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[(mu 5-Cp*RE)6(mu 6-kappa 3:kappa 3:kappa 3-Te3)(mu-kappa 2:kappa 2-Te2)(mu 3-eta 2:kappa:kappa 1-Te2)(mu 3-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 Te2-, Te22- dianions, and a previously unknown tri-tellurido ligand Te34-, upon which the six RE atoms are hinged into a pseudo-D3d arrangement. Density functional theory studies reveal that the linear hypervalent Te34- 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. A series of molecular rare-earth telluride clusters incorporating a three-centre, four-electron, tri-tellurido ligand (Te34-) are reported. These atomically precise clusters, possessing ultralow band gaps comparable to those of monocrystalline silicon and gallium arsenide, are potentially applicable as quantum materials and for optoelectronic applications.