Time-resolved infrared studies on two isomeric ruthenium(II)/rhenium(I) complexes containing a nonsymmetric quaterpyridine bridging ligand

The bridging ligand 2,2':3',2'':6'',2'''-quaterpyridine was observed to have two inequivalent metal binding sites (A and B) which perturb the metal-to-ligand charge transfer (MLCT) energy levels of the attached Re(I) or Ru(II). Time-resolved infrared difference spectra of ((bpy)2Ru(II)ABRe(I)(CO)3Cl)2+ were in agreement with a lowest lying Ru(III)-AB*- MLCT state, while spectra of ((CO)3ClRe(I)ABRu(II)(bpy)2)2+ indicated the presence of both Re(II)-AB*- and Ru(III)-AB*- MLCT excited states.