Largest Molecular Clusters in the Supertetrahedral Tn Series

Supertetrahedral Tn clusters are exact fragments of cubic ZnS-type lattice and are often formed in situ as building units for the construction of 3-D open-framework chalcogenide materials. Small Tn clusters can also be synthesized in discrete forms, allowing them to exist as soluble species in solution. In addition to their tunable electronic and optical properties, these soluble clusters can be used as precursors for the synthesis of porous semiconducting and optical materials. However, the synthesis of large Tn clusters is a significant challenge, and for several decades prior to this work, the size of the discrete Tn cluster remained at T3, with only 10 metal sites (e.g., [Cd10S4(SPh)(16)](4-) and [M5Sn5S20](10-), M = Zn, Co). Here we report a family of discrete chalcogenide T4 clusters ([M(x)Ga(18-x)Sn(2)Q(35)](12-), x = 2 or 4; M = Mn, Cu, Zn; Q = S, Se) whose discovery resulted from an unusual phase transformation from a 3-D T4 covalent framework into 0-D T4 molecular clusters. The driving force for such a transformation is the perfect match in both charge density and geometry between chalcogenide clusters and protonated amine, leading to the higher stability of isolated clusters. The perfect match is achieved by using complex quaternary compositions to maximize charge tunability of the cluster. These T4 clusters are the largest molecular Tn clusters known to date and can be made in various compositions showing tunable band structures in both solution and solid state.