Polarization-corrected electrostatic potential for probing cation binding patterns of molecules. 1. saturated hydrocarbons

Abstract

The molecular electrostatic potential (MESP) and the corresponding polarization corrected one (PMESP) of some saturated hydrocarbons, viz., methane, ethane, cyclopropane, cyclobutane, n-butane, and cyclohexane, have been examined at the ab initio SCF level. The topography of PMESP has been employed for predicting coordination of Li⁺ with these hydrocarbons. Coordination site of Li⁺ usually turns out to be in the direction guided by the corresponding PMESP critical points (CPs) of these hydrocarbons. An ab initio level minimum energy search along this direction is used to generate possible starting configurations of hydrocarbon...Li⁺ complexes. Hartree-Fock and second-order Moller-Plesset (MP2) calculations with 6-31G^∗∗ basis set are performed with these starting geometries for investigating the structures and energetics of the complexes. A remarkable correlation has been found between the PMESP values at CPs and the corresponding Li⁺ binding energies. General trends in geometries and interaction energies of the hydrocarbon...Li⁺ complex structures obtained at the HF level are almost unaffected by electron correlation as well as extension of the basis set beyond 6-31G. The Kitaura-Morokuma energy decomposition analysis brings out the importance of the polarization term, while the electrostatic term is seen to dominate selectively for cyclopropane. Complete exploitation of three-dimensional PMESP distribution thus offers a systematic way for studying cation...molecule interactions.