Trends in metal-ligand orbital mixing in generic series of ruthenium N-donor ligand complexes-effect on electronic spectra and redox properties

Generic series of complexes [Ru(bpy)(3-n)(LL)(n)](2+) (bpy = 2,2'-bipyridine), where LL is a diimine ligand including specifically 2,2'-bipyrazine (bpz), 2,2'-azobipyridine (abpy), and o-benzoquinonediimine (bqdi), are studied with respect to their electrochemistry, optical spectroscopy and electronic structure as elucidated using Zerner's INDO/S method. Characteristics of their electrochemistry and optical spectroscopy are explained in terms of mixing between ruthenium d orbitals and diimine ligand pi and pi* orbitals, increasing in importance from bpy to bpz to abpy to bqdi. In this last case, these species have characteristics not unlike fully delocalized organic molecules. (C) 1998 Elsevier Science S.A. All rights reserved.