Clustering of Zirconium Atoms in Zr 5 Te 6 : A Novel NiAs‐Type‐Related Telluride with Ordered Vacancies

Zr 5 Te 6 has been synthesized and its structure determined by means of single crystal X‐ray diffraction to be trigonal, $P {\bar 3} m1$ , Z =3, Pearson symbol hP 33, a =1172.8(2) pm, c =707.0(1) pm. Zr 5 Te 6 adopts a metal‐deficient, vacancy‐ordered 3 a ×3 a ×1 c superstructure of the NiAs type structure. In the Zr atom layers, alternately one and two out of nine Zr atoms are missing. The less densely populated layers (7/9) consist of star‐shaped Zr 7 clusters with intracluster contacts of 351.1 pm; the shortest Zr–Zr intercluster distance is 470.5 pm. In the more densely populated Zr atom layers (8/9), three quarters of the Zr atoms are arranged to pairs (326.4 pm). The distinctive distribution of the vacancies affords a topologically uniform fivefold Zr coordination (283.5–302.6 pm) for all three crystallographically inequivalent Te atoms. They are shifted towards the vacancies in the Zr atom layers. The associated corrugation of the Te atom layers is characterized by an amplitude of 28 pm. The Te–Te contacts are ≥368.1 pm. According to extended Hückel calculations, the defects in the Zr atom layers lead to a reduction in overall Zr–Te bonding interactions relative to ZrTe (NiAs). However, through the clustering the total attractive intralayer Zr–Zr interactions increase considerably, thus providing decisive stabilization of the structure. As revealed by thermal analyses, Zr 5 Te 6 undergoes a reversible phase transition at 1513±5 K. On the Zr‐rich side, Zr 5 Te 6 coexists with ZrTe (WC), and, above 1438±5 K with the hitherto unknown ZrTe (MnP). Zr 5 Te 6 exhibits temperature independent paramagnetic properties ( χ mol =0.7×10 −3  cm 3  mol −1 ) that are typical for a metallic conductor. An abrupt increase in the magnitude of the diamagnetic susceptibility below 2.2 K in a weak magnetic field indicates a superconducting transition.