Entropy-driven structures of the hexaaqua-sodium(I)

Abstract

Thermodynamic energies of hydrated sodium ions predicted by extensive ab initio calculations are in excellent agreement with experiment. The hexaaqua-Na(I) ion shows entropy-driven structures: the primary hydration number is 4 at low temperatures and 5 at near room temperatures in spite of the fact that the coordination number generally decreases with increasing temperature. One semi-free water molecule in the outer shell is responsible for the sudden decrease in the absolute magnitude of the successive entropy change.