Synthesis and formation of dinuclear mixed-valent complexes of ruthenium and osmium bridged by 2-(2-pyrimidyl)benzimidazolate

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) have been prepared from the reaction of M(bpy) 2 Cl 2 with a deprotonated mononulcear complex, [M(bpy) 2 (bimpm)] + (M = Ru and Os). The MLCT band for the dinuclear Ru complexes, [Ru(bpy) 2 (L)Ru(bpy) 2 ] n + , is shifted to longer wavelengths in the order of L = bibenzimidazolate (bibzim) > bibzim > bpm. Furthermore, the K c o m value of a mixed-valent complex, calculated from the potential difference between the first and second electron-transfer step, for the Ru complex is larger than that for the Os analogue. The mixed-valent complexes which were generated electrochemically show the intervalence charge transfer band at 1830 nm for Ru and 1300 nm for Os, respectively. The degree of electronic coupling between two metal centers is calculated as 650 cm - 1 for Ru and 360 cm - 1 for Os, respectively. By comparing the K c o m and H a b 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.