Molecular association and solvent effects in the electronic and NMR spectra of the tricyanoterpyridineruthenate(II) complex

Solvent effects on the electronic structure and NMR spectra of the [Ru(terp y)(CN)(3)](-) complex (terpy = 2,2':6',2"-terpyridine) have been investigat ed and interpreted using quantum mechanical semiempirical methods. A system atic splitting of the electronic bands in the visible is observed, in addit ion to their bathochromic shifts depending on the acceptor number of the so lvent. The solvent-induced splittings are rationalized in terms of the invo lvement of several charge-transfer transitions exhibiting distinct particip ation of the ruthenium (II), terpy, and CN- orbitals. Direct evidence of so lvent interaction at the cyanide ligands is observed in the [C-13]NMR spect ra. The most enhanced solvent effects are at the middle C-13-4' and H-1-4' atoms of terpy, in complete agreement with the theoretical calculations. In D2O, stacking interactions involving the terpy ligands are detected from t he [H-1]NMR spectra, leading to a bimolecular association constant of 90 mo l(-1)-dm(3). In acetone-D2O mixed solvents, the spectroscopic changes are i ndicative of preferential solvation departing from the ideal linear behavio r.