Solvent-Induced Electron Transfer and Electronic Delocalization in Mixed-Valence Complexes. Spectral Properties

Abstract

Spectra of the mixed-valence complexes [(bpy)2ClOs(L)Ru(NH3)5]4+ (L = 4,4‘-bipyridine, pyrazine; bpy = 2,2‘-bipyridine) are highly solvent dependent. They provide oxidation state specific spectral markers which show that oxidation states for L = 4,4‘-bpy are OsIII−RuII in solvents of donor number (DN) 15) they are OsII−RuIII. The isomers coexist at donor numbers 14−15 and the distribution between them tuned in mixtures of acetonitrile and propylene carbonate demonstrating that intramolecular electron transfer can be induced by varying the solvent. Both OsIII−RuII and OsII−RuIII display broad, solvent-dependent intervalence transfer (IT) bands in the near infrared (NIR). There are two isomers of [(bpy)2ClOs(pz)Ru(NH3)5]4+ as well. In one, which is dominant in solvents of DN < 22, the oxidation states are [(bpy)2ClOsIII(pz)RuII(NH3)5]4+. This is shown by the appearance of dπ → dπ marker bands for OsIII (at 4200 and 5800 cm-1 in CD3CN), ν(bpy) OsIII bands in the m...