The structure of FCOO − in aqueous solution: density functional methodologies and ab initio study

Abstract

The purpose of this paper is to predict the structure of the FCOO − anion in aqueous solution. For this purpose, the following effects of water molecules on the structure of FCOO − in aqueous solution are considered: (A) the effect of the first solvent shell; (B) the effect of water molecules around the O′ of FCOO −(H 2O′) 6; (C) the effect of water molecules around the F of FCOO −(H 2O) 6; (D) the effect of water molecules around H′ of FCOO −(HOH′) 6; and (E) the bulk effect. In order to estimate these effects, geometry optimization with B3LYP/6-311++G(2d, p) is carried out for FCOO −(H 2O) n ( n=0–7). FCOO −(H 2O) 6(HOH) m ( m=1,2) and HOH⋯FCOO −(H 2O) 6 are optimized with RHF/6-31++G(d). Also, in order to estimate the effect (E), SCRF calculation (Onsager model) with RHF/6-31++G(d) is performed for HOH⋯FCOO −(H 2O) 6. The maximum number of water molecules which can directly interact with carboxylate oxygen is six. The effect of the first solvent shell is significant. The effect of water molecules around the O′ of FCOO −(H 2O′) 6 is negligible. The effect of water molecules around the F of FCOO −(H 2O) 6 is significant. The effect of water molecules around the H′ of FCOO −(HOH′) 6 is negligible. The bulk effect is very small. Considering these effects, the structure of FCOO − in aqueous solution is predicted. The C–F bond length of FCOO − in aqueous solution is predicted to be smaller than that in the gas phase by 0.09 Å.