e– Scheme 1 h denotes the macrocycle centre Mox + Sred Mred • + – + Sox (1) Mox + Sred + Mred • + – + Sox (2) H+ H+2328 J.Chem. Soc., Dalton Trans., 1997, Pages 2327–2330 H8 81. The system, though not a perfect fit to the abovementioned redox potential requirements, does indeed provide a simple example of the switching behaviour depicted in equation (1). In addition to the thermal process, an interesting photoinduced electron-transfer process is also observed in this system. Results Cyclic voltammetry experiments carried out on 4.5 × 1023 M Fe(CN)6 32 aqueous solutions (0.04 M acetate buffer, pH = 4.4) showed that an anodic shift of 0.180 V takes place in the Fe(CN)6 32–Fe(CN)6 42 reduction potential upon addition of 4.8 × 1023 or 6.9 × 1023 M [32]aneN8H8 81.‡ Solutions containing 5 × 1024 M Fe(CN)6 32 and 5 × 1023 M iodide in aqueous solution (pH 4.4, acetate buffer) were stable in the dark on the time-scale of the experiments.Upon addition of 5 × 1024 M [32]aneN8H8 81 a reaction takes place as indicated by pronounced UV spectral variations (Fig. 1).The reaction was completed in ca. 1 h. Inspection of the spectral variations indicate the formation of two new intense bands at 350 and 289 nm, characteristic of the species I3 2.13 The global reaction taking place can thus be written as in equation (3). 2 Fe(CN)6 32?[32]aneN8H8 81 1 3 I2 2 Fe(CN)6 42?[32]aneN8H8 81 1 I3 2 (3) The kinetics of equation (3), under the experimental conditions used, was that of a first-order process, with the rate constant increasing with increasing temperature (Table 1).The final absorbance values reached at 25 8C correspond to an I3 2 equilibrium concentration of 3.4 × 1025 M (i.e., to ca. 14% reduction of the Fe complex).§ The extent of conversion increased, as expected, with increasing iodide concentration and also increased markedly by decreasing the temperature (inset of Fig. 1). Equilibrium constants of reaction (3), calculated from such experiments, are reported in Table 1.The reaction can be completely reversed, as shown by spectral variations leading back to the initial spectrum, by changing the pH to alkaline values. Fig. 1 Spectral changes induced by addition of 5 × 1024 M [32]- aneN8H8 81 to a solution of 5 × 1024 M Fe(CN)6 32 and 5 × 1023 M iodide (pH = 4.4, acetate buffer, 25 8C, in the dark). In order of increasing UV optical densities, 0, 5, 10, 15, 20, 25, 30 and 40 ]] ] 90 min. In the inset: temperature dependence of the 350 nm equilibrium absorbance ‡ Under slightly different experimental conditions, an increase of 0.165 V was obtained in previous work.6 § Upon standing for long periods (e.g., 12 h) in the dark, some degradation is observed (slight but measurable decrease of absorbance at 350 nm).The process is more pronounced at high temperature. All the measurements were performed on freshly prepared solutions and at temperatures not higher than 25 8C, where degradation is completely negligible.The influence of light on the system was also investigated, by irradiating a thermally equilibrated aqueous solution {5 × 1024 M Fe(CN)6 32, 5 × 1023 M iodide, 5 × 1024 M [32]aneN8H8 81, pH 4.4} with a flash of visible light (l > 400 nm, flash duration ª 20 ms). Flash irradiation gives rise to an instantaneous increase in the I3 2 absorption bands, followed by a slow decrease in the dark leading back to the initial absorption spectrum (Fig. 2).¶ The kinetics of the thermal back reaction was appreciably first order (Fig. 2) with the rate constant increasing with temperature (Table 1). The thermal and photochemical results described above are independent of the presence of molecular oxygen, as checked by comparison between air-equilibrated and nitrogen-purged solutions. Discussion The formation of supramolecular adducts between Fe(CN)6 n2 (n = 3 or 4) and [32]aneN8H8 81 was previously characterized.6 Under the experimental conditions used in this work (pH 4.4), both forms of the co-ordination compound can be considered to be completely associated with the macrocycle, with a plausible supramolecular structure as presented in Fig. 3. In the absence of the macrocycle, the standard reduction potential of Fe(CN)6 32 is E8 = 0.358 V,15 and oxidation of iodide (E8 = 0.536 V)15 is thermodynamically unfavorable. In the presence of [32]aneN8H8 81, the redox potential of the co-ordination compound is increased by 0.180 V, and thus reaction (3) becomes essentially isoergonic (DG8 = 10.002 eV, 1 eV ª 96.488 kJ mol21) allowing the formation of measurable amounts of products.The equilibrium constant measured by UV/VIS absorption spectrophotometry (Table 1) is not far from unity at 25 8C, in reasonable agreement with these expectations. When the pH Fig. 2 Variation in the 350 nm absorbance of equilibrated solutions (same conditions as Fig. 1) following flash irradiation (s); first-order plot of the decay kinetics (.) Table 1 Equilibrium constants (K) for reaction (3), and pseudo-firstorder rate constants of thermal equilibration in the forward and in the backward direction (kobs, measured following addition of the macrocycle; kobs, measured in the dark after flash excitation) T/8C 15 20 25 K*/M22 65 20 7 104 kobs */s21 3.1 6.1 8.9 104 k2obs */s21 3.9 6.7 11.7 * Estimated errors: ± 5%.¶ In these experiments, the final spectrum after the dark back reaction is actually lower by a very small amount (less than 1%) than the initial one.This suggests that an additional irreversible photochemical reaction takes place, albeit in relatively small yields. Such a process, most probably associated with the intrinsic photoreactivity 14 of Fe(CN)6 32, can be clearly seen in continuous irradiation experiments and is enhanced by the use of UV light.J. Chem. Soc., Dalton Trans., 1997, Pages 2327–2330 2329 is changed to alkaline values, the supercomplex dissociates and the reverse exergonic reaction takes place.This behaviour provides a simple example of a switchable redox system based on supercomplex formation. In the present case, the switching effect is only partial (from 0–14% conversion at 25 8C, from 0–26% at 15 8C) but systems with 100% on/off response can be easily designed, in principle, by a suitable choice of the redox potential of the reaction partner (see above). The standard enthalpy change of reaction (3) can be calculated through a van’t Hoff plot of the equilibrium data of Table 1, giving DH8 = 2160 kJ mol21.Thus, the process is substantially exothermic and the very small driving force must arise from a large unfavourable entropic factor (with K = 7 M22 at 25 8C, DG8 = 24.8 kJ mol21 and DS8 = 20.54 kJ mol21 K21). As far as the photochemical reaction is concerned, the exceedingly short lifetime of the Fe(CN)6 32 excited states forbids any type of bimolecular process.On the other hand, several examples have been described 13,16–19 of unimolecular photoinduced electron transfer taking place in ion-pairs involving iodide and positively charged co-ordination compounds. A qualitative energy level diagram as shown in Fig. 4 can be useful to discuss the photoinduced reaction. Independently of whether the ion-pair charge transfer (IPCT) state is populated directly by light absorption or indirectly through upper molecular excited states, the first event that originates from the IPCT state, taking place on a time-scale much faster than the lifetime of the flash lamp, is the formation of the one-electron redox products, an FeII complex and atomic iodine.|| This high-energy species is probably stabilized by formation of the transient radical anion I2~2, which can either give back electron transfer to reform the reactants or reduce, in a second one-electron transfer step, an additional FeIII species.To the extent to which the Fig. 3 Schematic structure of the supercomplex between Fe(CN)6 n2 (n = 3 or 4) and [32]aneN8H8 81 Fig. 4 Schematic energy level diagram for the photoinduced electrontransfer reaction; FeIII and FeII refer to the supercomplexes with 32[ane]N8H8 81 which are, at least partially, ion-paired with I2 + *FeIII FeIII + 3 l– 2 FeIII + FeII + l• + 2 l– FeIII + FeII + l2 •– + l– 2 FeII + l2 + l– 2 FeII + l3 – FeIII + 3 l– FeIII IPCT h n h n || It is assumed that the IPCT state is dissociative, i.e., the primary products originate from the lower vibrational level.secondary forward pathway takes place, the concentration of the final product, I3 2, is suddenly altered upon flash excitation and subsequent relaxation to the thermal equilibrium can be observed as a dark process. It may be noticed that, in this system, evolution towards the equilibrium can be monitored by two independent pathways: (i) in the forward direction, after switching on the process by addition of the macrocycle; (ii) in the opposite direction, after perturbing the equilibrium by flash excitation.Both relaxation processes experimentally follow first-order kinetics, and the two rate constants appreciably coincide (Table 1). Thus the system behaves as a typical first-order equilibrium, where the relaxation kinetics gives, independent of the direction in which it is observed, the sum of forward and back reaction rate constants. The reason for the forward reaction being (pseudo)first-order is obvious, as one of the reactants, I2, is present in vast excess.For the back reaction no obvious explanation is available, although arguments based on ion pairing between I3 2 and FeIII supercomplex products could be invoked to justify the observed firstorder behaviour. Conclusion The results described in this work exemplify the ability of polyazamacrocycles to promote (otherwise impossible) reactions of metal cyanide complexes. In the case of the thermal oxidation of iodide by hexacyanoferrate(III) the role of the macrocycle is to provide extra stabilization to the product complex, making the reaction thermodynamically accessible.In the case of the photochemical process, the thermodynamic requirements are largely offset by the photon energy and the main role of the macrocycle is to make the process kinetically allowed: the switch of charge type of hexacyanoferrate(III) upon supercomplexation permits the formation of strong ion-pairs between iodide and the complex, in which optical or ultrafast photoinduced electron transfer can take place.Experimental The preparation of [32]aneN8?8HClO4 was carried out as described previously.7 The other reagents were commercially available and of analytical grade. All measurements were carried out in acetate buffer (pH 4.4) prepared from 0.4 M NaO2- CMe and HClO4. Absorption measurements were carried out on a Perkin-Elmer lambda 6 spectrophotometer, and flash lamp experiments were conducted according to previous work.20 Cyclic voltammetry experiments were run on a PAR 273 potentiostat connected to a conventional three-electrode cell assembly (Ag–AgCl, Pt wire, glassy carbon); solutions were Ar purged for 15 min.Acknowledgements This work was supported by Ministero dell’Università e della Ricerca Scientifica e Technologica and Consiglio Nazionale delle Ricerche (Italy) and Junta Nacional de Investigação Científica e Tecnológica (Portugal) Bilateral Program.A. J. P. and F. P. thank NATO for a grant (No. 950797). References 1 J.-M. Lehn, in Supramolecular Photochemistry, ed. V. Balzani, Reidel, Dordrecht, 1987. 2 V. Balzani and F. Scandola, Supramolecular Photochemistry, Horwood Chichester, England, 1991, ch. 10. 3 V. Balzani, N. Sabbatini and F. Scandola, Chem. Rev., 1986, 86, 319. 4 M. F. Manfrin, L. Moggi, V. Castelvetro, V. Balzani, M. W. Hosseini and J.-M. Lehn, J. Am. Chem. Soc., 1985, 107, 6888; F.Pina, L. Moggi, M. F. Manfrin, V. Balzani, M. W. Hosseini and J.-M. Lehn, Gazz. Chim. Ital., 1989, 119, 85; A. J. Parola and F. Pina, J. Photochem. Photobiol., A, 1992, 66, 337.2330 J. Chem. Soc., Dalton Trans., 1997, Pages 2327–2330 5 J. Sotomayor, A. J. Parola, F. Pina, E. Zinato, P. Riccieri, M. F. Manfrin and L. Moggi, Inorg. Chem., 1995, 34, 6532. 6 F. Peter, M. Gross, M. W. Hosseini and J.-M. Lehn, J. Electroanal. Chem. Interfacial Electrochem., 1983, 144, 729; M.W. Hosseini, in Perspectives in Coordination Chemistry, eds. A. Williams, C. Floriani and A. E. Merbach, VCH, Weinheim, 1992, p. 333. 7 M. A. Rampi, M. T. Indelli, F. Scandola, F. Pina and A. J. Parola, Inorg. Chem., 1996, 35, 3355. 8 B. Dietrich, M. W. Hosseini, J.-M. Lehn and R. B. Sessions, J. Am. Chem. Soc., 1981, 103, 1282. 9 A. Bencini, A. Bianchi, P. Dapporto, E. Garcia-España, M. Micheloni, J. A. Ramirez, P. Paoletti and P. Paoli, Inorg. Chem., 1992, 31, 1902. 10 H. M. Colquhoun, J. F. Stoddart and D. J. Williams, Angew. Chem., Int. Ed. Engl., 1986, 25, 487. 11 M. D. Todd, Y. Dong, G. Horney, D. I. Yoon and J. T. Hupp, Inorg. Chem., 1993, 32, 2001 and refs. therein. 12 I. Ando, H. Fujimoto, K. Nakayama, K.Ujimoto and H. Kurihara, Polyhedron, 1991, 10, 1139. 13 F. Pina, M. Maestri, R. Ballardini, G. Q. Mulazzini, M. D’Angelantonio and V. Balzani, Inorg. Chem., 1986, 25, 4249. 14 V. Balzani and V. Carassiti, Photochemistry of Coordination Compounds, Academic Press, London, 1970. 15 Handbook of Chemistry and Physics, ed. R. D. Lide, CRC Press, Boca Raton, FL, 72nd edn., 1992. 16 F. Pina, M. Ciano, L. Moggi and V. Balzani, Inorg. Chem., 1985, 24, 844. 17 N. Rudgewich-Brown and R. Cannon, J. Chem. Soc., Dalton Trans., 1984, 25, 479. 18 A. Vogler and H.Kunkely, Top. Curr. Chem., 1990, 158, 1. 19 A. Vogler and J. Kisslinger, J. Am. Chem. Soc., 1982, 104, 2311. 20 M. J. Melo, F. Pina, R. Ballardini and M. Maestri, J. Chem. Educ., in the press. Received 3rd March 1997; Paper 7/01488K

