Synthesis and formation of dinuclear mixed-valent complexes of ruthenium and osmium bridged by 2-(2-pyrimidyl)benzimidazolate
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Indian Journal of Chemistry, Section A: Inorganic, Bio-inorganic, Physical, Theoretical & Analytical Chemistry 42A (9): 2290--2299 (2003)

Mononuclear Ru/Os complexes, M(bpy)2(Hbimpm)2+, where Hbimpm = 2-(2-pyrimidyl)benzimidazole, behaves as a monobasic acid to form the conjugate base, M(bpy)2(bimpm)2+ where bimpm = 2-(2-pyrimidyl)benzimidazolate. Novel dinuclear Ru/Os complexes bridged by 2-(2-pyrimidyl)benzimidazolate (bimpm) were prepd. from the reaction of M(bpy)2Cl2 with a deprotonated mononuclear complex, M(bpy)2(bimpm)+(M = Ru and Os). The MLCT band for the dinuclear Ru complexes, Ru(bpy)2(L)Ru(bpy)2n+, is shifted to longer wavelengths in the order of L = bibenzimidazolate (bibzim) \textgreater bibzim \textgreater bpm. Also, the Kcom value of a mixed-valent complex, calcd. from the p.d. between the 1st and 2nd electron-transfer step, for the Ru complex is larger than that for the Os analog. The mixed-valent complexes which were generated electrochem. show the intervalence charge transfer band at 1830 nm for Ru and 1300 nm for Os, resp. The degree of electronic coupling between two metal centers is calcd. as 650 cm-1 for Ru and 360 cm-1 for Os, resp. By comparing the Kcom and Hab values with those of the analogous bridged ligand system such as bpm and bibzim, a synergetic contribution of both electron exchange and hole exchange mechanisms is operative for metal-metal communications in the present bimpm -bridged mixed-valent complexes. on SciFinder(R)
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