Synthesis, crystal structure, antimicrobial screening and density functional theory calculation of nickel(II), cobalt(II) and zinc(II) mononuclear Schiff base complexes

Nickel(II), cobalt(II) and zinc(II) mononuclear Schiff base complexes of general formula [(ML)-L-II(H2O)(3)]center dot 2H(2)O (where M = Ni, Co and Zn) have been synthesized using a new Schiff base ligand (LH2 = 2-((Pyridin-2-yl) methyleneamino) benzene-1,4-dioic acid). All the complexes and the ligand have been characterized by various physical measurements such as elemental analyses, FT-IR and UV-Vis spectroscopic techniques. The crystal structure analyses of the complexes revealed that extensive supramolecular interactions such as hydrogen bond and pi-pi stacking results 3D array of packing. The hydrogen bonding interaction distances are very similar in all complexes and are around 2.0 angstrom and for the pi-pi interactions the values are close to 3.8 angstrom. The interaction energies are comparable for Ni and Co complexes and is somewhat stronger for Zn complex. The strength of the aforementioned interactions have been evaluated by means of DFT calculations. For in vitro antimicrobial activity study, the complexes were screened against some bacteria and fungi. This study shows that the zone of inhibition against growth of microorganisms is much larger for Zn complex due to strong binding energy. The Hirshfeld surfaces of Ni, Co and Zn complexes were also analyzed to clarify the nature of the intermolecular interactions. Thermogravimetric analyses were performed to investigate the thermal stability of the complexes. (C) 2014 Elsevier B.V. All rights reserved.