Spectroscopic and Electrochemical Evidence for Significant Electronic Coupling in Mixed-Valence Hydrogen-Bonded Adducts of Ruthenium Cyano and Ethylenediamine Complexes

Abstract

Spectroscopic and electrochemical investigations have been carried out on a collection of hydrogen-bonded mixed-valence adducts of ruthenium complexes. The electron donors (H-bond acceptors) are Ru(II) cyano species and the electron acceptors (H-bond donors) are Ru(III) ethylenediamine species, and NIR spectroscopic transitions in the adducts are assigned to intervalence transfer through the hydrogen bonds holding the adducts together (HBIT). Spectroscopic studies using Job's method indicate that the adducts are 2:1 ternary aggregates of formulations such as [((trpy)(bpy)RuII(CN))2,(en)2RuIII(bpy)]5+ and [((bpy)2RuII(CN)2)2,(en)2RuIII(bpy)]3+. Voltammetric investigations show substantial repulsion of the redox waves of the parent complexes in mixtures containing both donor and acceptor. Comparison with known electronic coupling data for mixed-valence ruthenium dimers covalently bound through dithiaspiroalkane bridging ligands indicates that the electronic coupling through H bonds of this type is 65−75% as strong as through σ-covalent bonds.

Molecular Recognition and Reactivity of Ruthenium(II) Bipyridine Barbituric Acid Guests in the Presence of Complementary Hosts: Ruthenium(II) Promoted Enolization of Barbituric Acids in Guest−Host Complexes

“…These weak interactions can be major contributors to the binding of drugs to proteins and DNA targets and can form the basis for developing sensors to monitor the concentration of specific ions or molecules. [8][9][10][11][12][13][14][15][16][17][18] We have demonstrated the presence of efficient long-range electron-transfer pathways in conformationally rigid peptides that are covalently linked to metal ion donors and acceptors. 7 Several model systems describing charge transfer processes that occur across H-bonding interfaces have been reported.…”

Efficient electron transfer across hydrogen bond interfaces by proton-coupled and -uncoupled pathways

“…The study led to a remarkable conclusion that the extent of EC through HBs is greater than via C–C σ bonds, but lower than across a π-conjugated bridge. However, significant discrepancies have arisen from subsequent experimental 5 and theoretical 6 studies, and thus the efficiency of EC mediation by an HB interface, relative to covalent bonds, remains controversial.…”

Electrocatalytic oxidation of alcohols by a [Ru(tpy)(phen)(OH2)]2+-modified electrode

“…The electrolysis was performed with the nucleophilic alcohol derivative instead of the carboxylate precursor without recycling to maintain highest concentration possible of the reactive alcohol at the electrode surface. The grafted phenanthroline was allowed to react with Ru(Cl 3 )(tpy) [29] to form the immobilized [Ru(tpy)-(phen)Cl] + complex. Further reaction with CF 3 SO 3 H followed by addition of water led to the immobilized [Ru-(tpy)(phen)(OH 2 )] 2+ complex.…”