ISSN:1477-9226    

DOI:10.1039/a701488k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2331–2334 2331 Structural, spectroscopic and redox studies of mer-[RuX3L3] (L = PMe2Ph or AsMe2Ph, X = Cl or Br). Crystal structures of mer-[RuX3(AsMe2Ph)3] (X = Cl or Br) and [Ru2X5(EMe2Ph)4] (X = Br, E = P or As; X = I, E = As) Nicholas J. Holmes, Anthony R. J. Genge, William Levason * and Michael Webster Department of Chemistry, University of Southampton, Southampton, UK SO17 1BJ The complexes mer-[RuX3L3] (X = Cl or Br, L = PMe2Ph or AsMe2Ph) have been re-examined and assignments for their UV/VIS spectra proposed.Attempts to prepare analogues with X = I or L = SbR3 have been unsuccessful. Cyclic voltammetry revealed only irreversible oxidation and reduction processes and chemical oxidation with halogens resulted in decomposition to [RuX6]22, in contrast to the chemistry of related osmium compounds. The crystal structures of mer-[RuX3(AsMe2Ph)3] (X = Cl or Br) have been determined and confirm the geometrical isomer formed.Crystal structures were also determined for [Ru2X5L4] (X = Br, L = PMe2Ph or AsMe2Ph; X = I, L = AsMe2Ph) obtained by decomposition of mer-[RuX3L3] in solution, which are the first structurally characterised examples of Ru2 51 dimers of this type with bromide or iodide co-ligands. The structures are consistent with a formal Ru]Ru bond order of ��� . In previous studies we have described the effects of systematic variation of both neutral and halide ligands upon the stability, spectroscopic properties and redox chemistry of several series of osmium complexes including trans-[OsX4L2]0/2 (ref. 1), mer- [OsX3L3]0/1 (ref. 2) and trans-[OsX2L4]0/1/21 (ref. 3) (L = PR3, AsR3 or SbR3; X = Cl or Br, sometimes I). Limited information is available for ruthenium complexes with monodentate ligands, in part because of the much greater reactivity and their tendency to rearrange into halide-bridged dimers,4,5 Here we report studies of representative mer-[RuX3L3] complexes and the structures of some mixed-valence RuII]RuIII dimers formed by their decomposition.Results and Discussion Synthesis and properties The complexes mer-[RuCl3L3] (L = PMe2Ph or AsMe2Ph) were made by reaction of RuCl3?xH2O with the ligand in ethanol– concentrated HCl and converted into the bromides by metathesis with LiBr.6 Only one example of a mer-[RuI3L3] (L = AsMePh2) is mentioned in the literature,7 made by reaction of AsMePh2 with K2[RuCl5(H2O)] and KI in ethanol and with little characterisation.In our hands repeated attempts to make mer-[RuI3L3] (L = PMe2Ph or AsMe2Ph) by metathesis of the chloro complexes with LiI in a variety of solvents failed, the major products being ruthenium(II) complexes of type trans- [RuI2L4], along with smaller amounts of other uncharacterised ruthenium species. In situ monitoring of the UV/VIS spectra of these reactions showed the rapid development of species with intense absorptions at ca. 10 000 cm21, which are probably I(p)Æ RuIII(t2g) charge-transfer (CT) bands,8 but the spectra rapidly decay into ones characteristic of RuII. The reaction of [Ru(dmf)6]31 (dmf = dimethylformamide)9 with L and LiI in ethanol also gave trans-[RuI2L4] 10 along with some [Ru2I5L4] (see below). It seems possible that mer-[RuI3L3] may form transiently, but decompose too rapidly to be isolated. In a similar vein, reaction of RuX3?xH2O (X = Cl or Br) with SbMe2Ph under a variety of conditions gave trans-[RuX2(SbMe2Ph)4] 10 as major products and no examples of mer-[RuX3(SbR3)3] are known.† † We have shown elsewhere 11 that whilst trans-[RuCl2(SbPh3)4]BF4 can be made, there is no good evidence for mer-[RuCl3(SbPh3)3], although osmium(III) analogues are well characterised.2 The IR and ESR spectra of the mer-[RuX3L3] complexes (Experimental section) are in agreement with literature data.12 Electrospray mass spectrometry (MeCN solution) gave features with the appropriate isotope patterns for [RuX2L3]1, [RuX2L2]1 and [RuXL3]1 ions.The rich UV/VIS spectra of these complexes are listed in Table 1 and examples are shown in Fig. 1. The assignments of the major features in terms of ligand-tometal CT transitions in C2v symmetry follows from those of the analogous mer-[OsX3L3].2 For the osmium complexes corresponding bands are found ca. 3000–4000 cm21 to high energy compared with the ruthenium complexes, reflecting the greater ease of reduction of the latter. For osmium a small number of fac-[OsCl3L3] (L = PMe2Ph, PEt2Ph or AsMe2Ph) are known,2,6,13 but no ruthenium analogues have been characterised.Our attempts to convert mer-[RuCl3L3] into the fac isomer, by sequential treatment with NaBH4 and HCl (as used for the osmium complexes),13 failed and mer-[RuCl3L3] in toluene were not isomerised by photolysis (254 nm, 96 h). Crystal structures of mer-[RuX3(AsMe2Ph)3] (X = Cl or Br) The two compounds are isomorphous and are shown by the X-ray study to be the mer geometrical isomer with angles at the Ru atom within 98 of the idealised octahedral values (see Fig. 2 and Table 2). Despite the fact that mer-[RuX3L3] compounds Fig. 1 The UV/VIS spectra of mer-[RuX3(AsMe2Ph)3] [X = Cl (—) or Br (. . .)] in CH2Cl22332 J. Chem. Soc., Dalton Trans., 1997, Pages 2331–2334 Table 1 The UV/VIS data for the mer-[RuX3L3] complexes a Complex s(L) t2g(Ru) s(L) 1 s(X) t2g(Ru) p(X) t2g(Ru) Others b [RuCl3(PMe2Ph)3] 15.6 (240) 19.7 (1 460) 22.9 (990) 35.8 (21 160), 38.8 (16 250) [RuBr3(PMe2Ph)3] 14.5 (780) 16.5 (sh) (900) 18.1 (1000), 22.5 (840) 34.5 (12 500), 38.2 (15 000) [RuCl3(AsMe2Ph)3] 12.6 (1290), 15.3 (sh) 20.0 (1500) 23.2 (1140) 34.0 (14 770), 38.2 (19 900) [RuBr3(AsMe2Ph)3] 12.5 (1360), 14.1 (sh) 16.8 (1230) 18.8 (1160), 22.3 (970) 32.6 (13 300), 36.5 (17 450) a Emax/103 cm21 (emol/dm3 mol21 cm21) in CH2Cl2 solution.b p Æ p* of aryl rings will occur in this region.have long been known and are useful precursors to other ruthenium complexes, none has been structurally characterised, although with nitrogen donors there are a few examples of octahedral ruthenium(III) chloro complexes. There are also a few examples 14–16 of the anionic ruthenium(III) species trans- [RuCl4(PR3)2]2 (R = Et, Bu or Ph). The Ru]Cl distances in the present compound [2.339(5)–2.387(5) Å] appear typical and may be compared 14 with 2.367(4) and 2.361(4) Å found in Fig. 2 The structure of mer-[RuBr3(AsMe2Ph)3] showing the atom labelling scheme. Ellipsoids are drawn at the 50% probability level and H atoms are omitted for clarity. The corresponding chloro compound has essentially the same structure Table 2 Selected bond lengths (Å) and angles (8) for mer-[RuX3- (AsMe2Ph)3] (X = Cl or Br) X = Cl X = Br Ru]X(1) 2.339(5) 2.461(2) Ru]X(2) 2.387(5) 2.513(2) Ru]X(3) 2.345(5) 2.476(2) Ru]As(1) 2.456(2) 2.467(2) Ru]As(2) 2.473(2) 2.482(2) Ru]As(3) 2.495(2) 2.509(2) As]C 1.90(2)–1.97(2) 1.91(1)–1.96(1) C]C 1.36(3)–1.40(2) 1.35(2)–1.42(2) X(1)]Ru]X(2) 92.2(2) 91.7(1) X(1)]Ru]X(3) 173.2(2) 173.0(1) X(2)]Ru]X(3) 93.8(2) 93.7(1) As(1)]Ru]As(2) 95.9(1) 96.8(1) As(1)]Ru]As(3) 168.4(1) 168.6(1) As(2)]Ru]As(3) 93.0(1) 92.2(1) X(1)]Ru]As(1) 89.3(1) 88.4(1) X(1)]Ru]As(2) 84.6(1) 85.1(1) X(1)]Ru]As(3) 98.9(1) 99.4(1) X(2)]Ru]As(1) 82.5(1) 81.8(1) X(2)]Ru]As(2) 176.5(1) 176.5(1) X(2)]Ru]As(3) 88.9(1) 89.6(1) X(3)]Ru]As(1) 88.1(1) 88.0(1) X(3)]Ru]As(2) 89.3(1) 89.4(1) X(3)]Ru]As(3) 84.6(1) 85.0(1) trans-[RuCl4(PEt3)2]2.Structurally determined Ru]As bonds are rare and the present values [2.456(2)–2.509(2) Å] can be compared 17 with those in trans-[RuBr2{C6F4(AsMe2)2-o}2]1 [2.457(1), 2.460(1) Å] and this cation provides a comparator Ru]Br distance [2.455(1) Å]. Redox chemistry An initial aim of this study was to probe the redox chemistry of mer-[RuX3L3] type complexes. As background it is useful to recall that the osmium(III) analogues mer-[OsX3L3] undergo irreversible one-electron reductions to osmium(II) species which readily undergo halide substitution and/or dimerisation depending upon the conditions.18 In contrast electrochemically reversible one-electron oxidation produces mer-[OsX3L3]1, which can be isolated as BF4 2 salts by HNO3–HBFtment of mer-[OsX3L3].2 Cyclic voltammetric studies of mer-[RuX3L3] in CH2Cl2 containing 0.2 mol dm23 [NBun 4][BF4] at scan rates of 0.02–0.2 V s21 showed completely irreversible reduction and oxidation processes at ca. 10.1 and 11.4 V (versus ferrocene– ferrocenium at 10.58 V) showing that neither [RuX3L3]2/1 are stable on this time-scale. Attempted chemical oxidation was also unsuccessful. Addition of the appropriate halogen in CCl4 to CH2Cl2 solutions of mer-[RuX3L3] produced immediate colour changes, but the UV/VIS spectra identified the ruthenium product as the corresponding [RuX6]22,19 whilst the solid complexes decolourised rapidly when added to concentrated HNO3–HBF4 at 0 8C.Crystal structures of [Ru2X5(EMe2Ph)4] (X = Br, E = P or As; X = I, E = As) During the attempted crystallisation of several of the mer species described above, there were often crystals formed with the same colour but two distinct morphologies. Typically a few large block crystals formed in the presence of many smaller rhombic shaped ones. Hand selection and X-ray examination of these smaller crystals established that the structures were dinuclear. In the iodo case below the dinuclear product was obtained from the solution decomposition of trans- [RuI2(AsMe2Ph)4] during crystal growth.We now report the structure of the following three species: [Ru2Br5(PMe2Ph)4], [Ru2Br5(AsMe2Ph)4] and [Ru2I5(AsMe2Ph)4]. The chloro species [Ru2Cl5(PMe2Ph)4] also formed in this way and was identified by comparison with the unit-cell dimensions previously reported.15 All three compounds are of the RuII]RuIII mixedvalence type and are isomorphous.The [Ru2Br5(PMe2Ph)4] compound is shown in Fig. 3 and selected bond lengths and angles in Table 3. It was refined in the space group C2/c where the molecule has C2 crystallographic symmetry and is isomorphous with the chloro compound.15 The Ru]Ru distance [3.083(2) Å] is longer and the Ru]Br]Ru angles are more acute [73.24(6), 74.01(5)8] than the chloro derivative [2.9941(4) Å, 74.41(4) and 75.41(3)8 respectively]. As expected the terminal Ru]Br is shorter than the bridging distances and the bridging bromine not on the two-fold axis is bonded unsymmetrically to the Ru atoms (0.12 Å difference). The compounds [Ru2Br5(AsMe2Ph)4] and [Ru2I5(AsMe2Ph)4] were again refined in the space group C2/c and key structural parameters are shown in Table 3 (see also Fig. 3). As commented on recently 20 for RuII]RuII species [Ru2X3L6]1, theJ. Chem. Soc., Dalton Trans., 1997, Pages 2331–2334 2333 replacement of P by As results in a shorter Ru]Ru and the same trend is observed for these mixed-valence compounds.The Ru]X]Ru angles for X = I are about the same (728) as for X = Br and this together with the longer Ru]I bonds results in an increased Ru]Ru distance [3.197(5) Å]. The [Ru2Cl5(PMe2Ph)4] complex has been studied in some detail by Cotton and Torralba,15 and the compounds reported here are the first examples of bromide and iodide analogues. Although obtained serendipitously and at present in too small yield for detailed spectroscopic study, the structures strongly suggest that they can be regarded as having a metal oxidation state of 2.5, with a delocalised electron and a formal Ru]Ru bond order of ��� .As would be expected, the Ru]Ru distance varies with the identity of the bridging halide from 2.99 (X = Cl) 15 to 3.20 Å (I), but even in the latter the distance is shorter than in the unsymmetrical dimer [(Bu3P)3RuCl3- RuCl2(PBu3)] (3.28 Å)15 which is considered as valence-trapped RuII]RuIII with no metal–metal bond.Experimental Physical measurements were made as described previously.2 Electrospray mass spectra were obtained using a Hewlett- Packard series 1050 mass spectrometer operating in positive electrospray mode using solutions in MeCN and ESR spectra from powdered solids at 150 K on a Bruker ECS 106 spectrometer. Preparations mer-[RuCl3(PMe2Ph)3]. The compound RuCl3?xH2O (0.63 g, 2.4 mmol) was dissolved in ethanol (30 cm3) along with concen- Fig. 3 The structure of [Ru2Br5(PMe2Ph)4] showing the atom labelling scheme.Ellipsoids are drawn at the 50% probability level and H atoms are omitted for clarity. The two other compounds [Ru2Br5(AsMe2Ph)4] and [Ru2I5(AsMe2Ph)4] have essentially the same structure Table 3 Selected bond lengths (Å) and angles (8) for [Ru2X5(EMe2Ph)4] (X = Br or I, E = P or As)* X = Br, E = P X = Br, E = As X = I, E = As Ru]Ru9 3.083(2) 2.941(2) 3.197(5) Ru]X(br 1) 2.585(2) 2.528(2) 2.712(4) Ru]X(br 2) 2.501(1) 2.473(2) 2.677(3) Ru9]X(br 2) 2.619(2) 2.546(2) 2.738(4) Ru]X(t) 2.486(2) 2.431(2) 2.714(3) Ru]E(1) 2.311(3) 2.405(1) 2.435(4) Ru]E(2) 2.310(3) 2.410(2) 2.430(5) E]C 1.81(1)–1.83(1) 1.92(1)–1.96(1) 1.95(3)–2.00(3) Ru]X(br 1)]Ru9 73.2(1) 71.1(1) 72.2(1) Ru]X(br 2)]Ru9 74.0(1) 71.7(1) 72.3(1) X(br 2)]Ru]X(t) 178.0(1) 178.1(1) 176.9(1) * t = terminal, br = bridge (br 1 on two-fold axis).Symmetry labels: (9) 1 2 x, y, ��� 2 z [1 2 x, y, 3– 2 2 z (X/E = Br/As only)].trated HCl (1 cm3). To this PMe2Ph (0.98 g, 7.1 mmol) was added and the mixture heated to reflux under nitrogen for ca. 5 min and then cooled. A brown solid separated from the solution and was filtered off, washed with diethyl ether (2 × 15 cm3) and dried in vacuo (0.72 g, 48% based on RuCl3?xH2O) (Found: C, 46.1; H, 5.2. Calc. for C24H33Cl3P3Ru: C, 46.3; H, 5.4%). n(Ru]Cl)/cm21 (Nujol mull) 327, 300 and 270. Electrospray mass spectrum: m/z = 586, 550 (calc.for C24H33 35Cl2P3 101Ru 585, C24H33 35ClP3 101Ru 550). mer-[RuBr3(PMe2Ph)3]. The complex mer-[RuCl3(PMe2Ph)3] (0.53 g, 0.85 mmol) was suspended in ethanol (30 cm3). To this LiBr (1.77 g, 20 mmol) was added and the mixture heated to reflux under nitrogen for ca. 10 min and then cooled. A deep purple solid separated from a similar coloured solution and was filtered off, washed with water (2 × 10 cm3) and dried in vacuo (0.38 g, 59%) (Found: C, 37.9; H, 4.1. Calc. for C24H33Br3P3Ru: C, 38.2; H, 4.4%).n(Ru]Br)/cm21 (Nujol mull) 242 and 225. Electrospray mass spectrum: m/z = 675, 595 and 537 (calc. for C24H33 79Br2P3 101Ru 673, C24H33 79BrP3 101Ru 594, C16H22 79Br2P2- 101Ru 535). mer-[RuCl3(AsMe2Ph)3]. The compound RuCl3?xH2O (1.28 g, 4.90 mmol) was dissolved in ethanol (25 cm3) along with concentrated HCl (2.5 cm3). To this AsMe2Ph (3.33 g, 18.3 mmol) was added and the mixture heated to reflux under nitrogen for ca. 1 h and then cooled. A dark green solid separated which was filtered off, washed with diethyl ether (2 × 15 cm3) and dried in vacuo (3.07 g, 83%) (Found: C, 38.3; H, 4.1.Calc. for C24H33As3Cl3Ru: C, 38.3; H, 3.8%). n(Ru]Cl)/cm21 (Nujol mull) 323, 310 and 270. ESR (powdered solid 150 K): g = 2.27, 2.05 and 1.92. Electrospray mass spectrum: m/z = 718, 682 and 536 (calc. for C24H33As3 35Cl2 101Ru 717, C24H33As3 35Cl101Ru 682, C16H22As2 35Cl2 101Ru 535). mer-[RuBr3(AsMe2Ph)3]. The complex mer-[RuCl3- (AsMe2Ph)3] (1.0 g, 1.33 mmol) was suspended in ethanol (30 cm3).To this LiBr (2.30 g, 26.4 mmol) was added and the mixture heated to reflux under nitrogen for ca. 10 min and then cooled. A black solid separated and was filtered off, washed with water (2 × 10 cm3) and dried in vacuo (0.8 g, 68%) (Found: C, 33.0; H, 3.6. Calc. for C24H33As3Br3Ru: C, 32.5; H, 3.8%). n(Ru]Br)/cm21 252, 226 and 197. ESR (powdered solid 150 K): g = 2.27, 2.06 and 1.91. Electrospray mass spectrum: m/z = 807, 727 and 625 (calc.for C24H33As3 79Br2 101Ru 805, C24H33As3- 79Br101Ru 726, C16H22As2 79Br2 101Ru 625). Crystallography Details of the crystallographic studies are presented in Table 4. Data were collected on a Rigaku AFC7S diffractometer equipped with Mo-Ka radiation (l = 0.710 69 Å) and a graphite monochromator. Selected crystals were mounted on glass fibres following oil immersion and held at 150 K using an Oxford Cryosystems low-temperature device. The Lorentz-polarisation corrections and any correction for the small amount of decay were applied during data reduction.Crystal solution was by means of SHELXS 8621 and full-matrix least-squares refinement on F was carried out with the TEXSAN he space group of the binuclear systems was either Cc or C2/c with the N(z) test favouring the centrosymmetric space group and the analysis was successfully carried out in this space group. Some of the thermal ellipsoids of the carbon atoms were suggestive of disorder although individual atom sites could not be recognised.This problem could be associated with the empirical absorption corrections used and the rather large m values, genuine disorder, or the possibility of the lower-symmetry space group as difficulties over the choice of Cc versus C2/c are well known.23 Hydrogen atoms were usually included in the model at calculated positions [d(C]H) = 0.95 Å]. Other details for individual structures are as follows.2334 J.Chem. Soc., Dalton Trans., 1997, Pages 2331–2334 Table 4 Crystallographic details * mer-[RuCl3(AsMe2- Ph)3] mer-[RuBr3(AsMe2- Ph)3] [Ru2Br5(PMe2- Ph)4] [Ru2Br5(AsMe2- Ph)4] [Ru2I5(AsMe2Ph)4] Formula C24H33As3Cl3Ru C24H33As3Br3Ru C32H44Br5P4Ru2 C32H44As4Br5Ru2 C32H44As4I5Ru2 Mr 753.72 887.07 1154.25 1330.05 1565.05 Space group P21/c (no. 14) P21/c (no. 14) C2/c (no. 15) C2/c (no. 15) C2/c (no. 15) a/Å 16.070(3) 16.112(7) 16.268(9) 15.978(6) 16.214(5) b/Å 10.358(4) 10.380(2) 11.200(41) 11.508(4) 12.228(4) c/Å 18.120(4) 18.206(6) 21.479(7) 21.421(7) 22.592(8) b/8 113.68(2) 112.32(3) 102.66(3) 101.28(3) 113.32(2) U/Å3 2762(1) 2816(2) 3818(13) 3862(2) 4113(2) 2q Range for cell/8 19.0–21.0 19.0–21.0 26.6–38.2 18.8–22.2 19.0–22.8 Dc/g cm23 1.812 2.091 2.008 2.287 2.526 F(000) 1484 1700 2236 2524 2884 Crystal size/mm 0.30 × 0.20 × 0.10 0.80 × 0.60 × 0.40 0.3 × 0.4 × 0.2 0.10 × 0.25 × 0.20 0.40 × 0.30 × 0.03 Total no.observations 5368 5465 3702 3731 3957 No.unique observations (Rint) 5175 (0.079) 5268 (0.060) 3566 (0.045) 3592 (0.031) 3810 (0.21) Absorption correction y Scan y Scan y Scan DIFABS24 DIFABS Maximum, minimum transmission 0.79, 1.00 0.463, 1.000 0.734, 1.000 0.615, 1.000 0.634, 1.000 No. data in refinement 2645 [I > 4s(I)] 3577 [I > 3s(I)] 2083 [I > 3s(I)] 2203 [I > 4s(I)] 1750 [I > 3s(I)] No. parameters 240 270 195 195 115 m/cm21 44.37 82.3 62.30 93.95 77.25 hkl Ranges 0–19, 0–12, 221 to 19 0–19, 0–12, 221 to 20 0–19, 0–13, 225 to 24 0–18, 0–13, 225 to 24 0–19, 0–14, 226 to 24 S 2.66 3.37 1.75 1.94 2.49 Maximum shift/e.s.d. 0.05 0.07 0.03 0.01 0.00 Residual electron density/e Å23 2.11 to 22.53 2.01 to 21.82 1.19 to 21.41 0.91 to 21.47 1.54 to 21.47 R 0.061 0.052 0.043 0.044 0.052 R9 0.081 0.057 0.053 0.055 0.071 * In common: monoclinic; T = 150 K; Z = 4; scan mode w–2q; w21 = s2(Fo); maximum 2q = 508; R = S |Fo| 2 |Fc| /S|Fo|; R9 = [Sw(Fo 2 Fc)2/ SwFo 2]� �� . mer-[RuCl3(AsMe2Ph)3].Dark brown crystals were obtained by liquid diffusion of EtOH into a CH2Cl2 solution of the target material. Eight C atoms were treated as isotropic since anisotropic thermal parameters resulted in non-positive definite ellipsoids indicative of possible disorder problems. mer-[RuBr3(AsMe2Ph)3]. Dark brown crystals were obtained as above. Two C atoms were treated as isotropic (see comments above). [Ru2Br5(PMe2Ph)4]. Dark brown crystals were obtained by liquid diffusion of EtOH into a CH2Cl2 solution of mer- [RuBr3(PMe2Ph)3]. All C atoms were treated as anisotropic.[Ru2Br5(AsMe2Ph)4]. Dark brown crystals were obtained by liquid diffusion of EtOH into a CH2Cl2 solution of mer- [RuBr3(AsMe2Ph)3]. All C atoms were treated as anisotropic. [Ru2I5(AsMe2Ph)4]. Dark brown crystals were obtained by liquid diffusion of EtOH into a CH2Cl2 solution of [RuI2(As- Me2Ph)4]. Crystal decay was observed (8.5%). The carbon atoms were retained with isotropic thermal parameters as anisotropic ones gave no improved fit to the data and a few non-positive definite ellipsoids. No H atoms were included in the model.Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/529.Acknowledgements We thank the EPSRC for support and funds to purchase the X-ray diffractometer and for access to the Chemical Database Service at Daresbury. References 1 R. A. Cipriano, W. Levason, R. A. S. Mould, D. Pletcher and M. Webster, J. Chem. Soc., Dalton Trans., 1990, 339. 2 R. A. Cipriano, W. Levason, R. A. S. Mould, D. Pletcher and M. Webster, J. Chem., Dalton Trans., 1990, 2609. 3 N. R. Champness, W. Levason, R. A. S. Mould, D. Pletcher and M.Webster, J. Chem. Soc., Dalton Trans., 1991, 2777; N. R. Champness, C. S. Frampton, W. Levason and S. R. Preece, Inorg. Chim. Acta, 1995, 233, 43. 4 P. W. Armit, A. S. F. Boyd and T. A. Stephenson, J. Chem. Soc., Dalton Trans., 1975, 1663. 5 J. Chatt and R. G. Hayter, J. Chem. Soc., 1961, 896. 6 J. Chatt, G. J. Leigh, D. M. P. Mingos and R. J. Paske, J. Chem. Soc. A, 1968, 2636. 7 F. P. Dwyer, J. E. Humpoletz and R. S. Nyholm, Proc. R. Soc. NSW, 1946, 80, 217. 8 N. R. Champness, W. Levason, S. R. Preece, M. Webster and C. S. Frampton, Inorg. Chim. Acta, 1996, 244, 65. 9 R. J. Judd, R. Cao, M. Biner, T. Armbruster, H.-B. Bürgi, A. E. Merbach and A. Ludi, Inorg. Chem., 1995, 34, 5080. 10 N. J. Holmes, unpublished work, 1996. 11 N. R. Champness, W. Levason and M. Webster, Inorg. Chim. Acta, 1993, 208, 189. 12 J. Chatt, G. J. Leigh and D. M. P. Mingos, J. Chem. Soc. A, 1969, 1674. 13 P. G. Douglas and B. L. Shaw, J. Chem. Soc. A, 1970, 334. 14 F. A. Cotton and R. C. Torralba, Inorg. Chem., 1991, 30, 4386. 15 F. A. Cotton and R. C. Torralba, Inorg. Chem., 1991, 30, 2196. 16 J. R. Polam and L. C. Porter, J. Coord. Chem., 1993, 28, 297. 17 N. R. Champness, W. Levason, D. Pletcher and M. Webster, J. Chem. Soc., Dalton Trans., 1992, 3243. 18 V. T. Coombe, G. A. Heath, T. A. Stephenson, J. D. Whitelock and L. J. Yellowlees, J. Chem. Soc., Dalton Trans., 1985, 947. 19 J. C. Collingwood, P. N. Schatz and P. J. McCarthy, Mol. Phys., 1975, 30, 469. 20 G. A. Heath, D. C. R. Hockless and B. D. Yeomans, Acta Crystallogr., Sect. C, 1996, 52, 854. 21 G. M. Sheldrick, SHELXS 86, Program for crystal structure solution, Acta Crystallogr., Sect. A, 1990, 46, 467. 22 TEXSAN, Single crystal structure analysis software, version 1.7-1, Molecular Structure Corporation, The Woodlands, TX, 1995. 23 W. H. Bauer and D. Kassner, Acta Crystallogr., Sect. B, 1992, 48, 356. 24 N. Walker and D. Stuart, DIFABS, Acta Crystallogr., Sect. A, 1983, 39, 158. Received 24th February 1997; Paper 7/

