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 calixarene functionalities. These clusters are obtained from a synthesis feed containing binary mixtures of tetrathiolated calixarene 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 calixarenes to the Au 25 cluster surface with two or four thiolates per moiety. © 2014 American Chemical Society.