Interplay of Hydrogen, Halogen, Lithium and Beryllium Bonds in Complexes of Thiirane

Abstract

Hydrogen, halogen, lithium and beryllium bonding are briefly surveyed as a prelude to a report of a computational study of the interplay between these various non-covalent interactions. Our study used model dimers and trimers involving the thiirane molecule, (CH 2 ) 2 S, complexed with small molecules like HF, ClF, BrF, LiF and BeH 2 to assess and investigate the interplay between the different noncovalent interactions. The model trimer systems show positive cooperative effects when thiirane is one of the terminal molecules, whereas a negative cooperative effect is evident when it is at the center of the trimer. The changes in selected molecular properties, including the redistribution of charge densities obtained by the natural population analysis (NPA), implemented in the natural bond orbital (NBO) procedure, and an Atoms in Molecules (AIM) topological analysis, were useful in understanding these cooperative effects. Introduction Overview of Non-Covalent InteractionsNon-covalent interactions in molecular systems is a topic of much scientific interest as it spans a number of scientific subdisciplines. They are responsible for the existence of condensed phases, for which the forces operative between interacting neutral molecules are strong enough to limit the volume of samples of a particular material but weak enough to ensure the fluidity of such materials in bulk.Such interactions are usually dominated by classical electrostatic forces, through the interaction between the permanent multipole moments of the interacting molecular species. These electrostatic forces are usually augmented by classical polarization and quantum-mechanical dispersion forces, and their long-range behavior dependent on some inverse power of their molecular separation (usually measured by the distance between the center of masses of the interacting molecules). At equilibrium