Noriyuki Nakasuka

Complex formation of copper(II) acetate with pyridine bases in anhydrous acetic acid

Abstract A spectrophotometric ESR and NMR study was carried out to find the principle governing the interactions of copper(II) acetate with pyridine bases in acetic acid as a solvent, with special emphasis laid on the characterization of the species formed. Copper(II) acetate was found to react with 3,4-, 3,5-dimethyl, 3-chloro and non-substituted pyridines (B) to give rise to two monomeric complexes Cu(OAC)2Bj (j = 1, 2). Formation of the monomer species was confirmed quantitatively by NMR and ESR techniques. The number of species present in the solution was determined as three by the matrix rank method. Direct coordination of nitrogen atoms to the copper(II) ion was confirmed by 13C NMR spectra in the case of pyridine bases without substitution at the α-position, in contrast with the complexation of Co(II) and Ni(II) acetates. Analysis of spectral data gave the formation constant for a 1:j complex, β1j, which is not necessarily the larger for a pyridine base with the larger pKa value in water. When the ionization constant,, Kion, of a pyridine base, however, was taken into consideration as β1j0 = β1j (1 + Kion)2j, the corrected constant β1j0 proved to increase with pKa. This fact illustrates the importance of taking into account the ionization process for chemical reactions in anhydrous acetic acid as solvent.