POLARIZATION-CORRECTED ELECTROSTATIC POTENTIAL FOR PROBING CATION-BINDING PATTERNS OF MOLECULES - 1 - SATURATED-HYDROCARBONS

The molecular electrostatic potential (MESP) and the corresponding pol arization 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 PMES P has been employed for predicting coordination of Li+ with these hydr ocarbons. Coordination site of Li+ usually turns out to be in the dire ction guided by the corresponding PMESP critical points (CPs) of these hydrocarbons. An ab initio level minimum energy search along this dir ection is used to generate possible starting configurations of hydroca rbon ... Li+ complexes. Hartree-Fock and second-order Moller-Plesset ( MP2) calculations with 6-31G* basis set are performed with these star ting 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 tren ds in geometries and interaction energies of the hydrocarbon ... Li+ c omplex structures obtained at the HF level are almost unaffected by el ectron correlation as well as extension of the basis set beyond 6-31G . The Kitaura-Morokuma energy decomposition analysis brings out the i mportance of the polarization term, while the electrostatic term is se en to dominate selectively for cyclopropane. Complete exploitation of three-dimensional PMESP distribution thus offers a systematic way for studying cation molecule interactions.