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

Abstract

Solvent effects on the electronic structure and NMR spectra of the[Ru(terpy)(CN)3] complex(terpy = 2,2′,6′,2″-terpyridine) have beeninvestigated and interpreted using quantum mechanical semiempirical methods.A systematic splitting of the electronic bands in the visible is observed, in addition to theirbathochromic shifts depending on the acceptor number of the solvent. The solvent-inducedsplittings are rationalized in terms of the involvement of several charge—transfertransitions exhibiting distinct participation of the ruthenium (II), terpy, and CN−orbitals. Direct evidence of solvent interaction at the cyanide ligands is observedin the [13C]NMR spectra. The most enhanced solvent effects are at the middle13C-4′ and 1H-4′ atoms of terpy, in complete agreement with the theoreticalcalculations. In D2O, stacking interactions involving the terpy ligands are detectedfrom the [1H]NMR spectra, leading to a bimolecular association constant of90 mol−1-dm3. In acetone—D2O mixed solvents, the spectroscopic changes areindicative of preferential solvation departing from the ideal linear behavior.