Structure of Chloric Acid Hydrates and Equilibrium Composition of the HClO4–H2O System.

Composition, structure, energy parameters, and existence regions of hydrate complexes formed in the HClO4–H2O system are studied by IR spectroscopy and quantum chemical methods. Three concentration-structural regions are determined. The HClO4–H2O solutions diluted to the 1:13.3 molar ratio of components contain and solvate-separated ions, each hydrated by four water molecules. More concentrated solutions (1:13.3-1:5) contain hydrated ion pairs that are contact ion pairs if the [HClO4]:[H2O] ratio falls within the region 1:9-1:5. As the acid concentration increases further up to the transition of the HClO4–H2O system into the solid phase, pair complexes are formed. The structure of the latter is formed by a cycle of two contact ion pairs connected by two H-bonds. The solid phase consists of interacting polymer chains formed by and ion pairs. [ABSTRACT FROM AUTHOR]