Salt Shakes Up Scientific World
SB Professor Artem Oganov Upends the Rules of Chemistry
There’s a high salt content in the conversations taking place in the scientific community these days, but it’s not linked to higher blood pressure, but rather, to raised elevations of intellectual ferment. That’s the kind of stir Artem R. Oganov has caused with the publication of his work in the December 20, 2013 issue of Science.
The paper, titled “Unexpected stable stoichiometries of sodium chlorides,” documents his predictions about, and experiments in, compressing sodium chloride—rock salt—to form new compounds. Oganov, a Professor in the Department of Geosciences, believed his work might be the beginning of a revolution in chemistry. Others are now agreeing.
The original Stony Brook press release has been reprinted in numerous languages around the world; the commentary has been similarly global. A January 11, 2014 article in The National, published in Abu Dhabi, was titled Upending chemistry’s atomic law. It was written by Robert Matthews, a visiting reader in science at Aston University in Birmingham, England. Matthews is a member of the Institute of Physics and fellow in the Royal Astronomical Society.
“Common salt is NaCl: one atom of sodium, plus one atom of chlorine,” Matthews writes. “Nothing else works, and there is no way around it: it is the laws of chemistry. Or at least it was until late last month, when researchers announced the creation of a whole family of the mutant relatives of common salt, with crazy formulas like NaCl3 and Na2Cl. Standard chemistry forbids such compounds, and yet now they have been created in experiments reported in the leading journal Science. This is no mere party trick, either. It is confirmation of a radically new means of creating compounds that could transform our world.”
Adds Andy Extance, a member of the London-based Royal Society of Chemistry, writing in Chemistry World, “The discovery that NaCl3 and Na3Cl can be stable at increased pressures shows that core chemistry principles can be overturned.” Yanming Ma, a theoretical physicist and Professor of Physics at Jilin University in Changchun, China, says in the same article, “The work demonstrates again that high pressure is a powerful tool in the synthesis of novel materials, violating conventional wisdom established at ambient pressure.”
And Science Codex posted this, from Lomonosov Moscow State University: “In the very beginning of the school chemistry course, we are told of NaCl as an archetypal ionic compound. All the rules predict NaCl to be the only possible compound formed by chlorine and sodium. The research team led by Artem R. Oganov, Professor of Crystallography at Stony Brook University, has discovered new sodium chlorides that call for revision of textbook chemistry.”
Standard chemistry textbooks say that sodium and chlorine must form a compound with a well-defined composition, and the only possible combination of these atoms in a compound is 1:1—rock salt, or NaCl. “The simple, well-established fact is that the columns in the periodic table make it easy to see why sodium and chlorine form the crystalline form NaCl, and not something crazy like Na3Cl or NaCl7,” says Dan M. Davis, Professor and Chair, Stony Brook Department of Geosciences. “But Artem's research group has shown that what we all ‘knew’ about how those, and other ‘crazy’ sodium chlorides, wouldn’t exist is wrong.”
Oganov discovered, at low pressures achievable in the lab, stable compounds that contradict the classical rules of chemistry. This raises all kinds of possibilities. “The ‘impossible’ combination of three sodium atoms and one of chlorine [Na3Cl] announced last month appears to be like an atomic layer cake, with ordinary salt alternating with layers of pure sodium,” says Extance. “This structure will pique the interest of technologists, as salt does not conduct electricity very well, while sodium does—and having an atomic-scale sandwich of the two could have some practical applications in the electronics and power industries.”
The discovery may have application in the planetary sciences, where high-pressure phenomena abound. The new structures were calculated using a crystal structure prediction technique invented by Oganov—Universal Structure Predictor: Evolutionary Xrystallography, or USPEX—and nowused by more than 1,600 scientists globally. Professor Oganov and his colleagues are using USPEX—the Russian word for success—to explore modifications to atomic structure to stabilize the new compounds at everyday pressures to exploit their unique properties.
“If the team’s algorithm lives up to its promise, it will rate as one of the breakthroughs of the century,” Matthews says.
Perhaps the biggest success is the triumph of scientific curiosity.
“For a long time, this idea was haunting me—when a chemistry textbook says that a certain compound is impossible, what does it really mean, impossible?” Oganov says. “Certainly, I can compute their energies using quantum mechanics, and that energy will be unfavorable only by a finite amount, and only at normal conditions. The rules of chemistry can be broken, because impossible only means ‘softly’ impossible! We have learned an important lesson—that even in well-defined systems, like sodium chloride, you can find totally new chemistry, and totally new and very exciting materials.”