Zirconium phosphates partially exchanged with transition-metal ions: characterisation and stereochemical changes induced by heat treatment

Abstract

The α and γ forms of zirconium phosphate partially exchanged (between 20 and 90%) with Co²⁺, Ni²⁺, or Cu²⁺ have been characterised, and changes in stereochemistry about the metal ion followed using mainly electronic reflectance spectroscopy. The stereochemistries found in the room-temperature forms are the same as for the 100%-exchanged α form reported previously, i.e. octahedral. After heating these materials at 400 °C (i.e. when layer structures are still present), the stereochemistries about the metal ions are different from those in 100%-exchanged forms. Further heating, to 900 °C (destruction of layer structure), leads to further stereochemical changes. The other phases remaining in such materials thus influence the geometry of the cavity between the layers. Evidence is presented for the presence of five-co-ordinate geometries (both trigonal bipyramidal and square-based pyramidal) for Co²⁺- and Ni²⁺-containing materials.