ИСТИНА

One of the relatively recent discoveries in the field of metal-rich inorganic compounds has been a family of metal-rich nickel - p-metal chalcogenides Ni7-xMCh2 and Ni10- xM2Ch2 (M = group 13-15 metal; Ch = S, Se, Te) containing AuCu3-type heterometallic fragments. In their structures, single- or double-stacked along the c axis Ni3M heterometallic fragments alternate with nickel-chalcogenide Ni3Ch2 fragments. Another important structural feature of these compounds is the possibility of varying the Ni3Ch2 fragment type (antifluorite plus defective Cu2Sb, or defective Cu2Sb).1 Presently, the least studied compounds of this type are those containing group 13 metals, particularly aluminum-containing ones, most probably due to the serious difficulties in obtaining single-phase samples by standard solid-state synthesis. In this work, we have synthesized samples of the compounds Ni6.01AlS2, Ni5.61AlSe2 and Ni7- хAlТe2 containing minimum amount of impurities by high-temperature ampoule synthesis using the KCl-LiCl salt mixture as a flux. The crystal structures of Ni6.01AlS2 and Ni5.61AlSe2 were refined by the full-profile Rietveld method against powder diffraction data. The Ni6.01AlS2 profile was described in the tetragonal system (a = 3.5438(3) Å, c = 18.1058(2) Å, V = 227.38(5) Å3, Rp/Rw/RBragg = 0.025/0.033/0.0051). It was found that nickel-sulfur fragments have two types — defective Cu2Sb-type and antifluorite type, as in other previously described sulfides Ni7-xMS2. The nickel-aluminum selenide profile can also be described in the tetragonal system within the Ni7-xMSe2 structure model (a = 3.5886(5) Å, c = 18.555(3) Å, V = 238.96(5) Å3, Rp/Rw/RBragg = 0.053/0.069/0.014); however, this compound only has one type of nickel-selenium blocks, the one with Cu2Sb-type structure. It should be noted that the samples contained a small amount of a metallic nickel impurity (~ 1%) in case of Ni6.01AlS2, and Ni3Se2 (~ 6%) in case of Ni5.61AlSe2. Electronic structure of Ni7-хAlCh2 (Ch = S, Se) was characterized based on the DFT calculations and electron localization function topology. All compounds are expected to be 3D metallic conductors and display an array of multi-centered heterometallic bonds.