Thermodynamic and spectroscopic properties of mixed-ligand complexes of copper(II) with pyridine, 2,2′-bipyridyl, and 2,2′ : 6′,2″-terpyridyl in aqueous solution

Abstract

Thermodynamic and e.s.r. studies in aqueous solution have been carried out on the following systems: Cu–bipy–py, Cu–terpy–py, and Cu–terpy–bipy, where bipy, terpy, and py are 2,2′-bipyridyl, 2,2′ : 6′,2″-terpyridyl, and pyridine respectively. Two ternary species [Cu(bipy)(py)]²⁺ and [Cu(bipy)(py)₂]²⁺ were found in the first system, while only one species is present in the second and the third systems. The experimental data clearly indicate tetragonally distorted octahedral geometries except in [Cu(terpy)(bipy)]²⁺, for which five-co-ordination involving a square-pyramidal stereochemistry is proposed. The use of the stabilization parameters, Δ log K and log K_m, in comparison with a combined thermodynamic and spectroscopic approach, is also critically discussed.