Nickel – p-block metal mixed chalcogenides based on AuCu3-type fragments: iodine-assisted synthesis as a way of obtaining new structures

Abstract

Two new mixed nickel–gallium chalcogenides, Ni_9.39Ga₂S₂ and Ni_5.80GaTe₂, and a new mixed nickel–indium telluride, Ni_5.78InTe₂, have been synthesized by a high-temperature ampoule route with the addition of iodine, and characterized from single-crystal or powder diffraction data. They belong to the relatively uncommon Ni_7−xMQ₂/Ni_10−xM₂Q₂ type of structures (M = Ge, Sn, Sb, In), and are built from p-block metal-centered nickel cuboctahedra, alternating along the c axis with defective Cu₂Sb-type nickel–chalcogen ones. Both tellurium-containing compounds show a small degree of orthorhombic distortion with respect to the idealized tetragonal structure, only detectable in the powder diffraction data. No phase transition to the tetragonal structure was detected for Ni_5.80GaTe₂ by the in situ powder diffraction measurements from room temperature to 550 °C. DFT calculations show close relationships of electronic structures of these ternary compounds to their parent intermetallics, Ni₃M (M = Ga, In). Metallic conductivity and paramagnetic properties are predicted for all three with the latter confirmed by magnetic measurements. The bonding patterns, investigated via the ELF topological analysis, show multi-centered nickel – p-block metal bonds in the AuCu₃-type fragments and pairwise covalent interactions in the nickel–chalcogen fragments. Both Ni_7−xMTe₂ compounds showed no structural or compositional changes upon high-temperature mid-pressure hydrogenation.