ISSN:1477-9226    

DOI:10.1039/a701295k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2335–2339 2335 Synthesis, electrochemistry and photophysics of ruthenium(II) diimine complexes of 1,19-bis(diphenylphosphino)ferrocene (dppf). Crystal structure of [Ru(bipy)2(dppf)]21 (bipy = 2,29-bipyridine) † Vivian Wing-Wah Yam,* Vicky Wing-Man Lee and Kung-Kai Cheung Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong A series of ruthenium(II) diimine complexes of 1,19-bis(diphenylphosphino)ferrocene (dppf), [Ru(L]L)2(dppf)]21 [L]L = 2,29-bipyridine (bipy), 4,49-dimethyl-2,29-bipyridine, 4,49-di-tert-butyl-2,29-bipyridine, or 1,10- phenanthroline] have been synthesized and their photophysical properties studied.The crystal structure of [Ru(bipy)2(dppf)]21 has been determined. These complexes have been shown to exhibit low-energy emission at ca. 550 nm at 77 K, attributed to a dp(Ru) æÆ p*(L]L) metal-to-ligand charge transfer triplet excited state. The spectroscopic changes upon oxidation suggest it to occur on the ferrocene moiety.The intriguing photophysical and photochemical properties of ruthenium(II) polypyridine complexes have rendered this class of complexes attractive to study, in particular their abilities to exhibit properties of importance to redox electrocatalysis and solar-energy conversion.1,2 Recent developments have been extended towards the design and synthesis of chromophoreelectroactive quencher systems in which electron acceptors such as 4,49-bipyridinium, and/or donors such as phenothiazine, are covalently attached to the chromophore, [Ru(bipy)3]21 (bipy = 2,29-bipyridine).3 The ferrocene moiety, being a redox-active electron-donor component, appears to be an attractive candidate for incorporation into the ruthenium(II) polypyridine system.Although there have been reports 4,5 on such introduction, focus was placed on the synthetic and electrochemical aspects with less attention being paid to the spectroscopic properties. In this paper a series of ruthenium(II) polypyridine complexes containing the ferrocene moiety have been synthesized through the attachment of 1,19-bis(diphenylphosphino)ferrocene (dppf).The spectroscopic, photophysical and electrochemical properties have been studied. In addition, the tuning of the spectroscopic properties of the complexes through a change in the oxidation state of the pendant ferrocenyl ligand and variation of the spectator ligands have also been investigated.Experimental 2,29-Bipyridine and 1,10-phenanthroline (phen) were obtained from Aldrich Chemical Company, 1,19-bis(diphenylphosphino)- ferrocene from Strem Chemicals Inc. The compounds 4,49- dimethyl-2,29-bipyridine (dmbipy), 4,49-di-tert-butyl-2,29- bipyridine (dbbipy) and the precursor complexes were prepared according to literature methods.6 All solvents were purified and distilled by standard procedures before use. All other reagents were of analytical grade and used as received.Synthesis of ruthenium(II) complexes [Ru(bipy)2(dppf)][PF6]2 1. A mixture of cis-[Ru(bipy)2Cl2]? 2H2O (131 mg, 0.25 mmol) and AgO3SCF3 (104 mg, 0.50 mmol) was stirred in acetone (15 cm3) under nitrogen for 3 h. The mixture was then filtered to remove the precipitated AgCl and the filtrate added to a suspension of dppf (277 mg, 0.50 mmol) in acetone (15 cm3). The mixture was then brought to reflux for 24 h, after which the resultant clear light orange solution was evaporated to dryness, extracted with MeOH–water † Non-SI unit employed: eV ª 1.6 × 10219 J.(1 : 1 v/v) and then filtered to remove any unchanged reactants. Addition of a saturated solution of NH4PF6 afforded an orange solid. Slow diffusion of diethyl ether into an acetonitrile solution of the complex afforded 1 as orange crystals. Yield: 250 mg, 85%. 1H NMR [300 MHz, (CD3)2CO, 298 K]: d 9.57 (d, 2 H, J 5.6, bipy), 8.49 (d, 2 H, J 8.1, bipy), 8.27 (d, 2 H, J 7, bipy), 8.11–8.20 (m, 4 H, bipy), 7.69–7.76 (m, 4 H, bipy), 7.47 (t, 4 H, J 7 Hz, Ph), 7.32 (m, 2 H, bipy; 4 H, Ph), 7.06–7.26 (m, 8 H, Ph), 6.90 (m, 4 H, Ph), 5.31 (s, 2 H, C5H4), 4.94 (s, 2 H, C5H4), 4.65 (s, 2 H, C5H4) and 4.39 (s, 2 H, C5H4).Positive-ion fast atom bombardment (FAB) mass spectrum: m/z 1112, [M 1 PF]1; 965 M1 and 812 [M 2 bipy]1 (Found: C, 51.4; H, 3.4; N, 4.2. Calc. for C54H44F12FeN4P4Ru: C, 51.5; H, 3.5; N, 4.45%). [Ru(dmbipy)2(dppf)][PF6]2 2.The procedure was similar to that for complex 1 except that [Ru(dmbipy)2Cl2] (138 mg, 0.25 mmol) was used instead of [Ru(bipy)2Cl2]?2H2O to give orange crystals of 2. Yield: 273 mg, 85%. 1H NMR [300 MHz, (CD3)2CO, 298 K]: d 9.04 (d, 2 H, J 6 Hz, bipy), 7.85 (s, 2 H, bipy), 7.62 (s, 2 H, bipy), 7.22–7.41 (m, 6 H, bipy; 8 H, Ph), 7.20–6.99 (m, 8 H, Ph), 6.73 (m, 4 H, Ph), 4.87 (s, 2 H, C5H4), 4.84 (s, 2 H, C5H4), 4.55 (s, 2 H, C5H4), 4.33 (s, 2 H, C5H4), 2.54 (s, 6 H, CH3) and 2.46 (s, 6 H, CH3).Positive-ion FAB mass spectrum: m/z 1023, M1; 512, M21 and 840, [M 2 dmbipy]1 (Found: C, 57.05; H, 4.35; N, 4.35. Calc. for C56H48Cl2FeN4- O8P2Ru: C, 56.95; H, 4.3; N, 4.6%). [Ru(dbbipy)2(dppf)][PF6]2 3. The procedure was similar to that for compound 1 except that [Ru(dbbipy)2Cl2] (159 mg, 0.25 mmol) was used instead of [Ru(bipy)2Cl2]?2H2O to yield orange crystals of 3. Yield: 296 mg, 80%. 1H NMR [300 MHz, (CD3)2CO, 298 K]: d 9.49 (d, 2 H, J 6.1, bipy), 8.49 (d, 2 H, J 1.7, bipy), 8.38 (d, 2 H, J 2.2, bipy), 7.82 (dd, 2 H, J 2.2, 6.1, bipy), 7.48 (t, 2 H, J 7.3, Ph), 7.25–7.41 (m, 4 H bipy; 6 H, Ph), 7.13 (t, 4 H, J 7.3 Hz, Ph), 7.02 (m, 4 H, Ph), 6.95 (m, 4 H, Ph), 5.31 (s, 2 H, C5H4), 4.88 (s, 2 H, C5H4), 4.59 (s, 2 H, C5H4), 4.03 (s, 2 H, C5H4), 1.43 (s, 18 H, But) and 1.31 (s, 18 H, But).Positive-ion FAB mass spectrum: m/z 1338, [M 1 PF6]1; 1192, M1; 597, M21 and 926 [M 2 dbbipy]1 (Found: C, 57.0; H, 5.15; N, 4.35. Calc for C62H60F12FeN4P4Ru?CH3CN: C, 56.75; H, 5.25; N, 4.6%).[Ru(phen)2(dppf)][PF6]2 4. The procedure was similar to that for complex 1 except that [Ru(phen)2Cl2] (134 mg, 0.25 mmol) was used instead of [Ru(bipy)2Cl2]?2H2O to yield orange crystals of 4. Yield: 287 mg, 88%. 1H NMR [300 MHz, (CD3)2CO, 298 K]: d 10.07 (d, 2 H, J 5.7, phen), 8.79 (d, 2 H, J 8.3, phen), 8.70 (d, 2 H, J 8.5 Hz, phen), 8.09–8.23 (m, 8 H, phen), 7.582336 J. Chem. Soc., Dalton Trans., 1997, Pages 2335–2339 (m, 2 H, phen), 7.42 (m, 2 H, Ph), 7.27 (m, 8 H, Ph), 7.00 (m, 2 H, Ph), 6.74 (m, 4 H, Ph), 6.54 (m, 4 H, Ph), 5.43 (s, 2 H, C5H4), 4.96 (s, 2 H, C5H4), 4.68 (s, 2 H, C5H4) and 4.58 (s, 2 H, C5H4).Positive-ion FAB mass spectrum: m/z 1161, [M 1 PF6]1; 1016, M1 and 836, [M 2 phen]1 (Found: C, 57.15; H, 3.25; N, 4.75. Calc. for C58H44F12FeN4P4Ru: C, 57.35; H, 3.65; N, 4.6%). Physical measurements and instrumentation The UV/VIS spectra were obtained on a Hewlett-Packard 8452A diode-array spectrophotometer, and steady-state excitation and emission spectra on a Spex Fluorolog 111 spectro- fluorometer. Low-temperature (77 K) spectra were recorded by using an optical Dewar sample holder.Proton NMR spectra were recorded on a Bruker DPX-300 Fourier-transform spectrometer with chemical shifts reported relative to tetramethylsilane, positive-ion FAB mass spectra on a Finnigan MAT95 spectrometer. Elemental analysis of the new complexes were performed by Butterworth Laboratories Ltd.Emission lifetime measurements for Stern–Volmer quenching studies were performed using a conventional laser system. The excitation source was the 355 nm output (third harmonic) of a Quanta-Ray Q-switched GCR-150-10 pulsed Nd-YAG laser. Luminescence decay signals were recorded on a Tektronix model TDS 620A digital oscilloscope and analysed using a program for exponential fits. All solutions for photophysical studies were prepared under vacuum in a round-bottomed flask (10 cm3) equipped with a side-arm 1 cm fluorescence cuvette and sealed from the atmosphere with a Kontes quick-release Teflon stopper.Solutions were rigorously degassed with no fewer than four freeze–pump–thaw cycles. Electrochemical measurements were carried out with a PAR model 175 universal programmer and 173 potentiostat. Cyclic voltammograms were recorded with a Kipp & Zonen BD90 X-Y recorded at scan rates 50–500 mV s21. The electrolytic cell used was a conventional two-compartment cell.The reference electrode was Ag–AgNO3 (0.1 mol dm23 in acetonitrile) with a Vycor glass interfacing the working electrode compartment. Studies were performed in a non-aqueous medium (0.1 mol dm23 NBu4PF6 in acetonitrile) with a glassy carbon (Atomergic Chemetal V25) electrode or a 5 × 30 × 50 mm graphite plate as working electrode for cyclic voltammetry and controlledpotential electrolysis, respectively, and a piece of platinum gauze as counter electrode separated from the working electrode by a sintered-glass frit.The ferrocenium-ferrocene couple was used as the internal reference in non-aqueous media for the cyclic voltammetric measurement. Crystallography Crystals of complex 1 were obtained by slow diffusion of diethyl ether into an acetonitrile solution of 1. Crystal data. [C54H44FeN4P2Ru]212PF6 2, M = 1257.77, tetragonal, space group I41cd (no. 110), a = 17.244(3), b = 17.244(3), c = 34.491(4) Å, U = 10 256.1(1.0) Å3, Z = 8, Dc = 1.629 g cm23, m(Mo-Ka) = 7.78 cm21, F(000) = 5072, T = 298 K.A crystal of dimensions 0.25 × 0.15 × 0.30 mm was used for data collection at 25 8C on a Nonius-Enraf CAD4 diffractometer with graphite-monochromated Mo-Ka radiation (l = 0.710 73 Å) using w–2q scans with w-scan angle (0.5 1 0.35 tan q)8 at a scan speed of 1.18–8.288 min21. Intensity data (in the range of 2qmax = 458; h 0–15, k 0–18, l 0–37; three standard reflections measured after every 2 h showed decay of 3.30%) were corrected for decay and for Lorentz-polarization effects, and empirical absorption corrections based on the y scan of four strong reflections (minimum and maximum transmission factors 0.905 and 1.000).Upon averaging the 4681 reflections, 463 of which were uniquely measured (Rint = 0.048), 1663 with I > 3s(I) were considered observed and used in the structural analysis. The space group was determined from systematic absences and the structure was solved by Patterson and Fourier methods and refinement by full-matrix least squares using the SDP Program7 on a Micro VAX II computer.A crystallographic asymmetric unit of 61 atoms consists of half of the complex cation with the Ru and Fe atoms at special positions and one PF6 2 anion. All 39 non-H atoms were refined anisotropically. Twenty-two hydrogen atoms at calculated positions with isotropic thermal parameters equal to 1.3 times that of the attached C atoms were included in the least-squares calculations but not refined.Convergence for 343 variable parameters by least-squares refinement on F with w = 4Fo 2/s2(Fo 2), where s2 (Fo 2) = [s2(I) 1 (0.040Fo 2)2] for 1663 reflections having I > 3 s(I) was reached at R = 0.032 and R9 = 0.040 with a goodness of fit of 1.15; (D/s)max = 0.01. The final Fourier-difference map was featureless, with maximum positive and negative peaks of 0.35 and 0.27 e Å23, respectively. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/510. Results and Discussion The complexes [Ru(L]L)2(dppf)]21 (L]L = bipy, dmbipy, dbbipy or phen) were synthesized by the reaction of dppf with the corresponding bis(acetone)ruthenium(II) diimine precursor under reflux condition, a typical synthetic method for the preparation of heteroleptic ruthenium(II) complexes [Ru(L]L)2L9]21 where L9 is a bidentate ligand.8 All the newly synthesized complexes gave satisfactory elemental analyses and have been characterized by positive-ion FAB mass spectrometry and 1H NMR spectroscopy.Complex 1 has also been characterized by X-ray crystallography. The 1H NMR spectrum of complex 1 shows resonances in the aromatic region which are assigned to protons of the bipyridyl units and the phenyl ring on the dppf ligand.The ferrocenyl protons show resonances in the region d 4.4–5.5, appearing as four singlets. This is different from that observed in other related 1,19-disubstituted ferrocene compounds where the ferrocenyl signals usually appear as two triplets corresponding to the AA9BB9 spin system with a coupling constant of ca. 2 Hz for an eclipsed arrangement of the C5H4 rings.9 This is suggestive of a staggered arrangement for the two C5H4 rings in 1, which has been confirmed by X-ray crystallographic studies. Similar findings have been reported for [Re(CO)3Cl(dppf)] with the C5H4 rings in a staggered conformation.10 A perspective drawing of the cation of complex 1 with the atomic numbering is depicted in Fig. 1. Selected bond distances and angles are listed in Table 1. The complex adopts a distorted Table 1 Selected bond lengths (Å) and angles (8) for complex 1 with estimated standard deviations in parentheses Ru]P(1) 2.393(2) P(1)]Ru]N(1) 96.9(1) Ru]N(1) 2.103(5) P(1)]Ru]N(2) 167.8(1) Ru]N(2) 2.115(5) N(1)]Ru]N(2) 77.5(2) Fe]C(1) 2.023(6) C(1)]Fe]C(2) 41.4(2) P(1)]C(1) 1.831(6) C(1)]Fe]C(3) 68.8(2) P(1)]C(6) 1.851(6) C(1)]Fe]C(4) 69.0(2) P(1)]C(12) 1.840(6) Ru]P(1)]C(1) 123.2(2) N(1)]C(18) 1.328(8) Ru]P(1)]C(6) 110.8(2) N(1)]C(22) 1.363(8) Ru]P(1)]C(12) 118.0(2) N(2)]C(23) 1.340(8) Ru]N(1)]C(18) 127.7(4) N(2)]C(27) 1.350(8) Ru]N(1)]C(22) 115.1(4) C(1)]C(2) 1.441(8) C(18)]N(1)]C(22) 117.2(6) C(1)]C(5) 1.445(9) Fe]C(1)]P(1) 130.3(4) C(2)]C(3) 1.425(9) Fe]C(1)]C(2) 70.3(3) C(3)]C(4) 1.41(2) P(1)]C(1)]C(2) 129.5(5) C(4)]C(5) 1.424(9) P(1)]C(1)]C(5) 122.7(4)J.Chem. Soc., Dalton Trans., 1997, Pages 2335–2339 2337 Table 2 Electrochemical and photophysical data for complexes 1–4 E2� 1 a/V vs. SCE Emission Complex Reduction Oxidation Absorption l/nm (e/dm3 mol21 cm21) b l/nm (n& M/cm21) c 1 21.30 10.91 239 (sh) (50 205), 288 (27 040), 324 (sh) (10 815), 396 (6120) 544 (1325) 21.53 (11.83) 2 21.39 10.90 246 (sh) (39 235), 286 (29 150), 320 (sh) (11 355), 393 (6075) 537 (1425) 21.59 (11.80) 3 21.43 10.91 246 (sh) (40 940), 288 (32 670), 318 (sh) (13 900), 390 (7195) 573 (1355) 21.63 (11.80) 4 21.28 10.90 232 (sh) (72 965), 266 (41 255), 300 (sh) (18 500), 368 (8510), 569 (1150) (21.48) (11.91) 410 (sh) (5955) a In acetonitrile solution with 0.1 mol dm23 NBu4PF6 as supporting electrolyte at room temperature.Working electrode, glassy carbon; scan rate 100 mV s21. Values in parentheses correspond to peak potentials of irreversible waves. b In acetonitrile at 298 K. c In ethanol–methanol (4 : 1 v/v) glass at 77 K. octahedral geometry at Ru. The N]Ru]N bond angle subtended by the chelating bipyridine is 77.68, much distorted from a regular octahedral geometry as a result of the steric requirement of bipyridine. The P]Ru]N angle of 96.98 is slightly larger than the ideal value of 908.The cyclopentadienyl rings in the bidentate dppf ligand are staggered, with a deviation from the eclipsed conformation of 24.098. A staggered conformation of the two cyclopentadienyl rings has also been reported in the square-planar complexes [Rh(nbd)(dppf)]1 (nbd = norbornadiene = bicyclo[2.2.1]hepta-2,5-diene),11 [PtCl2(dppf)] 12 and [PdCl2(dppf)] 13,14 and in the octahedral complexes [Re- (CO)3Cl(dppf)] 10 and [Mo(CO)4(dppf)],14 while an eclipsed conformation of the rings was observed for the tetrahedral complexes of Ni14 and Mn.15 The cyclopentadienyl rings are planar but deviate slightly from being parallel with a dihedral angle of 1.588.In addition, the P atoms are slightly displaced out of the plane by 0.186 Å away from the Fe atom. These conformational arrangements, ring tilt and P atom displacement are probably related to the steric requirements of the bonding to the Ru atom. Similar variations in geometry have been found in a series of related complexes of Rh, Pd, Ni and Mo.11,14 The separation between Fe and Ru is 4.51 Å, too long for any significant metal–metal interaction to exist. Electrochemical data for complexes 1–4 in acetonitrile are collected in Table 2.The cyclic voltmograms of all the Fig. 1 Perspective drawing of the cation of complex 1 with the atomic numbering. The thermal ellipsoids are shown at the 40% probability level [RuII(L]L)2(dppf~1)]31 1 e2 [RuII(L]L)2(dppf)]21 [RuII(L]L)2(dppf)]21 1 e2 [RuII(L]L)(L]L~2)(dppf)]1 [RuII(L]L)(L]L~2)(dppf)]1 1 e2 [RuII(L]L~2)2(dppf)] Scheme 1 complexes display a reversible oxidation couple at ca. 10.90 V vs. SCE, independent of scan rate, and with a DEp of ca. 60 mV. Possible origins of this couple could be either a metal-centred Ru31/21 couple or the dppf ligand-centred oxidation, localized on the redox-active ferrocene moiety. The relative insensitivity of the potential to the nature of the spectator ligand, together with the fact that Ru31/21 couples for dicationic ruthenium(II) polypyridine complexes commonly occur in the range 11.20 to 11.75 V vs.SCE, suggest that the first oxidation is unlikely to be ruthenium(II) based but rather dppf based instead. The observation that this dppf-centred oxidation occurs at a more positive potential than that of free dppf, Epa 10.27 V vs. ferrocenium–ferrocene,10 is in line with its reduced ease of oxidation upon co-ordination to ruthenium(II).Upon scanning to a more positive potential a second oxidation process which is irreversible appears at ca. 11.80 V vs. SCE. This is tentatively suggested to be a result of the oxidation at the diphenylphosphine moiety to give a short-lived co-ordinated phosphenium cation. The Ru31/21 couple, which is commonly observed in the range 11.20 to 11.75 V vs. SCE for ruthenium(II) polypyridine dications, was not observed upon scanning to 11.80 V for the [Ru(L]L)2(dppf)]21 complexes.The ruthenium(II)-based oxidation probably occurs at a more positive potential than those of homoleptic ruthenium(II) polypyridine complexes such as [Ru(bipy)3]21 in view of the better p-acceptor ability of the phosphine ligand than those of ligands of the bipyridyl type. Thus the lower oxidation state ruthenium(II) would be more preferentially stabilized and a shift in the reduction potential to a more positive value would be observed. Furthermore, the prior oxidation of the dppf ligand would impose a higher overall positive charge on the complexes and render further oxidation of the complexes difficult.Thus it is likely that the metalcentred oxidation for [Ru(L]L)2(dppf)]21 occurs at a potential more positive than that of [Ru(bipy)2(Ph2PCH2PPH2)]21 [11.63 V vs. saturated sodium chloride electrode (SSCE)] and [Ru(bipy)2(cis-Ph2PCH]] CHPPh2)]21 (11.75 V vs. SSCE),8 and possibly so positive that it occurs beyond the solvent window for measurements.On the other hand, the reduction couples of the complexes correspond to sequential one-electron reductions of their diimine ligands. The reversible redox couples can be summarized as in Scheme 1. The UV/VIS absorption spectral data for complexes 1–4 are summarized in Table 2. The electronic absorption spectrum is dominated by an intense band in the UV region and a medium2338 J. Chem. Soc., Dalton Trans., 1997, Pages 2335–2339 band in the visible region.The band of 1 at ca. 288 nm in the UV region with a large absorption coefficient is tentatively assigned as a p æÆ p* transition localized on either the bipyridine ligands or the phenyl groups. The band at ca. 400 nm with an absorption coefficient of 6210 dm3 mol21 cm21 is assigned as the dp(Ru) æÆ p*(bipy) metal-to-ligand chargetransfer (m.l.c.t.) transition. Similar assignments have been reported for analogous mixed phosphine–bipyridine complexes of ruthenium(II).8 It is likely that any dppf-centred absorption which has a very small absorption coefficient and usually occurs at a similar region for free dppf (e420 = 210 dm3 mol21 cm21) would be masked by the intense m.l.c.t.band. The lower m.l.c.t. absorption energy of 1 than that of the related complexes [Ru(bipy)2(Ph2PCH2PPh2)]21 (384 nm) and [Ru(bipy)2- (cis-Ph2PCH]] CHPPh2)]21 (373 nm) is suggestive of a higher dp(Ru) orbital energy in 1, assuming the p*(L]L) orbital energy remains relatively constant for the same bipyridine ligand as reflected by the almost identical E2� 1 values for the diimine-based reduction of all the three complexes.This finding is in line with the comparatively poorer p-acceptor ability of the dppf ligand expected with its ferrocenyl moiety being a good electron donor. Excitation of degassed acetonitrile solutions of complexes 1– 4 at room temperature did not result in emission characteristic of the m.l.c.t. triplet state. An appreciable emission can only be observed at low temperatures. The photophysical data are collected in Table 2.The results reveal that the complexes are higher-energy emitters at 77 K in alcohol glasses than is [Ru(bipy)3]21. The emission spectra of the [Ru(L]L)2- (dppf)]21 complexes all display well resolved vibronic bands with vibrational progressional spacings (n& M) ranging from 1150 to 1425 cm21. Emission spectra of this type are typical for m.l.c.t. excited states with diimines as the chromophoric ligands.16 The vibrational progressions appear to be assignable to the n(L]L) framework vibrations. The observation of emissive properties upon lowering of temperature is commonly encountered in [Ru(L]L)2L92]21 (L = phosphine) complexes.16 The lack of luminescent properties of the [Ru(L]L)2L92]21 complexes at room temperature can be rationalized by the enhanced rate of the m.l.c.t.to d–d transition state as a result of the p acidity of the phosphine ligands which destabilizes the lowest m.l.c.t.state to a far greater extent than the d–d state compared, for example, to that of the luminescent [R(bipy)3]21.16 The presence of the ferrocenyl moiety, which would be expected to act as both a good reductive quencher (E2� 1 ª 10.377 V vs. SCE) and an energy acceptor (ET ª 1.65 eV) 17 for ruthenium(II) polypyridine complexes, may also be another contributing factor to the non-emissive property observed at room temperature.The quenching of [Ru(bipy)3]21 by dppf in acetonitrile solution (0.1 mol dm23 NBu4PF6) shows that the dppf ligand can act as an efficient electron- and energy-transfer quencher for the 3m.l.c.t. excited state of [Ru(bipy)3]21 with a bimolecular quenching rate constant, kq, of 1.3 × 109 dm3 mol21 s21 {E8[Ru(bipy)3 21*/1] = 10.77 V vs. SCE;18 Epa(dppf1/0) ª 10.65 V vs. SCE;10 E0-0- [Ru(bipy)3 21*/21] ª 2.13 eV}.18 It is therefore likely that coordination of dppf to the Ru(bipy)2 unit would also quench the emission of the complexes through very efficient intramolecular electron- and energy-transfer quenching processes, given the E8[Ru(bipy)2(dppf)21*/1] = 10.98 V vs.SCE and E0-0[Ru(bipy)2(dppf)21*/21] ª 2.28 eV estimated for complex 1. Similar excited-state reduction potentials and zero– zero emission energies have been reported for the related [Ru(bipy)2(Ph2PCH2CH2PPh2)]21 and [Ru(bipy)2(cis-Ph2PCH]] CHPPh2)]21 complexes.16 The UV/VIS spectral traces of complex 1 in acetonitrile (0.1 mol dm23 NBu4PF6) during the course of controlled-potential electrolysis at a potential slightly more positive than the first oxidation couple show the generation of a broad absorption band at ca. 620 nm with an absorption coefficient of 565 dm3 mol21 cm21, characteristic of the ferrocenium ion (lmax = 617 nm, e = 450 dm3 mol21 cm21).19 Similar observations have been reported for rhenium(I) dppf complexes.10 On the other hand, controlled-potential electrolysis of other related ruthenium(II) phosphine complexes but without the ferrocene moiety was reported by Meyer and co-workers 8 to show UV/VIS spectral data typical of the oxidized ruthenium(III) species. The [RuIII(bipy)2{Ph2P(CH2)3PPh2}]31 and [RuIII(bipy)2(cis-Ph2- PCH]] CHPPh2)]31 species generated by controlled-potential oxidation of the respective [Ru(bipy)2{Ph2P(CH2)3PPh2}]21 and [Ru(bipy)2(cis-Ph2PCH]] CHPPh2)]21 display absorption band at ca. 779 and 840 nm, respectively, assigned as ligand-to-metal charge-transfer (l.m.c.t.) transitions, while a band at ca. 385 nm has been assigned as either a pb(bipy) æÆ dp(RuIII) l.m.c.t. or dp(RuIII) æÆbipy) m.l.c.t. transition.8 The occurrence of the absorption band at ca. 620 nm upon oxidation of 1, which is of higher energy than those observed for [RuIII(bipy)2{Ph2P- (CH2)3PPh2}]31 and [RuIII(bipy)2(cis-Ph2PCH]] CHPPh2)]31 and typical of the ferrocenium ion, further supports the assignment of the first reversible oxidation to the ferrocene-centred one on the dppf ligand in the cyclic voltammetric studies.The UV/VIS spectral traces of complexes 1 and 3 upon titration with the oxidizing agent ammonium cerium(IV) nitrate in acetonitrile are shown in Figs. 2 and 3, respectively. Those of 1 upon chemical oxidation are similar to those obtained by controlled-potential electrolysis. A broad band at ca. 620 nm is generated and a shift of the m.l.c.t. absorption band at ca. 396 nm to higher energy at ca. 370 nm is observed, with two isosbestic points centred at 396 and 470 nm. The generation of the absorption band at ca. 620 nm with an absorption coefficient in the order of 102 dm3 mol21 cm21 indicates formation of the ferrocenium ion. Fig. 4 shows the titration curve for the cerium(IV) titration of 1 in acetonitrile, which levels off after addition of about 1 mol equivalent of ammonium cerium(IV) nitrate, indicating that the redox reaction is a one-electron process as cerium(IV) is a one-electron oxidant.The reaction that is likely to proceed is [Ru(L]L)2(dppf)]21 1 Ce41 æÆ [Ru(L]L)2- (dppf~1)]31 1 Ce31. The blue shift in the dp(Ru) æÆ p*(L]L) m.l.c.t. absorption energy upon oxidation may be attributed to the electronwithdrawing nature of the bis(diphenylphosphino)ferrocenium cation, which would render the metal centre less electron rich Fig. 2 The UV/VIS absorption spectral traces of complex 1 in acetonitrile upon oxidation with ammonium cerium(IV) nitrateJ.Chem. Soc., Dalton Trans., 1997, Pages 2335–2339 2339 Fig. 3 The UV/VIS absorption spectral traces of complex 3 in acetonitrile at 298 K upon oxidation with ammonium cerium(IV) nitrate Fig. 4 Titration curve for the oxidation of complex 1 with ammonium cerium(IV) nitrate in acetonitrile and less readily able to donate its electron in the m.l.c.t. transition. The oxidation would also render the dppf ligand a better p acceptor and therefore the dp orbitals of the ruthenium(II) centre would be more stabilized, leading to a lowering of the dp orbital energies, and hence a shift in the dp(RuII) æÆ p*(L]L) m.l.c.t.transition to higher energy would occur. Acknowledgements V. W.-W. Y. acknowledges financial support from the Research Grants Council and The University of Hong Kong. V. W.-M. L. acknowledges the receipt of a postgraduate studentship, administered by The University of Hong Kong. References 1 T. J. Meyer, Acc. Chem. Res., 1981, 22, 163. 2 J. S. Connolly, Photochemical Conversion and Storage of Solar Energy, Academic Press, New York, 1981. 3 E. Danielson, C. M. Elliott, J. W. Merkert and T. J. Meyer, J. Chem. Soc., Chem. Commun., 1994, 2075. 4 P. D. Beer and O. Kocian, J. Chem. Soc., Dalton Trans., 1990, 3283. 5 I. R. Butler, Organometallics, 1992, 11, 74. 6 W. H. F. Sasse, Org. Synth., 1973, Coll. Vol. V, 102. 7 SDP, Structure Determination Package, Enraf-Nonius, Delft, 1985. 8 B. P. Sullivan, D. J. Salmon and T. J. Meyer, Inorg. Chem., 1978, 17, 3334. 9 R. Broussier, A. Da Rold, B. Gautheron, Y. Dromzee and Y. Jeannin, Inorg. Chem., 1990, 29, 1817. 10 M. M. Timothy, J. A. Kazi and M. S. Wrighton, Inorg. Chem., 1989, 28, 2347. 11 W. R. Cullen, T. J. Kim, F. W. B. Einstein and T. Jones, Organometallics, 1983, 2, 714. 12 D. A. Clemente and G. Pilloni, Inorg. Chim. Acta, 1986, 115, L9. 13 T. Hayashi, M. Konishi, M. Kobori, M. Kumada, T. Higuchi and K. Hirotsu, J. Am. Chem. Soc., 1984, 106, 158. 14 I. R. Butler, W. R. Cullen, T.-J. Kim, S. J. Rettig and J. Trotter, Organometallics, 1985, 4, 972. 15 S. Onaka, Bull. Chem. Soc. Jpn., 1986, 59, 2359. 16 J. V. Caspar and T. J. Meyer, Inorg. Chem., 1983, 22, 2444. 17 W. G. Herkstroeter, J. Am. Chem. Soc., 1975, 97, 4161. 18 C. R. Bock, J. A. Connor, A. R. Gutierrez, T. J. Meyer, D. G. Whitten, B. P. Sullivan and J. K. Nagle, J. Am. Chem. Soc., 1979, 101, 4815. 19 Y. S. Sohn, D. N. Hendrickson and H. B. Gray, J. Am. Chem. Soc., 1971, 93, 3603. Received 21st November 1996; Paper 6/07923G

