Microhydration of a Carbonyl Group: How does the Molecular Electrostatic Potential (MESP) Impact the Formation of (H2O)n:(R2C═O)Complexes?

The presence of a carbonyl group in a molecule usually leads to the identification of a π-hole on the molecular electrostatic potential (MESP) of the species. How does this electrophilic site influence the formation of microhydrated complexes? To address this point, a panel of R 2 CO solutes with various MESPs was selected, and we identified the structures and properties of several complexes containing one, two, three and six water molecules. The following solutes were considered in the present study: H 2 CO, F 2 CO, Cl 2 CO,(NC) 2 CO and H 2 C═CO. Geometry optimizations and frequency calculations were carried out at the LC-ωPBE/6-311++G(d,p) level, with the GD3BJ empirical correction for dispersion. For a number of n water molecules around the R 2 CO solute, the structure and the features of the most stable (H 2 O) n :(R 2 CO) complexes are highly dependent on the MESP of the isolated R 2 CO solute. The formation of pi-hole bondings appears to play a decisive role in the initiation of a three-dimensional organization of water molecules around the solute.