Probing the Directionality of S···O/N Chalcogen Bond and Its Interplay with Weak C-H···O/N/S Hydrogen Bond Using...

The directionality of the chalcogen bond (Ch-bond) formed by S and its interplay with other weak interactions have important chemical and biological implications. Here, dimers made of CH₃-S-X and O/N containing nucleophiles are studied and found to be stabilized by coexisting S···O/N and C-H···O/N interactions. Based on experimentally accessible electron density and molecular electrostatic potentials (MESPs), we showed that reciprocity between S···O/N and C-H···O/N interactions in the stability of cumulative molecular interaction (ΔE) was dependent on the strength of the σ-hole on S (V_s,max). Direct correlation between ΔE of dimers with V_s,max of S supports the electrostatic nature of the Ch-bond. Such interplay of the Ch-bond is necessary for its directionality in complex nucleophiles (carbonyl groups) with multiple electron-rich centers, which is explained using MESP. A correlation between the MESP minima in the π-region and the strength of the S-π interaction explains the directional selectivity of the Ch-bond.