The preparation and crystal structure of a basic zirconium molybdate and its relationship to ion exchange gels

Abstract

ZrMo 2O 7(OH) 2(H 2O) 2 was prepared in microcrystalline form by refluxing precipitated zirconium molybdate gels in 1–4M HCl. Macroscopic single crystals have been grown under hydrothermal conditions. In their amorphous, precipitated-gel form the gels are known to function as cation-exchangers. The crystal structure of zirconium molybdate was determined from integrated precession photographs using MoKα radiation. Crystal data: tetragonal space group 14 1 cd (No. 110); a = 11·45±0·01 A ̊ c = 12·49±0·01 Å (25°C); ϱ obs = 4·0±0·1, ϱ calc = 3·774 g. cm −3. The structure, refined by block diagonal least squares to (conventional) R = 0·037, is a three-dimensional network of cross-linked chains built-up of quite regular [ZrO 3 eq (OH 2 eq O 2 ax ]-pentagonal bipyramids and distorted cis-MoO 4(OH)(H 2O-octahedra. The structure is held together primarily by [Zr-O (and OH)-Mo]-bridges; chains of hydrogen bonds involving the oxo-, hydroxo-, and aquo- groups play a secondary role. Intermatomic distances and angles are normal, however, one oxygen atom has unusual coordination geometry; it forms a three-way bridge in a (symmetry-required) planar [ZrOMo 2]-moiety. The structure provides a rationale for the thus far observed physical and chemical properties.