Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Research Reveals Halogen Characteristics


A stable cluster of aluminum atoms, Al13, acts as a single entity in chemical reactions, demonstrating properties similar to those of a halogen, reports a research team led by A. Welford Castleman Jr., the Evan Pugh Professor of Chemistry and Physics and the Eberly Family Distinguished Chair in Science at Penn State, in a paper to be published in the 2 April 2004 issue of the journal Science. Experimental results and theoretical calculations indicate that the cluster chemically resembles a "superhalogen" atom, retaining its properties during the reaction and in reaction products. Other team members include Denis E. Bergeron of the Penn State departments of chemistry and physics and Shiv N. Khanna of the Virginia Commonwealth University department of Physics. One implication of the research is the possibility of using such clusters as building blocks in nanoscale fabrication.

Figure 1: Charge density map of the highest occupied molecular orbital for the Al13I- cluster. Note the preservation of Al13I- icosahedral geometry, and the localized charge density on the aluminum cluster moiety. Color code: blue=aluminum; red=iodine.

Figure 2: Top Image: Lowest energy structure for Al13I-. Color code: blue=aluminum; red=iodine

Bottom Image: Charge density map of the highest occupied molecular orbital for Al13I-. Color code: blue=aluminum; red=iodine

The project focused on experimental evidence of the existence of a very stable cluster anion, Al13I-, prepared by the gas-phase reaction of aluminum clusters with HI gas. Mass spectrometric analysis indicated that the reaction produced relatively few products, the most abundant corresponding to Al13I-. Energy calculations to determine the bonding mechanism between the aluminum cluster and the iodine atom indicate that the extra electron is localized on the Al13 cluster, meaning that the cluster maintains its integrity throughout the reaction. Because the cluster has a greater electron affinity in the compound, or attraction to the free electron, than does iodine, it can be considered a "superhalogen."

"One of the themes of our research is using the clusters as building blocks for new nanoscale materials," says Castleman. "In many cases, people have worked from the top down; that is, subdividing matter to get it smaller and smaller. We’re trying to work with atoms and molecules and put them together--working our way from the bottom up. If we can retain the properties of aggregates, as we put them together, perhaps we will be able to construct new nanoscale materials." The key to using the aggregates as building blocks is that they retain their individual properties during the reaction and do not coalesce into a large aggregate.

One goal of the research is to test the Jellium model of stable clusters, which treats metal atoms in a small system as positive cores surrounded by the valence electrons. The model predicts certain closed-shell arrangements with high stability, called magic clusters. In the Jellium model, the cluster’s atomic nuclei and inner electrons are seen as a single, spherical, positively charged core, surrounded by valence electrons in electronic shells similar to those of atoms. Essentially, the magic clusters can be viewed as superatoms, capable of forming compounds.

"When we started looking at reactions, Al13 turned out to be a very interesting species for several reasons, " says Castleman. "It behaves very much like a halogen, somewhere between iodine and bromine the way it wants to bind an electron. If we could put an iodine atom in contact with Al133, the Al13 has a little higher electron affinity than iodine, which could allow the Al13 to retain the electron, thereby bonding the Al133 and I together."

Experimental observations indicated that the stability of the Al13I- ion is comparable to that of BrI-, a well-known and very stable molecular halogen ion. The ability of a cluster of aluminum atoms to behave like a halogen opens up the prospect that Al13 and other magic clusters can retain their properties as a building block for assembling new materials.

"This superhalogen is not disrupted even in the presence of the very reactive iodine atom in close proximity, but still keeps its properties," says Castleman. "Now that we have shown that this is possible, we see potential ways to make other clusters, maybe involving other metals or alloys. It should be possible to construct something in the Jellium framework that would have the properties not only of a halogen, but of other types of atoms as well. For example, the Al13- ion itself resembles a rare gas atom because it is so unreactive. Ideally, we could have a whole series of clusters--a ’three dimensional’ periodic table, not of elements but rather of clusters simulating the properties of the elements." The goal is to use these clusters as building blocks to tailor the design and formation of nanoscale materials with selected properties.

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

Barbara K. Kennedy | Penn State
Further information:

More articles from Materials Sciences:

nachricht For graphite pellets, just add elbow grease
23.03.2018 | Rice University

nachricht Sensitive grip
23.03.2018 | Fraunhofer-Institut für Produktionstechnik und Automatisierung IPA

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Space observation with radar to secure Germany's space infrastructure

Satellites in near-Earth orbit are at risk due to the steady increase in space debris. But their mission in the areas of telecommunications, navigation or weather forecasts is essential for society. Fraunhofer FHR therefore develops radar-based systems which allow the detection, tracking and cataloging of even the smallest particles of debris. Satellite operators who have access to our data are in a better position to plan evasive maneuvers and prevent destructive collisions. From April, 25-29 2018, Fraunhofer FHR and its partners will exhibit the complementary radar systems TIRA and GESTRA as well as the latest radar techniques for space observation across three stands at the ILA Berlin.

The "traffic situation" in space is very tense: the Earth is currently being orbited not only by countless satellites but also by a large volume of space...

Im Focus: Researchers Discover New Anti-Cancer Protein

An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.

The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

New solar solutions for sustainable buildings and cities

23.03.2018 | Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

Latest News

For graphite pellets, just add elbow grease

23.03.2018 | Materials Sciences

Unique communication strategy discovered in stem cell pathway controlling plant growth

23.03.2018 | Agricultural and Forestry Science

Sharpening the X-ray view of the nanocosm

23.03.2018 | Physics and Astronomy

Science & Research
Overview of more VideoLinks >>>