Nickel(II) complexes of two potentially heptadentate(N7) Tripodal Schiff-base ligands; X-ray crystal structure and theoretical studies

Abstract

In absolute methanol, one equivalent of tripodal tetraamines bis(3-aminopropyl)(2-aminoethyl)amine, ppe or (3-aminopropyl)-bis(2-aminoethyl)amine, pee condenses with three equivalents of 2-pyridinecarboxaldehyde. Upon the addition of Ni(II) salt to the solutions of produced Schiff base ligands, two new Schiff-base complexes, [Ni(py3ppe)](ClO4)2, (1), and [Ni(py3pee)](ClO4)2, (2), were prepared. Both complexes 1 and 2 were characterized by X-ray crystal structure analysis, CHN elemental analysis and FT-IR spectroscopy. The data show that both complexes have a distorted trigonal antiprism geometry for Ni(II) ion, in which the tertiary nitrogen atom has been not coordinated to the central metal ion. A DFT theoretical study at bp86/def2-tzvp level of theory on a series of this type of Ni(II) complexes shows that, interestingly, the values of metal–ligand interaction energies are very similar and are about 510 ± 2 kcal mol−1.