Hydrothermal Synthesis of Lanthanum Vanadates: Synthesis and Crystal Structures of Zircon-Type LaVO4 and a New Compound LaV3O9

In the course of hydrothermal synthesis of lanthanum vanadates, zircon-type LaVO4 and LaV3O9 have been obtained and structurally characterized. The former is a metastable phase, and the latter is a new compound. Single-crystal X-ray diffractometry confirmed the zircon-type structure for LaVO4: I41/amd with a=7.4578(7) ?, c=6.5417(9) ?, and Z=4; R= 0.020 and Rw=0.025 for 276 reflections with I>3(I). The structure consists of isolated VO4 tetrahedra which surround the La atom to form a LaO8 dodecahedron. LaV3O9 adopts the monoclinic system: P21/m with a=4.949(2) ?, b=9.547(3) ?, c= 7.411(2) ?, =100.76(2)°, and Z=2; R=0.035 and Rw=0.042 for 1868 reflections with I>3(I). The structure adopts a chaintype one consisting of a V3O9 chain along [010] which is made up of edge-sharing VO5 trigonal-bipyramid pairs and VO4 tetrahedra. The La atom residues between the V3O9 chains and is coordinated with ten oxygens. The present study demonstrates the applicability of hydrothermal method to the synthesis of new and/or metastable lanthanide vanadates.