Preparation, Purification, and Characterization of Binuclear Ruthenium(II) Complexes: Bridging Ligands Based on Diazafluorenes
Wang, Youxiang Perez, Willie J. Zheng, Greg Y. Rillema, D. Paul Huber, Connie L.
Wang, Youxiang
Perez, Willie J.
Zheng, Greg Y.
Rillema, D. Paul
Huber, Connie L.
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1998-05-04
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Article
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Citation
Inorganic chemistry. 1998 May 4; 37(9): 2227-2234.
Abstract
A series of bimetallic complexes of ruthenium(II) bridged by heterocyclic ligands formed by the condensation of 4,5-diazafluoren-9-one with various diamines, hydrazine, 1,4-phenylenediamine, benzidine, and 4,4'-methylenedianiline, results in metal centers separated by various distances. The complexes give rise to metal-to-ligand charge-transfer absorptions in the 450 nm region of the visible spectrum and intraligand pi --> pi transitions in the 300 nm region of the ultraviolet spectrum. The ruthenium(II) centers are oxidized in two closely spaced one-electron processes at potentials more positive than that for Ru(bpy)(3)(2+). The bridging ligands are reduced by two closely spaced one-electron processes at more positive potentials than that for reduction of the coordinated bipyridine ligands ( approximately -1.30 V), although the diazafluorene=N-N=diazafluorene bridging ligand is reduced reversibly in two single-electron steps at E(1/2) values of -0.29 and -0.52 V. After purification by eluting the "pure" complexes over a silica gel column with various concentrations of 0.10 M NH(4)PF(6) in methanol, emission occurs only in a glassy matrix at 77 K and at low temperatures in solution. The emission lifetimes at 77 K in a 4:1 ethanol:methanol glass are 5 +/- 1 &mgr;s. A variable-temperature emission lifetime study reveals the presence of a low-lying state with DeltaE = approximately 1500 cm(-)(1), and extrapolation to room temperature indicates the emission lifetimes are in the subnanosecond range.
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Publisher
American Chemical Society
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Inorganic chemistry
Inorg Chem
Inorg Chem
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1520-510X
0020-1669
0020-1669