Pnictogen Ring Boasts Aromaticity | Chemical & Engineering News
Volume 93 Issue 22 | p. 27 | Concentrates
Issue Date: June 1, 2015

Pnictogen Ring Boasts Aromaticity

Inorganic Chemistry: Anion made solely from phosphorus and nitrogen is stabilized by electron delocalization
Department: Science & Technology
News Channels: Organic SCENE
Keywords: pnictogen, aromatic, inorganic
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This image shows the electron density of an all-pnictogen aromatic anion. P = orange, N = blue.
Credit: Christopher Cummins
Electron density of the aromatic anion P2N3- with P in orange and N in blue.
 
This image shows the electron density of an all-pnictogen aromatic anion. P = orange, N = blue.
Credit: Christopher Cummins

Chemists at MIT have created a stable aromatic anion composed solely of pnictogens—the elements that make up the periodic table column to the right of carbon (Science 2015, DOI: 10.1126/science.aab0204). Christopher C. Cummins and Alexandra Velian made the inorganic aromatic ring, which has the formula P2N3, by transferring diphosphorus to the azide anion using a sodium cryptand cation. They crystallized a complex of the resulting salt and determined that the anion is planar and has an aromatic π-electron system, as indicated by electron structure calculations. Until now, the chemists note, to isolate compounds with multiple bonds between pairs of phosphorus atoms, chemists had to use bulky substituents to block the reactive π bond. But no such bulky groups were needed to isolate P2N3. “This stabilization is best construed as aromaticity,” Cummins and Velian point out, “an effect traditionally reserved for the domain of organic chemistry.”

 
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