Thermodynamic and spectroscopic properties of mixed complexes in aqueous solution. Copper(II) complexes of 2,2′-bipyridyl and dicarboxylic acids

Abstract

The heats of formation of mixed copper(II) complexes [Cu(bipy)L](bipy = 2,2′-bipyridyl; L = malonate, succinate maleate, or phthalate) have been determined calorimetrically at 25 °C in 0.1 mol dm^–3 Na[ClO₄], and have been used to calculate the relative enthalpies. Consideration of thermodynamic and e.s.r. and electronic spectroscopic data shows that all the mixed complexes have the same structure because of the requirements of the bipy ligand, the only exception being [Cu(bipy)(succ)] for which a square-pyramidal structure has been proposed. This difference in behaviour between the succinate anion and the other acid anions has also been found to occur for the simple complexes [CuL] as shown by a plot of their partial molar entropies against those of the corresponding ligands.