Syntheses, crystal structures and spectroscopic properties of Ag 2Nb[P 2S 6][S 2] and KAg 2[PS 4

Abstract

Ag 2Nb[P 2S 6][S 2] ( 1) was obtained from the direct solid state reaction of Ag, Nb, P 2S 5 and S at 500 °C. KAg 2[PS 4] ( 2) was prepared from the reaction of K 2S 3, Ag, Nd, P 2S 5 and extra S powder at 700 °C. Compound 1 crystallizes in the orthorhombic space group Pnma with a=12.2188(11), b=26.3725(16), c=6.7517(4) Å, V=2175.7(3) Å 3, Z=8. Compound 2 crystallizes in the non-centrosymmetric tetragonal space group I 4 ¯ 2 m with lattice parameters a=6.6471(7), c=8.1693(11) Å, V=360.95(7) Å 3, Z=2. The structure of Ag 2Nb[P 2S 6][S 2] ( 1) consists of [Nb 2S 12], [P 2S 6] and new found puckered [Ag 2S 4] chains which are along [001] direction. The Nb atoms are located at the center of distorted bicapped trigonal prisms. Two prisms share square face of two [S 2 2−] to form one [Nb 2S 12] unit, in which Nb–Nb bond is formed. The [Nb 2S 12] units share all S 2− corners with ethane-like [P 2S 6] units to form 14-membered rings. The novel puckered [Ag 2S 4] chains are composed of distorted [AgS 4] tetrahedra and [AgS 3] triangles that share corners with each other. These chains are connected with [P 2S 6] units and [Nb 2S 12] units to form three-dimensional frame work. The structural skeleton of 2 is built up from [AgS 4] and [PS 4] tetrahedra linked by corner-sharing. The three-dimensional anionic framework contains orthogonal, intersecting tunnels directed along [100] and [010]. This compound possesses a compressed chalcopyrite-like structure. The structure is compressed along [001] and results from eight coordination sphere for K +. Both compounds are characterized with UV/vis diffuse reflectance spectroscopy and compound 1 with IR and Raman spectra.