Unsymmetrical salen nickel (II) complex embracing phenol bridge: X-ray structure, redox investigation, computational calculations, antimicrobial and catalytic activities

•Use of an efficient stepwise template approach allowed the synthesis of a nickel(II) complex.•The square planar Ni(II) complex catalyzes efficiently the epoxidation of cyclohexene using H2O2 as an environmental oxidant.•In vitro biological activity of the NiLOH complex exhibited potent inhibitory to prevent the growth of bacteria than its native H2LOH ligand.•Excited electronic states, from TD-DFT, revealed a mixture of MLCT and ILCT transitions. An exhaustive description of the crystal structure, DFT, TD-DFT and redox properties of a non-symmetrical nickel complex NiLOH, N,N’-2,3-hydroxyphenol -2,3-dyil-bis (salicylideneimine)nickel(II), are reported. The complex crystallizes, in the monoclinic crystal system, with P21/c space group. Oxygen-atom of the phenolic spacer contributes in hydrogen bonding forming a zigzag chain along a axis. Cyclic voltammetric study of the complex revealed a quasi-reversible process Ni(II)/Ni(I) on a glassy carbon electrode at E1/2 = -1371, -1312, -1305 mV/SCE in DMSO, CH3CN and DCM, respectively. From DFT calculations, the electronic properties of NiLOH complex and its reactivity with DNA bases, in polar and non-polar media, shows a good agreement with the experimental results. TD-DFT revealed that the absorption electronic states correspond to a mixture of metal to ligand charge transfer (d→π*) and intra-ligand charge transfer (π→π*) transitions. The NiLOH complex as catalyst proved to be catalytically active in the cyclohexene epoxidation reaction. The ligand and the NiLOH complex were scrutinized for their antibacterial activity in agar medium by the disk diffusion method against some Gram positive and Gram negative strains. Better inhibitory potential towards some examined bacteria was shown. [Display omitted]