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

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