Synthesis, characterization, DFT study, and antibacterial activity of a coordination complex of Cu(II) with 1,10-phenanthroline and l-methionine ligands

A crystal of the coordination complex of Cu(II) with 1,10-phenanthroline (phen) and L-methionine anion ([Cu(Phen)(L-methionine)H2O]Cl·1.5H2O) was synthesized and investigated by powder X-ray diffraction (PXRD), Raman spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and ultraviolet-visible (UV–Vis) techniques combined with density functional theory (DFT) studies. Chemical, electronic and vibrational properties were properly investigated through experimental and theoretical approaches, including a solvation effects study with an implicit solvation method using ethanol and water as solvents. The electronic structure calculations indicated that the titled complex is chemically stable and showed that a smaller amount of energy is required for a HOMO-LUMO electronic transition in an aqueous medium. Characteristic bands of the d−d transition for five-coordinated Cu(II) were identified for the complex with minor differences in wavelengths of the UV-Vis spectra in water and ethanol. The Raman and infrared experimental results and the implemented calculations on the vibrational properties in different solvent conditions showed spectral changes, especially when comparing the results obtained in water and ethanol solvents in relation to vacuum. Additionally, biological evaluations indicated that the [Cu(Phen)(L-methionine)H2O]Cl·1.5H2O complex has good antibacterial activity against Gram-positive and Gram-negative bacteria, presenting a minimum inhibitory concentration (MIC) value of 50 μg/mL, suggesting it has a booster for commercialization.