Cs0.49NbPS6

The quaternary thiophosphate, Cs0.49NbPS6, caesium hexathioniobiophosphate(V), has been synthesized by the reactive halide flux method. The title compound is isotypic with Rb0.46TaPS6 and is made up of a bicapped trigonal–biprismatic [Nb2S12] unit and a tetrahedral [PS4] group. The [Nb2S12] units linked by the [PS4] tetrahedra form infinite chains, yielding a three-dimensional network with rather large van der Waals gaps along the c axis in which the disordered Cs+ ions reside. The electrons released by the Cs atoms are transferred to the pairwise niobium metal site and there are substantial intermetallic Nb—Nb bonding interactions. This leads to a significant decrease of the intermetallic distance in the title compound compared to that in TaPS6. The classical charge balance of the title compound may be represented as [Cs+]0.49[Nb4.51+][P5+][S2−]4[S2 2−].

The quaternary thiophosphate, Cs 0.49 NbPS 6 , caesium hexathioniobiophosphate(V), has been synthesized by the reactive halide flux method. The title compound is isotypic with Rb 0.46 TaPS 6 and is made up of a bicapped trigonal-biprismatic [Nb 2 S 12 ] unit and a tetrahedral [PS 4 ] group. The [Nb 2 S 12 ] units linked by the [PS 4 ] tetrahedra form infinite chains, yielding a three-dimensional network with rather large van der Waals gaps along the c axis in which the disordered Cs + ions reside. The electrons released by the Cs atoms are transferred to the pairwise niobium metal site and there are substantial intermetallic Nb-Nb bonding interactions. This leads to a significant decrease of the intermetallic distance in the title compound compared to that in TaPS

Comment
During an effort to find a new phase in the A x MPS 6 family (A=alkali metals; M=Ta, Nb), a new compound was isolated.
Here we report the synthesis and structure of the new quaternary thiophosphates, Cs 0.49 NbPS 6 .
The title compound is isostructural with the previously reported Rb 0.46 TaPS 6 (Gutzmann et al., 2004a). The structure of Cs 0.49 NbPS 6 is also very similar to that of ANb 2 P 2 S 12 (A=K, Rb, and Cs, Gieck et al., 2004) prepared from alkali metal sulfide fluxes. The only difference between them lies in the distribution of the alkali metals. There are two crystallographically independent sites for Cs atoms in ANb 2 P 2 S 12 , while we were able to find only one in Cs 0.49 NbPS 6 .
The structure of Cs 0.49 NbPS 6 is made up of the bicapped trigonal biprismatic [Nb 2 S 12 ] unit and the tetrahedral [PS 4 ] group. The niobium atom is coordinated by eight sulfur atoms in a distorted bicapped trigonal prismatic arrangement. Two NbS 8 prisms share a rectangular face to form the [Nb 2 S 12 ] dimeric core. Four sulfur atoms sharing rectangular prism faces are in pairs with two disulfide ions, (S-S) 2-. Each one of the capping sulfur atoms and one of the sulfur atoms at the corner of the [Nb 2 S 12 ] unit are bound to a phosphorous atom (Fig. 1) (Fig. 2). The structural array yields rather large channels, where the Cs + ions reside. The size of the cations is small compared to the diameter of the large channels and the cations can therefore rattle within the channels as indicated by the high anisotropic displacement parameters.
The Nb-S and P-S distances are in good agreement with those found in other related phases (Gutzmann et al., 2004b).

Experimental
Cs 0.49 NbPS 6 was prepared by the reaction of elements Nb, P, and S by the reactive halide-flux technique. A combination of the pure elements, Nb powder (CERAC 99.999%), P powder (CERAC 99.5%) and S powder (Aldrich 99.999%) were mixed in a fused silica tube in molar ratio of Nb:P:S=1:1:6 in the presence of CsCl as flux. The mass ratio of the reactants and the alkali halide flux was 1:2. The tube was evacuated to 0.133 Pa, sealed, and heated gradually (60 K/h) to 973 K, where it was kept for 72 h. The tube was cooled to room temperature at the rate 4 K/h. The excess halide was removed with distilled water and shiny black needle-shaped crystals were obtained. The crystals are stable in air and water. Qualitative supplementary materials sup-2 analysis of the crystals with an EDAX-equipped SEM indicated the presence of Cs, Nb, P, and S. The composition of the compound was determined by single-crystal X-ray diffraction.

Refinement
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