Spectroscopic and redox properties of (RhRuII)-Ru-III and (RuRuII)-Ru-II complexes derived from 2,2 '-bipyridine, pyrazole-3,5-bis(benzimidazole) and 1,2,4-triazole-3,5-dicarboxylic acid as bridging ligands

摘要

The heterovalent heterodinuclear complex [(bpy)(2)Ru-II(H(2)pzbzim)Rh-III(bpy)(2)](ClO4)(4)(.)3H(2)O (1) and the isovalent homodinuclear complex [(bpy)(2)Ru-II(trzdc)Ru-II(bpy)(2)](ClO4) (.) 5H(2)O (2), where H(3)pzbzim = pyrazole-3,5-bis(benzimidazole), H(3)trzdc = 1,2,4-triazole-3,5-dicarboxylic acid and bpy = 2,2'-bipyridine, have been synthesized and spectroscopically characterized. Complex I undergoes one electron oxidation at 1.20 V (versus Ag/AgCl) in acetonitrile, while for complex 2, two stepwise oxidations occur at 0.63 and 0.81 V with the comproportionation constant K-c, for the equilibrium (RuRuII)-Ru-II + (RuRuIII)-Ru-III reversible arrow 2Ru(II)Ru(III), equal to 1, 11 X 10(3) at 298 K. The acid dissociation constants of the benzimidazole moieties of complex I have been determined in acetonitrile-water (3:2) by spectrophotometric titrations. Both complexes I and 2 exhibit luminescence spectra and the quantum yields obtained for methanol-ethanol (1:4) glass (at 77 K) are phi = 3.1 X 10(-2) for I and 3.5 x 10(-2) for 2. (C) 2003 Elsevier Ltd. All rights reserved.