New layered caesium zinc hydrogen phosphate, CsZn2.5(HPO4)3· 2H2O; synthesis, crystal structure and thermal transformation

Abstract

The synthesis, crystal structure and thermal transformation of a new caesium zinc hydrogen phosphate hydrate, CsZn_2.5(HPO₄)₃·2H₂O, is reported. This material crystallised from a gel with molar composition 1 ZnO∶0.48 P₂O₅∶0.24 Cs₂O∶12 H₂O∶4.8 MeCO₂H, and pH of 1.0, after two months at room temperature. The crystal structure of CsZn_2.5(HPO₄)₃·2H₂O has layers built from PO₄ and ZnO₄ tetrahedra and with other zinc atoms forming octahedra by coordination to water molecules. The zinc octahedra are placed across pseudo 12-rings and caesium ions are placed above and below eight-ring openings. Thermal analysis was performed using thermogravimetric (TG) and differential scanning calorimetric (DSC) measurements. Two weight losses were detected and assigned to expulsion of crystal water and water from condensation of hydrogen phosphate. DSC was used to estimate enthalpy changes from three thermal events.