Electronic structure and redox properties of macrocyclic complexes [M(TAAB)]n+ (M = Ni,Cu)

The SCF-LCAO-MO method in the CNDO approximation has been used in calculating the electronic structure of complexes of nickel and copper with the macrocyclic ligand TAAB, complexes with the general formula M(TAAB)]ⁿ⁺ (n=0–3). From an analysis of the distribution of electron density and populations of the AOs of the central ion in these complexes, it has been established that the process of reduction of nickel compounds is accompanied by an increase in electron density on the carbon atoms of the macrocyclic ligand, whereas in the reduction of Cu(TAAB)]²⁺ a substantial increase is observed in the populations of the 3d AOs of the central ion, i.e., it is reduced. The difference in behavior of the complexes upon reduction is due to differences in the electronic configuration of the central ion. The structure and orbital composition of the frontier MOs have been analyzed, and it has been shown that in the reduced complexes of nickel Ni(TAAB)], which have strong nucleophilic properties, not only the central ion may act as a nucleophilic center, but also the carbon atoms of the macrocyclic ligand.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 4, pp. 421–428, July–August 1987.