Electronic structure and spectral, of ruthenium diimine complexes by density functional theory and INDO/S. Comparison of the two methods

Density functional theory calculations have been carried out on the series [Ru(bqdi)(n)(bpy)(3-n)](2+) (bpy = 2,2'-bipyridine, bqdi = o-benzoquinonedi imine) to explore the extent of coupling between metal 4d and ligand pi and pi* orbitals. Time-dependent density-functional response theory (TD-DFRT) has been used to predict the complex electronic spectra which are compared with their experimental data. The main thrust of the paper is a comparison of these calculations with those carried out using Zerner's frequently used INDO/S method. Different procedures for the electron population analysis o f molecular orbitals are described and discussed. The agreement in terms of orbital energies, orbital mixing and electronic spectra is remarkably good . This confirms that for these species, and probably for all non-solvatochr omic species in general, INDO/S is a good model reproducing very well the r esults of the computationally much more demanding, but also more reliable T D-DFRT calculations. (C) 2001 Elsevier Science B.V. All rights reserved.