Emission and Metal- and Ligand-Centered-Redox Characteristics of the Hexarhenium(III) Clusters trans- and cis-[Re6(
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- 作者：Takashi Yoshimura ; Keisuke Umakoshi ; Yoichi Sasaki ; Shoji Ishizaka ; Haeng-Boo Kim ; and Noboru Kitamura
- 刊名：Inorganic Chemistry
- 出版年：2000
- 出版时间：April 17, 2000
- 年：2000
- 卷：39
- 期：8
- 页码：1765 - 1772
- 全文大小：122K
- 年卷期：v.39,no.8(April 17, 2000)
- ISSN：1520-510X
文摘
Preparations of a series of face-capped octahedral hexarhenium(III) clusters having two N-heterocyclic ligands,[Bu4N]2[trans-{Re6(
3-S)8Cl4(L)2}] (Bu4N+ = tetra-n-butylammonium cation; L = pyrazine (1a), 4,4'-bipyridine(3a), 4-methylpyridine (5a), 4-(dimethylamino)pyridine (6a)) and their cis analogues (1b, 3b, 5b, and 6b,respectively), and their electrochemical and photophysical properties have been reported. An X-ray crystal structuredetermination has been carried out for 1a to confirm the trans configuration (C40H80N6S8Cl4Re6, orthorhombic,space group Cmca (No. 64), a = 19.560(5) Å, b = 19.494(4) Å, c = 18.592(4) Å, 
= 115.76(2)
, Z = 4). Theredox potential of the reversible ReIII6/ReIII5ReIV process of these complexes and previously reported [Bu4N]2[trans- and cis-{Re6(3-S)8Cl4(4-cyanopyridine)2}] (2a and 2b, respectively) and [Bu4N]2[trans- and cis-{Re6(3-S)8Cl4(pyridine)2}] (4a and 4b, respectively) in acetonitrile depends linearly on the pKa of the N-heterocyclicligands, with the potentials being more negative with basic ligands. The ligand-centered-redox waves for 1a, 1b,2a, and 2b were observed as split waves (
E1/2 = 90-140 mV), the extent of the splitting being larger for thecis isomer and largest for the pyrazine complexes. Electronic interaction between the two ligands through the[Re6(3-S)8]2+ core has been suggested. The second ligand-reduction wave was also observed for 3a and 3b, thepotential being shifted positively to coalesce with the first reduction wave on addition of the weak proton donorimidazole. This is accounted for by the proton-coupled redox reaction at the free pyridyl site of the 4,4'-bipyridineligands. All of the complexes show luminescence in acetonitrile at room temperature. While the complexes ofpyridine and 4-methylpyridine show photophysical characteristics (
em 740-750 nm, 
em 0.031-0.057, 
em 4.2-6.2 s) similar to those (770 nm, 0.039, and 6.3 s, respectively) of [Re6(3-S)8Cl6]4-, emissions of other complexesare significantly weak with em, em, and em values in the ranges 763-785 nm, 0.0010-0.0017, and 0.013-0.029 s, respectively. Suggestions are given for the excited states localized on the cluster core and the ligand 
*orbitals.
3-S)8Cl4(L)2}] (Bu4N+ = tetra-n-butylammonium cation; L = pyrazine (1a), 4,4'-bipyridine(3a), 4-methylpyridine (5a), 4-(dimethylamino)pyridine (6a)) and their cis analogues (1b, 3b, 5b, and 6b,respectively), and their electrochemical and photophysical properties have been reported. An X-ray crystal structuredetermination has been carried out for 1a to confirm the trans configuration (C40H80N6S8Cl4Re6, orthorhombic,space group Cmca (No. 64), a = 19.560(5) Å, b = 19.494(4) Å, c = 18.592(4) Å, = 115.76(2), Z = 4). Theredox potential of the reversible ReIII6/ReIII5ReIV process of these complexes and previously reported [Bu4N]2[trans- and cis-{Re6(3-S)8Cl4(4-cyanopyridine)2}] (2a and 2b, respectively) and [Bu4N]2[trans- and cis-{Re6(3-S)8Cl4(pyridine)2}] (4a and 4b, respectively) in acetonitrile depends linearly on the pKa of the N-heterocyclicligands, with the potentials being more negative with basic ligands. The ligand-centered-redox waves for 1a, 1b,2a, and 2b were observed as split waves (E1/2 = 90-140 mV), the extent of the splitting being larger for thecis isomer and largest for the pyrazine complexes. Electronic interaction between the two ligands through the[Re6(3-S)8]2+ core has been suggested. The second ligand-reduction wave was also observed for 3a and 3b, thepotential being shifted positively to coalesce with the first reduction wave on addition of the weak proton donorimidazole. This is accounted for by the proton-coupled redox reaction at the free pyridyl site of the 4,4'-bipyridineligands. All of the complexes show luminescence in acetonitrile at room temperature. While the complexes ofpyridine and 4-methylpyridine show photophysical characteristics (em 740-750 nm, em 0.031-0.057, em 4.2-6.2 s) similar to those (770 nm, 0.039, and 6.3 s, respectively) of [Re6(3-S)8Cl6]4-, emissions of other complexesare significantly weak with em, em, and em values in the ranges 763-785 nm, 0.0010-0.0017, and 0.013-0.029 s, respectively. Suggestions are given for the excited states localized on the cluster core and the ligand *orbitals.