A series of structurally related hcp-like silver clusters suggests faceted lateral cluster growth

While nanoparticles and metalloid clusters are increasingly important, their formation and growth remain incompletely understood. Due to the enormous inherent complexity, the elucidation of the respective processes is usually limited to templated reactions, approximate modelling and indirect mechanistic inference. Herein, we report the synthesis of a series of metalloid silver clusters with 128, 132, 146 and 160 silver atoms within their respective silver cores. All compounds are highly unstable towards light and temperature. Nevertheless, we were able to confirm their structure using single-crystal X-ray diffraction. We discovered strong similarities between them, e.g. an overall hexagonal-prismatic shape, an unusual hcp-derived arrangement of the silver atoms within their core and the absence of partly occupied lateral facets. The title compounds form from near-identical conditions. Accordingly, a common reaction pathway in which lateral growth occurs in discrete steps seems plausible. As no thiolates were used during the synthesis, only chlorides and phosphines act as stabilizing ligands. The position of the chloride ligands within the molecules might prove to be essential for the faceted growth of the title compounds. As quantum chemical calculations indicate small Kohn-Sham frontier-orbital gaps, the structure and composition might be mostly governed by geometric factors, providing insights into the formation process of faceted nanoparticles on an atomic scale.