FACTORS AFFECTING STABILITIES OF CHELATE, MACROCYCLIC AND MACROBICYCLIC COMPLEXES IN SOLUTION

The factors which contribute to the chelate, macrocyclic and cryptate effects are described. These include the dilution effect, translational entropy, intrinsic basicities of donor atoms, coulombic attractions and repulsions of charged ions and groups, and covalent character of the coordinate bonds. The reduction in hydration/solvation energies and the related coulombic repulsions of the donor atoms of multidentate ligands are related to preorganization of the ligands for complexation of metal ions. A not insignificant part of the chelate and macrocyclic effects is due to increase in the basicities of the donor atoms that occurs on ring formation, as well as to reduction of the steric repulsions of alkyl groups. The effects of ring size on stabilities are described. These factors are illustrated with stabilities of chelates, macrocyclic complexes and cryptates taken from the literature.