Crystal structure of the stoichiometric compound Cs2W3O10 with a fractional number of atoms in the unit cell

Abstract

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.

Resolving old problems with layered polytungstates related to hexagonal tungsten bronze: phase formation, structures, crystal chemistry and some properties

“…This is confirmed by a good agreement of their experimental diffractograms with the PXRD patterns calculated from the structural data (see the ESI†) despite a strong texture and X-ray absorption of the powder samples. The cation–oxygen distances in the average structures are generally in agreement with the corresponding bond lengths in other polytungstates and oxides, 5,9,18,21,26,27,31,67 excluding some shortened distances K–O and Rb–O (Table 3). It should be noted that these data confirm the compositions and idealized structural models of the compounds proposed by us in ref.…”

“…Rubidium tritungstate Rb 2 W 3 O 10 isostructural with Cs 2 W 3 O 10 26 was prepared by both solid-state synthesis from Rb 2 CO 3 + 3WO 3 at 650–800 °C for 50 h and spontaneous crystallization of the melting samples of the system Rb 2 WO 4 –WO 3 containing 65–70 mol% WO 3 at cooling rates of 3–0.3 °C h −1 in the temperature range of 900–800 °C. PXRD data of the samples with compositions Rb 2 O : WO 3 = 1 : 2, 1 : 2.5, 1 : 2.85 and 1 : 3.15 indicate no marked homogeneity regions for Rb 2 W 3 O 10 in contrast to the data of ref.…”

“…The unit cell parameters found in this work for the Rb 2 W 3 O 10 crystals are given in Table 1. The structures of A 2 W 3 O 10 ( A = Rb, Cs) were discussed in detail by us 26 as ordered defect derivatives of pyrochlore-like RbNiCrF 6 type 61 with the unique ‘substitution’ of some [W 4 O 6 ] tetrahedral groups by large A + ions and the unit cell contents A 20 W 32 O 108 [ A 20/11 (W 4 O 6 ) 2/11 ] or A 2 W 3 O 10 ( Z = 120/11).…”

“…6,7,16,17,[19][20][21][22][23] Cesium polytungstates of similar compositions were also revealed along with Cs 6 W 11 O 36 . 7,16,17,20,[24][25][26][27] However, our data on the system Cs 2 WO 4 -WO 3 28,29 did not confirm the existence of Cs 2 W 2 O 7 . In the less explored Tl 2 WO 4 -WO 3 system, different authors have found Tl 2 W 2 O 7 , Tl 2 W 3 O 10 , and Tl 2 W 4 O 13 and suggested the formation of Tl 2 W 6 O 19 .…”

Nonlinear optical and self-activated luminescent properties of A2W3O10 (A = Rb and Cs)

“…11 The nal R indices of Rb 2 W 3 O 10 and Cs 2 W 3 O 10 are 0.0488 and 0.0466, respectively, which are comparable with the literature. [6][7][8] Crystallographic data, atomic coordinates and the equivalent isotropic displacement parameters are listed in Table S1 and S2 in ESI. †…”