THE ELECTRONIC-STRUCTURE OF SOME RUTHENIUM(II) COMPLEXES RELATED TO [RU(BIPY)3]2+ - AN INVESTIGATION OF THE STEPWISE REPLACEMENT OF N,N-DONORS BY C,N-DONORS

An analysis of the electronic structures of members of the series of complexes [Ru(bipy)3-n(ppy)n](2-n)+ (bipy = 2,2′-bipyridine and Hppy = 2-phenylpyridine) is presented. The cyclometallated complexes (i.e. those in which one or more [ppy]- replace bipy ligands) exhibit a distinct separation of RuC and RuN σ-bonding character, and in cis-[Ru(bipy)(ppy)2], further separation of bonding character occurs to give MO's which possess either RuC, RuN[ppy], or RuNbipy components. Comparisons of the cis- and trans-isomers of [Ru(bipy)(ppy)2] and of the fac- and mer-isomers of [Ru(ppy)3]- suggest that the observed experimental preference for cis- over trans- and fac- over mer-structures may be due to the enhanced σ-donating ability of the carbon atom when it resides trans to a nitrogen rather than carbon donor. © 1990.