Interplay of Hydrogen, Pnicogen, and Chalcogen Bonding in X(H2O)n=1-5 (X = NO, NO+, and NO-) Complexes: Energetics Insights via a Molecular Tailoring Approach.

Abstract

Nitric oxide (NO) and its redox congeners (NO+ and NO-), designated as X, play vital roles in various atmospheric and biological events. Understanding the interaction between X and water is inevitable to explain the different reactions that occur during these events. The present study is a unified attempt to explore the noncovalent interactions in microhydrated networks of X using the MP2/aug-cc-pVTZ//MP2/6-311++G(d,p) level of theory. The interactions between X and water have been probed by the molecular electrostatic potential (MESP) by exploiting the features of the most positive (Vmax) and most negative potential (Vmin) sites. The individual energy and cooperativity contributions of various types of noncovalent interactions present in X(H2O)n=1-5 complexes are estimated with the help of a molecular tailoring-based approach (MTA-based). The MTA-based analysis reveals that among various possible interactions in NO(H2O)n complexes, the water···water hydrogen bonds (HBs) are the strongest. Neutral NO can form hydrogen and pnicogen bonds (PBs) with water depending on the orientation; however, such HBs and PBs are the weakest. On the other hand, in the NO+(H2O)n complexes, the NO+···water interactions that occur through PBs are the strongest; the next one is the chalcogen bonding (CB), and the water···water HBs are the weakest. In the case of the NO-(H2O)n complexes, the HB interactions via both N and O atoms of NO- and water molecules are the strongest ones. The strength of water···water HB interactions is also seen to increase with the increase in the number of water molecules in NO-(H2O)n. The present study exemplifies the applicability of MTA-based calculations for quantifying various types of individual noncovalent interactions and their interplay in microhydrated networks of NO and its related ions.