DFT and TD-DFT Study of [Tris(dithiolato)M]3- Complexes[M= Cr, Mn and Fe]: Electronic Structures, Properties and Analyses

Using Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) methods, transition metal complexes of benzene-1, 2-dithiolate (L2-) ligand from Cr to Fe have been studied theoretically. The ground state geometries, binding energies, UV-Visible spectra (UV-Vis), frontier molecular orbitals (FMOs) analysis, charge analysis and natural bond orbital (NBO) have been calculated. The structural parameters are in good accord with the experimental data. The metal-ligand binding energies are one (1) order of magnitude higher than the physisorption energy of a benzene-1, 2-dthiolate molecule on a metallic surface. In accordance with experiment the calculated electronic spectra of these tris complexes show bands at 565, 559 and 546 nm for Cr3+, Mn3+, and Fe3+ respectively which are mainly qualified to ligand-to metal charge transfer (LMCT) transitions. The electronic properties analysis demonstrate that the highest occupied molecular orbital (HOMO) is mostly centered on metal coordinated sulfur atoms whereas the lowest unoccupied molecular orbital (LUMO) is mainly located on the metal surface. By calculating natural bond orbital (NBO), the intramolecular interactions and electron delocalization was obtained. The results of NBO analysis illustrated the significant charge transfer from sulfur to central metal ions, as well as to the benzene of the complex. The calculated charges on metal ions are also reported at various charge schemes. The calculations show encouraging agreement with the available experimental data. Dhaka Univ. J. Sci. 67(1): 63-68, 2019 (January)