Coordination Behavior of Ni(2+), Cu(2+), and Zn(2+) in Tetrahedral 1-Methylimidazole Complexes: A DFT/CSD Study

The interaction between nickel (Ni(2+)), copper (Cu(2+)), and zinc (Zn(2+)) ions and 1-methylimidazole has been studied by exploring the geometries of eleven crystal structures in the Cambridge Structural Database (CSD). The coordination behavior of the respective ions was further investigated by means of density functional theory (DFT) methods. The gas-phase complexes were fully optimized using B3LYP/GENECP functionals with 6-31G(∗) and LANL2DZ basis sets. The Ni(2+) and Cu(2+) complexes show distorted tetrahedral geometries around the central ions, with Zn(2+) being a perfect tetrahedron. Natural bond orbital (NBO) analysis and natural population analysis (NPA) show substantial reduction in the formal charge on the respective ions. The interaction between metal d-orbitals (donor) and ligand orbitals (acceptor) was also explored using second-order perturbation of the Fock matrix. These interactions followed the order Ni(2+) > Cu(2+) > Zn(2+) with Zn(2+) having the least interaction with the ligand orbitals. Examination of the frontier orbitals shows the stability of the complexes in the order Ni(2+) > Cu(2+) < Zn(2+) which is consistent with the Irving–Williams series.