HYDRATION OF SMALL ANIONS - CALCULATIONS BY THE AM1 SEMIEMPIRICAL METHOD

The AM1 semiempirical molecular orbital method has been used to calculate successive heats of hydration of small anions, including hydride, hydroxide, and the halogen ions, for cluster sizes up to 11 water molecules surrounding the central anion. Heats of hydration agree with available experimental data to within a few kcal/mol. Structures, however, do not always agree well with available ab initio calculations on clusters with one or two water molecules. The results indicate that the AM1 semiempirical technique applied to finite-sized clusters must be used with caution in understanding how hydration affects the chemical reactions of anions.