Document Detail

Oxidation states and CO ligand exchange kinetics in a self-assembled monolayer of a triruthenium cluster studied by in situ infrared spectroscopy.
MedLine Citation:
PMID:  15977278     Owner:  NLM     Status:  PubMed-not-MEDLINE    
Oxidation states and CO ligand exchange kinetics in a self-assembled monolayer (SAM) of an oxo-centered triruthenium cluster [Ru(3)(mu3-O)(mu-CH3COO)6(CO)(L1)(L2)] (L1 = [(NC5H4)CH2NHC(O)(CH2)10S-]2, L2 = 4-methylpyridine) have been extensively investigated on the surface of a gold electrode in aqueous and nonaqueous solutions. The SAM exhibits three consecutive one-electron transfers and four oxidation states, which have been characterized by electrochemistry, in situ infrared spectroscopy, and in situ sum frequency generation (SFG) vibrational spectroscopy measurements. The original electron-localized state of the Ru cluster center was changed to electron delocalization states by oxidation or reduction of the central Ru ions. These changes are revealed by the IR absorptions of the CO ligand and the bridging acetate ligands of the triruthenium cluster in the SAM. The IR absorptions of the two kinds of ligands are strongly dependent on the oxidation state of the Ru cluster center. One-electron oxidation of the central Ru ion in the SAM triggers a CO ligand liberation process. Solvent molecules may then occupy the CO site to result in a CO-free SAM. One-electron reduction of this CO-free SAM in a CO-saturated solution leads to re-coordination of the CO ligand into the SAM. Both processes can be precisely controlled by tuning the electrode potential. The kinetics of the CO exchange cycle in the SAM, including liberation and coordination, has been investigated by in situ IR and SFG measurements for the first time. The CO exchange cycle is significantly dependent on the temperature. The reaction rate greatly decreases with decreasing solution temperature, which is an important factor in the CO ligand exchange process. The activation energies of both CO liberation and coordination have been evaluated from the reaction rate constants obtained at various temperatures.
Wei Zhou; Shen Ye; Masaaki Abe; Takuma Nishida; Kohei Uosaki; Masatoshi Osawa; Yoichi Sasaki
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Chemistry (Weinheim an der Bergstrasse, Germany)     Volume:  11     ISSN:  0947-6539     ISO Abbreviation:  Chemistry     Publication Date:  2005 Aug 
Date Detail:
Created Date:  2005-08-16     Completed Date:  2006-06-28     Revised Date:  2009-08-04    
Medline Journal Info:
Nlm Unique ID:  9513783     Medline TA:  Chemistry     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  5040-54     Citation Subset:  -    
Catalysis Research Center, Hokkaido University, Sapporo 001-0021, Japan.
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