Lattice-Matched Transition Metal Disulfide Intergrowths: The Metallic Conductors Ag2te(Ms2)(3) (M = V, Nb)

We present new chalcogenide compounds, Ag2Te(MS2)(3) (M = V, Nb), built up of alternating planes of [MS2] and [Ag2Te]. The Ag and Te atoms are linearly coordinated by S atoms in the [MS2] layers and held in place by covalent interactions. Structural polymorphism was found by single crystal X-ray diffraction studies, where long-range ordering or disorder of the Ag and Te atoms within the hexagonal planar [Ag2Te] layer yielded two distinct crystal forms. When the Ag and Te atoms are ordered, the two isostructural compounds crystallize in the non-centrosymmetric P (6) over bar 2m space group, with a = 5.5347(8) angstrom, c = 8.0248(16) angstrom, and V = 212 89(6) angstrom(3) for alpha-Ag2Te(VS2)(3) and a = 5.7195(8) angstrom, c = 8.2230(16) angstrom, and V = 232.96(6) angstrom(3) for alpha-Ag2Te(NbS2)(3). For the occupationally disordered Ag/Te arrangement, a subcell of the ordered phase that crystallizes in the non-centrosymmetric P (6) over bar m2 space group, with a = 31956(6) angstrom (=a(a)/(3)(1/2)), c = 8.220(2) angstrom, and V = 77.31(3) angstrom(3) for beta-Ag2Te(VS2)(3), was identified. Furthermore, pair distribution function analysis revealed local distortions in the [Ag2Te] layer. Band structure calculations at the density functional theory level were carried out to investigate the electronic structure of Ag2Te(MS2)(3). Electronic transport measurements on Ag2Te(MS2)(3) show that they exhibit p-type metallic behavior. Thermal analyses and temperature-dependent powder X-ray diffraction studies were focused on the stability and transformation/decomposition of the Ag2Te(MS2)(3) phases. Magnetic susceptibility data are also reported. The new intercalated Ag2Te(MS2)(3) system features a unique hypervalent Te with a three-center, four-electron bonding environment isoelectronic to that found in I-3(-).