Featured Research

from universities, journals, and other organizations

Exotic Structures Of Tomorrow's Technology Yield Secrets Of Bonding In Research By Cornell Chemists

Date:
September 15, 2000
Source:
Cornell University
Summary:
Two researchers at Cornell University have made important theoretical discoveries that have long eluded chemists: They have established the principles of crystal bonding of a group of thousands of compounds.

ITHACA, N.Y. -- In the 19th century, fundamental discoveries were made by unlocking the chemistry of carbon, but wide exploitation of these major discoveries came slowly. It took some years, for example, before this knowledge led to the development of new drugs and synthetic fibers.

Now, two researchers at Cornell University have made important theoretical discoveries that, similarly, have long eluded chemists: They have established the principles of crystal bonding of a group of thousands of compounds. But history repeats itself in that, thus far, nearly all of these unusual compounds have no industrial uses, although many have interesting electronic and magnetic properties.

"This is an important step in understanding the bonding in alloys and intermetallic compounds," says Roald Hoffmann, Cornell's Nobel laureate chemist who also serves as the Frank H.T. Rhodes Professor in Humane Letters. Hoffmann, despite his seniority, was led in this pioneering work by his graduate student, Garegin Papoian, who came from Armenia to study under the Cornell scientist and now is a postdoctoral researcher at the University of Pennsylvania. The two chemists have laid out a theory that extends the understanding of bonding in an important class of alloys.

Hoffmann's and Papoian's "novel bonding scheme" was described in more than 40 pages in the July 17 issue of the authoritative journal of chemistry Angewandte Chemie , published by the German Chemical Society.

The two researchers began by looking at the bonding of compounds of antimony, tellurium, tin and selenium, all called "main group elements," below carbon, nitrogen and oxygen in the periodic table. The compounds have names like europium and lithium antimonide and neodymiun distannide, and although they have been known for many decades, "experimentalists have said nothing about what holds these compounds together," says Hoffmann.

It was known that these compounds have in them curious structural motifs, quite uncommon in organic or other inorganic molecules. The compounds, in fact, blur the line between the different types of bonds that hold atoms together in a molecule or a crystal. In this case, the bonds are a melange of metallic bonds, covalent bonds -- created by the sharing of electrons -- and ionic bonds -- formed by the transfer of electrons.

These "isolated puzzles" are now explained by the two researchers in a formula that is based on "magic numbers." In physics and chemistry, magic numbers designate the sum of electrons in a molecule that leads to special stability. In the Papoian-Hoffmann bonding formula, magic numbers refer to the electron counts that indicate whether a stable compound is linear or square: seven electrons per atom for a linear chain; six electrons per atom for a two-dimensional square lattice; and five electrons per atom for a simple cube lattice.

The crystal structures themselves can be seen in a series of computer-generated drawings -- not based on theory but on direct experimental work -- that have an interlocking, architectural perfection. The molecular structures, ranging from simple geometries to complex lattices, reveal their bonding networks in a series of multidimensional building blocks. "Some look terribly complicated," says Hoffmann, "but take them apart and you can see square lattices with atoms above and below, and squares forming octahedrons -- fantastic structures with a certain 'Star Wars' quality."

But how can such structures reveal themselves sometimes as compounds of antimony and other times as tellurium or tin? "Because it's the number of electrons that determines the chemistry, less so the identity of the nucleus underneath," Hoffmann explains.

"What we have here is theory at its best -- qualitative theory, building connections between different parts of the chemical universe, even though to outsiders these units appear not to be close to each other," Hoffmann comments. "I pride myself on seeing connections, which is what I also try to build between science and humanities. Anything I can do to connect diverse things feels worth doing."

Papoian's and Hoffmann's paper in Angewandte Chemie is titled "Hypervalent Bonding in One, Two and Three Dimensions: Extending the Zintl-Klemm Concept to Nonclassical Electron-Rich Networks."


Story Source:

The above story is based on materials provided by Cornell University. Note: Materials may be edited for content and length.


Cite This Page:

Cornell University. "Exotic Structures Of Tomorrow's Technology Yield Secrets Of Bonding In Research By Cornell Chemists." ScienceDaily. ScienceDaily, 15 September 2000. <www.sciencedaily.com/releases/2000/09/000913203535.htm>.
Cornell University. (2000, September 15). Exotic Structures Of Tomorrow's Technology Yield Secrets Of Bonding In Research By Cornell Chemists. ScienceDaily. Retrieved September 2, 2014 from www.sciencedaily.com/releases/2000/09/000913203535.htm
Cornell University. "Exotic Structures Of Tomorrow's Technology Yield Secrets Of Bonding In Research By Cornell Chemists." ScienceDaily. www.sciencedaily.com/releases/2000/09/000913203535.htm (accessed September 2, 2014).

Share This




More Matter & Energy News

Tuesday, September 2, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Australian Airlines Relax Phone Ban Too

Australian Airlines Relax Phone Ban Too

Reuters - Business Video Online (Aug. 26, 2014) Qantas and Virgin say passengers can use their smartphones and tablets throughout flights after a regulator relaxed a ban on electronic devices during take-off and landing. As Hayley Platt reports the move comes as the two domestic rivals are expected to post annual net losses later this week. Video provided by Reuters
Powered by NewsLook.com
Hurricane Marie Brings Big Waves to California Coast

Hurricane Marie Brings Big Waves to California Coast

Reuters - US Online Video (Aug. 26, 2014) Huge waves generated by Hurricane Marie hit the Southern California coast. Rough Cut (no reporter narration). Video provided by Reuters
Powered by NewsLook.com
Chinese Researchers Might Be Creating Supersonic Submarine

Chinese Researchers Might Be Creating Supersonic Submarine

Newsy (Aug. 26, 2014) Chinese researchers have expanded on Cold War-era tech and are closer to building a submarine that could reach the speed of sound. Video provided by Newsy
Powered by NewsLook.com
Breakingviews: India Coal Strained by Supreme Court Ruling

Breakingviews: India Coal Strained by Supreme Court Ruling

Reuters - Business Video Online (Aug. 26, 2014) An acute coal shortage is likely to be aggravated as India's supreme court declared government coal allocations illegal, says Breakingviews' Peter Thal Larsen. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins