Spectroscopic Evidence for a Unique Bonding Interaction in Oxo-Molybdenum Dithiolate Complexes: Implications for Electron Transfer
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- 作者：Frank E. Inscore ; Rebecca McNaughton ; Barry L. Westcott ; Matthew E. Helton ; Robert Jones ; Ish K. Dhawan ; John H. Enemark ; and Martin L. Kirk
- 刊名：Inorganic Chemistry
- 出版年：1999
- 出版时间：April 5, 1999
- 年：1999
- 卷：38
- 期：7
- 页码：1401 - 1410
- 全文大小：137K
- 年卷期：v.38,no.7(April 5, 1999)
- ISSN：1520-510X
文摘
Solution and solid state electronic absorption, magnetic circular dichroism, and resonance Raman spectroscopieshave been used to probe in detail the excited state electronic structure of LMoO(bdt) and LMoO(tdt) (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate; bdt = 1,2-benzenedithiolate; tdt = 3,4-toluenedithiolate). The observed energies,intensities, and MCD band patterns are found to be characteristic of LMoO(S-S) compounds, where (S-S) is adithiolate ligand which forms a five-membered chelate ring with Mo. Ab initio calculations on the 1,2-ene-dithiolate ligand fragment, -SC=CS-, show that the low-energy S 
Mo charge transfer transitions result fromone-electron promotions originating from an isolated set of four filled dithiolate orbitals that are primarily sulfurin character. Resonance Raman excitation profiles have allowed for the definitive assignment of the ene-dithiolateSin-plane Mo dxy charge transfer transition. This is a bonding-to-antibonding transition, and its intensity directlyprobes sulfur covalency contributions to the redox orbital (Mo dxy). Raman spectroscopy has identified threetotally symmetric vibrational modes at 362 cm-1 (S-Mo-S bend), 393 cm-1 (S-Mo-S stretch), and 932 cm-1(Mo
O stretch), in contrast to the large number low-frequency modes observed in the resonance Raman spectrumof Rhodobacter sphaeroides DMSO reductase. These results on LMoO(S-S) complexes are interpreted in thecontext of the mechanism of sulfite oxidase, the modulation of reduction potentials by a coordinated ene-dithiolate(dithiolene), and the orbital pathway for electron transfer regeneration of pyranopterin dithiolate Mo enzymeactive sites.
Mo charge transfer transitions result fromone-electron promotions originating from an isolated set of four filled dithiolate orbitals that are primarily sulfurin character. Resonance Raman excitation profiles have allowed for the definitive assignment of the ene-dithiolateSin-plane Mo dxy charge transfer transition. This is a bonding-to-antibonding transition, and its intensity directlyprobes sulfur covalency contributions to the redox orbital (Mo dxy). Raman spectroscopy has identified threetotally symmetric vibrational modes at 362 cm-1 (S-Mo-S bend), 393 cm-1 (S-Mo-S stretch), and 932 cm-1(MoO stretch), in contrast to the large number low-frequency modes observed in the resonance Raman spectrumof Rhodobacter sphaeroides DMSO reductase. These results on LMoO(S-S) complexes are interpreted in thecontext of the mechanism of sulfite oxidase, the modulation of reduction potentials by a coordinated ene-dithiolate(dithiolene), and the orbital pathway for electron transfer regeneration of pyranopterin dithiolate Mo enzymeactive sites.