An X-ray diffraction study of Rh(III) coordination in a dilute aqueous solution of Rh(ClO4)3

A dilute aqueous solution of Rh(ClO₄)₃ in an excess of perchloric acid has been examined by X-ray diffraction. The existence of well defined Rh(H₂O)₆³⁺ ions has been established. Structural parameters regarding the first and second hydration shells of the Rh(III) ion have been determined. Polynuclear Rh³⁺ complexes are excluded by the experimental conditions. Satisfactory agreement with experimental data is achieved through a model in which the perchlorate anion is considered devoid of any discrete interaction with surrounding molecules, and the water not involved in hydration is assumed to retain the structure of pure water.