Theoretical study of structural and optical properties of lithium cation complexes with dimethyl sulfoxide

DFT and ab initio MP2 studies of optimal geometries, energetics, electron structure and electron spectra of [Li(DMSO)n]+ complexes, n = 1-6, are presented. The coordination number increase causes Li-O bond elongation and decreasing electron density transfer from oxygen to lithium. This is connected with the exponential decrease of the complex formation energy per DMSO ligand, weakens the Li-O bonds and lowers the DMSO structure deformation. The highest stability of [Li(DMSO)4]+ complexes in agreement with experimental data can be explained in the terms of the population analysis based on the topological analysis of electron density. TD-DFT calculations of vertical electronic transitions for IEFPCM polarizable continuum model in DMSO solutions and molecular orbital analysis indicate that the Li-DMSO bonding is responsible for the blue shift of the original DMSO excitation energy. These type complexes are important for the drug-transport through the cell membranes in biological systems.