Ternary Cu2+ Complexes: Stability, Structure, and Reactivity

The driving forces leading to the formation of ternary Cu2+ complexes are outlined; they are (i) statistical reasons, (ii) neutralization of charge in the mixed‐ligand complexes, (iii) steric factors (bulky groups, ring size of chelates), and (iv) formation of π bonds. The last point is important for achieving a large stability, as well as for the observation of discriminating qualities. An additional stability increase may possibly be achieved through a direct interaction between the two ligands bound to the same metal ion, i.e. Schiff base formation, hydrogen bonding or a charge‐transfer relation. The latter leads to distinct structures, i.e. metal ion‐bridged charge‐transfer complexes. The relation between stability and structure on the reactivity of mixed‐ligand complexes is emphasized. The relevance of the results for mixed‐ligand complexes containing metal ions other than Cu2+ is briefly outlined.