A theoretical study on the formation of “1 + 1” versus “2 + 2” macrocyclic Schiff base complexes in the absence of coordinated anions

This work reports a theoretical study on “1 + 1” against “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 indicate that in the absence of a coordinated anion the “1 + 1” macrocyclic Schiff base complexes are the preferred products for both Mg(II) and Pb(II) metal ions. However, with considering the coordinated anions the “2 + 2” macrocyclic Schiff base complex is preferred product for Pb(II) metal ion. Thus the results present the first theoretical evidence that the coordinated anions have an important role in the metal template synthesis of “2 + 2” against “1 + 1” macrocyclic Schiff base complexes. A theoretical study on “1 + 1” against “2 + 2” cyclocondensation reactions between 2,6-diacetylpyridine and three different amines in the presence of Pb(II) metal ion is also reported. The results confirm that in some cases the kinetic effects prevent formation of the thermodynamically preferred product.