Computational evidence of preferred energy and preferred binding energy in the formation of “1 + 1” versus “2 + 2” macrocyclic Schiff base complexes

This work reports a theoretical study on “1 + 1” versus “2 + 2” cyclocondensation reactions between 2,6-diacetylpyridine and 3,6-dioxaoctane-l,8-diamine in the presence of Mg(II) and Pb(II) metal ions. The results of calculations at DFT(B3LYP) level of theory using LanL2DZ, SDD and CEP-121G basis sets were consistent with the experimental observations and all showed that “1 + 1” and “2 + 2” macrocyclic Schiff base complexes are preferred products for Mg(II) and Pb(II) metal ions, respectively. It was shown that the prediction of the type of cyclocondensation reaction is possible if we calculate a “preferential energy” and/or a “preferential binding energy” for one of the corresponding products.