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Synthesis, Structures, and Redox Properties of Octa(&mgr;(3)-sulfido)hexarhenium(III) Complexes Having Terminal Pyridine
Takashi Yoshimura1, Keisuke Umakoshi, Yoichi Sasaki
1Graduate School of Science, Division of Chemistry, Hokkaido University, Kita-ku, Sapporo 060-0810, Japan, and Department of Inorganic and Structural Chemistry, The University of Newcastle, Newcastle-upon-Tyne NE1 7RU, U.K.
Abstract:
A series of &mgr;(3)-sulfido Re-Re bonded octahedral hexarhenium(III) clusters having mixed chloride-pyridine (py) or -4-cyanopyridine (cpy) terminal ligands, [Bu(4)N](2)[trans-{Re(6)S(8)Cl(4)(py)(2)}] (Bu(4)N(+) = tetra-n-butylammonium cation) (1a), [Bu(4)N](2)[cis-{Re(6)S(8)Cl(4)(py)(2)}] (1b), [Bu(4)N](2)[trans-{Re(6)S(8)Cl(4)(cpy)(2)}] (2a), [Bu(4)N](2)[cis-{Re(6)S(8)Cl(4)(cpy)(2)}] (2b), and [Bu(4)N][mer-{Re(6)S(8)Cl(3)(py)(3)}] (3), and their one-electron-oxidized Re(III)(5)Re(IV) species, [Bu(4)N][trans-{Re(6)S(8)Cl(4)(py)(2)}] (1a'), [Bu(4)N][trans-{Re(6)S(8)Cl(4)(cpy)(2)}] (2a'), and mer-[Re(6)S(8)Cl(3)(py)(3)] (3'), have been prepared and characterized by several physical methods. X-ray crystallographic studies for 1a, 2a, and 3 showed that the Re(6)S(8) 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 (Re(III)(6)/Re(III)(5)Re(IV)) 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 (1)H NMR line-broadening method is 1.2 x 10(9) M(-)(1) s(-)(1) (298.2 K) with DeltaH() = 30.2 +/- 2.1 kJ mol(-)(1) and DeltaS() = 30 +/- 8 J mol(-)(1) K(-)(1). It has been suggested that the previously reported protonated species [Re(6)S(7)(SH)Cl(6)](3)(-) would actually be a one-electron-oxidized [Re(6)S(8)Cl(6)](3)(-). Crystal data: [Bu(4)N](2)[trans-{Re(6)S(8)Cl(4)(py)(2)}] (1a), monoclinic, space group C2/c, a = 24.693(8) Å, b = 19.494(4) Å, c = 18.592(4) Å, beta = 115.76(2) degrees, Z = 4; [Bu(4)N](2)[trans-{Re(6)S(8)Cl(4)(cpy)(2)}] (2a), orthorhombic, space group Cmca, a = 19.304(3) Å, b = 17.894(7) Å, c = 18.773(4) Å, Z = 4; [Bu(4)N][mer-{Re(6)S(8)Cl(3)(py)(3)}] (3), monoclinic, space group P2(1)/n, a = 16.156(5) Å, b = 19.760(5) Å, c = 18.895(4) Å, beta = 108.94(2) degrees, Z = 4; [Bu(4)N][trans-{Re(6)S(8)Cl(4)(py)(2)}] (1a'), monoclinic, space group C2/c, a = 20.524(5) Å, b = 13.794(4) Å, c = 16.399(4) Å, beta = 109.72(2) degrees, Z = 4.