Synthesis, spectroscopic characterization, DFT studies and biological activity of bis (1-(ethyl) piperidine) diselenide (L) and its complexes with selected group 12 metal halides

Abstract

Abstract Se2−2 (generated insitu by NaBH4 reduction of Se) on reaction with 1-(2-chloroethyl) piperidine hydrochloride under N2 atmosphere resulted in bis(1-(ethyl) piperidine) diselenide (L) as an orange solid. It’s bimetallic complexes having the formula [Zn2Cl4L] (1), [Cd2Cl4L] (2) and [Cd2Br4L] (3) were also synthesized. L and its complexes 1–3 were characterized on the basis of physico-chemical and spectral (FT-IR, Mass, 1H, 13C, DEPT and 77Se NMR) studies. IR spectroscopy revealed that M (II) ions (zinc and cadmium) are coordinated through selenium and nitrogen forming a five membered ring around M (II) ions. Elemental analysis measurement along with 1H, 13C, DEPT and ESI mass data confirmed the tetradentate mode of coordination of the ligand L. Moreover the coordination from selenium atom is also supported by the downfield shift of signal in 77Se NMR spectroscopy. Powder XRD diffraction pattern reveals the crystalline nature of Ligand L and complexes 1–3. Heteroditopic ligand L (N, Se, Se, N) ligates through both selenium and nitrogen atoms to two respective metal halides in complexes 1–3, thus forming bimetallic complexes. Using DFT-based optimization of structures, the HOMO-LUMO energy gaps and molecular electrostatic potential surface of ligand L and complexes 1–3 were theoretically calculated at the B3LYP/LANL2DZ level of theory. These complexes adopt distorted tetrahedral geometry around M (II) ions as revealed by bond angles. HOMO-LUMO energy gap was calculated which allowed the calculation of relative properties like chemical hardness, chemical inertness, chemical potential, nucleophilicity and electrophilicity index of the synthesized products. The experimentally obtained IR and NMR results showed a good correlation with those of the theoretical ones. Ligand L and complex 1–3 displayed significant antibacterial and antifungal activity.