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.