Diastereoisomers as probes for solvent reorganizational effects on IVCT in dinuclear ruthenium complexes

IVCT solvatochromism studies on the meso and rac diastereoisomers of [{Ru(bpy)(2)}(2)(mu-bpm)](5+) (bpy = 2,2'-bipyridine; bpm = 2,2'-bipyrimidine) in a homologous series of nitrile solvents revealed that stereochemically directed specific solvent effects in the first solvation shell dominated the outer sphere contribution to the reorganizational energy for intramolecular electron transfer. Further, solvent proportion experiments in acetonitrile/propionitrile mixtures indicated that the magnitude and direction of the specific effect was dependent on the relative abilities of discrete solvent molecules to penetrate the clefts between the planes of the terminal polypyridyl ligands. In particular, the specific effects were dependent on the dimensionality of the clefts, and the number, size, orientation and location of the solvent dipoles within the interior and exterior clefts. IVCT solvatochromism studies on the diastereoisomeric forms of [{Ru(bpy)(2)}(2)(mu-dbneil)](5+) and [{Ru(pp)(2)}(2)(mu-bpm)](5+) {dbneil = dibenzoeilatin; pp = substituted derivatives of 2,2'-bipyridine and 1,10-phenanthroline} revealed that the subtle and systematic changes in the nature of the clefts by the variation of the bridging ligand, and the judicious positioning of substituents on the terminal ligands, profoundly influenced the magnitude of the reorganizational energy contribution to the electron transfer barrier. (c) 2005 Elsevier B.V. All rights reserved.