ISSN:1477-9226    

DOI:10.1039/a607923g

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2341–2345 2341 Synthesis of novel ruthenium complexes containing bidentate imidazole-based ligands Sarah Elgafi, Leslie D. Field,* Barbara A. Messerle,* Trevor W. Hambley and Peter Turner School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia Ruthenium(II) complexes containing the bidentate imidazole-based ligands (MeN2H2C3)2CO L1, (MeN2H2C3)2CHOH L2 and (MeN2H2C3)2CH2 L3 (where 1-MeN2H2C3 = 1-methylimidazol-2-yl), [Ru(PPh3)2H(CO)L1]Cl 1, [Ru(PPh3)2H(CO)L2]Cl 2 and [Ru(PPh3)2H(CO)L3]Cl 3, were synthesized by the reaction of L1–L3 with [Ru(PPh3)3H(Cl)(CO)] in toluene.The complexes were characterised by NMR spectroscopy and the crystal structures of [Ru(PPh3)2H(CO)L1]BF4 4 and [Ru(PPh3)2H(CO)L2]OH 5 determined. Transition-metal complexes with ligand systems containing nitrogen-donor atoms have been used successfully to promote the transformation of organic compounds,1 and also to act as structural mimics of metal centres in enzymes.2–5 Ruthenium complexes containing bidentate N-donor ligands with sp2- hybridised nitrogen atoms such as 2,29-bipyridyl,6 1,10- phenanthroline 6 and bis(pyrazol-1-yl)methane 7 have recently found use in catalytic hydrogenation reactions. Research into transition-metal complexes containing polyimidazole ligands has been concerned primarily with metalloenzyme mimicry, using metal complexes of zinc,2,8 iron,9,10 cobalt 2,8 and copper.11 A number of palladium,12,13 platinum14 and ruthenium 15 complexes of polyimidazole ligands have also been reported. In particular, platinum complexes of the bidentate imidazoles (MeN2H2C3)2CO L1 and (MeN2H2C3)2CHOH L2 where MeN2H2C3 = 1-methylimidazol-2-yl have been reported and show considerable cytostatic activity.16 Palladium( II) complexes of the bidentate ligand (MeN2H2C3)2CH2 L3 and closely related symmetrical and unsymmetrical bidentate N-donor ligands with pyridine, pyrazole and imidazole subunits have been investigated in detail.13 In this paper, we report the syntheses and structures of novel ruthenium(II) complexes of L1,9,13,17 L2,4 and L3.13 The complexes [Ru(PPh3)2H(CO)L1]Cl 1, [Ru(PPh3)2H(CO)L2]Cl 2 and [Ru(PPh3)2H(CO)L3]Cl 3 are readily formed by reaction of the appropriate L with [Ru(PPh3)3HCl(CO)] in toluene solvent.The complexes are charged and are of the general form [RuL- (PPh3)2H(CO)]Cl in which a single bidentate imidazole ligand L is bound to the metal centre with displacement of triphenylphosphine and Cl2 ligands from the precursor.The complexes were characterised by NMR spectroscopy and [Ru(PPh3)2- H(CO)L1]BF4 4 and [Ru(PPh3)2H(CO)L2]OH 5 were characterised by X-ray diffraction. Results and Discussion Ligand synthesis The bidentate ketone L1 was synthesized by deprotonation of N-methylimidazole and reaction with diethyl carbonate at low temperature using a modification of the procedure described by Lippard and co-workers.17 Although L1 has been synthesized using other methods,9,13,17 this route gave yields which were consistently above 60%. Bidentate ketones analogous to L1 have also been reported previously as intermediates in the synthesis of tridentate imidazoles.5,18 The bidentate alcohol L2 was synthesized by a modification of the method described by Breslow and co-workers.4 The bidentate alkane L3 was prepared following the method of Byers and Canty,13 by Wolff–Kishner reduction of L1.Synthesis of metal complexes Carbonylchlorohydridotris(triphenylphosphine)ruthenium(II) 19 [Ru(PPh3)3H(Cl)(CO)] was used as the precursor for the synthesis of ruthenium complexes. We have previously shown that tridentate imidazoles form clean products from this precursor,20 where only one tridentate ligand binds to the metal centre. The synthesis of the metal complexes containing bidentate imidazole ligands L involved refluxing solutions of [Ru(PPh3)3- H(Cl)(CO)] with each L in toluene solution over a period of hours, and isolation of the products.In all cases a single bidentate imidazole ligand L binds to the metal centre with displacement of PPh3 and Cl2 from the precursor. The resulting com-2342 J. Chem. Soc., Dalton Trans., 1997, Pages 2341–2345 plexes [RuL(PPh3)2H(CO)]Cl are charged and precipitate directly from the reaction mixture. Crystals of [Ru(PPh3)2H(CO)L1]1 cation containing the ligand L1 were obtained by addition of sodium tetrafluoroborate to a methanol solution of complex 1, giving the tetrafluoroborate complex 4.Crystals of the hydroxide salt, [Ru(PPh3)2- H(CO)L2]OH 5 were formed on slow crystallisation of [Ru- (PPh3)2H(CO)L2]Cl2 2 from methanol–water. Hydroxide resulted from exchange of Cl2 with water during recrystallisation. The complexes 1–3 have been analysed using NMR spectroscopy. Two-dimensional NMR techniques were used for assigning the resonances and determining the stereochemistry of the products.The structures of 4 and 5 were confirmed using single-crystal X-ray analysis. Projections of the structures of [Ru(PPh3)2H(CO)L1]BF4 4 and [Ru(PPh3)2H(CO)L2]OH 5 are shown in Fig. 1. Selected structural parameters are given in Table 1, crystallographic details in Table 2. Crystal structures The two complexes 4 and 5 have similar distorted-octahedral geometries about the metal centre. The P]Ru bonds are not collinear, with the P]Ru]P angle distorted by about 108 from linearity [171.6(4) for 4 and 168.9(6)8 for 5].The bite angle of the bidentate imidazole ligand is small, with bond angles Fig. 1 The ORTEP21 plots of (a) [Ru(PPh3)2H(CO)L1]BF4 4 and (b) [Ru(PPh3)2H(CO)L2]OH 5 with 30% thermal ellipsoids for the nonhydrogen atoms; hydrogen atoms have an arbitrary radius of 0.1 Å. Both complexes are viewed with the P]Ru]P axis lying horizontal N]Ru]N of 83.2(1)8 in 4 and 84.7(2)8 in 5. The two triphenylphosphine ligands lean towards the CO ligand and away from the imidazolyl rings of the ligand, with the angles between the P]Ru and C]Ru bonds on average less than 908 [85.9(1), 89.9(1) in 4, 88.1(2) and 92.8(2)8 in 5], and the angles between the P]Ru and N]Ru bonds larger than 908 [94.18(2) and 91.91(9) in 4, 98.3(1) and 92.4(1)8 in 5].The imidazolyl rings of complex 4 are planar to within 0.01 Å and form dihedral angles of 21.3 and 18.68 with the coordination plane defined by N(1)]N(2)]C(1) and H(Ru).The metal ion is slightly displaced from the co-ordination plane, by 0.03 Å. Atoms N(1), N(2) and C(1) reside on the least-squares plane, whereas H(1Ru) deviates from it by 0.02 Å. The imidazolyl rings of 5 are also planar to within 0.01 Å and form dihedral angles of 9.7 and 11.08 with the co-ordination plane defined by N(1), N(2), C(1) and H(Ru). The metal ion is 0.02 Å out of this plane. Atoms N(1), N(2) and C(1) of 5 reside on the least-squares plane, whereas H(Ru) deviates from it by 0.03 Å.Table 1 Selected bond distances (Å) and angles (8) for complexes [Ru(PPh3)2H(CO)L1]BF4 4 and [Ru(PPh3)2H(CO)L2]OH 5 Ru]N(1) Ru]N(2) Ru]P(1) Ru]P(2) Ru]CO Ru]H P(1)]Ru]P(2) P(1)]Ru]N(1) P(1)]Ru]N(2) P(1)]Ru]C(1) P(2)]Ru]C(1) N(1)]Ru]N(2) 4 2.176(3) 2.135(3) 2.357(1) 2.356(1) 1.829(4) 1.66(4) 171.61(4) 94.18(9) 91.91(9) 85.9(1) 89.9(1) 83.2(1) 5 2.181(5) 2.139(5) 2.336(2) 2.385(2) 1.845(7) 1.77(5) 168.96(6) 98.3(1) 92.4(1) 88.1(2) 92.8(2) 84.7(2) Table 2 Crystallographic data * for [Ru(PPh3)2H(CO)L1]BF4 4 and [Ru(PPh3)2H(CO)L2]OH 5 Empirical formula M Crystal colour, habit Crystal dimensions/mm a/Å b/Å c/Å b/8 U/Å3 Dc/g cm23 F(000) m/cm21 2qmax/8 hkl ranges No.reflections measured; total, unique (Rint) Transmission factors No. observations [I>2.50s(I)] No. variables Reflection/parameter ratio Residual R, R9 Goodness of fit Maximum, minimum peaks in final difference map/e Å23 4 C46H41BF4N4O2P2Ru 931.68 Red, prism 0.48 × 0.20 × 0.20 22.314(5) 14.745(3) 26.887(6) 103.19(2) 8612(3) 1.437 3808.00 4.99 49.9 226 to 26, 0–17, 0–32 8046, 7906 (0.020) 0.91–0.92 5603 540 10.38 0.044, 0.041 2.12 0.55, 20.59 5 C46H42N4O4P2Ru 877.88 Colourless, prism 0.43 × 0.32 × 0.11 28.919(9) 20.550(5) 18.910(4) 119.57(2) 9774(4) 1.193 3616.00 35.51 120.5 0–32, 0–23, 221 to 18 7718, 7547 (0.032) 0.35–0.70 5760 527 10.93 0.053, 0.061 3.89 0.58, 20.86 * Details in common: monoclinic, space group C2/c (no. 15); Z = 8; 21 8C; function minimised Sw(|Fo| 2 |Fc|)2; w21 = 4Fo 2/s2(Fo); anomalous dispersion on all non-hydrogen atoms; maximum shift/error in final cycle 0.00.J. Chem.Soc., Dalton Trans., 1997, Pages 2341–2345 2343 The deviation from coplanarity of the components of the bidentate imidazole ligands of complexes 4 and 5, provides a minor extension of the limited bite of the ligand co-ordinated to the large ruthenium ion. The larger deviation from coplanarity evident in 4 is probably driven by contact between the carbonyl O(2) atom and the methyl C(4) and C(8) atoms.The distance between O(2) and C(4) is 2.801(8) Å, and that between O(2) and C(8) is 2.770(8) Å. The O(2) to C(4) and C(8) distances in 5 are 3.24(1) and 3.28(1) Å. There are several close contacts between the imidazolyl rings of the bidentate imidazole ligand and the triphenylphosphine ligands. For example in complex 4 the N(1) to C(12) distance is 3.299(5) Å, N(2) to C(40) is 3.044(5) Å, N(2) to C(24) is 3.193(5) Å, N(2) to C(35) is 3.195(5) Å and N(2) to C(23) is 3.269(5) Å.Similar contacts are found in the structure of 5. In complex 5 the OH2 counter ion is hydrogen bonded to the metal carbonyl ligand while the solvent of crystallisation (H2O) is hydrogen bonded to the OH group on the ligand backbone. The Ru]P bond lengths in complex 4 are almost identical at 2.357(1) and 2.356(1) Å, and very similar to those in 5 [2.336(2) and 2.385(2) Å]. Comparison with the other known ruthenium complexes containing polydentate nitrogen donor ligands, tridentate imidazole-based ligands,20 tris(pyrazol-1-yl)methane and tris(pyrazol-1-yl)borane complexes, reveals very similar Ru]P bond lengths ranging between 2.33 and 2.37 Å.22,23 The Ru]N bond lengths are almost identical in 4 and 5, at 2.176(3) and 2.135(3) in 4 and 2.181(5) and 2.139(5) Å in 5.In each complex that opposite the metal-bound hydride is longer [2.176(3) and 2.181(5) Å] than the one opposite the metal-bound carbonyl [2.135(3) and 2.139(5) Å].Again, other known complexes of tridentate imidazole ligands and tris(pyrazol- 1-yl)methane and tris(pyrazol-1-yl)borate complexes with Ru have very similar Ru]N bond lengths, ranging between 2.12 and 2.17 Å.22,23 NMR Assignment of complexes 1–3 The 1H, 31P and 13C NMR spectra were completely assigned for complexes 1–3, using two-dimensional methods. In each of the complexes, the two imidazolyl rings in the ligand are nonequivalent, with one (A) trans to the hydride ligand and the other (B) trans to the carbonyl ligand.The assignment of protons to the heterocyclic rings A or B was achieved using two-dimensional 1H nuclear Overhauser effect spectroscopy (NOESY). One imidazolyl ring (B) is directed towards the metal-bound hydride and a NOESY interaction between H4 B and the metal-bound hydride is observed, while the protons (H4 and H5) on the other imidazolyl ring (A) do not interact with the hydride ligand.The assignments of the resonances of the two methyl groups on nitrogen to their respective imidazolyl rings was also achieved using the 1H NOESY NMR spectrum; NOESY interactions were observed between each methyl group and the proton H5 on the same imidazolyl ring. For complexes 1 and 3 the two trans triphenylphosphine ligands appear as a singlet in the 31P-{1H} NMR spectrum. In the case of [Ru- (PPh3)2H(CO)L2]Cl 2 the two trans triphenylphosphine ligands are non-equivalent.The 31P-{1H} NMR resonances for 2 appear as two tented doublets with a large 2JPP coupling constant of 287 Hz, characteristic of the trans disposition of the phosphines. Although no crystal structure was obtained for [Ru(PPh3)2- H(CO)L3]Cl 3, the NMR data indicate that the structure is analogous to those of 1 and 2. In 3, the two triphenylphosphine ligands are mutually trans and equivalent, as in 1, and the two imidazolyl rings of the ligand were assigned to A and B positions using the 1H NOESY NMR spectrum. Conclusion Three new ruthenium(II) complexes containing bidentate imidazole-based ligands L1–L3 have been synthesized and characterised.Reaction of the appropriate bidentate L with [Ru- (PPh3)3H(Cl)(CO)] in toluene solvent led to the formation of [Ru(PPh3)2H(CO)L1]Cl 1, [Ru(PPh3)2H(CO)L2]Cl 2 and [Ru- (PPh3)2H(CO)L3]Cl 3, in good yields of between 65 and 88%. The complexes contain a single bidentate imidazole ligand, two triphenylphosphines, a hydride and a carbonyl.X-Ray analysis shows that they are essentially octahedral. Distortion from perfect octahedral symmetry is primarily due to steric effects of the triphenylphosphine ligands and the small bite angle of the bidentate imidazole ligands. Experimental All manipulations of metal complexes and air-sensitive reagents were carried out using standard Schlenk or vacuum techniques,24 or in a Vacuum Atmospheres argon-filled drybox.Ruthenium(III) trichloride hydrate was obtained from both Aldrich and Johnson Matthey, and used without further purifi- cation. n-Butyllithium was used as a solution in hexane (ª2.4 mol dm23) as supplied by Aldrich and was titrated immediately prior to use against 2,5-dimethoxybenzyl alcohol.25 N-Methylimidazole was obtained from Aldrich and used without further purification. Tetrahydrofuran and toluene were stored over sodium wire and distilled under nitrogen immediately prior to use from sodium–benzophenone ketyl.Light petroleum refers to the fraction with bp 60–80 8C. The mass spectra of organic compounds were recorded on a Kratos MS9/MS50 double-focusing mass spectrometer, those of organometallic complexes on a Finnigan MAT TSQ-46 mass spectrometer (San Jose, CA, USA). In the case of organometallic complexes in which the overall mass spectrum is predominantly that of the ligands, spectra were recorded by scanning mass ranges greater than that of the free L, typically m/z >250.Peaks with low intensity are not quoted unless deemed signifi- cant. Infrared spectra were recorded on a Perkin-Elmer 1600 series FTIR spectrophotometer. Melting points were determined using a Gallenkamp apparatus and are uncorrected. The 1H, 31P and 13C NMR spectra were recorded on Bruker AMX400 and AMX600 spectrometers at 300 and 303 K respectively. Chemical shifts are internally referenced to residual solvent in the case of 1H and 13C, and to external neat trimethyl phosphite (d 140.85) in the case of 31P spectra.Carbonylchlorohydridotris(triphenylphosphine)ruthenium(II) was prepared by the method of Ahmad et al.19 Crystallography A red prismatic crystal of complex 4 was attached to a thin glass fibre, and mounted on an Enraf-Nonius CAD4 diffractometer employing graphite-monochromated Mo-Ka radiation (l 0.710 93 Å). C-Centred monoclinic cell constants were obtained from a least-squares refinement using the setting angles of 25 machine-centred reflections in the range 19.6 < 2q < 24.28.Data were collected using w–q scans with a scan width of (1.50 1 1.05 tan q)8. The intensities of three representative reflections measured every 60 min decreased by 3.2%, and a linear correction was accordingly applied to the data. The crystal faces were indexed and an analytical absorption correction was applied to the data. A colourless prismatic crystal of complex 5 was attached to a thin glass fibre and mounted on a Rigaku AFC7R diffractometer employing graphite-monochromated Cu-Ka radiation (l 1.541 78 Å) from a 12 kW direct drive rotating-anode generator.C-Centred monoclinic cell constants were obtained from a least-squares refinement using the setting angles of 25 automatically centred reflections in the range 90.42 < 2q < 97.638. Omega scans of several intense reflections made prior to data collection had an average width at half-height of 0.248.Data were collected using w–2q scans with a scan width of (1.68 1 0.35 tan q)8. The intensities of three representative2344 J. Chem. Soc., Dalton Trans., 1997, Pages 2341–2345 reflections measured every 150 decreased by 3.3% during the data collection, and a linear correction was applied to the data. Other details as for 4. All calculations were performed using the TEXSAN26 crystallographic software package. The data were corrected for Lorentz-polarisation effects. The data obtained from both complexes 4 and 5 showed systematic absences of hkl (h 1 k � 2n) and h0l (l � 2n), and the structures were solved in the space group C2/c (no. 15). The structures were solved by direct methods27 and expanded using Fourier-difference maps.28 The non-hydrogen atoms were refined anisotropically, and the hydrides were refined isotropically. The remaining hydrogen atoms were included in the full-matrix least-squares refinements at calculated positions with group thermal parameters.The tetrafluoroborate anion of 4 proved to be disordered and was refined with eight fluorine sites of equal occupancy. After several cycles of refinement the positions of the fluorine atoms were fixed. The crystal structure for complex 5 was modelled as [Ru(PPh3)2H(CO)L2]OH?H2O, with no hydrogens attached to the oxygen atoms, and the water oxygen equally distributed between two lattice sites. The residual weighting scheme was based on counting statistics and included a statistical uncertainty factor (p = 0.001 for 4 and 0.003 for 5).Neutral atom scattering factors were taken from Cromer and Waber.29 Anomalous dispersion effects were included in the structure-factor calculation,30 and the values for Df 9 and Df 0 were those of Creagh and McAuley.31 The values for the massattenuation coefficients were those of Creagh and Hubbell.32 Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/495. Synthesis of bidentate imidazoles Bis(1-methylimidazol-2-yl) ketone L1. There have been several reports of the synthesis of compound L1,9,13,17 a modification of the method described by Lippard and co-workers.17 was used. n-Butyllithium (110 mmol) was added to a solution of 1- methylimidazole (10 cm3, 125 mmol) in tetrahydrofuran (thf ) (150 cm3) at 278 8C under nitrogen.The solution was stirred for 1 h at 278 8C after which time diethyl carbonate (6 cm3, 50 mmol) was added. The solution changed from pale yellow to purple and thickened. It was allowed to warm to 240 8C over several hours, quenched by addition of solid carbon dioxide and then allowed to warm to room temperature. Water (100 cm3) was added and the product obtained by continuous liquid– liquid extraction into ethyl acetate (600 cm3) for 10–12 h.The ethyl acetate solvent was removed and the residue recrystallised from acetone. The product L1 was obtained as a colourless crystalline solid (6.6 g, 63%), m.p. 154–155.5 8C (lit.,13 145–148 8C). dH(400 MHz, CDCl3) 7.31 (s, 1 H, H4), 7.09 (s, 1 H, H5) and 4.02 (s, 3 H, NCH3); dC-{H}(100 MHz, CDCl3) 174.4 (C]] O), 143.4 (C2), 130.7 (C4), 127.2 (C5) and 36.6 (NCH3); m/z 191 (11, [M 1 1]1), 190 (88, M1), 162 (19), 161 (70), 109 (100), 96 (22), 95 (32), 82 (60), 54 (30), 53 (10), 52 (11), 42 (17) and 40 (14%).High-resolution mass spectrum (M1): m/z 190.0845; C9H10N4O requires 190.0855. Bis(1-methylimidazol-2-yl)methanol L2. This compound was synthesized using a modification of the procedure described by Breslow and co-workers.4 n-Butyllithium (40 mmol) was added to 1-methylimidazole (6.6 cm3, 83 mmol) in thf (200 cm3) at 278 8C under nitrogen. The solution was stirred for 1.5 h after which time ethyl formate (3 cm3) was added.The solution was allowed to warm to 10–20 8C over several hours, quenched with water (100 cm3) followed by continuous liquid–liquid extraction into ethyl acetate (400 cm3) for 10–12 h. The ethyl acetate solvent was removed and the residue recrystallised from acetone to yield L2 as a white crystalline solid (2.7 g, 70%), m.p. 199– 202 8C (lit.,4 188–189.5 8C). dH(400 MHz, CDCl3) 6.90 [d, 2 H, 3J(H4H5) = 1.2 , H4], 6.82 [d, 2 H, 3J(H4H5) = 1.2 Hz, H5), 6.02 (s, 1 H, CHOH) and 3.59 (s, 6 H, NCH3); dC-{H}(100 MHz, CDCl3) 146.6 (C2), 127.4 (C4), 123.3 (C5), 65.1 (COH) and 33.9 (NCH3); m/z 193 (10, [M 1 1]1), 192 (51, M1), 191 (39), 175 (8), 163 (10), 111 (42), 109 (35), 96 (100), 95 (22), 83 (100), 82 (39), 81 (27), 56 (17), 55 (11), 54 (17), 52 (10), 42 (51) and 41 (10%).Bis(1-methylimidazol-2-yl)methane L3. This compound was prepared using a modification of the method described by Byers and Canty.13 The ketone L1 (3.50 g, 18 mmol) was placed in a glass-sleeved stainless-steel reaction bomb (600 cm3) with hydrazine hydrate 33 (10.0 cm3, 194 mmol) and sodium hydroxide (1.50 g, 37.5 mmol). The vessel was sealed and heated to 150 8C for 4 h after which it was cooled to room temperature and opened carefully.The product was extracted into acetone and the solvent removed under vacuum. Compound L3 was recrystallised from acetone as a cream solid (1.27 g, 39%), m.p 152–154 8C (lit.,7 143–148 8C). dH(400 MHz, CDCl3) 6.84 [d, 1 H, 3J(H4H5) = 1.2 , H4], 7.09 [d, 1 H, 3J(H4H5) = 1.2 Hz, H5], 4.16 (s, 1 H, CH2) and 3.59 (s, 3 H, NCH3); dC-{H}(400 MHz, CDCl3) 144.2 (C2), 127.9 (C4), 122.1 (C5), 33.8 (NCH3) and 27.5 (CH2); m/z 177 (10, [M 1 1]1), 176 (75), 175 (27), 161 (20), 134 (10), 107 (13), 96 (65), 95 (100), 81 (23), 55 (12), 54 (38), 53 (10) and 52 (14%).High-resolution mass spectrum (M1): m/z 176.1062; C9H12N4 requires 176.1062.Synthesis of ruthenium complexes [Ru(PPh3)2H(CO)L1]Cl 1. A mixture of [Ru(PPh3)3H(Cl)- (CO)] (0.61 g, 0.64 mmol) and L1 (0.16 g, 0.82 mmol) in toluene (40 cm3) was refluxed for 2 h. The orange solution was allowed to cool to room temperature and the yellow precipitate which formed was filtered off and washed with hexane (20 cm3). The crude product was recrystallised from methanol to give [Ru(PPh3) 2H(CO)L1]Cl 1 as orange plates (0.50 g, 88%), m.p. 107 8C (decomposed without melting).dH(600 MHz, CDCl3) 7.71 (s, 1 H, H5 A), 7.36–7.23 (m, 31 H, PPh3 and H4 A), 7.09 (s, 1 H, H5 B), 6.50 (s, 1 H, H4 B), 3.97 (s, 3 H, NCH3A), 3.84 (s, 3 H, NCH3B) and 211.63 [t, 1 H, 2J(H]Ru]P) = 18.7 Hz, RuH]; dC-{H, P}(100 MHz, CDCl3) 204.9 (RuCO), 166.7 (CO of L1), 140.0, 139.4 (C2 A,B), 136.6 (C4 B), 134.6 (C4 A), 133.8 (PPh3), 132.4 (PPh3), 131.0 (PPh3), 130.7 (C5 B), 129.5 (C5 A), 128.9 (PPh3) and 39.9 (NCH3A,B); dP(162 MHz, CDCl3) 47.11 (s); FAB mass spectrum m/z 847 (15, [M 1 2]1), 846 (13, [M 1 1]1), 845 (22, M1), 844 (19), 843 (13), 842 (14), 586 (12), 585 (33), 584 (35), 583 (100), 582 (35), 581 (89), 580 (60), 579 (38), 578 (34), 577 (12), 575 (13), 556 (11), 555 (19), 554 (19), 553 (23), 552 (17) and 551 (14%); n& max/cm21 (Nujol) 1929m (Ru]C]] ] O), stretch corresponding to Ru]H not observed.Crystals of the complex [Ru(PPh3)2H(CO)L1]BF4 4 suitable for structure analysis were obtained by addition of a methanol solution of NaBF4 to a methanol solution of 1 followed by slow evaporation of the solvent.[Ru(PPh3)2H(CO)L2]Cl 2. A mixture of [Ru(PPh3)3H(Cl)- (CO)] (0.36 g, 0.38 mmol) and L2 (0.13 g, 0.68 mmol) in toluene (40 cm3) was refluxed for 2 h. The clear solution was allowed to cool to room temperature, the solvent removed and the residue dissolved in acetone. Light petroleum was added causing the precipitation of a white solid which was filtered off. The crude product was recrystallised from methanol to give [Ru(PPh3)2- H(CO)L2]Cl 2 as colourless needles (0.22 g, 65%), m.p. 140 8C (decomposed without melting). dH(400 MHz, CDCl3) 7.42–7.11 (m, 30 H, PPh3), 6.69 (s, 1 H, H4 A), 6.59 (s, 1 H, H5 A), 5.95 (s, 1 H, H5 B), 5.83 (s, 1 H, H4 B), 5.31 (s, 1 H, CHOH), 3.74 (s, 3 H, NCH3A), 3.69 (s, 3 H, NCH3B) and 211.91 [dd, 1 H, 2J(H]Ru]P) = 17.4, 22.0 Hz, RuH]; dC-{H,P}(100 MHz, CDCl3)J. Chem. Soc., Dalton Trans., 1997, Pages 2341–2345 2345 205.7 (RuCO), 145.1, 144.7 (C2 A,B), 134.5 (PPh3), 134.0 (PPh3), 133.7 (C4 B), 133.4 (C4 A), 128.6 (PPh3), 128.4 (PPh3), 123.2 (C5 A), 122.2 (C5 B) 5(COH) and 36.3 (NCH3A,B); dP(162 Hz, CDCl3) 47.7 [d, 2J(P]Ru]P) = 287] and 44.3 [d, 2J(P]Ru]P) = 287 Hz]; FAB mass spectrum m/z 849 (12, [M 1 2]1), 848 (11, [M 1 1]1), 847 (32, M1), 845 (17), 587 (24), 586 (28), 585 (80), 584 (56), 583 (100), 582 (67), 581 (47), 580 (37), 579 (13), 577 (16), 569 (17), 568 (16), 567 (21), 566 (18), 565 (13), 564 (10), 557 (15), 556 (14), 555 (29), 554 (21), 553 (20), 552 (14), 540 (11), 539 (15), 538 (13), 537 (14) and 536 (11%); n& max/cm21 (Nujol) 2014w (Ru]H), 1927m (Ru]C]] ] O).Crystals of the complex [Ru(PPh3)2H(CO)L2]OH 5 suitable for structure analysis were obtained by slow evaporation of a methanol–water (99 : 1) solution of 2. [Ru(PPh3)2H(CO)L3]Cl 3. A mixture of [Ru(PPh3)3H(Cl)- (CO)] (0.50 g, 0.52 mmol) and L3 (0.12 g, 0.68 mmol) in toluene (30 cm3) was refluxed for 3 h during which time a precipitate formed.The mixture was cooled to room temperature and the precipitate filtered off and washed with hexane (10 cm3). Complex 3 was obtained as a white solid (0.39 g, 86%), m.p. 215 8C (decomposed without melting). dH(400 MHz, CDCl3) 7.38–7.25 (m, 30 H, PPh3), 6.66 [d, 1 H, 3J(H4 AH5 A) = 1.7, H5 A], 6.58 [d, 1 H, 3J(H4 AH5 A) = 1.7, H4 A], 6.12 [d, 1 H, 3J(H4 BH5 B) = 1.7, H4 B), 6.08 [d, 1 H, 3J(H4 BH5 B) = 1.7, H5 B], 3.83 (s, 3 H, NCH3A), 3.68 (s, 2 H, CH2), 3.66 (s, 3 H, NCH3B) and 211.82 [t, 1 H, 2J(H] Ru]P) = 19.5 Hz, RuH]; dC-{H,P}(100 MHz, CDCl3) 205.2 (RuCO), 142.1, 142.0 (C2 A,B), 134.2 (PPh3), 133.9 (PPh3), 133.6 (C4 B), 132.74 (C4 A), 130.5 (PPh3), 128.7 (PPh3), 122.6 (C5 A), 121.4 (C5 B), 35.9 (NCH3A,B) and 24.5 (CH2); dP(162 MHz, CDCl3) 45.1 (s); FAB mass spectrum m/z 831 (3, M1), 657 (14), 655 (25), 654 (14), 640 (25), 638 (15), 607 (16), 606 (27), 605 (70), 604 (49), 603 (100), 602 (69), 601 (49), 600 (39), 599 (14), 597 (15), 569 (22), 568 (16), 567 (30), 566 (24), 565 (14), 564 (12), 525 (28), 524 (30), 519 (15), 518 (44), 517 (34), 516 (77), 515 (51), 514 (43), 513 (31) and 512 (15%); n& max/cm21 (Nujol); 1919m (Ru]C]] ] O), stretch corresponding to Ru]H not observed (Found: C, 61.4; H, 5.4; N, 6.2.Calc. for C46H43ClN4OP2Ru? 2H2O: C, 61.23; H, 5.25; N, 6.21%). Acknowledgements We gratefully acknowledge financial support from the Australian Research Council and thank Johnson-Matthey Pty.Ltd. for a generous loan of ruthenium salts. References 1 A. Togni and C. M. Venanzi, Angew. Chem., Int. Ed. Engl., 1994, 33, 497 and refs. therein. 2 R. S. Brown, N. J. Curtis and J. Huguet, J. Am. Chem. Soc., 1981, 103, 6953. 3 See, for example, T. N. Sorrell and A. S. Borovik, J. Am. Chem. Soc., 1987, 109, 4255; R. S. Brown, D. Solmom, N. J. Curtis and S. Kusuma, J. Am. Chem. Soc., 1982, 104, 3188; F. Chu, J. Smith, V. M. Lynch and S. J. Lippard, Inorg.Chem., 1995, 34, 5689. 4 C. C. Tang, D. Davilian, P. Huang and R. Breslow, J. Am. Chem. Soc., 1978, 100, 3918. 5 R. Breslow, J. T. Hunt, R. Smiley and T. Tarnowski, J. Am. Chem. Soc., 1983, 105, 5337. 6 P. Frediani, M. Bianchi, A. Salvini, R. Guanducci, L. C. Carluccio and F. Piancenti, J. Organomet. Chem., 1995, 498, 187. 7 F. A. Jalón, A. Otero, A. Rodríguez and M. Pérez-Manrique, J. Organomet. Chem., 1996, 508, 69. 8 L. K. Thompson, B. S. Ramaswamy and E. A. Seymour, Can.J. Chem., 1977, 55, 878. 9 X.-M. Chen, Z.-T. Xu and T. C. W. Mak, Polyhedron, 1995, 14, 319. 10 W. B. Tolman, S. Liu, J. G. Bensten and S. J. Lippard, J. Am. Chem. Soc., 1991, 113, 152. 11 T. N. Sorrell, W. E. Allen and P. S. White, Inorg. Chem., 1995, 34, 952; N. Wei, N. N. Murthy, Z. Tyeklár and K. D. Karlin, Inorg. Chem., 1994, 33, 1177. 12 P. K. Byers, A. J. Canty and R. T. Honeyman, J. Organomet. Chem., 1990, 385, 417; P. K. Byers and A. J. Canty, J. Chem. Soc., Chem. Commun., 1988, 639; P.K. Byers, A. J. Canty, B. W. Skelton and A. H. White, Organometallics, 1990, 9, 826; G. B. Brown, P. K. Byers and A. J. Canty, Organometallics, 1990, 9, 1231. 13 P. K. Byers and A. J. Canty, Organometallics, 1990, 9, 210. 14 M. J. Bloemink, H. Engelking, S. Karentzopoulos, B. Krebs and J. Reedijk, Inorg. Chem., 1996, 35, 619. 15 A. J. Canty, P. R. Traill, B. W. Skelton and A. H. White, Inorg. Chim. Acta, 1996, in the press. 16 M. Grebl and B. Krebs, Inorg.Chem., 1994, 33, 3877. 17 S. M. Gorun, G. C. Papaefthmiou, R. B. Frankel and S. J. Lippard, J. Am. Chem. Soc., 1987, 109, 4244. 18 R. J. Brown and J. Huguet, Can. J. Chem., 1980, 58, 889. 19 N. Ahmad, J. J. Levison, S. D. Robinson and M. F. Uttley, Inorg. Synth., 1974, 15, 45. 20 S. Elgafi, B. A. Messerle, L. D. Field, I. E. Buys and T. W. Hambley, J. Organomet. Chem., in the press. 21 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 22 L. P. Soler, B. A. Messerle, L. D. Field, I. E. Buys and T. W. Hambley, unpublished work. 23 N. W. Alcock, I. D. Burns, K. S. Claire and A. F. Hill, Inorg. Chem., 1992, 31, 2906. 24 D. F. Shriver and M. A. Drezdzon, The Manipulation of Air Sensitive Compounds, Wiley, New York, 1986. 25 M. R. Winkle, J. M. Lansinger and R. C. Ronald, J. Chem. Soc., Chem. Commun., 1980, 87. 26 TEXSAN, Crystal Structure Analysis Package, Molecular Structure Corporation, The Woodlands, TX, 1985 and 1992. 27 G. M. Sheldrick, SHELXS 86, Crystallographic Computing 3, eds. G. M. Sheldrick, C. Kruger and R. Goddard, Oxford University Press, 1985, pp. 175–189. 28 DIRDIF 94, P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Bosman, R. de Gelder, R. Israel and J. M. M. Smits, The DIRDIF 94 program system, Technical Report of the Crystallography Laboratory, University of Nijmegen, 1994. 29 D. T. Cromer and J. T. Waber, International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4, Table 2.2 A. 30 J. A. Ibers and W. C. Hamilton, Acta Crystallogr., 1964, 17, 781. 31 D. C. Creagh and W. J. McAuley, International Tables for Crystallography, ed. A. J. C. Wilson, Kluwer, Academic Publishers, Boston, 1992, vol. C, Table 4.2.6.8, pp. 219–222. 32 D. C. Creagh and J. H. Hubbell, International Tables for Crystallography, ed. A. J. C. Wilson, Kluwer, Academic Publishers, Boston, 1992, vol. C, Table 4.2.4.3, pp. 200–206. 33 Hazards in the Chemical Laboratory, ed. S. G. Luxon, 5th edn., The Royal Society of Chemistry, Cambridge, 1992, p. 419. Received 21st January 1997; Paper 7/00474E

