Thermodynamic stabilities of cobalt(II), nickel(II), and copper(II) complexes of O2N2-donor macrocyclic ligands

Abstract

Co-ordination compounds formed between two O₂N₂-donor macrocyclic ligands, one 14-membered (L¹) and one 16-membered (L²), and H⁺, Co²⁺, Ni²⁺, and Cu²⁺ in 65% ethanol have been studied potentiometrically at 25.0 °C and I= 0.10 mol dm^–3[N(CH₃)₄NO₃]. For each of these ligands the formation constants of the bivalent metal ions follow the Irving–Williams order of stability. For each of the bivalent metal ions the stabilities follow the macrocyclic ring-size sequence 16 < 14. It can be deduced that an alternating sequence of five- and six-membered chelate rings increases complex stability.