Molecular, electronic structure and spectroscopic properties of 6,6′-dimethyl-2,2′-bipyridine and HgI2 complex: Experimental and DFT investigations

•Dmbpy and [HgI2(dmbpy)] compounds are studied by DFT/B3LYP-D3 calculations.•Characterization using elemental analysis UV-Vis, IR and NMR techniques were performed.•Spectroscopic properties of the title compound were examined by FT-IR and FT-Raman, techniques and DFT method.•TD-DFT calculations for the UV-Vis spectra shows MLCT electronic transition for [HgI2(dmbpy)].•Quantum molecular descriptors indicate increase of the stability and decrease of reactivity of complex.

Transition metal-bipyridine complexes have been considered for use in various applications including catalysis, luminescent sensors, artificial photosynthesis, electrochemistry, nonlinear optical materials and organic light emitting diodes. Bipyridine derivative complexes have been studied from both experimental and theoretical point of views. In this study, we have carried out density functional theory (DFT) calculations for geometry optimization, charge distribution, molecular orbital description, energy gap, chemical hardness η and vibrational frequencies (IR) were performed at B3LYP level of theory for synthesized [HgI2(dmbpy)] (dmbpy is 6,6′-dimethyl-2,2′-bipyridine) complex. The calculated vibrational frequencies were found to be in reasonable to good agreement with experimental values. The vibrational modes obtained from solid-phase FT-IR spectra could be assigned based on our theoretical calculations.Using time-dependent DFT (TD-DFT) calculations the UV-Vis and electronic spectra of [HgI2(dmbpy)] were predicted to be in agreement with experimental data. Based on the description of the frontier molecular orbitals and the shifts in electron density during complexation, bonding characteristics in the complex were determined. Furthermore the π-π stacking interactions between the pyridine rings of adjacent molecules were investigated. Our DFT calculations show that van der Waals forces play an important role in the π-π stacking interactions for the [HgI2(dmbpy)] complex.