Synthesis and in silico studies of new mercaptobenzimidazole Schiff base and metal complexes

A new Schiff base ligand (1) derived from 2-mercaptobenzimidazole and the manganese(II) (2), nickel(II) (3), copper(II) (4), and silver(I) (5) complexes were synthesized and characterized using elemental analysis, FT-IR, and NMR spectroscopic techniques. Optimized geometries and frontier molecular orbital parameters were obtained using the density functional theory (DFT) (B3LYP/Def2-TZVP) calculations. Molecular docking simulations were employed to probe possible ligand–protein interactions with a prostate cancer-related target. The appearance of the –HC=N– proton singlet peak at 8.99 δ ppm confirmed the synthesis of 1. The frequency reduction in υC–N (1091 cm−1) and υC–O (1080 cm−1) in the infrared spectra of the metal complexes supported azomethine nitrogen and phenolic oxygen as donor atoms. The analytical and spectroscopic data supported an [ML2] formulation for the Mn(II) and Ni(II) complexes with NO bidentate coordination. The Cu(II) and Ag(I) complexes were formulated as [CuL(NO3)(H2O)] and [Ag(LH)(NO3)]·H2O, respectively. The DFT calculations revealed reduced HOMO–LUMO energy gaps for the metal complexes relative to the free ligand, suggesting enhanced chemical reactivity, while Ag(I) complex (5) exhibited the smallest band gap. The calculated binding energies suggested favorable ligand–protein interactions within the limitations of the docking model, with the Cu(II) complex showing the strongest predicted binding.