ISSN:1477-9226    

DOI:10.1039/a700474e

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年代:1997

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DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2347–2350 2347 Reversible proton-coupled ReVII–ReVI and ReVI–ReV couples and crystal structure of [ReVO2(OH2)(Me3tacn)]BPh4 (Me3tacn = 1,4,7- trimethyl-1,4,7-triazacyclononane) Chi-Ming Che,*,a Jack Y. K. Cheng,a Kung-Kai Cheung a and Kwok-Yin Wong b a Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong b Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hunghom, Kowloon, Hong Kong The electrochemistry of [ReVIIO3(Me3tacn)]PF6 (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) in aqueous solution has been studied.At pH 1 it shows two quasi-reversible couples I at 20.14 and II at 20.36 V vs. saturated calomel electrode. Constant-potential coulometry at 20.50 V shows that the total number of electrons transferred for these two couples is two. The Pourbaix diagram over the range pH 0.9–12.2 shows that E2� 1 of couple I shifts cathodically by 60 mV per pH unit.For couple II there are two straight-line segments with slopes of 2118 mV (0.9 < pH < 4.1) and 260 mV (pH > 4.1) per pH unit. The complex [ReVO2(OH2)(Me3tacn)]BPh4 was prepared and structurally characterized by X-ray crystal analysis: monoclinic, space group P21/n (no. 14), a = 10.387(9), b = 21.176(4), c = 15.452(2) Å, b = 91.38(63)8, Z = 4. The Re]OH2 distance is 2.10(2) Å and the Re]] O distances are 1.78(1) and 1.82(1) Å. The two oxo groups are cis to each other with an angle of 106.7(5)8.Proton-coupled electron-transfer reactions constitute an important area in the oxidation chemistry of high-valent oxometal complexes. Extensive studies on the electrochemistry of some d1–d4 oxo-metal complexes in aqueous solution have been reported. With a pyrolytic edge-plane graphite electrode, it has been possible to observe the reversible M]] O æÆ M]OH couple in aqueous solution.1 The E8 values of these couples provide useful information in understanding the reactivities of these oxometal complexes.Surprisingly, there are only few reports on the proton-coupled electron-transfer reactions of d0 oxometal complexes 2 which exhibit promising oxidation chemistry. 3 It would be interesting to determine the E8 of ReVII]] O complexes, which provides a quantitative measure of the oxidizing strength of this class of complexes. Our previous work revealed that macrocyclic amines are good ligand systems for investigating the redox chemistry of high-valent oxometal complexes in aqueous solution.4 Herein is described the electrochemistry of [ReVIIO3(Me3tacn)]PF6 (Me3tacn = 1,4,7-trimethyl- 1,4,7-triazacyclononane) and the crystal structure of [ReVO2(OH2)(Me3tacn)]BPh4. The latter is one of the few examples of a six-co-ordinate d2 cis-dioxometal complexes to be structurally characterized.Experimental Materials All preparations were performed using standard Schlenk techniques. The compound Re2O7 was obtained from Strem; 1,4,7- trimethyl-1,4,7-triazacyclononane 5 and the complex [ReVIIO3- (Me3tacn)][ReO4] 6 were prepared by published procedures.Physical measurements Cyclic voltammetry was performed with a Princeton Applied Research model 273 A potentiostat. Rotating-disc voltammetry was performed with a Pine Instrument model AFMRX rotator. The working electrode used was edge-plane pyrolytic graphite (Union Carbide). The E2� 1 values were taken as the average of the anodic and cathodic peak potentials.All potentials are quoted with reference to the saturated calomel electrode (SCE). Constant-potential electrolysis was performed in a threecompartment cell under a nitrogen atmosphere with a carbon cloth obtained from Sigri Carbon as working electrode. The UV/VIS absorption spectra were recorded on a Milton Roy 3000 spectrophotometer. X-Ray crystallography A pale blue crystal of complex 2 of dimensions 0.20 × 0.05 × 0.35 mm was used for data collection at 25 8C on a Rigaku AFC7R diffractometer with graphite-monochromatized Mo-Ka radiation (l = 0.710 73 Å) using w–2q scans with w-scan angle (0.73 1 0.35 tan q)8 at a scan speed of 16.08 min21 [up to four scans for reflection I < 15s(I )].Intensity data (in the range of 2qmax = 508; h 0–11, k 0–23, l 217 to 17; three standard reflections measured after every 300, 3.67% decay), were corrected for decay and for Lorentz-polarization effects and empirical absorption corrections were applied based on the y scan of four strong reflections (minimum and maximum transmission factors 0.391 and 1.000).Upon averaging the 6401 reflections, 6054 of which were uniquely measured, 3225 with I > 3s(I) were considered observed and used in the structural analysis. The space group was determined from systematic absences and the structure solved by direct methods (SIR 927) and Fourier-difference syntheses and refined by full-matrix least squares using the software package TEXSAN8 on a Silicon Graphics Indy computer.All non-H atoms except the B atom were refined anisotropically. Hydrogen atoms at calculated positions with thermal parameters equal to 1.3 times that of the attached C atoms were not refined. The two H atoms of the H2O molecule were not included. Convergence for 366 variable parameters by least-squares refinement on F with w = 4Fo 2/ s2(Fo 2), where s2(Fo 2) = [s2(I) 1 (0.026 Fo 2)2] for 3225 reflections with I > 3s(I), was reached at R = 0.053 and R9 = 0.068.The final Fourier-difference map was featureless. The ORTEP9 drawing of the complex cation shows thermal ellipsoids at the 50% probability level. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/513.2348 J.Chem. Soc., Dalton Trans., 1997, Pages 2347–2350 Syntheses [ReVIIO3(Me3tacn)]X 1 (X = PF6 2 or BPh4 2). The complex [ReVIIO3(Me3tacn)][ReO4] (0.1 g) was dissolved in distilled water (30 cm3). The solution was filtered if necessary and addition of an excess of NH4PF6 or NaBPh4 caused immediate precipitation of [ReVIIO3(Me3tacn)]PF6 or [ReVIIO3(Me3tacn)]BPh4. The product was filtered off and washed with water and diethyl ether.Yield 80%. 1H NMR (CD3CN) of [ReVIIO3(Me3tacn)]- BPh4: d 7.29–7.20 (m, 8 H, Haryl), 7.05–6.95 (m, 8 H, Haryl), 6.87– 6.82 (m, 4 H, Haryl), 3.54–3.36 (m, 6 H, CH2), 3.30 (s, 9 H, Me) and 3.3–3.14 (m, 6 H, CH2). [ReVO2(OH2)(Me3tacn)]BPh4 2. A mixture of [ReVIIO3- (Me3tacn)]BPh4 (0.1 g) and an excess of zinc dust in aqueous MeOH (30 cm3, 95%) was refluxed for 4 d. The reaction mixture was filtered through Celite and the filtrate evaporated to dryness.The pale green residue was extracted with acetonitrile. Diffusion of diethyl ether into the acetonitrile extract gave pale green crystals; yield 5%. 1H NMR (CD3CN): d 7.29–7.20 (m, 8 H, Haryl), 7.05–6.95 (m, 8 H, Haryl), 6.87–6.82 (m, 4 H, Haryl), 3.88–3.52 (m, 2 H, CH2), 3.45–3.32 (m, 2 H, CH2), 3 41 (s, 3 H, Me), 3.16 (s, 6 H, Me), 3.14–3.04 (m, 3 H, CH2) and 2.83–2.75 (m, 5 H, CH2) [Found (Calc.): C, 54.1 (54.55); H, 6.20 (5.92); N, 5.40 (5.78)%]. Results and Discussion d0 Oxometal complexes have long been known to be effective oxidative catalysts and one of the recent examples is methyltrioxorhenium( VII).3 However, no electrochemical study has been carried out on the ReVII]] O æÆ ReV]OH couple.The only analogous example is [MoO3(Me3tacn)],2 which shows a quasireversible two-electron four-proton transfer couple at E8 = 20.075 V vs. the normal hydrogen electrode in 0.1 mol dm23 MeSO3H, equation (1). [MoVIO3(Me3tacn)] 1 2e2 1 4H1 [MoIVO(OH2)2(Me3tacn)]21 (1) In this work, the cyclic voltammograms of [ReVIIO3(Me3- tacn)]PF6 recorded at edge-plane pyrolytic graphite at various pH are shown in Fig. 1. Two quasi-reversible couples I and II are observed. At pH 1.0 the E2� 1 values of I and II are 20.14 and 20.36 V vs. SCE respectively. Constant-potential couloat 20.50 V indicated that the total number of electrons transferred for these two couples is two. As shown in Fig. 2, the plateau currents for couples I and II from a rotating-disc voltammetric experiment are similar in magnitude; hence, it is reasonable to assign them to the ReVII]ReVI and ReVI]ReV couples respectively. The reversibility of these two couples and particularly that of II depends on pH.At pH < 7 the peak-topeak separations for couples I and II are much larger than the 60 mV value expected for a reversible one-electron couple. For couple II and at low pH the reoxidation wave is usually broad. The two couples become more reversible at higher pH.With reference to previous electrochemical studies on Ru]] O æÆ Ru]OH2 couples,10 the above finding is ascribed to the kinetic barrier associated with protonation/deprotonation electron-transfer reactions. The cyclic voltammetry data are listed in Table 1 and the Pourbaix diagram over the range pH 0.9–12.2 is shown in Fig. 3. At pH 0.9–12.2 the E2� 1 of couple I shifts cathodically by 60 mV per pH unit. For couple II two straight-line segments with slopes of 2118 (0.9 < pH < 4.1) and 260 mV per pH unit (pH > 4.1) are found.On the basis of these results, the electrode reactions are assigned as in equations (2)–(6). For couple II, the electrochemical data could not differentiate [ReVO(OH2)(OH)(Me3tacn)]21 from [ReV- (OH)3(Me3tacn)]21 or [ReVO2(OH2)(Me3tacn)]1 from [ReVO- (OH)2(Me3tacn)]1. Attempts to isolate the reduced species of 1 by constant-potential electrolysis were unsuccessful but chem- Couple I [ReVIIO3(Me3tacn)]1 1 H1 1 e2 [ReVIO2(OH)(Me3tacn)]1 (2) Couple II 0.9 < pH < 4.1 [ReVIO2(OH)(Me3tacn)]1 1 2H1 1 e2 [ReVO(OH2)(OH)(Me3tacn)]21 (3) or [ReVIO2(OH)(Me3tacn)]1 1 2H1 1 e2 [ReV(OH)3(Me3tacn)]21 (4) pH > 4.1 [ReVIO2(OH)(Me3tacn)]1 1 H1 1 e2 [ReVO2(OH2)(Me3tacn)]1 (5) or [ReVIO2(OH)(Me3tacn)]1 1 H1 1 e2 [ReVO(OH)2(Me3tacn)]1 (6) ical reduction of 1 by zinc powder in aqueous methanol (95%) afforded [ReVO2(OH2)(Me3tacn)]BPh4 2 which was isolated in low yield.Fig. 1 Cyclic voltammogram of [ReVIIO3(Me3tacn)]1 at various pH; scan rate 100 mV s21 Fig. 2 Rotating-disc voltammetric studies of [ReVIIO3(tmtacn)]1 at pH 5.9; scan rate 5 mV s21, disc rotation rate 400 revolutions min21J. Chem. Soc., Dalton Trans., 1997, Pages 2347–2350 2349 Fig. 4 shows the perspective view of [ReVO2(OH2)(Me3tacn)]1, crystallographic details are given in Table 2 and selected bond lengths and angles in Table 3. The co-ordination geometry of the rhenium atom is a highly distorted octahedron comprised of three nitrogen atoms from the macrocyclic tmtacn and three oxygen atoms from one aqua and two cis oxides.The Re]O(1) and Re]O(2) distances of 1.78(1) and 1.82(1) Å are slightly longer than the average bond distance of 1.761 Å for transdioxorhenium( V) complexes.11 Interestingly, these distances are even 0.06 Å longer than those in cis-[ReVO2(bipy)(py)2]1 (bipy = 2,29-bipyridine, py = pyridine) average Re]O 1.74 Å).12 This may be correlated with the O]] Re]] O angle, which has a smaller value in 2 [106.7(5)8] than in cis-[ReVO2(bipy)(py)2]1 [121.4(4)8].Indeed, the O]] Re]] O angle of 2 is comparable to the related values of 112.0(4) and 105.9(2)8 in cis-[RuVIO2L]21 (L = Table 1 Values of E2� 1 (V vs. SCE) for redox couples of [ReVIIO3- (Me3tacn)]1 at different pH values pH Couple I Couple II 0.9 20.14 20.36 1.8 20.20 20.51 2.6 20.25 20.54 3.6 20.30 20.68 4.7 20.36 20.76 5.9 20.44 20.86 7.0 20.52 20.91 8.0 20.58 20.99 9.2 20.63 21.03 9.9 20.67 21.07 11.4 20.74 21.12 12.2 20.80 21.19 Table 2 Crystal data for complex 2 Empirical formula M C33H43BN3O3Re 726.74 Crystal colour, habit Blue, plate Crystal dimensions/mm 0.20 × 0.05 × 0.35 Crystal system Monoclinic Space group P21/n (no. 14) a/Å 10.387(9) b/Å 21.176(4) c/Å 15.452(2) b/8 91.38(3) U/Å3 3397(2) Z 4 Dc/g cm23 1.421 F(000) 1464 m(Mo-Ka)/cm21 36.12 No. reflections measured 6401 No. unique reflections (Rint) 6054 (0.034) Function minimized Sw(|Fo| 2 |Fo|)2 No.observations [I > 3.00s(I)] 3225 No. variables 366 R, R9 0.053, 0.068 Goodness of fit 2.23 Maximum shift/error in final cycle 0.01 Maximum, minimum peaks in final difference map/e Å23 1.34, 21.01 Table 3 Selected bond lengths (Å) and angles (8) for complex 2 Re]O(1) 1.78(1) Re]O(2) 1.82(1) Re]O(3) 2.10(2) Re]N(1) 2.199(8) Re]N(2) 2.26(1) Re]N(3) 2.26(1) O(1)]Re]O(2) 106.7(5) O(1)]Re]O(3) 101.2(5) O(1)]Re]N(1) 87.5(4) O(1)]Re]N(2) 162.1(4) O(1)]Re]N(3) 89.6(5) O(2)]Re]O(3) 99.4(5) O(2)]Re]N(1) 90.2(5) O(2)]Re]N(2) 84.9(4) O(2)]Re]N(3) 160.0(5) O(3)]Re]N(1) 164.5(5) O(3)]Re]N(2) 90.1(5) O(3)]Re]N(3) 88.4(5) N(1)]Re]N(2) 78.7(4) N(1)]Re]N(3) 78.7(4) N(2)]Re]N(3) 76.6(4) N,N,N9,N9-3,6-hexamethyl-3,6-diazaoctane-1,8-diamine) 13 and [MoVIO2(OMe)(Me3tacn)]1 respectively.14 Interestingly, the Mo]] O of 1.786 Å in [MoVIO2(OMe)(Me3tacn)]1 is also larger than that in other oxomolybdenum complexes.The Re]O(3) distance in 2 of 2.10(2) Å is indicative of a single bond and as expected longer than that of the Re]O (alkoxide) distance of 1.94 Å in [ReVO(O2C2H4)(Me3tacn)]1.15 On comparing with the complexes [ReVOCl2(tu)2(H2O)]1 and [ReVOCl3(tu)(H2O)] (tu = thiourea) for which the Re]OH2 distances are 2.231(10) and 2.291(20) Å respectively,16,17 it is reasonable to assign O(3) to a co-ordinated aqua group.On the basis of the 18-electron rule, the Re]] O bonds in 2 are double in character and exert a trans effect on the Re]N(2) and Re]N(3) bonds which are 0.06 Å longer than Re]N(1), which is trans to O(3).Such a trans effect of the ReV]] O bonds is less important than that in the [ReVO- (O2C2H4)(Me3tacn)]1 complex. In the latter case, the O]ReV bond is considered as triple in character [D(Re]Ntrans to oxo) 2 (Re]Ncis to oxo) = 0.09 Å]. The UV/VIS spectrum of complex 2 is shown in Fig. 5. It Fig. 3 Pourbaix diagram of [ReVIIO3(Me3tacn)]1 over the range pH 0.9–12.2 Fig. 4 Perspective view of [ReVO2(OH2)(Me3tacn)]12350 J.Chem. Soc., Dalton Trans., 1997, Pages 2347–2350 shows similar low-energy d–d transition(s) to those of [ReO(O2C2H4)(tacn)]1 and [ReO(OMe)2(tacn)]1 (tacn = 1,4,7- triazacyclononane).15 Based on these findings and the result from electrochemical studies, the electrode reactions of 1 can be assigned as (2) and (3) at 0.9 < pH < 4.1, and (2) and (5) at pH > 4.1. The break point of the E2� 1 versus pH plot for couple II occurs at pH 4.1, which is assigned to the pKa value of [ReVO(OH)(OH2)(Me3tacn)]21. There are relative few electrochemical studies on the d0 M]] O æÆ d2 M]OH2 couple.Compared to the E8 of [MoO3(Me3tacn)] (20.075 V vs. normal hydrogen electrode) at the same pH, 1 is less oxidizing. Acknowledgements We acknowledge support from the University of Hong Kong, the Hong Kong Polytechnic University, the Croucher Foundation and the Hong Kong Research Grants Council. Fig. 5 Room-temperature absorption spectrum of complex 2 measured in acetonitrile solution (7.8 × 1024 mol dm23) References 1 C.M. Che and V. W. W. Yam, Adv. Inorg. Chem., 1992, 39, 233; Adv. Transition Met. Coord. Chem., 1996, 1, 209. 2 W. Herrmann and K. Wieghardt, Polyhedron, 1986, 5, 513. 3 W. A. Herrmann, W. Wagner, U. N. Flessner, U. Volkhardt and H. Komber, Angew. Chem., Int. Ed. Engl., 1991, 30, 1636; W. A. Herrmann, R. W. Fischer and D. W. Marz, Angew. Chem., Int. Ed. Engl., 1991, 30, 1638; W.A. Herrmann and M. Wang, Angew. Chem., Int. Ed. Engl., 1991, 30, 1641; Z. Zhu and J. H. Espenson, J. Org. Chem., 1996, 61, 324; J. Mol. Catal., 1995, 103, 87. 4 C. M. Che, K. Y. Wong and C. K. Poon, Inorg. Chem., 1985, 24, 1797; C. M. Che, T. F. Lai and K. Y. Wong, Inorg. Chem., 1987, 26, 2289; C. M. Che, W. T. Tang, W. T. Wong and T. F. Lai, J. Am. Chem. Soc., 1989, 111, 9048; C. M. Che, W. T. Tang, W. O. Lee, W. T. Wong and T. F. Lai, J. Chem. Soc., Dalton Trans., 1989, 2011; C.M. Che, W. T. Tang, K. Y. Wong and C. K. Li, J. Chem. Soc., Dalton Trans., 1991, 3277; Y. P. Wang, C. M. Che, K. Y. Wong and S. M, Inorg. Chem., 1993, 32, 5827. 5 K. Wieghardt, P. Chaudhuri, B. Nuber and J. Weiss, Inorg. Chem., 1982, 21, 3086. 6 W. A. Herrmann, P. W. Roesky, F. E. Kühn, W. Scherer and M. Kleine, Angew. Chem., Int. Ed. Engl., 1993, 32, 1714. 7 A. Altomare, M. Cascarano, C. Giacovazzo, A. Guagliardi, M. C. Burla, G. Polidori and M. Camalli, SIR 92, J. Appl. Crystallogr., 1994, 27, 435. 8 TEXSAN, Crystal Structure Analysis Package, Molecular Structure Corporation, Houston, TX, 1985 and 1992. 9 C. K. Johnson, ORTEP II, Report ORNL-5318, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 10 C. M. Che, K. Y. Wong and F. C. Anson, J. Electroanal. Chem. Interfacial Electrochem., 1987, 226, 211. 11 J. M. Mayer, Inorg. Chem., 1988, 27, 3899. 12 R. L. Blackbourn, L. M. Jones, M. S. Ram, M. Sabat and J. T. Hupp, Inorg. Chem., 1990, 29, 1791. 13 C. K. Li, C. M. Che, W. F. Tong, W. T. Tang, K. Y. Wong and T. F. Lai, J. Chem. Soc., Dalton Trans., 1992, 2109. 14 K. S. Bürger, G. Haselhorst, S. Stötzel, T. Weyhermüller, K. Wieghardt and B. Nuber, J. Chem. Soc., Dalton Trans., 1993, 1987. 15 G. Böhm, K. Wieghardt, B. Nuber and J. Weiss, Inorg. Chem., 1991, 30, 3464. 16 T. Lis, Acta Crystallogr., Sect. B, 1976, 32, 2707. 17 T. Lis, Acta Crystallogr., Sect. B, 1977, 33, 944. Received 24th February 1997; Paper 7/01300K

