The quinternary thiophosphate Cs0.5Ag0.5Nb2PS10

The quinternary thiophosphate Cs0.5Ag0.5Nb2PS10, cesium silver tris(disulfido)[tetrathiophosphato(V)]diniobate(IV), has been prepared from the elements using a CsCl flux. The crystal structure is made up of ∞ 1[Nb2PS10] chains expanding along [010]. These chains are built up from bicapped trigonal-prismatic [Nb2S12] units and tetrahedral [PS4] groups and are linked through a linear S—Ag—S bridge, forming a two-dimensional layer. These layers then stack on top of each other, completing the three-dimensional structure with an undulating van der Waals gap. The disordered Cs+ ions reside on sites with half-occupation in the voids of this arrangement. Short [2.8843 (5) Å] and long [3.7316 (4) Å] Nb—Nb distances alternate along the chains, and anionic S2 2− and S2− species are observed. The charge balance of the compound can be represented by the formula [Cs+]0.5[Ag+]0.5[Nb4+]2[PS4 3−][S2 2−]3.


Experimental
Crystal data

Comment
During an effort to expand representatives of group 5 transition metal thiophosphates by substituting various monovalent cations, we were able to prepare a new derivative in this system. Here we report the synthesis and characterization of the new layered quinternary thiophosphate, Cs 0.5 Ag 0.5 Nb 2 PS 10 . The disordered Cs + cations reside in the voids of this arrangement.
The Nb-S and P-S distances are in agreement with those found in other related phases (Brec et al., 1983). Along the chain, The Nb(1)···Nb (2) interactions alternate in the sequence of one short (2.8843 (5) Å) and one long (3.7316 (4) Å) distance. The short distance is close to that of the typical Nb 4+ -Nb 4+ bond (Angenault et al., 2000), and the long Nb···Nb distance shows that there is no significant intermetallic bonding interaction. Such an arrangement is consistent with the high electric resistivity of the crystal along the needle axis (b axis).
The coordination around the Ag atom (1 symmetry) can be described as a [2 + 4] interaction. Four S atoms are bound to the Ag atoms in the plane (Ag-S6, 3.139 (3) Å, Ag-S9, 3.232 (3) Å), whereas two trans S atoms are coordinated to the Ag atom at short distances of Ag-S1 = 2.4625 (13)  were mixed in a fused silica tube in a molar ratio of Ag:Nb:P:S=1:2:1:10 and then CsCl was added in a weight ratio of AgNb 2 PS 10 :CsCl=1:3. The tube was evacuated to 0.133 Pa, sealed and heated gradually (50 K/h) to 973 K, where it was kept for 72 h. The tube was cooled to room temperature at the rate of 4 K/h. The excess halide was removed with distilled water and dark red needle-shaped crystals were obtained. The crystals are stable in air and water. A qualitative X-ray fluorescence analysis of the needles indicated the presence of Cs, Ag, Nb, P, and S. The composition of the compound was determined by single-crystal X-ray diffraction.

Refinement
Refinement went smoothly but the anisotropic displacement parameters (ADPs) of the Cs (Wyckoff position 4e) and Ag (2a) atoms were large compared with those of the other atoms. Because non-stoichiometry in these phases is sometimes observed and the distance between Cs atoms is too short if full occupancy is assumed, the occupancies of each metal atom were checked by refining the site occupation factors (SOFs) while those of the other atoms were fixed. With the non-stoichiometric model, the SOF of the Cs site was reduced significantly from 1 to 0.49 and the residuals improved also. As no evidence was found for ordering of the Cs site at Wyckoff position 2c, a statistically disordered structure was finally modelled.  Fig. 1. A view of the Cs 0.5 Ag 0.5 Nb 2 PS 10 structure. Anisotropic displacement ellipsoids are drawn at the 90% probability level. Symmetry codes are given in Table 1.