DFT calculations, spectroscopic studies, thermal analysis and biological activity of supramolecular Schiff base complexes

Metal complexes of Schiff base (H2L) prepared from condensation reaction of o-phenylenediamine and 6-formyl-7-hydroxy-5-methoxy-2-methylbenzopyran-4-one with metal ions: Mn(II), Co(II), Ni(II) and Cu(II) were synthesized. Different analysis tools such as elemental analyses, mass spectra, Fourier transform infrared (FTIR), thermal analysis, conductivity, electronic spectra and magnetic susceptibility measurements are all used to elucidate the structure of the prepared metal complexes. The ligand behaves as a monobasic bidentate in case of mononuclear NiHL and CoHL complexes and acts as dibasic tetradentate in binuclear Mn2L and Cu2L complexes. All formed complexes are non-electrolytes. The thermal decomposition of Mn2L and CoHL complexes was studied by thermogravimetry/derivative thermogravimetry (TG/DTG). The Schiff base and its complexes were screened for antibacterial activities. The Mn2L Complex has the highest antimicrobial activity among the complexes almost close to that of the standard. Density Functional Theory (DFT) calculations at the B3LYP/3-21G level of theory have been carried out to investigate the equilibrium geometry of the ligand. The optimized geometry parameters of the complexes were evaluated using LANL2DZ basis set. Moreover, total energy, energy of HOMO and LUMO and Mullikan atomic charges were calculated. In addition, dipole moment and orientation have been performed.