Elimination-Fusion Self-Assembly of a Nanometer-Scale 72-Nucleus Silver Cluster Caging a Pair of [EuW10O36](9-) Polyoxometalates

The largest known polyoxometalate (POM)-templated silver-alkynyl cluster, [(EuW10O36)(2)@Ag-72(tBuC equivalent to C)(48)-Cl-2 center dot 4BF(4)] (SD/Ag20), was isolated under solvothermal conditions and structurally characterized. It was confirmed by single-crystal X-ray diffraction (SCXRD) as a {EuW10}(2)-in-{Ag-72} clusters-in-cluster rod-like compound. The high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) shows that such a double anion-templated cluster is assembled from a crucial single anion-templated Ag-42 intermediate in the solution. The crystallization of Ag-42 species (SD/Ag21), followed by SCXRD, gave an important clue about the assembly route of SD/Ag20 in solution: the Ag-42 cluster eliminates six silver atoms laterally, then fuses together at the vacant face to form the final Ag-72 cluster (elimination-fusion mechanism). The characteristic emission of [EuW10O36](9-) is well maintained in SD/Ag20. This work not only provides a new method for the synthesis of larger silver clusters as well as the functional integration of the silver cluster and POMs, but also gives deep insights about the high-nuclear silver cluster assembly mechanism.