Mixed-Monolayer-Protected Au25 Clusters with Bulky Calix[4]arene Functionalities

Although various complex, bulky ligands have been used to functionalize plasmonic gold nanoparticles, introducing them to small, atomically precise gold clusters is not trivial. Here, we demonstrate a simple one-pot procedure to synthesize fluorescent magic number Au25 clusters carrying controlled amounts of bulky calix[4]­arene functionalities. These clusters are obtained from a synthesis feed containing binary mixtures of tetrathiolated calix[4]­arene and 1-butanethiol. By systematic variation of the molar ratio of ligands, clusters carrying one to eight calixarene moieties were obtained. Structural characterization reveals unexpected binding of the calix[4]­arenes to the Au25 cluster surface with two or four thiolates per moiety.