Hydrated Sulfate Clusters SO42-(H2O) n ( n = 1-40): Charge Distribution Through Solvation Shells and Stabilization.

ABSTRACT

Investigations of inorganic anion SO42- interactions with water are crucial for understanding the chemistry of its aqueous solutions. It is known that the isolated SO42- dianion is unstable, and three H2O molecules are required for its stabilization. In the current work, we report our  computational study of hydrated sulfate clusters SO42-(H2O) n ( n = 1-40) in order to understand the nature of stabilization of this important anion by water molecules. We showed that the most significant charge transfer from dianion SO42- to H2O takes place at a number of H2O molecules n ≤ 7. The SO42- directly donates its charge only to the first solvation shell and surprisingly, a small amount of electron density of 0.15| e| is enough to be transferred in order to stabilize the dianion. Upon further addition of H2O molecules, we found that the cage effect played an essential role at n ≤ 12, where the first solvation shell closes. During this process, SO42- continues to lose density up to 0.25| e| at n = 12. From this point, additional water molecules do not take any significant amount of electron density from the dianion. These results can help in development of understanding how other solvent molecules could stabilize the SO42- anion as well as other multicharged unstable anions.