Elimination-Fusion Self-Assembly of a Nanometer-Scale 72-Nucleus Silver Cluster Caging a Pair of [EuW O ] Polyoxometalates.

The largest known polyoxometalate (POM)-templated silver-alkynyl cluster, [(EuW O ) @Ag (tBuC≡C) Cl ⋅4 BF ] (SD/Ag20), was isolated under solvothermal conditions and structurally characterized. It was confirmed by single-crystal X-ray diffraction (SCXRD) as a {EuW } -in-{Ag } 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 intermediate in the solution. The crystallization of Ag species (SD/Ag21), followed by SCXRD, gave an important clue about the assembly route of SD/Ag20 in solution: the Ag cluster eliminates six silver atoms laterally, then fuses together at the vacant face to form the final Ag cluster (elimination-fusion mechanism). The characteristic emission of [EuW O ] 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.