Supramolecular capsules spontaneously assembled from molecular building blocks have long captivated chemists due to their abilities to encapsulate guest molecules, to serve as molecular flasks for chemical reactions, and to stabilize reactive intermediates and unstable species. In this regard, a polynuclear metal cluster, a highly reactive species in a multimetallic assembly, could possibly be embedded in a supramolecular capsule. Such encapsulation may afford a viable means to permit control over the coordination environments of individual metal atoms and facilitate the rational design of new clusters. In addition, encapsulation of metal clusters inside an isolated cavity may produce novel functional materials that own unique physical properties different from their bulk phase.
Professors Mei-Xiang Wang and Liang Zhao's research group recently reported the synthesis of a new metal cluster-encapsulated supramolecular capsule by use of a bowl-shaped macrocyclic ligand azacalix[6]pyridine (Py6). A (CºC)@Ag5-6 multinuclear silver carbide cluster aggregate is fully encapsulated by two Py6 ligands through both metal−ligand coordination and cation−p interactions, spotlighting a new synthetic strategy for supramolecular capsules. Encapsulation of reactive and unstable metal clusters within organic hosts further provides a promising practical means for their stabilization, thereby making their existing applications more feasible and potentiating some new applications. This work has been published on J. Am. Chem. Soc. 2012, 134, 824-827 (Cai-Yan Gao, Liang Zhao,* and Mei-Xiang Wang*).
