Stabilization of a Cl^--Cl^- anion pair in the gas phase: Ab initio microsolvation study

Despite the confirmation of Cl^--Cl^- association in aqueous solution and crystalline state, there have been no reports about the existence of stable dichloride anion pair in the gas phase. In the current work we performed a systematic ab initio study of microsolvation of dichloride anion pair. The stepwise solvation mechanism observed for free gaseous [Cl₂(H₂O)_n]^2- (n = 2-10) clusters was found to be quite interesting. The lowest structure for dichloride hexahydrate closely resembles cubic water octamer W8 in which two water molecules in the corners of the cube are substituted by two chloride anions. We have also shown that Cl^--Cl^- pair may be completely stabilized by about 36 water molecules in the gas phase. Stabilization of the pair leads to the formation of cyclic H₂O structures that bridge the Cl^- ions. It has been predicted that the large clusters of [Cl₂(H₂O)₃₆]^2- and [Cl₂(H₂O)₄₀]^2- may exhibit properties analogous to bulk aqueous solutions, therefore they could become good molecular models for understanding complicated processes of solvation of Cl^- in the bulk. (Chemical Equation Presented).