Atomically precise semiconductor clusters of rare-earth tellurides

Atomically precise clusters are important for understanding structure–property relationships of bulk materials. Here we report clusters of the general formula [K(2,2,2-cryptand)]₂[(μ₅-Cp*RE)₆(μ₆-κ³:κ³:κ³-Te₃)(μ-κ²:κ²-Te₂)(μ₃-η₂:κ:κ¹-Te₂)(μ₃-Te)₃] (Cp*, pentamethylcyclopentadienyl; RE = Y, Gd, Tb, Ho, Er). They are potential precursors to rare-earth tellurides, a class of topical quantum materials with interesting thermoelectric, magnetic, semiconducting and charge density wave properties. Crystallographic analyses reveal a common trigonal antiprismatic core of RE₆Te₁₀ with six RE atoms supported by three different types of tellurido ligands, namely Te^2–, Te₂^2– dianions, and a previously unknown tri-tellurido ligand Te₃^4–, upon which the six RE atoms are hinged into a pseudo-D_3d arrangement. Density functional theory studies reveal that the linear hypervalent Te₃^4– ion has the electronic structure characteristics of a three-centre, four-electron bond. Studies by ultraviolet–visible–near infrared spectroscopy and theoretical analyses suggest that these clusters are semiconductors with comparable band gaps to those of monocrystalline silicon and gallium arsenide.