ISSN:1477-9226    

DOI:10.1039/a701300k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2351–2355 2351 Kinetics of oxidation of thiosulfate ion with [MnIV 2(Ï-O)2- (Ï-MeCO2)(H2O)2(bipy)2]31 (bipy 5 2,29-bipyridine) and its hydrolytic derivatives Anup Kumar Bhattyacharya, Anath Bandhu Mondal and Rupendranath Banerjee * Department of Chemistry, Jadavpur University, Calcutta 700 032, India The complex [MnIV 2(m-O2)2(m-MeCO2)(H2O)2(bipy)2]31 1 (bipy = 2,29-bipyridine) has been found to co-exist in rapid equilibrium with [Mn2O2(H2O)4(bipy)2]41 2 and [Mn2O2(MeCO2)(H2O)4(bipy)]31 3 in aqueous buffer containing an excess of bipy and MeCO2 2 in the range pH 4.0–5.5. Equilibrium constants (mol dm23) for 1 2 1 MeCO2 2 and 1 3 1 bipy are 1022 and 1023, respectively.Water molecules co-ordinated to the manganese(IV) centres are stable at least up to pH 5.5. Reduction of the binuclear manganese(IV) species by thiosulfate ion proceeded via [(bipy)2MnIIIO2MnIV(bipy)2]31 4, in the presence of an excess of bipy.An excess of thiosulfate reduced complex 4 further and ultimately produced MnII. Rate constants for reduction of 1–3 to 4, as determined under second-order conditions, increase with increasing number of water molecules at the manganese centre. A plausible mechanism is proposed and the relevance of the results to photosystem II discussed. The active site of the transmembrane protein complex called photosystem II (PS II) contains an oxomanganese cluster, where water molecules are oxidised to oxygen.1 Since water is the substrate of the catalytic oxidation, it must bind to or be present in the close vicinity of the oxomanganese cluster to be oxidised.It is also known that the manganese ions in the cluster are ligated by O and N atoms from amino acid residues.2 Attempts to model the oxygen-evolving centre (OEC) in PS II have stimulated considerable research on the co-ordination compounds of high-valent manganese. As a result dinuclear oxomanganese(IV) cores have been assembled in both aqueous and non-aqueous media.1b,3 However, the compound [Mn2O2(MeCO2)(H2O)2(bipy)2]31 1 (bipy = 2,29-bipyridine) is the first to include simultaneously a bridging ethanoate ligand, two oxo bridges and two water molecules, each directly coordinated to manganese(IV).4 We initiated the present work with the belief that investigations on the kinetic and thermodynamic properties of 1 should be helpful in understanding the aqueous chemistry of higher-valent manganese clusters and their relevance in biological systems.In the long run, such knowledge may assist in the elucidation of the conditions that stabilise manganese–water bonds during oxidative charge build up5 on the oxygen-evolving centre of PS II, and lead ultimately to the development of model compounds for the active site in the natural system. Experimental Materials The complex salt hydrate [MnIV 2O2(MeCO2)(H2O)2(bipy)2]- [ClO4]3?H2O 1 was synthesized according to a known procedure4a involving oxidation of Mn21 by Ce41 in the presence of ethanoate and bipyridine.The crystals obtained were suf- ficiently pure and used without further purification (Found: C, 30.2; H, 3.1; N, 6.3. C22H25Cl3Mn2N4O19 requires C, 30.5; H, 2.9; N, 6.5%). Its equivalent weight found by iodometry (217) is in good agreement with the calculated value (216). Sodium thiosulfate (A.R., BDH) was recrystallised from hot water. Its solutions in water were prepared and standardised by iodometry.They were always freshly prepared each day. Aqueous solutions of NaNO3 and MeCO2Na (both A.R., BDH) were prepared in freshly boiled doubly-distilled water and standardised by passing through a Dowex 50W X8 strong cation-exchange column in the H1 form and titrating the liberated acid with standard NaOH to a phenolphthalein end-point. 2,29-Bipyridine (G.R., E. Merck) was used as provided. All other chemicals were of reagent grade. Physical measurements and kinetics All absorbances and electronic spectra were recorded with a Shimadzu (1601 PC) spectrophotometer using 1.00 cm quartz cells.The kinetics was monitored in situ at 550 nm in the thermostatted (25.0 ± 0.1 8C) cell-housing (CPS-240A). The ionic strength was 2.0 mol dm23 (NaNO3). A high ionic strength was necessary to keep the reaction rate within the limits of our measuring device. The reactions are very fast at any lower, standard ionic strength (e.g. 1.0 mol dm23). Solutions were buffered in the range pH 3.0–5.5 with mixtures of sodium ethanoate and 2,29-bipyridine. The total 2,29-bipyridine concentration, cbipy(= [bipy] 1 [Hbipy1]), being in the range 10–35 mmol dm23, and the total ethanoate concentration, cea(= [MeCO2 2] 1 [MeCO2H]), being in the range 0.005–0.2 mol dm23. Solution pH values were measured with an Orion 710 A2 pH/ion meter and an Orion Ross combination (model 81-02) electrode. The linearity of the electrode was established using pH 4, 7 and 9 buffers.The electrode was calibrated to read 2log[H1] directly using a series of acid solutions at the ionic strength used for kinetic experiments. The [H1] in these solutions were determined by titration against standard NaOH solutions. The reaction kinetics was measured under secondorder conditions using [S2O3 22] = [complex] = 0.10 mmol dm23. Reactions under first-order conditions using an excess of thiosulfate were too fast for conventional spectrophotometry; moreover, consecutive reactions complicated the kinetics.Stoichiometric measurements The reaction stoichiometry was determined under non-kinetic conditions in the presence of an excess of Na2S2O3. Unspent S2O3 22 was determined iodimetrically. Typically, complex 1 (1.0 mmol dm23) and S2O3 22 (6.0 mmol dm23) were mixed at pH 4.5 and cbipy = 6.0 mmol dm23 and allowed to react until the solution became colourless. Formation of a polythionate was demonstrated according to a method of Kolthoff and Belcher.6 It was reduced to S2O3 22 by using an excess of KCN.Thiosulfate, thus formed was estimated iodimetrically. Equilibrium measurements The electronic spectra of the MnIV 2 complexes under different conditions indicated partial aquation of 1 to 2 and 3 [equations2352 J. Chem. Soc., Dalton Trans., 1997, Pages 2351–2355 [MnIV 2O2(MeC 1 O2)(H2O)2(bipy)2]31 1 2H2O KA [Mn2O2(H2 2 O)4(bipy)2]41 1 MeCO2 2 (1) 112H2O KB [Mn2O2(MeCO 3 2)(H2O)4(bipy)]311bipy (2) (1) and (2)].The overall equilibrium constants KA and KB were determined spectrophotometrically at 400 nm. The total complex concentration at equilibrium, ce = [1] 1 [2] in the presence of an excess of bipy, but [1] 1 [3] in the presence of an excess of ethanoate, and expressions (3) and (4) can be written where Ae ct(Ae 2 A0)21 = [MeCO2 2][KA(De)]21 1 (De)21 (3) ct(Ae9 2 A0)21 = [bipy][KB(De9)]21 1 (De9)21 (4) represents the equilibrium absorbance of an aqueous solution of 1 in the presence of a fixed excess of bipy and varying [MeCO2 2], Ae9 is the equilibrium absorbance for an aqueous solution of 1 in the presence of a fixed excess of MeCO2 2 and varying [bipy] and A0 is the absorbance of an aqueous solution of pure 1 and was determined as described later; De = e1 2 e2 and De9 = e1 2 e3, where the es are the respective molar absorption coefficients of species indicated as subscripts.A plot of the left-hand side of equation (3) vs.[MeCO2 2] should yield a straight line with slope 1/KA(De) and intercept 1/De. Similarly, a plot of the left-hand side of equation (4) vs. [bipy] should be a straight line of slope 1/KB(De9) and intercept, 1/De9. Determination of the second-order rate constant Under the second-order reaction conditions the solution species absorbing at 550 nm are 1, the two hydrolytic derivatives 2 and 3, and the product complex [MnIIIMnIVO2(bipy)4]31 4. Also, at any time (t), the total concentration of dimanganese( IV) species is, ct = [1] 1 [2] 1 [3], and solution absorbance at any time (t) is given by equation (5/6) where c0 is the initial At = e1[1] 1 e2[2] 1 e3[3] 1 e4[4] (5) = ecct 1 e4[4] = ecct 1 e4(c0 2 ct) = (ec 2 e4)ct 1 e4c0 (6) complex concentration and expressions (7)–(11) are valid.ec = e1[MeCO2 2][bipy] 1 e2KA[bipy] 1 e3KB[MeCO2 2] [MeCO2 2][bipy] 1 KA[bipy] 1 KB[MeCO2 2] (7) A• = e4[4]• = e4c0 (8) A0 = ecc0 (9) (At 2 A•) = (ec 2 e4)ct (10) ct = (At 2 A•)/(ec 2 e4) (11) Under second-order conditions 7 we can write equation (12) 1/ct = 1/c0 1 kt (12) where k is the second-order rate constant. Expression (13) then (At 2 A•)21 = [ec/(ec 2 e4)A0] 1 kt(ec 2 e4)21 (13) follows. Hence a plot of (At 2 A•)21 vs.time (t) should yield a straight line with slope = k(ec 2 e4)21, and k can be evaluated since ec and e4 are known. Results and Discussion Stoichiometry and reduction products Non-kinetic conditions using an excess of thiosulfate indicated an overall 1 : 4 stoichiometry (14). Addition of an excess of [Mn2O2(MeCO2)(H2O)2(bipy)2]31 1 4H1 1 4S2O3 22 æÆ 2MnII 1 2bipy 1 4H2O 1 MeCO2 2 1 2S4O6 22 (14) KCN to the product solution generated extra S2O3 22 equal to half the amount of S2O3 22 consumed in reaction (14).This supports the correctness of equation (14) and the production of S4O6 22, which reacts with the excess of KCN according to equation (15).Stoichiometries other than (14) can occur in S4O6 22 1 2CN2 1 H2O æÆ S2O3 22 1 SCN2 1 SO4 22 1 2HCN (15) oxidations of thiosulfate.However, formation of tetrathionate is probably the most common.8 It might, however, be pointed out that the manganese product under kinetic conditions is [MnIIIMnIVO2(bipy)4]31 not MnII (see kinetics). Equilibrium studies The electronic spectrum of complex 1 in bipyridine buffer at pH 4.5 agrees well with those reported by Reddy et al.4a However, we have noted that it depends appreciably on pH, cbipy and cea.Table 1 displays a representative variation of the equilibrium absorbance at 400 nm as a function of [MeCO2 2] and [bipy]. Similar changes were observed at 550 nm. The Ae values for an aqueous solution of 1 in the presence of a fixed excess of bipy and varying [MeCO2 2] were fitted by the polynomial Ae = a1 1 a2[MeCO2 2] 1 a3[MeCO2 2]2 1 . . . 1 an[MeCO2 2]n. The value obtained for a1 was taken as the absorbance for pure 2 and yielded e2. The value for Ae in the presence of a large excess of bipy decreases with increasing [MeCO2 2] and ultimately becomes fairly constant at [MeCO2 2] > 0.20 mol dm23.This minimum value for Ae was used to evaluate e1. Similarly values of Ae9 [defined in equation (4)] were fitted by a polynomial equation in [bipy] and e3 and e1 could be evaluated. The two values of e1 agree very well. The De and De9 values in equations (3) and (4) were calculated using this e1 value and the Ae and Ae9 data in Table 1.We thus obtained excellent straight lines (r > 0.98), which provided the values for KA, KB, e1, e2 and e3. Thus KA = 0.01 ± 0.001 mol dm23 and KB = 1023 ± 1024 mol dm23, while e1, e2 and e3 are 480, 700 and 720 dm3 mol21 cm21 respectively at 550 nm and 2500, 3600 and 3750 dm3 mol21 cm21 at 400 nm at 25 8C, I = 2.0 mol dm23. The values of e2 and e3 thus obtained agree very well with those found from the polynomial fitting technique. The excellent fit (r > 0.98) of the absorbance data in Table 1 by the linear equations (3) and (4) supports the presumption of equilibria (1) and (2) and indicates no deprotonation of the co-ordinated water molecules within the experimental range of pH.Unusually water is present in the co-ordination sphere of MnIV in complex 1. Two other manganese(IV) complexes containing water are9,10 [MnIV 3O4(H2O)2(bipy)]41 and its 1,10-phenanthroline analogue. The ligand sets in these complexes are suf- ficiently strongly donating to stabilise an unusually high-valent metal centre to the extent that the co-ordinated water remains fully protonated.10 In a short communication Dave et al.4b reported that a millimolar solution of 1 in water is acidic (pH 1.6).Accordingly, they proposed deprotonation of the aqua ligands. However, these workers synthesized 1 by the disproportionation of [MnIII 2O(MeCO2)2(H2O)2(bipy)2]21 with 70% HClO4. They formulated the product as [MnIV 2O2(MeCO2)- (H2O)(bipy)2]?3HClO4?H2O (no anions to balance cationic charge!), which contains three HClO4 of crystallisation.Obviously, its aqueous solution should be acidic, whether or not theJ. Chem. Soc., Dalton Trans., 1997, Pages 2351–2355 2353 aqua ligands deprotonate. However, the observed pH value corresponds to a surprisingly high [H1] (= 2.5 × 1022 mol dm23), which requires that 25 H1 be released per molecule of complex 1! Apparently, the complex has either adhered HClO4 from the mother-liquor, or suffered extensive decomposition in aqueous solution.Overall, the results of Dave et al. are inconclusive on the question of the acidity of co-ordinated H2O molecules. The present equilibrium studies indicate that the ethanoate bridge in 1 is fairly labile. Such lability is possibly a consequence of its structural characteristics. The MnIVO2MnIV ring departs from planarity due to the constraints exerted by the ethanoate bridge.4a This greatly weakens the antiferromagnetic interaction (J = 243.7 cm21)4 and destabilises the complex as a whole.Removal of the ethanoate bridge increases the stability and is therefore favoured. The lability of a bipy ligand in 1 is also noteworthy. The equatorial Mn]N distances in 1 are significantly longer than the axial ones, reflecting the trans influence of the bridging oxygen atoms on the equatorial nitrogen atoms.4 This influence should weaken and labilise the equatorial Mn]N bond.The ethanoate bridge may further weaken the bond. Our equilibrium studies demonstrate that, contrary to the usual belief,11 higher oxidation states of manganese can be quite labile in aqueous solutions.12 Kinetics The overall reaction (14) must be a multistep process. It was reported earlier4a that the electronic spectrum of complex 1 dissolved in bipy–Hbipy1 buffer (pH 4.5) slowly changes to that of the mixed-valence [Mn2O2(bipy)4]31 complex 4; after 72 h, 80% of 1 has changed to 4. Under the present experimental conditions, however, solutions of 1 are stable at least up to an hour, which is substantially longer than required for the present kinetic measurements.Mixing of equimolar thiosulfate and 1 generated the spectrum of 4, provided cbipy > 0.01 mol dm23. The product solution is further reduced if an excess of S2O3 22 is used and the rate of such reduction is close (within 3%) to the known13 rate of reaction of 4 with S2O3 22 under similar conditions.However, the spectral and kinetic behaviours of the solution differ noticeably from those of 4, if cbipy < 0.01 mol dm23. Apparently, the overall reaction (14) proceeds via the manganese( III,IV) complex 4, which is eventually the end product if the reaction is carried out in the presence of an excess bipy and only 1 equivalent of S2O3 22 [equation (16)]. However, 4 is 2[Mn2O2(MeCO 1 2)(H2O)2(bipy)2]31 1 2S2O3 22 1 4bipy æÆ 2[MnIIIMn 4 IVO2(bipy)4]311S4O6 2212MeCO2 212H2O (16) either not formed or formed only partially if cbipy < 0.01 mol dm23.Table 1 Representative equilibrium absorbance of a solution of 0.20 mmol dm23 of complex 1 at 400 nm pH cea/mol dm21 cbipy/mol dm23 102- [MeCO2 2]/ mol dm23 102[bipy]/ mol dm23 Ae Ae9 4.5 4.5 5.0 5.0 5.5 5.5 4.5 4.5 5.0 4.5 4.5 5.0 5.0 5.0 0.21 0.14 0.04 0.016 0.005 0.001 0.208 0.208 0.117 0.208 0.210 0.208 0.117 0.088 0.035 0.035 0.024 0.024 0.020 0.020 0.025 0.010 0.010 0.025 0.035 0.030 0.035 0.035 7.5 5.0 2.5 1.0 0.59 0.12 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 1.91 1.91 1.91 1.91 1.91 1.91 0.137 0.546 0.792 1.37 1.91 2.40 2.77 3.23 0.530 0.530 0.556 0.615 0.685 0.725 0.722 0.671 0.621 0.563 0.540 0.532 0.530 0.530 We have recently reported13 the kinetics of reaction of complex 4 with an excess of S2O3 22 and found 4 to be reduced to MnII according to equation (17).As expected, equations (16) 2[MnIIIMnIVO2(bipy)4]31 1 6S2O3 22 1 8H1 æÆ 4MnII 1 8bipy 1 3S4O6 22 1 4H2O (17) and (17) combined together give the stoichiometric equation (14) for the reaction of 1 with an excess of S2O3 22.In all probability, therefore we have measured the kinetics of reaction (16) under second-order conditions and cbipy > 0.01 mol dm23. Plots of (At 2 A•)21 vs. time (t) were found to be excellent straight lines (r > 0.98) for at least three half-lives. Values of the secondorder rate constant k under different reaction conditions are collected in Table 2, which shows that k decreases with increasing [MeCO2 2] and [bipy].Such dependences further support the presumption of equilibria (1) and (2) and suggest reactions of 1–3 with S2O3 22. Since the final reaction product under the experimental conditions is 4, the reactions must be one-electron transfer processes, which should initially produce [MnIIIMnIVO2( MeCO2)(H2O)2(bipy)2]21 5 from 1, and S2O3 22 will be concomitantly oxidised to S2O3 2. Similar products will be formed from 2 and 3.How the one-electron reduction products of 1–3 are transformed to 4 may be speculated from the well known electrochemistry of [Mn2O2(m-HPO4)(bipy)2(H2PO4)2] 6, which is a close analogue of 1. The electrochemical reduction of 6 in phosphate buffer12 produces first the manganese(III,IV) dimer 7, equation (18). However, 7 is not stable and immediately changes [MnIV 2O2(m-HPO4)(bipy)2(H2PO4)2] 1 e2 æÆ [MnIIIMnIVO2(m-H 7 PO4)(bipy)2(H2PO4)2]2 (18) to the dimer 4 [equation (19)], which may undergo further re- [MnIIIMnIVO2(m-HPO4)(bipy)2(H2PO4)2]212bipy1H1 æÆ [MnIIIMnIVO2(bipy)4]31 1 3H2PO4 2 (19) Table 2 Second-order rate constants for the reaction of complex 1 with S2O3 22 at 25.0 8C, I = 2.0 mol dm23, [complex] = [S2O3 22] = 0.10 mmol dm23 pH cbipy/ mol dm23 cea/ mol dm23 103[bipy]/ mol dm23 102- [MeCO2 2]/ mol dm23 k*/dm3 mol21 s21 4.50 4.73 4.92 5.00 5.17 5.33 5.50 4.50 0.035 0.01 0.015 0.020 0.025 0.030 0.035 0.3 0.005 0.015 0.020 0.025 0.040 0.050 0.060 0.070 0.080 0.100 0.200 19.1 23.5 26.6 27.6 29.7 31.2 32.2 5.5 8.1 10.7 13.7 16.4 19.1 10.8 14.7 18.0 19.2 21.8 23.8 25.5 10.8 0.18 0.54 0.72 0.91 1.40 1.80 2.20 2.50 2.90 3.60 7.20 11.4 (11.6) 9.7 (9.8) 8.60 (8.80) 8.30 (8.50) 8.10 (8.30) 7.60 (7.70) 7.40 (7.50) 25.6 (25.3) 19.3 (19.3) 16.3 (16.0) 13.8 (14.0) 12.5 (12.6) 35.6 (35.1) 28.5 (28.8) 26.5 (26.6) 25.1 (24.9) 21.0 (21.3) 19.8 (19.7) 18.2 (18.5) 17.8 (17.5) 16.9 (16.7) 15.3 (15.5) 12.8 (12.7) *Average of two or three determinations; standard deviation, 1.5–4%.2354 J.Chem. Soc., Dalton Trans., 1997, Pages 2351–2355 [MnIV 2O2(MeCO 1 2)(H2O)2(bipy)2]31 1 2H2O KA [Mn2O2(bip 2 y)2(H2O)4]41 1 MeCO2 2 (1) 1 1 2H2O KB [Mn2O2(MeCO2) 3 (H2O)4(bipy)]31 1 bipy (2) 1 1 S2O3 22 k1 [MnIIIMnIVO2(MeC 5 O2)(H2O)2(bipy)2]21 1 S2O3 2 (20) 2 1 S2O3 22 k2 [MnIIIMnIVO2 8 (H2O)4(bipy)2]31 1 S2O3 2 (21) 3 1 S2O3 22 k3 [MnIIIMnIVO2(Me 9 CO2)(H2O)4(bipy)]21 1 S2O3 2 (22) 5 1 2bipy fast 4 1 MeCO2 2 1 4H2O (23) 8 1 2bipy fast 4 1 4H2O (24) 9 1 3bipy fast 4 1 4H2O 1 MeCO2 2 (25) S2O3 2 1 S2O3 22 fast S4O6 32 (26) S4O6 32 1 MnIV 2 fast MnIII,IV 1 S4O6 22 (27) Scheme 1 duction. We anticipate that chemical changes in [MnIIIMnIVO2- (MeCO2)(H2O)2(bipy)2]21 5 are analogous to those for 7 in solution and propose Scheme 1 as a plausible explanation for our results on the chemical reduction of 1 and its hydrolytic derivatives by S2O3 22 under second-order conditions at high cbipy.A [MnIIIMnIVO2(MeCO2)]21 core analogous to those in 5 and 9 has been isolated.14,15 Also it is well established from the kinetics of reduction of 4 by NO2 2 and S2O3 22 that deaquation of 8 by bipy rapidly produces 4 in aqueous bipy–Hbipy1 buffer.13,16 Hence, equation (24) represents a known chemical reaction. Condensation of S2O3 2 with S2O3 22, followed by oneelectron oxidation of the resultant S4O6 32 to S4O6 22 is also a well established general process17 in the oxidation of S2O3 22 to S4O6 22.Equations (26) and (27) in Scheme 1 are therefore logical. Reactions (19), (23) and (25) indicate the lability of the di-m-oxo-m-acido-dimanganese(III,IV) unit, [MnIII,IV 2O2(macido)] 21, and stability of the {Mn2O2}31 core in complex 4. Such lability, in turn, may be the reason for the rarity of this unit.14,15 For Scheme 1, one can derive equations (28) and (29). Values k = k1[MeCO2 2][bipy] 1 k2KA[bipy] 1 k3KB[MeCO2 2] [MeCO2 2][bipy] 1 KA[bipy] 1 KB[MeCO2 2] (28) k([MeCO2 2][bipy] 1 KA[bipy] 1 KB[MeCO2 2]) = k1[MeCO2 2][bipy] 1 k2KA[bipy] 1 k3KB[MeCO2 2] (29) of the second-order rate constant k, at fixed [bipy] (0.0191 mol dm23) but varying [MeCO2 2], were used to plot the left-hand side of equation (29) against [MeCO2 2].An excellent straight line (r = 0.987) was obtained as expected. Again the k data at fixed [MeCO2 2] (0.0108 mol dm23) but varying [bipy] were used to plot the left-hand side of equation (29) against [bipy] and an excellent straight line was obtained (r = 0.99).If [MeCO2 2] and [bipy] in equation (28) are substituted with cea and cbipy using equations (30) and (31) then one obtains equations (32)–(35). A plot of the left-hand side of equation (32) against [H1] at constant cea and cbipy yielded an excellent [MeCO2 2] = Keacea([H1] 1 Kea)21; Kea = 1.8 × 1025 dm3 mol21 (30) [bipy] = KHbipycbipy([H1] 1 KHbipy)21; KHbipy = 3.85 × 1025 dm3 mol21 (31) kD = A 1 B[H1] (32) A = KeaKHbipy(k1ceacbipy 1 k2KAcbipy 1 k3KBcea) (33) B = k2KAKHbipycbipy 1 k3KBKeacea (34) D = KeaKHbipy(ceacbipy 1 KAcbipy 1 KBcea) 1 (KAKHbipycbipy 1 KBKeacea)[H1] (35) straight line (r = 0.98) again supporting the validity of Scheme 1.In an attempt to evaluate the rate constants k1, k2 and k3, all the k values in Table 2 were fitted by equation (29) with the help of a program (LINEQ) developed in FORTRAN 77 for simultaneous linear equations. Only k1, k2 and k3 were treated as variables; KA and KB values obtained from spectrophotometric determinations were used.The best-fit values for the rate constants (dm3 mol21 s21) thus obtained are: k1 = 2.0 ± 0.02, k2 = 40 ± 1 and k3 = 145 ± 4 respectively at 25.0 8C and I = 2.0 mol dm23. These values reproduce very well the experimental secondorder rate constant k (see the parenthetical values in Table 2). The observed order of rate constants k1 < k2 < k3 shows that the rate of oxidation increases with the increased number of water molecules attached to the manganese centre.Among complexes 1–3, the maximum number (3) of water molecules at any manganese centre is present in 3, which is oxidised with the highest rate constant k3. A similar increase in kinetic activity with increased extent of aquation was observed previously for mono-18 and bi-nuclear13,16,19 manganese complexes. It is likely that increased aquation makes the oxidant more electron deficient, more closely approachable for attack by the reductant and more flexible with a reduced Franck–Condon barrier to electron transfer.Moreover, aquated complexes may form adducts stabilised by hydrogen bonding with the reductant.16 The extent of such stabilisation increases with increasing number of H2O molecules in the co-ordination sphere of the oxidising complex. Conclusion Kok et al.5 showed that the OEC in PS II cycles among different combinations of oxidation states of manganese. Every step in the cycle is an one-electron step.The OEC must also be resistant to decomposition in aqueous media, but preferably be able to pick up water molecules in the process of oxidative charge build up. The present kinetic study shows that consecutive oneelectron changes are possible in the model compound, that such models may be reasonably stable in aqueous solution, yet can undergo facile aquation. The stability of the water molecules in these models is noteworthy.The manganese ions in OEC are ligated to O and N atoms from amino acid residues.2 The present investigation indicates that such Mn]O and Mn]N bonds may be quite labile and undergo rapid aquation. Whether or not such aquation provides the substrate water for the OEC is unclear from this study, but evidently higher-valent manganese ions, when aquated, oxidise at a faster rate. By analogy, water molecules (if present) in the OEC may be instrumental in the rapidity of its redox reactions.This role may be additional to the function of water as a redox substrate for OEC.J. Chem. Soc., Dalton Trans., 1997, Pages 2351–2355 2355 Acknowledgements Financial assistance from the Department of Science and Technology (New Delhi) is gratefully acknowledged. We thank Mr. S. Kar and Mr. R. N. Bhattacharya for developing the program LINEQ for our use. References 1 (a) R. Manchanda, G. W. Brudvig and R. H. Crabtree, Coord. Chem. Rev., 1995, 144, 1; (b) K. Wieghardt, Angew.Chem., Int. Ed. Engl., 1989, 28, 1153; (c) L. Que, jun. and A. E. True, Prog. Inorg. Chem., 1990, 38, 97; (d ) V. L. Pecoraro (Editor), Bioinorganic Chemistry of Manganese, VCH, New York, 1992. 2 R. D. Guiles, J. L. Zimmerman, A. E. McDermott, V. K. Yachandra, J. L. Cole, S. L. Dexheimer, R. D. Britt, K. Wieghardt, U. Bossek, K. Sauer and M. P. Klein, Biochemistry, 1990, 29, 471; V. J. De Rose, V. K. Yachandra, A. E. McDermott, R. D. Britt, K. Sauer and M. P. Klein, Biochemistry, 1991, 30, 1335; J.Amesz, Biochim. Biophys. Acta, 1983, 726, 1. 3 K. Wieghardt, U. Bossek, B. Nuber, J. Weiss, J. Bonvoisin, M. Corbella, S. E. Vitols and J. J. Girerd, J. Am. Chem. Soc., 1988, 110, 7398. 4 (a) K. R. Reddy, M. V. Rajasekharan, S. Padhye, F. Dahan and J. P. Tuchagues, Inorg. Chem., 1994, 33, 428; (b) B. C. Dave, R. S. Czernuszewicz, M. C. Bond and C. J. Carrano, Inorg. Chem., 1993, 32, 3593. 5 B. Kok, B. Forbush and M. P. McGloin, Photochem. Photobiol., 1970, 11, 457. 6 I. M. Kolthoff and R. Belcher, Volumetric Analysis, 3rd edn., Interscience, New York, 1957. 7 A. A. Frost and R. G. Pearson, Kinetics and Mechanism, 2nd edn., Wiley International, New York, 1961, p. 13. 8 R. Sarala and D. M. Stanbury, Inorg. Chem., 1992, 31, 2771. 9 J. E. Sarneski, H. H. Thorp, G. W. Brudvig, R. H. Crabtree and G. K. Shulte, J. Am. Chem. Soc., 1990, 112, 7225. 10 K. R. Reddy, M. V. Rajasekharan, N. Arulsamy and D. J. Hodgson, Inorg. Chem., 1996, 35, 2283. 11 V. L. Pecoraro, Photochem. Photobiol., 48, 249. 12 J. E. Sarneski, L. J. Brzezinski, B. Anderson, M. Didiuk, R. Manchanda, R. H. Crabtree, G. W. Brudvig and G. K. Shulte, Inorg. Chem., 1993, 32, 3265. 13 B. Mondal, S. Kundu and R. Banerjee, Polyhedron, in the press. 14 J. S. Bashkin, A. R. Schake, J. B. Vincent, H. R. Chang, Q. Li, J. C. Huffman, G. Christou and D. N. Hendrickson, J. Chem. Soc., Chem. Commun., 1988, 700. 15 U. Bossek, M. Sahar, T. Weyhermuller and K. Wieghardt, J. Chem. Soc., Chem. Commun., 1992, 1780. 16 S. Chaudhuri, S. Mukhopadhyay and R. Banerjee, J. Chem. Soc., Dalton Trans., 1995, 621. 17 M. Schoneshofer, Int. J. Radiat. Phys. Chem., 1973, 5, 375; R. Mehnert, O. Brede and I. Janovsky, Radiochem. Radioanal. Lett., 1982, 53, 299; R. Mehnert and O. Brede, Inorg. J. Radiat. Phys. Chem., 1984, 23, 2463. 18 R. Banerjee, R. Das and A. K. Chakraburtty, J. Chem. Soc., Dalton Trans., 1990, 3277; Transition Met. Chem., 1992, 17, 277; S. Mukhopadhyay, S. Chaudhuri, R. Das and R. Banerjee, Can. J. Chem., 1993, 71, 2155; S. Mukhopadhyay and R. Banerjee, J. Chem. Soc., Dalton Trans., 1993, 933. 19 S. Kundu, A. K. Bhattyacharya and R. Banerjee, J. Chem. Soc., Dalton Trans., 1996, 3951. Received 4th December 1996; Paper 6/08193B

