Antifungal, antibacterial and DNA binding profile of three novel Zn(II), Cd(II) and Hg(II) complexes of a pyrazole-based Schiff-base ligand: synthesis, crystal structures, DFT studies and spectroscopic investigation

Three new mononuclear Zn(II), Cd(II) and Hg(II) complexes, [Zn(MPAFA)3](ClO4)2 (1), [Cd(MPAFA)3](ClO4)2 (2) and [Hg(MPAFA)Cl2] (3) of a pyrazole based ‘NN’ bidentate Schiff-base ligand, N-(furan-2-ylmethyl)-1-(5-methyl-1H-pyrazol-3-yl)methanimine, (MPAFA) (L) were synthesized and characterized by elemental analyses, conductance, IR, NMR (1H and 13C), UV-Vis and fluorescence spectral techniques. Molar conductance measurements identified both 1 and 2 as 1:2 electrolytes, while 3 as a non-electrolyte. Single crystal X-ray diffraction studies recognized complexes 1 and 2 as distorted octahedral species with a N6 donor set. The presence of strong non-covalent interactions, such as intramolecular hydrogen bonding and π···π stacking within the complex molecules has been found to contribute to the enhanced stability of the complexes. In absence of single crystal, the structural feature of complex 3 has been confirmed by DFT studies and it has been found to adopt a distorted square-planar geometry with a N2Cl2 coordination. DFT calculations have also been conducted for 1 and 2. The TD-DFT absorption spectral studies supported the experimental results, indicating that the simulated peaks aligned reasonably well with the experimentally resolved peaks. Furthermore, the ligand and all its complexes exhibited effective antifungal activity against Colletotrichum siamense (AP1) and Fusarium equisetum (F.E) fungi. They also displayed promising antibacterial activity against both the gram-negative bacterium Klebsiella sp. (KS) and the gram-positive bacterium Methicillin-resistant Staphylococcus aureus (MRSA). The binding interactions of 1, 2 and 3 with calf-thymus DNA (CT-DNA) have also been studied using a combination of UV-Vis and fluorescence spectroscopic methods.