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)Ru II (CN)) 2,(en) 2 Ru III (bpy)] 5+ and [((bpy) 2 Ru II (CN) 2 ) 2,(en) 2 Ru III (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.