Supertetrahedral chalcogenide clusters, Tn, – n indicates the number of metal sites along the edge of the tetrahedron – are structurally precise fragments of the well-known cubic ZnS-type semiconductors. They can be regarded as the smallest semiconductor nanoparticles and have also been found to exhibit size-dependent optical properties. Unlike colloidal nanoparticles, supertetrahedral clusters can be crystallized and their structures analyzed with single crystal X-ray diffraction, which may provide insight into various structure/property relationships such as size-dependent band structures.

Tn clusters up to T4 with 20 metal sites can be synthesized in a discrete molecular form. Synthesis of larger discrete supertetrahedral clusters still remains a great challenge, likely due to the rapidly increasing negative charge on the cluster as the size goes up.

By using organic superbases (1,5-diazabicyclo[4.3.0]non-5-ene (DBN) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)) to help stabilize the negative charge, Pingyun Feng, University of California, Riverside, USA, and colleagues have made a family of discrete supertetrahedral chalcogenide clusters with sizes spanning from T3 (10 metal sites) to T5 (35 metal sites). The T5 cluster represents the largest molecular supertetrahedral Tn cluster known to date.

The use of organic superbases in the synthesis of chalcogenide materials opens a new route in the development of novel semiconducting clusters and frameworks.

• Superbase Route to Supertetrahedral Chalcogenide Clusters,
  Tao Wu, Xianhui Bu, Puhong Liao, Le Wang, Shou-Tian Zheng, Richard Ma, Pingyun Feng,
  J. Am. Chem. Soc. 2012.
  DOI: 10.1021/ja210039u