DFT study on X⁻·(H₂O)(n=1-10) (X=OH, NO₂, NO₃, CO₃) anionic water cluster

A theoretical study to understand the interaction between anion and the water molecules through the hydration (X(-)·(H2O)n (X=OH, NO2, NO3, CO3), where n=1-10), using the density functional theory method with B3LYP functional and 6-311++G(d,p) basis set has been carried out systematically. In these hydrated clusters we notice three different cases of bond arrangements, namely, symmetrical double hydrogen bond, single hydrogen bond and inter-water hydrogen bond. All the complexes are dominated by the O-H⋯O hydrogen bond, in which the anion act as a proton acceptor, while the water molecule act as a proton donor. A linear correlation is obtained between the solvent stabilization energy and the size (n) of the hydrated cluster for all the anions. The weighted average interaction energy values, shows that the water molecules strongly bind with the OH(-) anion. Besides, the solvation of the OH(-) anion requires less number of water molecules when compared with the other anions. Energy decomposition analysis (EDA) shows the strong dominance of the electrostatic energy component within the interaction energy. The total NPA charges on the anions indicate an increase in the solvation due to hydration. From AIM analysis, excellent linear inverse correlation is observed for both the electron density and Laplacian of the electron density with respect to the hydrogen bond length. Natural bonding orbital analysis (NBO) predicts large charge transfer between the OH(-) anion and the water molecules.