Tertiary-amine ligands are known to be poorer er donor ligands than the corresponding primary- or secondary-amine ligands. They are known to shift the redox potentials of given couples to the anodic direction relative to the corresponding complexes with primary- or secondary-amine ligands. A review of data in the literature and of recent results on nickel complexes with tetra-azamacrocyclic ligands and copper complexes with open chain polyamine ligands suggests that the major source for these effects is the poorer solvation of the complexes with the tertiary-amine complexes due to the lack of hydrogen bonding between the complexes and the solvent, or the counter ions. Thus the stabilisation of low valent transition metal complexes by tertiary-amine ligands is due to thermodynamic reasons. On the other hand, tertiary-aminemacrocyclic ligands stabilise high valent complexes because the route to the formation of imine groups is kinetically inhibited in these complexes.
Bibliographical noteFunding Information:
This study was supported by a grant from the Israel Academy of Science and Humanities and by a grant from the Budgeting and Planning Committee of the Council of Higher Education and the Israel Atomic Energy Com- mission. D. M. wishes to express his thanks to Mrs. kene Evens for her ongoing interest and support.