Superatom

In chemistry, a superatom is any cluster of atoms that seem to exhibit some of the properties of elemental atoms. One example of a superatom is the cluster Template:Chem.

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.Template:Cn

Aluminium clusters

Certain aluminium clusters have superatom properties. These aluminium clusters are generated as anions (Template:Chem 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 Template:Chem. 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 Template:Chem ion is similar to an iodide ion or better still a bromide ion. The related Template:Chem cluster is expected to behave chemically like the triiodide ion.

Similarly it has been noted that Template:Chem 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 Template:Chem cluster, Template:Chem. 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.

• Template:Chem = the property is similar to germanium atoms.
• Template:Chem = the property is similar to halogen atoms, more specifically, chlorine.
  • Template:Chem, where Template:Chem.Template:Unreliable source
• Template:Chem = the property is similar to alkaline earth metals.
  • Template:Chem, where Template:Chem.
• Template:Chem
• Template:Chem
• Template:Chem

Other clusters

• Template:Chem2 = the Template:Chem2 interior causes 2 valence electrons from the Li to orbit the entire molecule as if it were an atom's nucleus.
• Template:Chem2 = has one diffuse electron orbiting around Template:Chem2 core, i.e., mimics an alkali-metal atom.Template:Unreliable source
• Template:Chem2 = has two diffuse electrons orbiting around Template:Chem2 core, i.e., mimics He-atom.

• Template:Chem2 = has ionic bonding.
• A cluster of 13 platinum atoms becomes highly paramagnetic, much more so than platinum itself.

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 (Template:Mvar) which correspond to a magic number:

$n_e=N{\nu }_A-M-z$

where Template:Mvar is the number of metal atoms (A) in the core, Template:Mvar is the atomic valence, Template:Mvar is the number of electron withdrawing ligands, and Template:Mvar 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

• Template:Chem2
• Template:Chem2
• Template:Chem2

Other superatom complexes

• Template:Chem2
• Template:Chem2
• Template:Chem2 – In 2018 researchers produced 15-nm-thick flakes of this superatomic material. They anticipate that a monolayer will be a superatomic 2-D semiconductor and offer new 2-D materials with unusual, tunable properties.
• Organo− Zintl-based superatoms: [[[:Template:Chem2]]] and [[[:Template:Chem2]]]
• Template:Chem2

See also

• Bose–Einstein condensate
• Catenation
• Metal aromaticity
• Quantum dot

References

• "Designer Magnetic Superatoms", J.U. Reveles, et al. 2009 Template:Doi
• "A unified view of ligand-protected gold clusters as superatom complexes", M. Walter et al. 2008 Template:Doi
• "Gold Superatom Complexes", P.D. Jadzinsky et al. 2007 Template:Doi
• "Multiple Valence Superatoms", J.U. Reveles, S.N. Khanna, P.J. Roach, and A.W. Castleman Jr., 2006 Template:Doi