Differential Ion-pairing and Temperature Effects on Intervalence Charge Transfer (IVCT) in a Series of Dinuclear Ruthenium Complexes

Thermochromism and anion-dependence studies on the intervalence charge transfer (IVCT) properties of the diastereoisomers of [{Ru(bpy)2}2(m-BL)] 51 {BL 5 dpb0, dpq0, and dpb: dpb0 5 dipyrido(2,3-a;30,20-c)benzophenazine; dpq0 5 dipyrido(2,3-a;30,20-c)phenazine; dpb 5 2,3bis(2-pyridyl)-1,4-benzoquinoxaline} are reported. IVCT thermochromism studies revealed that the level of delocalisation may differ between the diastereoisomers for a system, and a slight temperature dependence in meso-[{Ru(bpy)2}2(m-dpb)] 51 which was dependent on the identity of the counter-anion {PF6 or B(C6F5)4 } Anion effects on the IVCT properties of the diastereoisomeric forms of the three complexes were observed to be somewhat unpredictable. X-ray crystal structure determinations on meso[{Ru(bpy)2}2(m-dpb)] 41 (as the PF6 and [ZnCl4] 2salts), meso-[{Ru(bpy)2}2(m-dpb 0)]41 (PF6 salt) and meso[{Ru(bpy)2}2(m-dpq 0)]([ZnCl4] 2salt) revealed considerable distortion in the bridging ligand, particularly in the dpb-bridged species where the distortion was also dependent on the anion.