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From Nature magazine
An elite chemical club has a new member, after a team in Germany found a way to link two boron atoms together with a stable triple bond. Boron joins carbon and nitrogen as one of the few elements in the periodic table known to form stable compounds featuring triple bonds.
Theory had predicted that such boron structures should be possible, says Holger Braunschweig, a chemist at the University of Würzburg who led the research. After all, nitrogen–nitrogen and carbon–carbon triple bonds are stable: the nitrogen molecules that make up the majority of our air are held together by a triple bond, for example. And boron is next to carbon and nitrogen in the periodic table, so should have comparable properties. “One would expect something similar for boron,” says Braunschweig. “The major problem has been the synthesis.”
Until now, the closest that anyone had come was a molecule made by using a laser to vaporize boron in the presence of carbon monoxide (CO) at very low temperatures. This compound seemed to incorporate a boron–boron triple bond, surrounded by CO groups, but fell apart at temperatures above about -263 °C.
Braunschweig’s compound, by contrast, is stable up to 234 °C, if kept isolated from the air. “Under inert conditions, this is a very stable molecule,” says Braunschweig.
Share and share alike
To make the compound, the team swapped CO for bulky, highly electron-donating chemical groups called N-heterocyclic carbenes (NHCs). Atoms of main-group elements are generally most stable when they have eight electrons in their outer electron shells. If they don't have this number as single atoms, they often share with their neighbours, each electron pair constituting a single chemical bond. Boron atoms have only three electrons in their outer shells, so in Braunschweig’s compound, two atoms share all six of their electrons between them to make a triple bond. The remaining two electrons are supplied by NHC groups.
Other research teams have attempted to synthesize boron–boron triple bonds using two boron atoms each bearing one NHC group and three bromines. The idea was that the bromines would be removed one by one, and the two boron atoms would come together to form a boron–boron single bond, followed by a double and finally a triple bond. However, the process of forming the single bond was slow, and the bromine-stripped boron atoms tended to first react with the surrounding solvent before reacting with each other of each other.
So Braunschweig’s group started with a precursor that already had one boron–boron bond in place: B2Br4, stabilized with two NHCs. “This precursor is a very difficult to work with — it will degrade above -40°C — but we showed that we could selectively convert this compound first to make the boron–boron double bond, and in the second step to make the triple bond,” says Braunschweig.
Structural integrity
X-ray crystal structures confirmed that the compound possesses true triple bond character. As expected, the distance between the boron atoms was shorter in the triple-bonded structure than in the compound with a double bond, matching closely with predicted figures. The molecule is also linear, just as the equivalent triple-bonded carbon compound would be.
“Braunschweig has elegantly seen the problem of starting with a mononuclear precursor, and used a precursor with a boron–boron bond already in place,” says Cameron Jones, a chemist at Monash University in Melbourne, Australia, who has worked on theoretical studies of the boron–boron triple bond. The results, he says, although stable under heat, “are highly reactive species, and they will find applications”.
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6 Comments
Add CommentYet another very potentially important discovery goes unnoticed. I am amazed that if the article talks about global climate change, air pollution, religion or some other esoteric sometimes not even scientific subject it receives hundreds of comments.
Reply | Report Abuse | Link to thisIf on the the other hand it offers up hope to better, cleaner and more efficient solutions to problems that need to be solved or improved it ends up in the area where dust collects. Sad, no wonder Scientific America had to become Scientific USA Today.
I empathize with your sentiments, but as an uninformed lay reader, the article only hints at some possible application like LEDs, not revolutionary solutions to unnamed critical problems that you refer to.
Reply | Report Abuse | Link to thisAs stated, the resulting crytal is stable unless exposed to air or moisture. Unless some reactive products can be produced that are more stable it would seem that practical applications might be limited.
As stated in the article http://www.newscientist.com/article/dn21927-triplebonded-boron-opens-new-chemical-world.html
"It's too early to predict if or how the new compound might be useful."
While I've found individual chemists quoted waxing poetic about new gardens, no real information is divulged.
Without more information, how can a lay reader guess how important this new development might be? Is it possible to speculate about the potential apparently imagined for this development?
There is no confirmed link with sterility in men and even if there were it would require toxic dosage. Shooting people is a very effective contraceptive but I trust you won't be recommending it!
Reply | Report Abuse | Link to thisThat's not really true "curmudgeon". Were I live in West Virginia, there is a lot of coal mining and natural gas fracking, and the waste water, that gets into the drinking water, from both contains larger than recommended doses of boron and other dangerous heavy metals, and doctors found dangerous levels of boron in young boys bodies and they noticed that the boys with larger than normal doses of boron in their body; their genitalia looked like grapes that had been left out in the sun too long and they were barely functional, and the older boys were not producing sperm. That research was done at West Virginia University (WVU) if you want to look it up.
Reply | Report Abuse | Link to thisWOW 5 comments and counting. I do believe in fairies (Hang in there tinkerbelle), I do believe in fairies.
Reply | Report Abuse | Link to thisThe comment of delivery system didn't even hit me right away. I was/am thinking of some of the organic uses and what it may offer instead of a carbon based container.
The fact that we can imbed (a drug, gene, vitamin whatever) in a non lethal container and getting to the right destination is required, I am all for the more variables vs less data when making a life/death delivery systems.
Another direction I was trying to move to is organic like chemistry. If that is possible, then wow that creates opportunities that dwarf this small place to share an opinion. I think the ideal of nano engineering is more than just carbon, but I think with Si, C, O, H , Fe, S, N are a lot easier obtained and renewable than Palladium.
A first thought with seeing the structure of this molecule: How might the Boron configuration(s) be combined or integrated with fullerenes? Imagine the possibilities with new materials.
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