2D metal slabs in new nickel-tin chalcogenides Ni(7-delta)SnQ(2) (Q=Se, Te): average crystal and electronic structures, chemical bonding and physical properties

摘要

A systematic search for mixed low-valence, nickel-tin chalcogenides performed by establishing phase relations in the parts of Ni-Sn-Se and Ni-Sn-Te ternary systems resulted in the discovery of two new compounds, Ni5.62SnSe2 and Ni5.78SnTe2 Single crystals of both compounds were prepared by chemical transport with iodine and crystal structures were determined by single crystal X-ray investigation. The ED patterns for Ni5.78SnTe2 showed the presence of satellite reflections, which indicate a modulated structure with qapproximate to0.4a*. Average crystal structures of both compounds were determined to be of tetragonal symmetry (Sp.gr.I4/mmm, Z = 2) with a = 3.6890(8) Angstrom, c = 18.648(3) Angstrom, R-w = 0.0716 and a = 3.7680(5) Angstrom, c = 19.419(4) Angstrom, R-w, 0.0832, correspondingly, and are isostructural to known Ni5.72SbSe2 and Ni5.66SbTe2. Measurements were carried out for both compounds with respect to thermal, electrical and magnetic properties. Ab initio band structure calculations were also performed to take a first glance into the electronic structure of such type compounds. The anisotropy of their band structure was found. Physical property measurements showed both compounds to be the anisotropic metallic conductors and paramagnetics. Calculated difference charge density maps revealed pairwise covalent and multicenter metallic nature of the d-metal-chalcogen and d-metal-p-metal interactions, respectively. (C) 2004 Elsevier Inc. All rights reserved.