Solvation energies of the ferrous ion in water and in ammonia at various temperatures

The solvation of metal ions is crucial to understanding relevant properties in physics, chemistry, or biology. Therefore, we present solvation enthalpies and solvation free energies of the ferrous ion in water and ammonia. Our results agree well with the experimental reports for the hydration free energy and hydration enthalpy. We obtained \({-1888.7}\) $-1888.7$  kJ mol \(^{-1}\) ${}^{-1}$ for the hydration free energy and \({-1900.7}\) $-1900.7$  kJ mol \(^{-1}\) ${}^{-1}$ for the hydration enthalpy of ferrous ion in water at room temperature. At ambient temperature, we obtained \({-2065.7}\) $-2065.7$  kJ mol \(^{-1}\) ${}^{-1}$ as the \(Fe^{2+}\) $F{e}^{2+}$ ammoniation free energy and \({-2124.2}\) $-2124.2$  kJ mol \(^{-1}\) ${}^{-1}$ for the ammoniation enthalpy. In addition, the free energy of solvation is deeply affected when the temperature increases. This pattern can be attributed to the rise of entropy when the temperature rises. Besides, the temperature does not affect the ammoniation enthalpies and the hydration enthalpy of the \(Fe^{2+}\) $F{e}^{2+}$ ion.

All the geometry optimizations are performed at the MP2 methods associated with the 6-31++g(d,p) basis set of Pople. solvated phase structures of \(Fe^{2+}\) $F{e}^{2+}$ ion in water or in ammonia are performed using the PCM model. The \(Gaussian \ 16\) $Gaussian16$ program suite was used to perform all the calculations. The program TEMPO was also used to evaluate the temperature sensitivity of the different obtained geometries.