Structure of the complex ion in aqueous solutions of zirconyl and hafnyl oxyhalides

Abstract

X-ray scattering by aqueous solutions of MOX2·8H 2O (M = Zr and Hf, X = Cl and Br) can be explained if one assumes the existence of a complex [M4(OH)3 (H2O) 16]X3. The metal atoms in this complex are arranged in a square and are held together by double OH bridges along each edge. In addition, each metal atom is bound to four additional water molecules in such a manner that the configuration about the metal is a square Archimedes antiprism. The halogen ions are not bound directly to the metal. They do, however occupy definite positions in the complex, and are presumably held in place by electrostatic forces. The structure is very similar to that which has been found in the crystalline oxyhalides.