Metal binding selectivity of oxa-aza macrocyclic ligand: a DFT study of first- and second-row transition metal for four coordination systems

A detailed theoretical study of the 1,7,1l,17-tetraoxa-2,6,12,16-tetraaza-cycloeicosane ligand ([20]AneN₄O₄) coordinated to Fe²⁺, Co²⁺, Ni²⁺, Ru²⁺, Rh²⁺, and Pd²⁺ transition metal ions was carried out with the B3LYP method. Two different cases were performed: when nitrogen is the donor atom (1a _q ) and also with the oxygen as the donor atom (1b _q ). For all the cases performed in this study 1a _q structures were always more stable than the 1b _q ones. Considering each row is possible to see that the energy increases with the increase of the atomic number. The M²⁺ cation binding energies for the 1a _q complexes increase with the following order: Fe²⁺ < Ru²⁺ < Co²⁺ < Ni²⁺ < Rh²⁺ < Pd²⁺.