In chemistry, a superatom is any cluster of atoms that seem to exhibit some of the properties of elemental atoms. Sodium atoms, when cooled from vapor, naturally condense into clusters, preferentially containing a magic number of atoms (2, 8, 20, 40, 58, etc.), with the outermost electron of each atom entering an orbital encompassing all the atoms in the cluster. Superatoms tend to behave chemically in a way that will allow them to have a closed shell of electrons, in this new counting scheme.

Aluminum clusters

Certain aluminum clusters have superatom properties. These aluminium clusters are generated as anions ( with n = 1, 2, 3, … ) in helium gas and reacted with a gas containing iodine. When analyzed by mass spectrometry one main reaction product turns out to be. These clusters of 13 aluminium atoms with an extra electron added do not appear to react with oxygen when it is introduced in the same gas stream, indicating a halide-like character and a magic number of 40 free electrons. Such a cluster is known as a superhalogen. The cluster component in ion is similar to an iodide ion or better still a bromide ion. The related cluster is expected to behave chemically like the triiodide ion. Similarly it has been noted that clusters with 42 electrons (2 more than the magic numbers) appear to exhibit the properties of an alkaline earth metal which typically adopt +2 valence states. This is only known to occur when there are at least 3 iodine atoms attached to an cluster,. The anionic cluster has a total of 43 itinerant electrons, but the three iodine atoms each remove one of the itinerant electrons to leave 40 electrons in the jellium shell. It is particularly easy and reliable to study atomic clusters of inert gas atoms by computer simulation because interaction between two atoms can be approximated very well by the Lennard-Jones potential. Other methods are readily available and it has been established that the magic numbers are 13, 19, 23, 26, 29, 32, 34, 43, 46, 49, 55, etc.

Other clusters

Superatom complexes

Superatom complexes are a special group of superatoms that incorporate a metal core which is stabilized by organic ligands. In thiolate-protected gold cluster complexes a simple electron counting rule can be used to determine the total number of electrons (ne) which correspond to a magic number via, where N is the number of metal atoms (A) in the core, v is the atomic valence, M is the number of electron withdrawing ligands, and z is the overall charge on the complex. For example the Au102(p-MBA)44 has 58 electrons and corresponds to a closed shell magic number.

Gold superatom complexes

Other superatom complexes