Electron Transfer on the Infrared Vibrational Time Scale in the Mixed Valence State of 1,4-Pyrazine- and 4,4'-Bipyridine-Bridged Ruthenium Cluster Complexes
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- 作者：Tasuku Ito ; Tomohiko Hamaguchi ; Haruko Nagino ; Tadashi Yamaguchi ; Hiroaki Kido ; Igor S. Zavarine ; Todd Richmond ; John Washington ; and Clifford P. Kubiak
- 刊名：Journal of the American Chemical Society
- 出版年：1999
- 出版时间：May 19, 1999
- 年：1999
- 卷：121
- 期：19
- 页码：4625 - 4632
- 全文大小：143K
- 年卷期：v.121,no.19(May 19, 1999)
- ISSN：1520-5126
文摘
Intramolecular electron transfers within the mixed valence states of the ligand bridged hexarutheniumclusters Ru3(
ntities/mgr.gif">3-O)(ntities/mgr.gif">-CH3CO2)6(CO)(L)(ntities/mgr.gif">-L')Ru3(ntities/mgr.gif">3-O)(ntities/mgr.gif">-CH3CO2)6(CO)(L) (L' = 1,4-pyrazine; L = 4-dimethylaminopyridine (1), pyridine (2), 4-cyanopyridine (3), or L' = 4,4'-bipyridine; L = 4-dimethylaminopyridine (4), pyridine (5), 4-cyanopyridine (6)) were examined. Two discrete and reversible single electronreductions are evident by cyclic voltammetry in the redox chemistry of 1-5, and the intercluster charge-transfer complexes are well-defined. The splitting of the reduction waves, 
E, is related to the electroniccoupling HAB between the triruthenium clusters, and varies from 80 mV for 5 to 440 mV for 1. In the case of6, the splitting of the reduction waves, E, is <50 mV and the intercluster charge-transfer complex is notdefined. The mixed valence states of 1-3 also exhibit intervalence charge transfer (ICT) bands in the region12 100 (1) to 10 800 cm-1 (3) which provide spectroscopic estimates of HAB in the range 2180 (1) to 1310cm-1 (3). The magnitude of the electronic coupling HAB is found to strongly influence the IR spectra of thesingly reduced (-1) mixed valence states of 1-6 in the 
nu.gif" BORDER=0 >(CO) region. In the case of relatively weak electroniccoupling (4-6), two nu.gif" BORDER=0 >(CO) bands are clearly resolved. In the cases of strong electronic coupling (1-3), thesebands broaden to a single nu.gif" BORDER=0 >(CO) absorption band. These data allow the rate constants, ke, for electron transferin the mixed valence states of 1, 2, and 3 to be estimated by simulating dynamical effects (Bloch-type equations)on nu.gif" BORDER=0 >(CO) absorption band shape at 9 × 1011, 5 × 1011, and ca. 1 × 1011 s-1, respectively. The less stronglycoupled 4,4'-bipyridine-bridged complexes 4-6 exhibit IR line shapes in the -1 mixed valence states that arenot as strongly affected by electron-transfer dynamics. The rate constant for the -1 mixed valence state of 4is close to the lower limit that can be estimated by this approach, between 1 × 1010 and 1 × 1011 s-1.
ntities/mgr.gif">3-O)(ntities/mgr.gif">-CH3CO2)6(CO)(L)(ntities/mgr.gif">-L')Ru3(ntities/mgr.gif">3-O)(ntities/mgr.gif">-CH3CO2)6(CO)(L) (L' = 1,4-pyrazine; L = 4-dimethylaminopyridine (1), pyridine (2), 4-cyanopyridine (3), or L' = 4,4'-bipyridine; L = 4-dimethylaminopyridine (4), pyridine (5), 4-cyanopyridine (6)) were examined. Two discrete and reversible single electronreductions are evident by cyclic voltammetry in the redox chemistry of 1-5, and the intercluster charge-transfer complexes are well-defined. The splitting of the reduction waves, E, is related to the electroniccoupling HAB between the triruthenium clusters, and varies from 80 mV for 5 to 440 mV for 1. In the case of6, the splitting of the reduction waves, E, is <50 mV and the intercluster charge-transfer complex is notdefined. The mixed valence states of 1-3 also exhibit intervalence charge transfer (ICT) bands in the region12 100 (1) to 10 800 cm-1 (3) which provide spectroscopic estimates of HAB in the range 2180 (1) to 1310cm-1 (3). The magnitude of the electronic coupling HAB is found to strongly influence the IR spectra of thesingly reduced (-1) mixed valence states of 1-6 in the nu.gif" BORDER=0 >(CO) region. In the case of relatively weak electroniccoupling (4-6), two nu.gif" BORDER=0 >(CO) bands are clearly resolved. In the cases of strong electronic coupling (1-3), thesebands broaden to a single nu.gif" BORDER=0 >(CO) absorption band. These data allow the rate constants, ke, for electron transferin the mixed valence states of 1, 2, and 3 to be estimated by simulating dynamical effects (Bloch-type equations)on nu.gif" BORDER=0 >(CO) absorption band shape at 9 × 1011, 5 × 1011, and ca. 1 × 1011 s-1, respectively. The less stronglycoupled 4,4'-bipyridine-bridged complexes 4-6 exhibit IR line shapes in the -1 mixed valence states that arenot as strongly affected by electron-transfer dynamics. The rate constant for the -1 mixed valence state of 4is close to the lower limit that can be estimated by this approach, between 1 × 1010 and 1 × 1011 s-1.