Palladium(II) complexes of N-sulfonylamino acids. Part 3. Ternary adducts with 2,2′-bipyridine

Abstract

The equilibria involved in the formation of ternary adducts of Pd²⁺ with N-sulfonylamino acids (H₂L) and 2,2′-bipyridine were investigated through d.c. polarography, ¹H NMR and electronic spectroscopy in aqueous solution starting from strongly acidic conditions. The formation of the ternary species appears to proceed through the initial binding of the heteroaromatic base to Pd²⁺ followed, at higher pH values, by ligation of one amino acid dianion. The pK_NH value of the latter, ranging from 3.2 to 4.7 for the different amino acids, is unchanged or slightly higher compared to that observed in the formation of the [PdL₂]2^– species from the precursor [PdL] in the binary Pd²⁺–L^2– systems. A comparison is made with the corresponding ternary complexes of Cu²⁺, Cd²⁺ and Zn²⁺.