Complexes of meso- and (±)-butane-2,3-diamine with manganese-, cobalt-, nickel-, copper-, zinc-, and lead-(II): a potentiometric, calorimetric, and spectroscopic study

Abstract

The formation constants of complexes of meso- and (±)-butane-2,3-diamine with Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Pb²⁺ have been measured potentiometrically at 25 °C and I= 0.10 mol dm^–3(K[NO₃]), and the enthalpy changes on complex formation with Ni²⁺, Cu²⁺, and Zn²⁺ have been measured calorimetrically. The results are interpreted in terms of the possible conformational differences in the chelate rings and the formation of square-planar bis complexes with Ni²⁺(particularly with the meso isomer of the ligand) and of tetrahedral bis complexes with Zn²⁺. The existence of square-planar bis complexes of Ni²⁺ has been confirmed spectroscopically, and the square-planar–octahedral equilibrium constants have been estimated.