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/Source:/       *Penn State / Eberly College Of Science*        
/Date:/         2005-02-08
/URL:/  http://www.sciencedaily.com/releases/2005/02/050205125336.htm

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   Clusters Of Aluminum Atoms Found To Have Properties Of Other
   Elements Reveal A New Form Of Chemistry

January 13, 2005 -- A research team has discovered clusters of aluminum 
atoms that have chemical properties similar to single atoms of metallic 
and nonmetallic elements when they react with iodine. The discovery 
opens the door to using 'superatom chemistry' based on a new periodic 
table of cluster elements to create unique compounds with distinctive 
properties never seen before. The results of the research, headed 
jointly by Shiv N. Khanna, professor of physics at Virginia Commonwealth 
University and A. Welford Castleman Jr., the Evan Pugh Professor of 
Chemistry and Physics and the Eberly Family Distinguished Chair in 
Science at Penn State University, will be reported in the 14 January 
2005 issue of the journal Science.

"Depending on the number of aluminum atoms in the cluster, we have 
demonstrated 'superatoms' exhibiting the properties of either halogens 
or alkaline earth metals," says Castleman. "This result suggests the 
intriguing potential of this chemistry in nanoscale synthesis." The 
discovery could have practical applications in the fields of medicine, 
food production and photography.

The researchers examined the chemical properties, electronic structure, 
and geometry of aluminum clusters both theoretically and experimentally 
in chemical compounds with iodine atoms. They found that a cluster of 13 
aluminum atoms behaves like a single iodine atom, while a cluster of 14 
aluminum atoms behaves like an alkaline earth atom. "The discovery of 
these new iodine compounds, which include aluminum clusters, is critical 
because it reveals a new form of 'superatom' chemistry," said Khanna. 
"In the future, we may apply this chemistry, building on our previous 
knowledge, to create new materials for energy applications and even 
medical devices."

To make their discovery, the research team replaced iodine atoms with 
the aluminum clusters in naturally occurring chains or networks of 
iodine atoms and molecules known as polyiodides. When the researchers 
substituted the iodine atom with the aluminum cluster, Al13, they 
observed that the entire chemistry of the compound changed--causing the 
other iodine molecules to break apart and bind individually to the 
cluster. The researchers then were able to bind 12 iodine atoms to a 
single Al13 cluster, forming a completely new class of polyiodides. "Our 
production of such a species is a stirring development that may lead to 
new compounds with a completely new class of chemistry and 
applications," says Castleman. "Along with the discovery that Al14 
clusters appear to behave similarly to alkaline earth atoms when 
combined with iodine, these new results give further evidence that we 
are really on our way to the development of a periodic table of the 
'cluster elements'."

The researchers conducted experimental reactivity studies that indicate 
that certain aluminum-cluster superatoms are highly stable by nature. 
The team's related theoretical investigations reveal that the enhanced 
stability of these superatoms is associated with a balance in their 
atomic and electronic states. While the clusters resemble atoms of other 
elements in their interactions, their chemistry is unique, creating 
stable compounds with bonds that are not identical to those of single atoms.

Using stable clusters provides a possible route to an adaptive chemistry 
that introduces the aluminum-cluster species into nanoscale materials, 
tailoring them to create desirable properties. "The flexibility of an 
Al13 cluster to act as an iodine atom shows that superatoms can have 
synthetic utility, providing an unexplored 'third dimension' to the 
traditional periodic table of elements," said Khanna. "Applications 
using Al13 clusters instead of iodine in polymers may lead to the 
development of improved conducting materials. Assembling Al13I units may 
provide aluminum materials that will not oxidize, and may help overcome 
a major problem in fuels that burn aluminum particles."

The theoretical investigations for this project were conducted by Khanna 
with N.O. Jones, a graduate student in the physics department at 
Virginia Commonwealth University, and the experimental work was 
conducted by Castleman with Denis Bergeron and Patrick J. Roach, 
graduate students in the chemistry department at Penn State.

This research was supported by the U. S. Air Force Office of Scientific 
Research and the U. S. Department of Energy.

*Editor's Note:* The original news release can be found here 
<http://www.science.psu.edu/alert/Castleman1-2005.htm>.

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/This story has been adapted from a news release issued by Penn State / 
Eberly College Of Science./