Solute–solute–solvent interactions in Cu(O2CR)2–pyridine–diluent systems; the influence of the carboxylate ligand

Abstract

Electronic spectra (350–800 nm) have been recorded for Cu(O₂CR)₂–pyridine–chlorobenzene systems [R = Et, (CH₂)₄CH₃ and partly Me] and the equilibrium concentration quotients c_b/c_m²{b = binuclear [Cu₂(O₂CR)₄(py)₂], m = mononuclear [Cu(O₂CR)₂(py)₂]} for varying pyridine concentrations have been calculated. No dependence of c_ba_py²/c_m²(a= activity) on R has been observed in contrast to similar Cu(O₂CR)₂L_n complexes where L is an α-substituted pyridine derivative. At higher a_py(>0.6) an equilibrium between two mononuclear forms [Cu(O₂CR)₂(py)₂] and [Cu(O₂CR)₂(py)₃] is postulated. The determined solubility isotherms for the system Cu(O₂CEt)₂-pyridine–chlorobenzene and for analogous acetate complexes reveal a dramatic increase in solubility accompanying the addition of a CH₂ group in the alkane chain. The activity coefficients of the bi- and mono-nuclear complexes in solution are discussed.