Synthesis and crystal structure of double sodium zirconium molybdates

The double molybdates of the Na2Zr(MoO4)3 (1:1) and Na4Zr(MoO4)4 (2:1) compositions are found in the Na2MoO4-Zr(MoO4)2 system. The compounds are melted at 610 deg (1:1) and 625 deg C (2:1) with decomposition. The monocrystals are obtained from solution in the Na2Mo2O7 melt. The crystal structures are determined and refined by the method of least squares according to the three-dimensional diffraction data up to R=0.09 and 0.092 (in isotropic approximation). In the Na2Zr(MoO4)3 structure the coordination polyhedrons (Na- and Zr-octahedrons and Mo-tetrahedrons) and their bonds are similar to scheelite ones. The analogous coordination (8 and 4) is characteristic for Zr atoms in the Na4Zr(MoO4)4 structure but coordination of Na atoms is decreased to octahedral one. The relationship of both structures with scheelite structure is analyzed