A new insight for chalcogen bonding based on Point-of-Charge approach

Abstract

This study investigated the chalcogen bond from an electrostatic perspective using Point-of-Charge (PoC) approach. Two molecular models –namely CX2 and H2X, where X = O, S, and Se– were studied. 2D stabilization energy surfaces were generated for all studied molecules. Moreover, Chal···PoC distance, A-Chal···PoC angle (θ) and solvent effects on chalcogen bond strength were investigated. Natural bond orbital (NBO) calculations were also performed for all studied molecules. Results found that chalcogen bond strength increased with increasing Lewis basicity (i.e., PoC negativity), with closing A-Chal···PoC angle (θ) to 180°, and with increasing chalcogen atomic size in the order O < S < Se. Polarization of the negative PoC on the σ-hole size was revealed. Aqueous medium contributions to molecular stabilization resulted from: (i) the favorable solvent contribution to the positive σ-hole, and (ii) the unfavorable solvent contribution to the negative electrostatic regions of the molecules. σ-node phenomenon was also investigated and explained in the chalcogen-containing molecules. It could thus be concluded that the chalcogen bond is electrostatic and a sum of (i) attractive electrostatic interaction between the σ-hole of chalcogen atom and the Lewis base, and (ii) repulsive electrostatic interaction between the negative belt of chalcogen atom and the Lewis base.