Syntheses, crystal structures and spectroscopic properties of Ag2Nb[P2S6][S2] and KAg2[PS4]

Ag2Nb[P2S6][S2] (1) was obtained from the direct solid state reaction of Ag, Nb, P2S5 and S at 500 °C. KAg2[PS4] (2) was prepared from the reaction of K2S3, Ag, Nd, P2S5 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) Å3, Z =8. Compound 2 crystallizes in the non-centrosymmetric tetragonal space group View the MathML sourceI4¯2m with lattice parameters a=6.6471(7), c=8.1693(11) Å, V=360.95(7) Å3, Z=2. The structure of Ag2Nb[P2S6][S2] (1) consists of [Nb2S12], [P2S6] and new found puckered [Ag2S4] 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 [S22−] to form one [Nb2S12] unit, in which Nb–Nb bond is formed. The [Nb2S12] units share all S2− corners with ethane-like [P2S6] units to form 14-membered rings. The novel puckered [Ag2S4] chains are composed of distorted [AgS4] tetrahedra and [AgS3] triangles that share corners with each other. These chains are connected with [P2S6] units and [Nb2S12] units to form three-dimensional frame work. The structural skeleton of 2 is built up from [AgS4] and [PS4] 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.