A rare hetero-bimetallic Zn(II)/Ca(II) Schiff base complex: Synthesis, crystal structure, DFT, molecular docking and unveiling antimicrobial activity

Abstract

A new hetero-bimetallic Zn(II)/Ca(II) complex, [Zn2(LOMe-pn)2(ƞ1-NCS)2Ca] (1) has been synthesized using a potentially hexadentate N2O4 proligand, H2LOMe-pn = N,N-bis(3-methoxysalicylidene)-2,2-dimethylpropane-1,3 diamine and structurally well characterized by different physicochemical techniques. Single crystal X-ray diffraction study of the complex revealed that, de-protonic form of the ligand utilizes two pockets, one is occupied by Zn(II) ion and other is housed by a Ca(II) ion. The Zn centres are fitted into the N2O2 compartment with distorted square pyramidal geometry while a large open O2O2′ compartment is occupied by a Ca(II) ion in a octacoordinated environment. DFT studies were successfully carried out using DFT/M06 functional level and 6–31 G * basis set (over all the atoms) to delineate the complex optimized structure, composition of the frontier molecular orbitals, global reactivity, total energy frameworks, MEP, total dipole moment, average polarizability and first hyperpolarizability. First hyperpolarizability value (59.62 × 10−31 esu) suggests that complex is a good NLO material. Hirshfeld surface revealed the presence of many short intermolecular contacts like C⋯H/S⋯H/N⋯H/O⋯H/H⋯H/C⋯C and S⋯S in the crystal structure. The experimental absorption spectra are comparable with the electronic transitions assigned from TD-DFT studies. CHEF based (π→π*) luminescence property has been measured in DMSO solvent at room temperature. Concentration dependant antibacterial efficacy was investigated against gram-negative bacterial strains viz. E. coli (ATCC 25,922) & Pseudomonas aeruginosa (ATCC 27,853) and gram-positive bacterial strains viz. Staphylococcus aureus (ATCC 25,923) & Bacillus subtilis (ATCC 6633). The bacterial killing efficiency and solvent effect of the complex was compared with that of ligand. Finally, a docking study with the active site of DNA Gyrase and DNA Polymerase III proteins has been carried out to corroborate the experimental findings.