Synthesis, Characterization and Computational Studies of Rhenium(I) Tricarbonyl Complex bearing Bidentate N,N-Heteroaromatic Ligand

Abstract

This study reports on the synthesis, characterization and computational studies of rhenium(I) tricarbonyl complexes bearing N,N-chelating heteroaromatic ligand. Ligand (L) was prepared by reacting equimolar of 2-(1H-imidazol-2-yl)pyridine and benzoyl chloride in dry tetrahydrofuran while the corresponding complex [Re(CO)₃Cl(L)] was prepared by refluxing the metal precursor, [Re(CO)₅Cl] with the ligand L, affording yellow crystalline solids. Characterization of the samples was conducted by Fourier Transform Infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopy for the structural analysis. The computational studies of the samples were performed through Density Functional Theory (DFT) and Molecular Electrostatic Potential (MEP) analysis. The optimized geometry of complex [Re(CO)₃Cl(L)] confirms retention of a facial octahedral coordination geometry, with the ligand chelating through the pyridine and imidazole nitrogen atoms. Subtle variations in calculated orbital energies and electron density distribution across the ligand framework reflect intramolecular charge redistribution within the imidazole–pyridine moiety upon coordination. The ESP profile of complex [Re(CO)₃Cl(L)]  falls within the electrostatic potential range (≈ –30 to +50 kcal mol⁻¹) typically associated with metal complexes exhibiting favourable DNA affinity and electrostatic complementarity. The relatively symmetric distribution of electron density in ReL1H, compared to strongly substituted analogues, suggests a balanced electronic environment that supports stable metal–ligand coordination while maintaining sufficient polarization for biomolecular interaction.