The crystal structure of Cs2W3010 (a = 16.103, c = 10.169 A, 14, Z = 120/11) was determined from three-dimensional X-ray diffraction data (CAD-4 automatic diffractometer, 1612 reflections, R = 0.044 In the course of investigations of the Cs2WO4-WO3 system [1], we confirmed formation of the Cs2W3010 compound, which has no pronounced homogeneity region according to XRPA data. Examination of these colorless isometric crystals of cesium polytungstate in a RKOP chamber (Mo radiation, Lane and oscillating crystal methods) showed that they correspond to the Cs22W320107 phase [2], whose structure is isotypical to the rubidium analog studied in [2, 3]. According to the structure refinement [3], the composition of the latter compound is expressed by the formula Rb2o+x(W406)l/3_x/12W3201os, suggesting the presence of a certain homogeneity region. To resolve this contradiction concerning the composition of cesium tritungstate we undertook an X-ray diffraction investigation of this compound.For structure determination we chose an isometric sample with an average size of about 0.2 ram. The parameters of the tetragonal unit cell (a = 16.103(2), c = 10.169(2) ~, V = 2536.9 ~3) were refined, and the intensities of 3277 reflections were measured ("Enraf-Nonius" CAD-4 automatic diffractometer, MoK a radiation, graphite monochromator, 09/20 scan mode, 20 < 60~ The intensities of the measured reflections were recalculated to structural amplitudes including absorption corrections estimated from transmission curves (u(MoKa) = 441.7 era-l); the calculations were performed on a PDP-11 computer with the SDP program package. Other structure calculations were accomplished with SHELXL-93 programs [4] using 1612 unique reflections with I > 2xr(/).Systematic extinctions (hkl : h + k + l = 2n) in the array of diffraction data satisfied three space groups:/4, 14, and 14/m. All further calculations were performed in space group/4, which was determined for the isotypical rubidium analog [2, 3], using the set of coordinates of heavy atoms from [2] as an initial approximation. The isotropic refinement of the set led to R = 0.120; the difference Fourier synthesis gave all 14 independent oxygen atoms and the W(5) defective site as shown by additional maxima in the vicinity of Cs(5) (the site was found earlier in [2]). The isotropic refinement of all atomic coordinates using the experimental weighting scheme yielded R = 0.082; anisotropic refinement including secondary extinction gave R = 0.044. In the final cycle of refinement, two partly defective oxygen positions, found from the Ap(xyz) synthesis, were added to the model of the structure; the sites were ascribed the same occupancy as for the coordinating W(5) atom. This minor addition did not alter the residual. The f'mal positional and Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences.
