The Structure of Na2W2O7· H2O Synthesized under High Pressure and Temperature

A new compound, Na2W2O7· H2O, has been found in the Na2O–WO3–H2O system. It is the fourth compound in the Na2W2O7·xH2O system and the second phase containing water. The crystals were prepared at a pressure of 1.5 GPa and a temperature of 900°C. Na2W2O7· H2O crystallizes in the triclinic space group, P , Z=2, with lattice constants of a=8.4902(6) ?, b=7.6636(6) ?, c=5.1501(3) ?, alpha=91.959(7)°, beta=96.521(8)° and gamma=111.678(7)°. The structure is built up from double chains of WO6 octahedra running along c, interconnected by two-dimensional nets of NaO6 polyhedra. Sodium coordinates to six oxygens forming both octahedra and trigonal prisms.