ISSN:1477-9226    

DOI:10.1039/a608193b

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2357–2361 2357 Crystal structures and non-linear optical properties of cluster compounds [MAu2S4(AsPh3)2] (M 5 Mo or W)† He-gen Zheng,a Wei Ji,b Michael L. K. Low,b Genta Sakane,c Takashi Shibahara c and Xin-quan Xin *,a a State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, Nanjing University, Nanjing, 210093, People’s Republic of China b Department of Physics, National University of Singapore, Singapore 119260, Republic of Singapore c Department of Chemistry, Okayama University of Science, Okayama 700, Japan The compounds [MAu2S4(AsPh3)2] (M = Mo 1 or W 2) were synthesized by reactions of [NEt4]2[MS4] (M = Mo or W), HAuCl4?4H2O and AsPh3 in CH2Cl2 solution.X-Ray crystallographic structure determinations show that the co-ordination of Mo(W) is slightly distorted from tetrahedral and those of the Au are distorted from trigonal planar. High non-linear susceptibilities of these gold-containing clusters were also observed for the first time.Z-Scan data measured with 532 nm nanosecond laser pulses showed that effective third-order non-linearities a2 = 7.9 × 1025 and 13 × 1025 dm3 cm W21 mol21 and n2 = 28.0 × 10210 and 19 × 10210 dm3 cm2 W21 mol21, respectively, for a 0.64 mmol dm23 solution of compound 1 and a 0.54 mmol dm23 solution of 2. The Mo(W)]Cu(Ag)]S cluster compounds have been studied extensively in the past two decades, because of their relevance to biological systems and catalytic processes.1,2 Recently, we have noticed that they also exhibit very interesting non-linear optical (NLO) properties.For example, strong NLO behaviour has been reported in nest-shaped clusters [NBun 4]2[MoCu3- OS3(NCS)3] and [NBun 4]2[MoCu3OS3BrCl2], a supracageshaped cluster [NBun 4]4[Mo8Cu12O8S24], and a twin nest-shaped cluster [NEt4]4[Mo2Cu6OS6Br2I4].3–5 Butterfly-shaped clusters [MCu2OS3(PPh3)n] (M = Mo or W, n = 3 or 4) and a half-open cage-shaped cluster [NEt4]3[W(CuBr)3OS3(m-Br)]?2H2O exhibit large NLO refraction.6,7 Cubane-like clusters [NBun 4]3- [MM93S4Br(X)] (M = Mo or W, M9 = Cu or Ag, X = Cl or I) possess strong NLO absorption.8 A very large optical limiting effect has been observed in a hexagonal prism-shaped cluster [Mo2Ag4S8(PPh3)4], which is about ten times larger than that observed in C60.9 In order to explore this field further, we have synthesized a series of new Mo(W)]Au]S cluster compounds. In this article we report the synthesis, characterization and NLO properties of gold-containing compounds with a linear structure, [MoAu2S4(AsPh3)2] 1 and [WAu2S4(AsPh3)2] 2.Experimental Materials Compounds [NEt4]2[MoS4] and [NEt4]2[WS4] were prepared according to a literature method.10 Other chemicals were of AR grade and used without further purification. Preparations [MoAu2S4(AsPh3)2] 1. Triphenylarsine (120.3 mg, 0.3931 mmol) dissolved in CH2Cl2 (5 cm3) was slowly added to HAuCl4?4H2O (81 mg, 0.1966 mmol) in absolute ethanol (5 cm3). The light yellow solution was stirred for 2 h and refrigerated at 5 8C overnight. The resulting colourless crystals were dissolved in CH2Cl2 (15 cm3) and [NEt4]2[MoS4] (47.64 mg, 0.0983 mmol) was added.After stirring for 1 h the red-black solution was filtered and PriOH (10 cm3) was added dropwise to † Non-SI unit employed: eV ª 1.60 × 10219 J. the top of the solution. The red crystals were obtained several days later (Found: C, 35.15; H, 2.4.Calc. for C36H30As2Au2- MoS4: C, 35.15; H, 2.45%). IR (KBr pellet, cm21): C]H in AsPh3, 734.1vs, 689.3vs; Au]P, 614.6w; Mo]Sb, 453.4vs. [WAu2S4(AsPh3)2] 2. The synthetic method was similar to that used for compound 1, [NEt4]2[WS4] being used instead of [NEt4]2[MoS4]. Yellow crystals were obtained (Found: C, 32.75; H, 2.32. Calc. for C36H30As2Au2S4W: C, 32.8; H, 2.3%). IR (KBr pellet, cm21): C]H in AsPh3, 737.5vs, 688.3vs; Au]P, 519.5w; W]Sb, 477.3vs, 442.2vs, 407.0w.X-Ray crystallography A red crystal of compound 1 was mounted in a glass capillary. All measurements were made on a Rigaku AFC6S diffractometer with graphite-monochromated Mo-Ka radiation (l = 0.7107 Å). The lattice parameters shown in Table 1 were refined using 21 reflections in the range 9.4 < q < 12.78. The data collection with w–2q scans between 3 and 258 resulted in 6949 intensity values, 4591 with I >1.50s(I) being used for the structure determination.The structure was solved by heavyatom Patterson methods11 and expanded using Fourier techniques. 12 The non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included but not refined. The final cycle of full-matrix least-squares refinement converged with unweighted and weighted agreement factors R = 0.0299 and R9 = 0.0387. For compound 2, an orange crystal was mounted in a glass capillary for X-ray data collection. All measurements were made on a Mac Science MXC-18 diffractometer.The lattice parameters (Table 1) were refined using 39 reflections in the range 10.0 < q < 15.08. The data collection with w–2q scans between 3 and 308 resulted in 11 491 intensity values, 7676 with I >1.50s(I) being used for the structure determination. The structure was solved by direct methods13 and expanded using Fourier techniques. The refinement was based on F. An empirical absorption correction using the program DIFABS14 was applied. The data were corrected for Lorentz-polarization effects, and the final R = 0.0638 and R9 = 0.0859.The function minimised was Sw(|Fo| 2 |Fc|)2, where w = 1/s2(Fo). All calculations were performed using the TEXSAN15 crys-2358 J. Chem. Soc., Dalton Trans., 1997, Pages 2357–2361 3[MO2S2]22 2[MOS3]22 1 [MO4]22 4[MOS3]22 3[MS4]22 1 [MO4]22 Scheme 2 tallographic software package. Selected bond distances and angles are given in Tables 2 and 3. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/499. Physical measurements Infrared spectra were recorded on a Fourier Nicolet FT-10SX spectrophotometer with pressed KBr pellets, electronic spectra with a Hitachi U-3410 spectrophotometer.Carbon and hydrogen analyses were performed on a PE-240C elemental analyser. Non-linear optical measurements The NLO properties of compounds 1 and 2 dissolved in CH2Cl2 were determined by using a standard Z-scan set up with a Q-switched, frequency-doubled Nd:YAG laser. The pulse repetition rate was 10 Hz. The details of the set-up can be found elsewhere.16 The solutions were contained in 1 mm thick quartz cells with concentrations of 6.4 × 1024 and 5.4 × 1024 mol dm23 for compounds 1 and 2, respectively. Results and Discussion Synthesis The compounds were synthesized from [NEt4]2[MS4] (M = Mo or W), HAuCl4?4H2O and AsPh3 in CH2Cl2 solution.When [NEt4]2[MO2S2] was used instead of [NEt4]2[MS4], the same compounds were obtained, as in Scheme 1. The transformation from [MO2S2]22 to [MS4]22 may take place as in Scheme 2. Therefore, the [MS4]22 anion reacts with [Au(AsPh3)]1 to give the products. However, an interesting fact is that [MoOS3- (AuPPh3){Au(PPh3)2}] was synthesized in poor yield by reaction of Cs2[MoOS3] and [Au(PPh3)Cl].17 Structures of [MAu2S4(AsPh3)2] (M = Mo 1 or W 2) Figs. 1 and 2 show the crystal structures of compounds 1 and 2, Figs. 3 and 4 the packings of the clusters in the solid state. The skeletons, consisting of one M, four m-S and two Au atoms, show linear structures with crystallographic C2v symmetry. The Au]Mo]Au and Au]W]Au angles are 178.51(3) and 178.27(2)8, respectively. The M (Mo or W) atom has essentially tetrahedral co-ordination and MS4 22 acts as a tetradentate ligand co-ordinating to two Au atoms through its four m-S atoms.Each Au atom is co-ordinated by two m-S atoms and one AsPh3 ligand, forming a planar trigonal geometry. The MS1S2Au1 and MS3S4Au2 (M = Mo or W) cores in compounds 1 and 2 are planar to within 0.0056 (0.0083) and 0.0125 (0.0136) Å, respectively. Their dihedral angle is 89.65 (89.73)8, which means that they are essentially perpendicular to each other.There are two types of structures in related linear compounds as depicted in Scheme 3; the main bond lengths are listed in Table 4, which reveals several structural trends. First, in all linear-shaped compounds MS2M92 (M = Mo or W; M9 = Cu, Scheme 1 [NH4]2[MO2S2] + HAuCl4•4H2O + AsPh3 (Ph3As)Au S M S S S Au(AsPh3) Ag or Au), each Au atom in compounds 1, 2, 6 and 10 is in a trigonal-planar co-ordination; one Cu(Ag) atom in 3–5 and 7–9 is tetrahedrally co-ordinated and the other is trigonally co-ordinated.However, the co-ordination modes of two Au atoms in the nest-shaped compound [MoOS3(AuPPh3){Au- (PPh3)2}] are the same as those observed in linear-shaped Mo(W)]Cu(Ag)]S cluster compounds. Secondly, the M]S bond lengths of four gold-containing linear compounds are similar to each other. Owing to the influences of the ligands, the Mo]Au, W]Au and Au]S bond lengths are different. The Au]As bond lengths are, of course, longer than corresponding Au]P distances.The explanation for this fact is that the covalent radius (1.21 Å) of As is longer than that (1.10 Å) of P. Thirdly, the Au]P bond length [2.272(2) Å for 6] trigonally coordinated in Mo]M9]L (M9 = Cu, Ag or Au) compounds 3, 4, Fig. 1 Crystal structure of [MoAu2S4(AsPh3)2] Fig. 2 Crystal structure of [WAu2S4(AsPh3)2] Fig. 3 Packing of [MoAu2S4(AsPh3)2] in the solid stateJ. Chem. Soc., Dalton Trans., 1997, Pages 2357–2361 2359 and 6 is between the Cu]P [2.210(5) Å] and Ag]P distances [2.380(4) Å], though atom covalent radii vary as Au > Ag > Cu, showing that the Au]P bond is stronger than the Cu]P and Ag]P.The same trend is observed in W]M9]S compounds 7, 8 and 10. Fourthly, M9]P, M9]S and M]M9 bond lengths in tetrahedral co-ordination are longer than those in trigonal coordination in compounds 3–5 and 7–9. However, the opposite trend is found in M]S bond distances. NLO properties of [MAu2S4(AsPh3)2] (M = Mo 1 or W 2) The similarity in the structures of the two compounds should lead to similar UV/VIS spectra, which is confirmed by Fig. 5. The red shift in the spectrum of compound 1 is expected since it contains one Mo atom instead of one W atom. The first absorption peaks are located at 500 (2.48) and 410 nm (3.02 eV) for compounds 1 and 2, respectively. Their Z-scan results are shown in Fig. 6, where the filled and open circles were measured Fig. 4 Packing of [WAu2S4(AsPh3)2] in the solid state Table 1 Crystal data and experimental parameters for complexes 1 and 2 * Formula M Crystal size/mm a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 T/K Dc/g cm23 F(000) m(Mo-Ka)/cm21 2qmax/8 Scan speed/8 min21 No.observations [I >1.5s(I)] RR 9 Goodness of fit indicator Maximum, minimum peaks in final difference map/e Å23 1 C36H30As2Au2MoS4 1230.59 0.41 × 0.20 × 0.16 9.580(4) 10.753(4) 19.838(8) 88.12(4) 80.20(4) 67.39(3) 1857(1) 290.2 2.200 1152.00 102.55 50.0 2.0 4591 0.0299 0.0387 1.108 0.96, 20.71 2 C36H30As2Au2S4W 1318.50 0.50 × 0.41 × 0.30 9.572(2) 10.803(2) 19.816(4) 88.15(1) 80.30(2) 67.52(2) 1865.2(7) 295.2 2.348 1216.00 129.64 60.0 8.0 7676 0.0638 0.0859 0.935 6.85, 25.29 * Details in common: triclinic, space group P1� ; Z = 2; 407 variables; maximum shift in final cycle 0.00.with and without the aperture, respectively. To obtain the NLO parameters we employed a Z-scan theory which considers effective non-linearities of third-order nature only: a = a0 1 a2 I Scheme 3 Table 2 Selected bond distances (Å) and angles (8) for compound 1 Au(1)]Mo Au(1)]S(1) Au(2)]Mo Au(2)]S(3) Mo]S(1) Mo]S(3) Mo]Au(1)]As(1) Mo]Au(1)]S(2) As(1)]Au(1)]S(2) Mo]Au(2)]As(2) Mo]Au(2)]S(4) As(2)]Au(2)]S(4) Au(1)]Mo]Au(2) Au(1)]Mo]S(2) Au(1)]Mo]S(4) Au(2)]Mo]S(2) Au(2)]Mo]S(4) S(1)]Mo]S(3) S(2)]Mo]S(3) S(3)]Mo]S(4) Au(1)]S(2)]Mo Au(2)]S(4)]Mo 2.7837(7) 2.395(2) 2.7690(7) 2.378(2) 2.216(2) 2.214(2) 172.74(3) 49.93(5) 133.10(6) 174.86(3) 50.10(5) 125.23(6) 178.51(3) 55.80(6) 124.70(6) 123.01(7) 56.18(6) 109.07(10) 108.13(10) 111.86(9) 74.28(7) 73.72(7) Au(1)]As(1) Au(1)]S(2) Au(2)]As(2) Au(2)]S(4) Mo]S(2) Mo]S(4) Mo]Au(1)]S(1) As(1)]Au(1)]S(1) S(1)]Au(1)]S(2) Mo]Au(2)]S(3) As(2)]Au(2)]S(3) S(3)]Au(2)]S(4) Au(1)]Mo]S(1) Au(1)]Mo]S(3) Au(2)]Mo]S(1) Au(2)]Mo]S(3) S(1)]Mo]S(2) S(1)]Mo]S(4) S(2)]Mo]S(4) Au(1)]S(1)]Mo Au(2)]S(3)]Mo 2.3745(8) 2.392(2) 2.3715(8) 2.396(2) 2.213(2) 2.213(2) 49.97(5) 126.55(6) 99.89(7) 50.26(6) 134.31(6) 100.36(8) 55.86(6) 123.44(7) 125.34(6) 55.68(6) 111.65(9) 108.24(9) 107.92(10) 74.15(7) 74.06(7) Table 3 Selected bond distances (Å) and angles (8) for compound 2 Au(1)]W Au(1)]S(1) Au(2)]W Au(2)]S(3) W]S(1) W]S(3) W]Au(1)]As(1) W]Au(1)]S(2) As(1)]Au(1)]S(1) W]Au(2)]As(2) W]Au(2)]S(4) As(2)]Au(2)]S(4) Au(1)]W]Au(2) Au(1)]W]S(2) Au(1)]W]S(4) Au(2)]W]S(2) Au(2)]W]S(4) S(1)]W]S(3) S(2)]W]S(3) S(3)]W]S(4) Au(1)]S(2)]W Au(2)]S(4)]W 2.8103(4) 2.427(3) 2.7951(4) 2.400(3) 2.213(2) 2.213(3) 172.38(3) 49.55(6) 134.02(6) 174.63(3) 49.71(6) 125.34(6) 178.27(2) 55.70(7) 124.77(7) 122.93(7) 56.27(6) 108.6(1) 108.3(1) 112.08(10) 74.75(7) 74.02(7) Au(1)]As(1) Au(1)]S(2) Au(2)]As(2) Au(2)]S(4) W]S(2) W]S(4) W]Au(1)]S(1) As(1)]Au(1)]S(1) S(1)]Au(1)]S(2) W]Au(2)]S(3) As(2)]Au(2)]S(3) S(3)]Au(2)]S(4) Au(1)]W]S(1) Au(1)]W]S(3) Au(2)]W]S(1) Au(2)]W]S(3) S(1)]W]S(2) S(1)]W]S(4) S(2)]W]S(4) Au(1)]S(1)]W Au(2)]S(3)]W 2.3733(9) 2.406(3) 2.3698(9) 2.418(3) 2.217(2) 2.218(2) 49.32(6) 126.65(6) 98.86(8) 49.72(6) 135.12(7) 99.42(9) 56.28(7) 123.15(7) 125.11(7) 55.81(7) 111.96(10) 108.14(10) 107.9(1) 74.40(7) 74.47(8)2360 J.Chem. Soc., Dalton Trans., 1997, Pages 2357–2361 Table 4 Comparison of main bond distances (Å) a 13 4 5 627 8 9 10 11 Compound [MoAu2S4(AsPh3)2] [MoCu2S4(PPh3)3]?0.8CH2Cl2 [MoAg2S4(PPh3)3]?0.8CH2Cl2 [NEt4][MoAg(CuCN)S4(PPh3)2] [MoAu2S4(PPh3)2] [WAu2S4(AsPh3)2] [WCu2S4(PPh3)3]?0.8CH2Cl2 [WAg2S4(PPh3)3]?0.8CH2Cl2 [NEt4][WAg(CuCN)S4(PPh3)2] [WAu2S4(PMePh2)2] [MoOS3(AuPPh3){Au(PPh3)2}] M]Sb 2.214(2) 2.218(5) 2.198(5) * 2.215(5) 2.195(5) * 2.202(6) 2.189(5) * 2.214(2) 2.215(2) 2.224(8) 2.204(3) * 2.219(1) 2.195(5) * 2.202(5) 2.189(5) * 2.219(3) 2.261(2) 2.241(2) * M]M9b 2.7764(7) 2.642(3) 2.775(2) * 2.860(2) 3.030(2) * 2.622(3) 3.075(2) * 2.810(1) 2.8027(4) 2.670(3) 2.809(3) * 2.886(2) 3.056(2) * 2.638(3) 3.099(2) * 2.841(1) 2.838(1) 3.133(1) * M9]Sb 2.390(2) 2.220(5) 2.313(5) * 2.459(5) 2.572(5) * 2.209(7) 2.584(5) * 2.405(2) 2.413(3) 2.232(9) 2.333(3) * 2.476(6) 2.579(5) * 2.219(6) 2.596(5) * 2.429(3) 2.419(2) 2.644(2) * M9]L 2.373(8) 2.210(5) 2.303(5) * 2.380(4) 2.471(4) * 1.87(2) 2.484(5) * 2.272(2) 2.372(9) 2.209(8) 2.307(8) * 3.362(5) 2.460(1) * 1.82(2) 2.479(5) * 2.268(3) 2.277(2) 2.325(2) * Ref.This work 18 19 20 17 This work 19 19 21 22 17 a M = Mo or W; M9 = Cu, Ag or Au. b Average values. * The starred bond lengths are those when the Cu or Ag has tetrahedral co-ordination and the S or P atom is bonded to the Cu or Ag.and n = n0 1 n2 I, where a, a0 and a2 are the total, linear and non-linear absorption coefficients, n, n0 and n2 the total, linear and non-linear refractive indices and I is the light irradiance. The details of the theory can be found elsewhere.16 The good fits between the theory and the Z-scan data suggest that the observed non-linearities can be expressed effectively by thirdorder susceptibilities.The values of a2 and n2 extracted from the best fits are listed in Table 5. The modulus of the third-order molecular susceptibility was calculated from equation (1) where |g| = 1 NF4÷S9 × 108e0n0 2c2a2 4pw D2 1 Scn0 2n2 80p2 D2 (1) e0 and c are the permittivity and the speed of light in a vacuum, respectively, w is the angular frequency of the light, N the compound concentration, and F4 the local Lorentz field. In this expression all the units are SI except that N is in cm23 and |g| is in esu.Assuming that F4 = 3, we calculate that |g| = 3.0 × 10229 and 6.5 × 10229 esu (esu = 7.162 × 1013 m5 v22) for compounds 1 and 2, respectively. Note that such a large value is measured in the transparent region for compound 2, and is several orders of magnitude greater than those in well known NLO materials in the transparent part of their spectra (for example: 5.6 × 10235– Fig. 5 Electronic spectra of [MoAu2S4(AsPh3)2] (9.6 × 1025 mol dm23) (– – –) and [WAu2S4(AsPh3)2] (4.2 × 1024 mol dm23) (——) in CH2Cl2.Optical path 1 cm 8.6 × 10234 esu for Group 10 metal alkynyl polymers at 1064 nm,23,24 1 × 10232–1 × 10231 esu for metallophthalocyanines at 1064 nm25 and 7.5 × 10234 esu for C60 at 1910 nm).26 It is also interesting to compare these two new compounds with clusters that we have previously reported. Table 5 shows that compound 2 compares favourably with all the clusters in terms of figures of merit, a2/a0 and n2/a0. It should be emphasized that the Z scans reported here could not reveal the origins of the observed non-linearities.Excitedstate absorption and non-linear scattering are possible for the measured absorptive non-linearity. The change in the sign of the measured refractive non-linearity may give a hint as to the cause of the non-linear refraction. The signs of refractive nonlinearities for all the clusters, listed in Table 5, show that n2 alters from positive to negative as the ratio of the photon energy (hw) to that of the first absorption peak (hw0) approaches 1 : 1.The turning point is located at around hw/ hw0 ª 0.8 : 1, which is consistent with a recently developed theory on bound-electronic effects.27 Fig. 6 Z Scans of [MoAu2S4(AsPh3)2] (6.4 × 1024 mol dm23) and [WAu2S4(AsPh3)2] (5.4 × 1024 mol dm23) with 532 nm, 7 ns laser pulses. Optical path 1 mm. Incident energy of pulses 20 mJ. Transmittance of the aperture 0.34. The experimental data were measured with (d) and without (s) the aperture, respectively. The solid curves represent fits based on Z-scan theory.The Z scans of [WAu2S4(AsPh3)2] have been vertically displaced by 0.4 for clarityJ. Chem. Soc., Dalton Trans., 1997, Pages 2357–2361 2361 Table 5 NLO Parameters for clusters measured at photon energy hw = 2.33 eV Cluster [WCu2OS3(PPh3)4] a [MoCu2OS3(PPh3)3] a [Mo2Ag4S8(PPh3)4] b [NEt4]3[WOS3(CuBr)3(m-Br)]?2H2Oc [WAu2S4(AsPh3)2] d [NBun 4]2[MoCu3OS3(NCS)3] e [MoAu2S4(AsPh3)2] d [NBun 4]4[Mo8Cu12O8S24] f hw0/eV 4.85 4.80 4.75 3.55 3.02 2.50 2.48 2.43 hw/hw0 0.48 0.49 0.49 0.66 0.77 0.93 0.94 0.96 1023 a0/dm3 cm21 mol21 2.5 15 6.4 5.3 0.44 1.2 4.5 7.5 105 a2/dm3 cm W21 mol21 ª0 35 100 6.6 13 0.18 7.9 28 1010 n2/dm3 cm2 W21 mol21 6.7 68 120 12 19 21.7 28.0 223 108 a2a0 21/cm2 W21 ª0 2.3 16 1.2 29 0.15 1.8 3.7 103 |n2/a0|/cm3 W21 2.7 4.5 19 2.3 42 1.4 1.8 3.1 a Ref. 5. b Ref. 9. c Ref. 7. d This work. e Ref. 3. f Ref. 4. References 1 R. H.Holm, Chem. Soc. Rev., 1981, 10, 455. 2 E. D. Simhon, N. C. Baenziger, M. Kanatzidis, M. Draganjac and D. Coucouvanis, J. Am. Chem. Soc., 1981, 103, 1218. 3 S. Shi, W. Ji, W. Xie, T. C. Chong, H. C. Zeng, J. P. Lang and X. Q. Xin, Mater. Chem. Phys., 1995, 39, 298; W. Ji, P. Ge, W. Xie, S. H. Tang and S. Shi, J. Lumin., 1996, 66/67, 115; H. W. Hou, X. R. Ye, X. Q. Xin, J. Liu, M. Q. Chen and S. Shi, Chem. Mater., 1995, 7, 472. 4 S. Shi, W. Ji and X. Q. Xin, J. Phys. Chem., 1995, 99, 894; W.Ji, W. Xie, S. H. Tang and S. Shi, Mater. Chem. Phys., 1995, 43, 45. 5 H. W. Hou, X. Q. Xin, J. Liu, M. Q. Chen and S. Shi, J. Chem. Soc., Dalton Trans., 1994, 3211. 6 Z. R. Chen, H. W. Hou, X. Q. Xin, B. Yu and S. Shi, J. Chem. Phys., 1995, 99, 8717. 7 S. Shi, H. W. Hou and X. Q. Xin, J. Phys. Chem., 1995, 99, 4050. 8 S. Shi, W. Ji, S. H.Tang, J. P. Lang and X. Q. Xin, J. Am. Chem. Soc., 1994, 116, 3615; S. Shi, W. Ji, J. P. Lang and X. Q. Xin, J. Phys. Chem., 1994, 98, 3570; W.Ji, H. J. Du, S. H. Tang and S. Shi, J. Opt. Soc. Am. B, 1996, 12, 876. 9 W. Ji, S. Shi, H. J. Du, P. Ge, S. W. Tang and X. Q. Xin, J. Phys. Chem., 1995, 99, 17 297. 10 J. W. McDonald, G. D. Friesen, L. D. Rosenhein and W. E. Newton, Inorg. Chim. Acta, 1983, 72, 205. 11 PATTY, P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Bosman, S. Garcia-Granda, R. O. Gould, J. M. M. Smits and C. Smykalla, The DIRDIF program system, Technical Report of the Crystallography Laboratory, University of Nijmegen, 1992. 12 P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Bosman, R. Gelder, R. Israel and J. M. M. Smits, The DIRDIF 94 program system, Technical Report of the Crystallography Laboratory, University of Nijmegen, 1994. 13 SHELXS 86, G. M. Sheldrick, in Crystallographic Computing 3, eds. G. M. Sheldrick, C. Kruger and R. Goddard, Oxford University Press, 1985, pp. 175–189. 14 DIFABS, N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158. 15 TEXSAN, Crystal Structure Analysis Package, Molecular Structure Corporation, Houston, TX, 1995. 16 H. Hou, B. Liang, X. Xin, K. Yu, P. Ge, W. Ji and S. Shi, J. Chem. Soc., Faraday Trans., 1996, 92, 2343. 17 J. M. Charnock, S. Bristow, J. R. Nicholson, C. D. Garner and W. Clegg, J. Chem. Soc., Dalton Trans., 1987, 303. 18 A. Müller, H. Bogge and U. Schimanski, Inorg. Chim. Acta, 1980, 45, L249. 19 A. Müller, H. Bogge and U. Schimanski, Inorg. Chim. Acta, 1983, 69, 5 and refs. therein. 20 S. W. Du, N. Y. Zhu, P. C. Chen, X. T. Wu and J. X. Lu, J. Chem. Soc., Dalton Trans., 1992, 339. 21 S. W. Du, N. Y. Zhu, P. C. Chen, X. T. Wu and J. X. Lu, Polyhedron, 1992, 11, 109. 22 J. C. Huffman, R. S. Roth and A. R. Siedle, J. Am. Chem. Soc., 1976, 98, 1310. 23 S. Guha, C. C. Frazier, P. L. Porter, K. Kang and S. E. Finberg, Opt. Lett., 1989, 14, 952. 24 W. J. Blau, H. J. Byrne, D. J. Cardin and A. P. Davey, J. Mater. Chem., 1991, 1, 245. 25 J. S. Shirk, J. R. Lindle, F. J. Bartoli, Z. H. Kafafi and A. W. Snow, in Materials for Nonlinear Optics, eds. S. R. Marder, J. E. Sohn and G. D. Stucky, American Chemical Society, Washington, 1992, p. 626. 26 Y. Wang and L. T. Cheng, J. Phys. Chem., 1992, 96, 1530. 27 M. Sheik-Bahae, D. C. Hutching, D. J. Hagan and E. W. Van Stryland, Phys. Rev. Lett., 1991, 65, 96; R. DeSalvo, A. A. Said, D. J. Hagan, E. W. Van Stryland and M. Sheik-Bahae, IEEE J. Quantum Electron., 1996, 32, 1324. Received 4th December 1996; Paper 6/08190H

