Tricopper tetrathioniobate(V), Cu3NbS4, has been synthesized by chemical transport reaction using iodine as the transport agent. The compound crystallizes in the sulvanite (Cu3VS4) structure type in space group P3m. The structure is composed of CuS4 and NbS4 tetrahedra sharing corners and edges.

No abstract

No abstract

The crystal structure of mercurous iodide, Hg2I2, has been determined previously from X-ray powder diffraction data [Havighurst (1926 ▶). J. Am. Chem. Soc. 48, 2113–2125]. The results of the current redetermination based on single-crystal X-ray diffraction data provide more precise geometrical data and also anisotropic displacement parameters for the Hg and I atoms, which are both situated on positions with site-symmetry 4mm. The structure consists of linear dimers I—Hg—Hg—I extending along the c axis with an Hg—Hg distance of 2.5903 (13) Å. The overall coordination sphere of the Hg+ atom is a considerably distorted octa­hedron. The crystal specimen under investigation was twinned by non-merohedry with a refined twin domain fraction of 0.853 (14):0.147 (14).

Single crystals of 2H and 3R niobium diselenide were grown by a chemical transport reaction. The current determinations by single crystals X-ray diffraction reveal a non-stoichiometric composition. The structures are built from Se—Nb—Se slabs with Nb in trigonal prismatic coordination whereas the extra or additional Nb atoms are located in the octahedral holes between the slabs giving rise to the formula 2H and 3R-Nb1+xSe2 with 0.07 < x < 0.118. In particular, vacancy and Nb-Nb interactions may play an important role on the non-stoichiometry and the stacking mode in NbSe2. By increasing the number of additional Nb atoms in the pure 2H-NbSe2, a transition 2H to 3R polytype should occur in order to minimize the Nblayer—Nbextra—Nblayer repulsions between these adjacent slabs. The theoretical study shows that both 2H and 3R-Nb1+xSe2 are thermodynamically stable in the range 0 < x < 0.1.