ABSTRACT
This chapter examines the types of metal clusters which truly reinvented the relevance of the superatomic concept, by making it applicable to clusters outside of vacuum chambers, and that can exist in solution. A ligand is a molecule that bonds to a metal atom. The bond can range between ionic and covalent in character, which influences the distribution of electronic charge at the surface of the cluster. Gold is well known to like forming bonds to sulfur, so it is no surprise that thiolate ligands are successful in stabilising gold clusters. While sulfur based ligands withdraw electron density from the gold core, this is not necessarily the behaviour of all ligands, some of which can instead actually donate electron density to the superatomic core. This is the case for phosphine ligands, as phosphorus had five valence electrons, and forms three covalent bonds in a phosphine molecule, leaving a lone pair of electrons which can donate into the metal cluster.
