Novel copper (II) and zinc (II) complexes with enrofloxacin and oxolinic acid: synthesis, characterization, Hirshfeld surface and DFT/CAM-B3LYPD3BJ studies: NBO, QTAIM and RDG analysis

This study aimed to investigate the crystal structure of the synthesized complexes of Cu (II) and Zn (II) with enrofloxacin and oxolinic acid. The characterization of the complexes was carried out using single–crystal x-ray diffraction, Hirshfeld surface and 1H NMR spectroscopy. In addition, a DFT/6-31g(d) investigation was conducted to assess the performance of two exchange-correlation functionals CAM-B3LYP and CAM-B3LYPD3BJ to predict both covalent and non-covalent bonds lengths, and the vibrational frequencies of the metallic complexes. The main findings of this study indicate that the interaction between each metallic ion and the corresponding ligand leads to significant modifications in bond lengths, Mulliken charge distribution and electrostatic potential values in the complex molecules as compared to the ligands alone. To gain further insights into these complexes, several calculations were performed, such as Natural Atomic orbitals (NAO), Natural Bond orbitals (NBO), and Quantum Theory of Atoms in Molecules (QTAIM) analysis. The non-covalent interactions were explored and visualized in two and three-dimensional spaces with the help of the Reduced electron Density Gradient (RDG) approach.