Rigid rodlike dinuclear Ru/Os complexes of a novel bridging ligand. Intercomponent energy and electron-transfer processes

The PF6- salts of the dinuclear complexes [(bpy)2Ru(PAP)Ru(bpy)2]4+ (RuIIPAPRuII), [(bpy)2Os(PAP)Os-(bpy)2]4+ (OsIIPAPOsII), and [(bpy)2Ru(PAP)Os(bpy)2]4+ (RuIIPAPOsII) have been prepared, where bpy = 2,2′-bipyridine and PAP is a rodlike bridging ligand made of an adamantane-based spacer collinear with the coordination axis of two 1,10-phenanthroline units. In the prepared complexes, the metal - metal distance is 2.1 nm. In the RuIIPAPOsII compound, photoinduced energy transfer from the RuII-based to the OsII-based unit takes place with rate constant 5.2 × 107 s-1 at room temperature and 2.4 × 107 s-1 at 77 K. In the mixed-valence RuIIPAPOsIII compound, the luminescent excited state of the RuII-based unit is quenched via electron transfer by the OsIII-based unit with rate constant 7.2 × 106 s-1. The rate constant for the backelectron-transfer reaction is 8.3 × 103 s-1.