First examples of nickel–Aluminum mixed chalcogenides based on the AuCu3-type fragments: Breaking a robust intermetallic bond system in Ni3Al

Three new mixed nickel-aluminum chalcogenides, Ni6.07AlS2, Ni5.61AlSe2, and Ni5.70AlTe2, have been synthesized by a high-temperature ampoule route using the addition LiCl and KCl. The former compound was characterized from single-crystal synchrotron and powder diffraction data, and the latter two by powder diffraction data. All compounds crystallize in the tetragonal system with I4/mmm space group and belong to the relatively uncommon Ni7-xMQ2 structure type (M ​− ​main-group metal). The compounds Ni5.61AlSe2 and Ni5.70AlTe2 represent first ternaries discovered in the respective systems. The main heterometallic structural units of all three compounds are aluminum-centered [Ni12Al] cuboctahedra of the AuCu3-type, single-stacked along the c axis, alternating with [Ni4-xQ2] (Q ​= ​S, Se, Te) along the c axis with either nickel-sulfur fragments of the Li2O and defective Cu2Sb/NaCl type, or with nickel-selenium/nickel-tellurium fragments of the defective Cu2Sb/NaCl type respectively. According to the DFT calculations, electronic structures of these ternary compounds are directly related to their parent intermetallic Ni3Al. Non-zero density of states (DOS) at the Fermi level for all compounds indicates metallic conductivity. The ELF topological analysis has shown four-center 3Ni ​+ ​Al bonds both in Ni3Al and ternary nickel-aluminum chalcogenides, with additional pairwise nickel-chalcogen interactions in the latter. Magnetic measurements on Ni6.07AlS2 show the temperature-independent Pauli-like paramagnetism, predicted by DFT calculations for all three chalcogenides, which is in contrast with ferromagnetic behavior of its parent intermetallic.