Nanocluster with one missing core atom: a three-dimensional hybrid superlattice built from dual-sized supertetrahedral clusters.

In addition to having size-dependent properties, nanoclusters also behave like large pseudo-atoms and serve as building blocks for the construction of superlattices with properties that differ from either individual clusters or the bulk. While colloidal nanoparticles usually self-assemble into close-packed lattices, supertetrahedral clusters that are regular fragments of the zinc blende-type lattice can form covalent lattices with large pore size and high pore volume. Unfortunately, the size of the known supertetrahedral cluster is still small, and only a few types are currently known. In addition, their superlattices invariably consist of clusters of identical size. Here we report an open framework sulfide (denoted as UCR-15) that extends the cluster size from 20 metal ions in a T4 supertetrahedron to 34 metal ions in a novel T5 supertetrahedron with a missing core atom, [In34S54]6-. T5 clusters are joined by smaller T3 clusters (i.e., [In10S18]6-) to form an extended superlattice. UCR-15 is the first example of a covalent open framework built from supertetrahedral clusters of different sizes, thus revealing new possibilities in the construction of crystalline nanoporous semiconducting superlattices. It is proposed here that the formation of the dual-sized T3 and T5 hybrid framework is related to the host-guest charge density matching.