ISSN:1477-9226    

DOI:10.1039/a608190h

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2363–2368 2363 S ? ? ? S Contact-assembled silver(I) complexes of 4,5-ethylenedithio- 1,3-dithiole-2-thione having unique supramolecular networks Jie Dai, Takayoshi Kuroda-Sowa, Megumu Munakata,* Masahiko Maekawa, Yusaku Suenaga and Yasuhiro Ohno Department of Chemistry, Kinki University, Kowakae 3-4-1 Higashi-Osaka 577, Japan Two silver(I) complexes of 4,5-ethylenedithio-1,3-dithiole-2-thione (C5H4S5), [{Ag(C5H4S5)3}ClO4?CH3CN]2 and [Ag(C5H4S5)CF3SO3]• have been synthesized and characterized crystallographically.They have unique dimeric and two-dimensional structures respectively and are assembled by S ? ? ? S contacts. The finding of the shortest S ? ? ? S contacts (3.284 and 3.262 Å) in these complexes indicated that the co-ordination linkage in metal complexes containing these types of sulfur donor compounds could be expected to control the intra- or inter-molecular interactions. The co-ordination mode of the C5H4S5 ligand has also been discussed. In order to achieve the goals of developing advanced materials, for chemists, the past ten years have brought a blossoming of a large field of supramolecular chemistry.1,2 Intermolecular interactions such as hydrogen bonding, S ? ? ? S contacts and p–p stacking are efficient organizing forces in supramolecular architecture and the design of new solid-state materials for a number of applications. Many research groups have succeeded in the strategy to control organic molecular aggregation by hydrogen bonding,3,4 and to synthesize organic conductors assembled by p–p stacking 5–7 or S ? ? ? S contacts.8–12 The unique physical properties of these compounds not only depend on the specific molecular properties of the individual components, but are also strongly influenced by the arrangement of interactions within the crystal lattice.In TTF and BEDT-TTF [bis(ethylenedithio)- tetrathiafulvalene] compounds13–15 and dmit (4,5-disulfanyl- 1,3-dithio-2-thionate) complexes [M(C3S5)2]n2 11,12 short S ? ? ? S contacts were found to play an important role in the conductivity of these sulfur-rich compounds.However in most of these organic donor–acceptor compounds or organic radical salts, the molecular packing that influences the S ? ? ? S interaction is mainly controlled by the identity of the molecule itself, the size of the counter ion and co-crystallized solvent molecules.16 More remarkable is the synthesis of metal complexes of these donor and acceptor compounds, which are assembled by both metal co-ordination bonds and weak molecular interactions. Metal ions have properties of special interest as components of supramolecular systems and linkers for self-assembly.The packing and interaction of organic molecules in the co-ordination compounds have more variety than is observed in pure organic compounds. To introduce metal ions to these donor–acceptor systems, the sulfur-rich compound 4,5-ethylenedithio-1,3-dithiole-2-thione (C5H4S5), which is well known as an electron donor17 and has available sites to co-ordinate to metal ions, was selected as a ligand in this work.The ligand is also a derivative of C3S5 and has a similar structure to half of BEDT-TTF. Silver(I) (d10) ions were used as co-ordination centres and metal bridges because of their affinity for soft sulfur atoms. Recently we have reported two complexes of C5H4S5, [Ag(C5H4S5)2NO3]• 318 and [Cu4I4(C5H4S5)4]• 4.19 Both of them have a polymeric chain structure bridged by C5H4S5 and a S ? ? ? S contact-assembled network.The shortest S ? ? ? S contact distances in these two complexes are 3.41 and 3.26 Å respectively. In this paper we report two new silver(I) complexes of C5H4S5 with short S ? ? ? S contacts and the co-ordination chemistry of the ligand. The electronic conductivity of the iodinedoped compounds has also been investigated. Experimental General comments The preparations were performed using Schlenk techniques.The reagent C5H4S5 was obtained from Tokyo Kasei Co. and used without further purification. Acetonitrile and tetrahydrofuran were dried and distilled by a standard method before use. Infrared spectra were measured as KBr discs on a JASCO FT/ IR 8000 spectrometer and electronic spectra were recorded with a Hitachi 150-20 spectrophotometer. Electrical resistivity was measured by a conventional two-probe method at room temperature with a compressed pellet.Preparation of the complexes with C5H4S5 Dimeric [{Ag(C5H4S5)3}ClO4?CH3CN]2 1. To an acetonitrile solution (4 cm3) of C5H4S5 (44.8 mg, 0.2 mmol) was added AgClO4?H2O (22.5 mg, 0.1 mmol) in acetonitrile (4 cm3). The solution was stirred for 30 min at room temperature under an argon atmosphere. A red precipitate was formed and it was separated and washed with acetonitrile (yield 40%). The filtrate was cooled to 230 8C for one week and after being warmed to room temperature a red oil formed.It was put aside for one month and single crystals for X-ray measurement were obtained (Found: C, 22.16; H, 1.61; N, 1.53. C34H30Ag2Cl2N2O8S30 requires C, 22.16; H, 1.64; N, 1.52%). Polymeric [Ag(C5H4S5)CF3SO3]• 2. To a tetrahydrofuran solution (8 cm3) of C5H4S5 (22.4 mg, 0.1 mmol) was added AgCF3SO3 (25.7 mg, 0.1 mmol) in tetrahydrofuran (4 cm3). The solution was stirred for 20 min at room temperature under an argon atmosphere.A red precipitate was formed and it was separated and washed with tetrahydrofuran (yield 56%). Crystals for X-ray measurement were obtained by slow evaporation of the filtrate (Found: C, 15.47; H, 0.85. C12H8Ag2F6O6S12 requires C, 14.97; H, 0.84%). Iodine-doped compounds. These were prepared by gaseous diffusion. Small amounts of powdered samples of complexes 1 or 2 and solid iodine were separately placed in an H-shaped tube which was then sealed under argon and allowed to stand for 1 month at ambient temperature.Dark brown I2-doped compounds were obtained. S S S S S C5H4S52364 J. Chem. Soc., Dalton Trans., 1997, Pages 2363–2368 X-Ray crystallography X-Ray diffraction experiments were performed at room temperature on a Rigaku AFC-7R diffractometer equipped with graphite-monochromated Mo-Ka radiation (l 0.710 69 Å). Unit-cell parameters were obtained from a least-squares refinement using the setting angles of 25 reflections.Intensity data were collected by using standard scan techniques (w–2q). An empirical correction based on azimuthal scans of several reflections was applied and the data were corrected for Lorentz and polarization effects. The structures were solved by direct methods (MITHRIL 84 for 1 and MULTAN 88 for 2) 20,21 and expanded using Fourier techniques (DIRDIF 94).22 The final full-matrix least-squares refinements for these structures were performed on these data having I > 3.00s(I).For complex 1 the perchlorate anions were refined isotropically for the disorder, while the rest of the nonhydrogen atoms were refined anisotropically. All the nonhydrogen atoms were refined anisotropically for complex 2. Hydrogen atoms of the two complexes were included but not refined. All crystallographic computations were performed on an INDY computer using the TEXSAN program system.23 Details of crystal data are summarized in Table 1. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/521. Results and Discussion Spectroscopic studies of the complexes The IR spectra of complexes 1 and 2 show significant changes in the range 1000–1100 cm21 [n(C]S) stretching frequency of the heterocyclic ring].The C]] S stretching frequency of 1477 cm21 for the free dithiole–thione 24 is split into three bands. The main peaks for n(C]S) are 1451 cm21 for 1 and 1453 cm21 for 2, Table 1 Crystallographic data for the complexes 1 and 2 1 2 Formula C34H30Ag2Cl2N2O8S30 C12H8Ag2F6O6S12 Formula weight 1843.06 962.64 Crystal colour, habit Red, brick Red, prismatic Crystal dimensions/mm 0.30 × 0.30 × 0.30 0.30 × 0.30 × 0.20 Crystal system Triclinic Triclinic Space group P1� P1� a/Å 15.334(2) 9.526(2) b/Å 17.951(3) 18.629(5) c/Å 12.756(4) 7.7966(8) a/8 92.85(2) 90.42(2) b/8 110.53(2) 101.84(1) g/8 98.72(1) 100.90(2) U/Å3 3229(1) 1328.2(5) Z 2 2 Dc/g cm23 1.895 2.407 F(000) 1840.00 936.00 m(Mo-Ka)/cm21 17.03 24.88 T/8C 20.0 20.0 2qmax/8 55.0 55.0 No.of total reflections 15 377 6457 No. of unique reflections 14 821 6093 No. of observations [I > 3s(I )] 10 959 5260 Ra 0.053 0.035 R9b 0.075 0.047 Goodness of fit 3.13 1.98 Maximum shift 0.04 0.00 Drmin, Drmax/e Å23 21.22, 1.39 21.54, 0.49 a R = S(|Fo| 2 |Fc|)/S|Fo|.b R9 = [Sw(|Fo| 2 |Fc|)2/Sw|Fo|2]� �� where w = 4Fo 2/Ss2(Fo 2). similar to that of the silver nitrate complex [Ag(C5H4S5)2- NO3]•.18 The characteristic broad peaks of the perchlorate anion (1088 cm21) and the triflate anion (1254 cm21) are also shown in the IR spectra of the complexes. Titration of a solution of C5H4S5 in acetone (1.0 × 1024 mol dm23) with excess AgClO4 in the same solvent clearly showed the shift of the p–p* band of the ligand (408 æÆ 431 nm, Fig. 1). The isosbestic point appeared at 420 nm suggesting that there are only two species existing in the system besides the silver perchlorate. One is the ligand and the other must be [Ag(C5H4S5)3]1. The equilibrium is Ag1 1 3C5H4S5 Ag- (C5H4S5)3 1, even in excess silver ion concentration. This is the reason why excess silver salts were used in the synthesis of the silver complexes. Crystal structure of [{Ag(C5H4S5)3}ClO4?CH3CN]2 1 An ORTEP25 view of the complex [{Ag(C5H4S5)3}ClO4? CH3CN]2, with selected atom labelling is shown in Fig. 2(a) (perchlorate anion and acetonitrile molecule which do not coordinate to the metal ion are omitted for clarity). The selected bond distances and angles are listed in Table 2. The molecule is assembled by two unidentical [Ag(C5H4S5)3]ClO4?CH3CN moieties. Each AgI ion is co-ordinated to three C5H4S5 molecules through thiocarbonyl sulfur atoms (C]] S) in a quasitriangle geometry.The silver–sulfur bond distances are in the range 2.474–2.567 Å, within that expected for Ag]S (thiocarbonyl sulfur).26 The bond angles around the Ag(1) atoms, S(1)]Ag(1)]S(6), S(6)]Ag(1)]S(11), S(1)]Ag(1)]S(11) are 95.99(5), 131.41(6) and 118.86(5)8 respectively and sum to 346.268. Similarly the bond angles around the Ag(2) atoms, S(16)]Ag(2)]S(21), S(21)]Ag(2)]S(26), S(16)]Ag(2)]S(26) are 139.07(5), 121.31(5) and 93.33(4)8 respectively and sum to 353.718. These data show some distortion from the sum of 3608 for ideal trigonal geometry. Owing to the weak co-ordination linkage between the pair of [Ag(C5H4S5)3]1, both Ag(1) and Ag(2) atoms lie out of the trigonal planes and are close to each other [Fig. 2(b)]. The Ag(1)]S(16) (2.91 Å) and Ag(2)]S(6) Fig. 1 The electronic spectra of titrating a solution of C5H4S5 in acetone (1.0 × 1024 mol dm23) with a solution of AgClO4 (a) 0.0, (b) 0.5 × 1021, (c) 1.0 × 1021, (d) 1.5 × 1021 and (e) 2.0 × 1021 mol dm23 in acetone Table 2 Selected bond lengths (Å) and angles (8) for [{Ag(C5H4- S5)3}ClO4?CH3CN]2 1 Ag(1)]S(1) 2.535(1) Ag(1)]S(6) 2.543(2) Ag(1)]S(11) 2.474(2) Ag(1)]S(16) 2.906(2) Ag(2)]S(16) 2.567(2) Ag(2)]S(21) 2.477(2) Ag(2)]S(26) 2.540(1) Ag(2)]S(6) 3.043(2) S(1)]C(1) 1.678(5) S(6)]C(6) 1.673(5) S(11)]C(11) 1.679(5) S(16)]C(16) 1.686(5) S(21)]C(21) 1.666(5) S(26)]C(26) 1.660(5) S(1)]Ag(1)]S(6) 95.99(5) S(1)]Ag(1)]S(11) 118.86(5) S(6)]Ag(1)]S(11) 131.41(6) S(16)]Ag(2)]S(21) 139.07(5) S(16)]Ag(2)]S(26) 93.33(4) S(21)]Ag(2)]S(26) 121.31(5)J.Chem. Soc., Dalton Trans., 1997, Pages 2363–2368 2365 (3.04 Å) distances are somewhat longer than ordinary Ag]S distances, but can still be assigned as weak co-ordination bonds.26 The Ag(1)]Ag(2) separation of 3.35 Å is longer than the metal–metal bond of metallic silver. Thereby complex 1 has a dimeric structure with two weak inter-co-ordinated quasitrigonal [Ag(C5H4S5)3]1 moieties.The S ? ? ? S contacts in 1 exist both intra- and intermolecularly and are less than the sum of van der Waals radii of two S atoms (3.60 Å). In 1 the shortest contact is 3.284 Å [intramolecular contact, Fig. 2(a)]. Since the average S ? ? ? S contact distances of highly conductive compounds of TTF, BEDTTTF and their derivatives are about 3.50 Å, the distance of 3.28 Å here is a rare example. Fig. 3 shows the molecular packing and the one-dimensional intermolecular S ? ? ? S contacts.Fig. 2 (a) An ORTEP view of the dimeric structure of {[Ag(C5H4- S5)3]2}21; (b) co-ordination sphere of the complex Table 3 Selected bond lengths (Å) and angles (8) for [Ag(C5H4S5)- CF3SO3]• 2 Ag(1)]S(1) 2.5495(9) Ag(1)]S(6) 2.584(1) Ag(1)]S(19) 2.920(1) Ag(1)]S(69) 2.894(1) Ag(1)]O(39) 2.621(3) Ag(2)]S(4) 2.596(1) Ag(2)]S(89) 2.841(1) Ag(2)]O(1) 2.509(3) Ag(2)]O(4) 2.409(3) Ag(2)]O(6) 2.454(4) S(1)]C(1) 1.688(3) S(6)]C(6) 1.679(4) S(19)]Ag(1)]S(69) 166.34(3) S(1)]Ag(1)]S(6) 137.63(3) S(6)]Ag(1)]O(39) 128.49(7) S(1)]Ag(1)]O(39) 93.85(7) S(4)]Ag(2)]S(8) 107.65(3) S(4)]Ag(2)]O(1) 96.87(7) S(4)]Ag(2)]O(4) 119.9(1) S(4)]Ag(2)]O(6) 118.85(9) Crystal structure of [Ag(C5H4S5)CF3SO3]• 2 The anion CF3SO3 2 is able to co-ordinate and it does so by bridging silver(I) atoms in the complex [Ag(C5H4S5)CF3SO3]• to form a two-dimensional polymer structure.There are two crystallographically independent silver(I) atoms. Although both Ag(1) and Ag(2) involve a five-co-ordinate environment, Ag(1) has a S4O donor set and is co-ordinated by four thiocarbonyl sulfur atoms of four separate C5H4S5 molecules and one oxygen atom of a triflate anion, whereas Ag(2) is bonded to a S2O3 donor set by two thioether sulfur atoms and three oxygen atoms of triflate anions.An ORTEP view of complex 2 with atom labelling is shown in Fig. 4. Selected bond distances and angles are given in Table 3. Stereochemistry of silver(I) complexes is dominated by fourand three-co-ordination.In contrast five-co-ordinate silver(I) compounds are unusual. In complex 2, the Ag(1) centre is in a distorted trigonal-bipyramidal geometry where the trigonal plane is defined by atoms S(1), S(6) and O(3) with distances 2.5495(9), 2.584(1) and 2.621(3) Å, respectively. The Ag(1) Fig. 3 Molecular packing and the one-dimensional intermolecular S ? ? ? S contacts of [{Ag(C5H4S5)3}ClO4?CH3CN]2 Fig. 4 An ORTEP view of the complex [Ag(C5H4S5)CF3SO3]•2366 J.Chem. Soc., Dalton Trans., 1997, Pages 2363–2368 atom also forms Ag]S bonds to two axial donor atoms S(19) and S(69) with longer distances of 2.920(1) and 2.894(1) Å. On the other hand, the Ag(2) co-ordination centre forms a distorted square-pyramidal geometry. The Ag]O distances of 2.409(3), 2.454(4) and 2.509(3) Å are shorter than that in other triflate complexes of silver(I).27,28 The Ag(2)]S(8) bond distance of 2.841(1) Å is a rather weak one, comparable to that in [Ag(C5H4S5)2NO3]•.However, the axial co-ordination of S(4) (thioether type) to Ag(2) is unexpectedly strong with a distance of 2.596(1) Å. The Ag(1) atoms are doubly-bridged by thiocarbonyl sulfur atoms of the ligands to form parallel one-dimensional chains along the c axis [Fig. 5, the triflate and Ag(2) atoms are omitted for clarity]. All the ligands are approximately perpendicular to the chain and S ? ? ? S contacts are found between them, the shortest being 3.262 Å.Therefore this chain is also connected by S ? ? ? S contacts. These chains are subsequently linked by Ag(2) and triflate anions to give a two-dimensional polymer structure, Fig. 6 gives a schematic view of this network. Co-ordination chemistry of C5H4S5 Until now, the only reported complex of C5H4S5 by other researchers is an antimony complex SbCl3(C5H4S5)1.5.24 Including the two previously reported complexes, i.e. [Ag(C5H4S5)2- NO3]• 318 and [Cu4I4(C5H4S5)4]• 4,19 a total of four new complexes containing this ligand have esized and characterized crystallographically by our group.Thereby the co-ordination modes of the C5H4S5 ligand can be classified into four types: monodentate co-ordination by the thiocarbonyl group (type I) as in [Cu4I4(C5H4S5)4]•; bridge formation by the sulfur of the thiocarbonyl group (type II) as in SbCl3- (C5H4S5)1.5; bidentate co-ordination by both the thiocarbonyl group and the thioether group (type III) as in [Ag(C5H4S5)2- NO3]• and [Cu4I4(C5H4S5)4]•; tridentate co-ordination by the Fig. 5 Thiocarbonyl sulfur bridged chain structure of Ag(1) atoms [triflate and Ag(2) atoms are omitted for clarity] Fig. 6 Schematic structure of the two-dimensional network of [Ag(C5H4S5)CF3SO3]• C5H4S5 CF3SO3 – Ag+ thiocarbonyl sulfur (acting as a bridge) and the thioether sulfur (type IV) as in the complex [Ag(C5H4S5)CF3SO3]•. The complex [{Ag(C5H4S5)3}ClO4?CH3CN]2 has mainly co-ordination of type I and if the weak linkage within the dimer is considered, the co-ordination can be classed as type II.The co-ordination types are schematically summarized in Fig. 7 and Table 4. With the exception of type I, the other co-ordination types usually give polymeric structures. The ethylene group in the six-membered ring of C5H4S5 is not conjugated with the other atoms of the ligand and has a distorted conformation similar to BEDT-TTF. In type I coordination, the anisotropic displacement parameters of the ethylene group are generally very high, such as in the complex [{Ag(C5H4S5)3}ClO4?CH3CN]2 [Fig. 2(a)]. This disorder is also found in the complex [Cu4I4(C5H4S5)4]• 19 and is a common phenomenon in BEDT-TTF compounds.29 However, this disorder can be largely reduced if the sulfur atoms in the sixmembered ring co-ordinate as in complexes 2, 3 and 4 (coordination types III or IV). Most of the compounds of TTF and BEDT-TTF and their analogues are not involved in direct co-ordination to the metal ions.Only two examples, namely (BEDT-TTF)Cu2Br3 and [Rh2(O2CCH3)4(TTF)2] 30,31 in which the sulfur atom in the fiveor six-membered ring directly co-ordinates to metal atoms have been reported. Continuing these findings, the three complexes 2, 3 and 4 reported by our group have been found to have coordination of the thioether sulfur in the six-membered ring of C5H4S5. It is noted that the Ag]S (thioether) distances are longer than the Ag]S (thiocarbonyl) distances (Table 4), therefore the co-ordination of thioether sulfur in the six-membered Fig. 7 Co-ordination types of the ligand C5H4S5 S S S S S S S S S S S S S S S S M M M M M M S S M S M S I II III IV Table 4 Co-ordination type and sulfur–metal distances (Å) of complexes containing C5H4S5 Complex Type M]S (thiocarbonyl) M]S (thioether) [{Ag(C5H4S5)3}ClO4? CH3CN]2 I (II) 2.474–2.567 [Ag(C5H4S5)CF3SO3]• IV 2.549, 2.584 2.841, 2.596 [Ag(C5H4S5)2NO3]• 16 III 2.561 2.827 [Cu4I4(C5H4S5)4]• 17 I, III 2.292, 2.280 2.432 SbCl3(C5H4S5)1.5 22 II 3.085–3.407J. Chem.Soc., Dalton Trans., 1997, Pages 2363–2368 2367 ring is weaker than that of the thiocarbonyl group. Resonance structures of C5H4S5 are shown in the paper by Drew et al.24 The terminal sulfur of the C]] S group lies in an electron-rich environment and the other sulfur atoms are in a partially conjugated state. The weak co-ordination ability of the thioethertype sulfur atoms may be due to the partial conjugation of the electrons in the p-system. The ether-type sulfur in the fivemembered ring is more difficult to co-ordinate to the metal ion than that in the six-membered ring.The unusually short Ag(2)]S(4) (ether type) distance of 2.596 Å in complex 2 is presumably formed because of the weaker co-ordination of the other atoms. S ? ? ? S Contacts of the complexes Supermolecules built from smaller molecules mainly involve intermolecular interactions.On the other hand, with polymeric molecules the supramolecular association may be either intermolecular occurring between low dimensional structures or intramolecular involving function sites located in the polymer. The S ? ? ? S contacts in the dimer complex 1 form a onedimensional chain, and the S ? ? ? S interactions of 2 give the two-dimensional network. The short S ? ? ? S distances for complexes 1 and 2 are listed in Table 5. The ‘side-by-side’ or ‘up–down’ arrangement of C5H4S5 molecules with short S ? ? ? S distances indicates an effi- cient intermolecular p–p orbital interaction, which forms a broadened energy band over the whole lattice.Most of the TTF and C3S5 based superconductors have this character. It is known that the stronger the S ? ? ? S contact, the more effective is the increase in the conductivity. When the temperature is decreased or the pressure increased, the S ? ? ? S distance is shorter than in ambient conditions and accordingly the conductivity is increased.32 In general, the S ? ? ? S contact distances are in the range 3.35– 3.65 Å.An unusually short S ? ? ? S contact of 3.23 Å which results from the Pt–Pt bond in a dimeric structure has been found in TTF[Pt(C3S5)2]3.33 Another example is TTF[Pd- (C3S5)2]2,34 the shortest S ? ? ? S distance of 3.26 Å also being due to metal–metal bonding. In the case of complexes of C5H4S5, the unusually short distances of 3.284 Å for 1 and 3.262 Å for 2 are attributable to the co-ordination bond linkage.In complex 4 the shortest distance of 3.257(2) Å between polymeric chains only occurs as a result of the effect of the molecular packing.19 To date, many conductive sulfur-rich compounds were designed by modification of the anion and the co-crystallized solvent molecules to change the crystal phase and molecular interactions.16 However, this is a poorly understood and dif- ficult to control ‘self-assembly’ process. Co-ordination linkage or co-ordination chemistry is a well known field, therefore it is possible to control the design of complexes in which the metal atom is directly co-ordinated to derivatives of TTF or BEDT-TTF.The S ? ? ? S contact is one of the most important factors by which the sulfur-rich compounds exhibit high conductivity. Table 5 S ? ? ? S Contact distances (Å) for complexes 1 and 2 [{Ag(C5H4S5)3}ClO4?CH3CN]2 S(1)]S(22) 3.514(2) S(1)]S(119) 3.524(2) S(2)]S(11) 3.573(2) S(4)]S(259) 3.585(3) S(6)]S(259) 3.549(2) S(7)]S(13) 3.440(2) S(11)]S(239) 3.447(2) S(12)]S(239) 3.504(2) S(13)]S(26) 3.317(2) S(14)]S(309) 3.390(3) S(15)]S(239) 3.545(2) S(18)]S(22) 3.284(2) S(21)]S(28) 3.492(2) S(21)]S(269) 3.493(2) [Ag(C5H4S5)CF3SO3]• S(1)]S(99) 3.393(1) S(1)]S(79) 3.589(1) S(2)]S(79) 3.262(1) S(2)]S(89) 3.530(1) Another important feature of the conductive compounds is that the constituent molecules are in a mixed-valence state (partial-oxidation, -reduction or charge-transfer).Halogendoping of the conjugated electron donor has been shown to be an effective strategy for the synthesis of electronically conductive compounds.35,36 The complexes 1 and 2 were partially oxidized by iodine-doping. Although the complexes and the iodine-doped free C5H4S5 are insulators (s < 10212 S cm21), the iodine-doped products of complexes 1 and 2 behave as semiconductors with conductivities of 6.9 × 1025 and 1.5 × 1024 S cm21 respectively at room temperature.Conclusion After having reported the complexes [Ag(C5H4S5)2NO3]• and [Cu4I4(C5H4S5)4]•, we have succeeded in the synthesis and characterization of two new complexes of 4,5-ethylenedithio-1,3- dithiole-2-thione with d10 metals, i.e. [{Ag(C5H4S5)3}ClO4? CH3CN]2 and [Ag(C5H4S5)CF3SO3]•. Unique dimers, and oneand two-dimensional structures were found. Furthermore, with the co-operation of co-ordination bonds and S ? ? ? S contacts they are assembled to form one-, two- and three-dimensional supermolecules. The main findings of this study are: (1) the coordination chemistry of the C5H4S5 ligand has been systematically explored with the finding of three new co-ordination types for this ligand (I, III and IV); (2) the finding of the shortest S ? ? ? S contacts (3.284 for 1 and 3.262 Å for 2) indicates that the co-ordination linkage in metal complexes with organic donors can be expected to control the intra- or inter-molecular interactions of supermolecules and that may be an important strategy in the search for new materials and crystal engineering. Acknowledgements This work was supported in part by a Grant-in-Aid for Science Research No. 08454214 and Grant-in-Aid for Priority Area No. 08231267 from the Ministry of Education, Science, Sports and Culture in Japan. The authors are also grateful to Kinki University for financial support (9626). References 1 J.-M. Lehn, Supramolecular Chemistry, VCH, Weinheim, 1995. 2 J.-M. Lehn, Angew.Chem., Int. Ed. Engl., 1990, 29, 1304. 3 J. C. 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ISSN:1477-9226    

DOI:10.1039/a701176h

出版商:RSC    

年代:1997

数据来源: RSC