The role of π electrons in the formation of benzene-containing lithium-bonded complexes.

The intermolecular interactions in C(6)H(6)···LiX (X=OH, NH(2), F, Cl, Br, NC, CN) complexes are investigated by using second-order Møller-Plesset perturbation theory (MP2) calculations and quantum theory of "atoms in molecules" (QTAIM) studies, and the role of π electrons is studied in the formation of these benzene-containing lithium-bonded complexes. The molecular electrostatic potentials of benzene and LiX determine the geometries of the lithium-bonded complexes. The electron densities at the lithium bond critical points in the πC(6)H(6)···LiX complexes are obviously stronger than those in the σC(6)H(6)···LiX complexes, which indicates that the intermolecular interactions in the C(6)H(6)···LiX complexes are mainly attributable to π-type interaction. The topological and energy properties at the lithium bond critical points in both the C(6)H(6)···LiX and πC(6)H(6)···LiX complexes are linear with the interaction energies, thereby showing the crucial role of the π electrons in the formation of these complexes. Electron localization function (ELF) analysis indicates that the formation of the lithium bonds leads to the reduction of the ELF π-electron density and volume, and the reduction of the π-electron volume is linear with the interaction energies with the correction coefficient 0.9949.