Electronic Structure and Physical Properties of Hf 5 Sb 9 containing a Unique T Net of Sb Atoms

Hf 5 Sb 9 was the first and thus far only example of an inorganic material that contains a pure T net, i.e. a planar layer of three‐bonded Sb atoms. It crystallizes in a super structure of the ZrSiS type, wherein the originally square layers are diluted and deformed to form said T net. Each Sb atom of this net, labeled Sb3, is connected to three symmetry equivalent Sb atoms at distances of about 3Å, reminiscent of molecular T examples such as BrF 3 . According to electronic structure calculations, these three Sb3–Sb3 interactions correspond to medium strong bonds. Hf 5 Sb 9 is a high‐temperature antimonide that decomposes slowly under formation of HfSb 2 at intermediate temperatures such as 750 °C, while it can be stored literally for years at room temperature. Like all other studied binary hafnium antimonides, Hf 5 Sb 9 is metallic with a small Seebeck coefficient.