Molecular and electronic structures, bonding analysis, and UV-Vis spectra predictions of quinolino[3,2-b]benzodiazepine and quinolino[3,2-b]benzoxazepine metal transition M(L)2Cl2 and M(L)Cl2 complexes

Density functional theory (DFT) calculations were carried out on ML2Cl2 (M = Co, Ni) and M'LCl2 (M'= Zn, Cd) and L=(BDQ) quinolino[3,2-b]benzodiazepine or L = (BDO) = quinolino[3,2-b]benzoxazepine) transition metal complexes. The geometry optimizations and frequency calculations of the aforementioned complexes were performed at the Becke, 3-parameter, Lee-Yang-Parr/triple zeta polarization (B3LYP/TZP) level, followed by the partitioning of the interaction energies using the energy decomposition analysis scheme (EDA) to assess the interaction strength in function of L ligand and the nature of the metal. Indeed, the total bonding energies are more significant for Zn(II) cation in the presence of (QBD) ligand than those of the Cd(II) one and (QBO). The findings show that the electrostatic interaction energy is the most important contributing by two third into the total interaction energy of each of the complex systems. Calculations and analyses were performed by means of the natural bond orbital analyses (NBO) giving rise to significant natural population of the M(II) cations. As concerns of the structures corresponding to odd electron counts, the unpaired electrons are chiefly localized on the metal center with regard to the spin density values. UV-Vis spectra are mainly pi ->pi* electronic transitions corresponding to intra-ligand charge transfers (ILCT) but showed weak influence of the introduction of the MCl2 metallic fragment.