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Synthesis, Structures, and Redox Properties of Octa(μ 3 -sulfido)hexarhenium(III) Complexes Having Terminal Pyridine Ligands

1999; American Chemical Society; Volume: 38; Issue: 24 Linguagem: Inglês

10.1021/ic9907922

1520-510X

Takashi Yoshimura, Keisuke Umakoshi, Yōichi Sasaki, A. Geoffrey Sykes,

Iron-based superconductors research

A series of μ3-sulfido Re−Re bonded octahedral hexarhenium(III) clusters having mixed chloride−pyridine (py) or −4-cyanopyridine (cpy) terminal ligands, [Bu4N]2[trans-{Re6S8Cl4(py)2}] (Bu4N+ = tetra-n-butylammonium cation) (1a), [Bu4N]2[cis-{Re6S8Cl4(py)2}] (1b), [Bu4N]2[trans-{Re6S8Cl4(cpy)2}] (2a), [Bu4N]2[cis-{Re6S8Cl4(cpy)2}] (2b), and [Bu4N][mer-{Re6S8Cl3(py)3}] (3), and their one-electron-oxidized ReIII5ReIV species, [Bu4N][trans-{Re6S8Cl4(py)2}] (1a'), [Bu4N][trans-{Re6S8Cl4(cpy)2}] (2a'), and mer-[Re6S8Cl3(py)3] (3'), have been prepared and characterized by several physical methods. X-ray crystallographic studies for 1a, 2a, and 3 showed that the Re6S8 core structures are not significantly affected by the type and number of pyridyl ligands. The mixed valent cluster 1a' is of a structurally delocalized type, structural parameters being very similar to those of 1a. Cyclic voltammograms in acetonitrile showed that there is no distinct difference in the redox potentials (ReIII6/ReIII5ReIV) between the cis and the corresponding trans isomers. Both 1a and 1b show a reversible redox wave at 0.77 V vs Ag/AgCl. Redox potentials are more positive for 2a and 2b (0.83 V) and 3 (0.97 V). Clusters 2a and 2b show two-step ligand-centered redox waves at −1.19 and −1.28 V, and −1.18 and −1.29 V, respectively. Temperature-dependent magnetic susceptibility measurements have revealed that 1a' and 3' have an S = 1/2 ground state. The electron self-exchange rate constant for the reaction of 2a with 2a' in dichloromethane as obtained by 1H NMR line-broadening method is 1.2 × 109 M-1 s-1 (298.2 K) with ΔH⧧ = 30.2 ± 2.1 kJ mol-1 and ΔS⧧ = 30 ± 8 J mol-1 K-1. It has been suggested that the previously reported protonated species [Re6S7(SH)Cl6]3- would actually be a one-electron-oxidized [Re6S8Cl6]3-. Crystal data: [Bu4N]2[trans-{Re6S8Cl4(py)2}] (1a), monoclinic, space group C2/c, a = 24.693(8) Å, b = 19.494(4) Å, c = 18.592(4) Å, β = 115.76(2)°, Z = 4; [Bu4N]2[trans-{Re6S8Cl4(cpy)2}] (2a), orthorhombic, space group Cmca, a = 19.304(3) Å, b = 17.894(7) Å, c = 18.773(4) Å, Z = 4; [Bu4N][mer-{Re6S8Cl3(py)3}] (3), monoclinic, space group P21/n, a = 16.156(5) Å, b = 19.760(5) Å, c = 18.895(4) Å, β = 108.94(2)°, Z = 4; [Bu4N][trans-{Re6S8Cl4(py)2}] (1a'), monoclinic, space group C2/c, a = 20.524(5) Å, b = 13.794(4) Å, c = 16.399(4) Å, β = 109.72(2)°, Z = 4.