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

• Three new monomeric Schiff base complexes of Ni(II), Co(II) and Zn(II) have been synthesized.
• These complexes form 3D supramolecular motif by means of hydrogen bonding and π–π interactions.
• The energetic of these interactions are also evaluated with theoretical DFT calculations.
• The biological properties of the complexes are also studied which show a significant result.

Nickel(II), cobalt(II) and zinc(II) mononuclear Schiff base complexes of general formula [MIIL(H2O)3]·2H2O (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 π–π stacking results 3D array of packing. The hydrogen bonding interaction distances are very similar in all complexes and are around 2.0 Å and for the π–π interactions the values are close to 3.8 Å. 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.

Three new monomeric Schiff base complexes of Ni(II), Co(II) and Zn(II) have been synthesized. These complexes form 3D supramolecular motif by means of hydrogen bonding and π–π interaction. The energetic of these interactions are also evaluated with theoretical DFT calculations. The biological properties such as antimicrobial and antibacterial activity of the complexes are also studied which show a significant result.Figure optionsDownload as PowerPoint slide