Aromatic hexazine [N6]4− anion featured in the complex structure of the high-pressure potassium nitrogen compound K9N56
Dominique Laniel, Florian Trybel, Yuqing Yin, Timofey Fedotenko, Saiana Khandarkhaeva, Andrey Aslandukov, Georgios Aprilis, Alexei I. Abrikosov, Talha Bin Masood, Carlotta Giacobbe, Eleanor Lawrence Bright, Konstantin Glazyrin, Michael Hanfland, Jonathan P. Wright, Ingrid Hotz, Igor A. Abrikosov, Leonid Dubrovinsky, Natalia Dubrovinskaia
Abstract
The recent high-pressure synthesis of pentazolates and the subsequent stabilization of the aromatic [N5]− anion at atmospheric pressure have had an immense impact on nitrogen chemistry. Other aromatic nitrogen species have also been actively sought, including the hexaazabenzene N6 ring. Although a variety of configurations and geometries have been proposed based on ab initio calculations, one that stands out as a likely candidate is the aromatic hexazine anion [N6]4−. Here we present the synthesis of this species, realized in the high-pressure potassium nitrogen compound K9N56 formed at high pressures (46 and 61 GPa) and high temperature (estimated to be above 2,000 K) by direct reaction between nitrogen and KN3 in a laser-heated diamond anvil cell. The complex structure of K9N56—composed of 520 atoms per unit cell—was solved based on synchrotron single-crystal X-ray diffraction and corroborated by density functional theory calculations. The observed hexazine anion [N6]4− is planar and proposed to be aromatic. Aromatic polynitrogen units can display both high stability and high energy content. A hexazine anion has now been identified in a complex compound, K9N56, which is formed at high pressures and temperatures under laser-heating in a diamond anvil cell. The [N6]4− ring is planar and proposed to be aromatic.