CsUV3O11, a new uranyl vanadate with a layered structure

A new cesium uranyl vanadate CsUV3O11 has been synthesized by solid state r eaction. Its crystal structure has been determined from single-crystal X-ra y diffraction data. It crystallizes in the monoclinic system with space gro up P2(1)/a and unit cell parameters a = 11.904(2) Angstrom, b = 6.8321(6) A ngstrom, c = 12.095(2) Angstrom, beta = 106.989(5)degrees, Z = 4, and D-exp = 4.89(2) g/cm(3). A full-matrix least squares refinement yielded R = 0.03 6 and R-w = 0.045 for 1831 independent reflections with I > 3 sigma(I) coll ected on a Nonius CAD4 diffractometer (MoK alpha radiation). The structure of CsUV3O11 is characterized by [UV3O11](infinity) layers parallel to the ( 001) plane. The layers, very similar to those found in UV3O10, are built up from VO5 square pyramids sharing corners of their equatorial bases and UO8 hexagonal bipyramids, the U atoms occupying the hexagonal holes created by the VO5 array. The Cs+ ions are located between two successive layers and hold them together; the Cs+ ions and two layers constitute a neutral "sandw ich" {(UV3O11-)-(Cs)(2)(2+)-(UV3CO11-)}. In this unusual structure, the neu tral sandwiches are stacked one above another along the [104] direction wit h no formal chemical bonds between the neutral sandwiches. The Cs mobilitie s in CsUV3O11 and Cs carnotite are compared. (C) 1999 Academic Press.