A novel square planar N42− ring with aromaticity in BeN4

A structural search leads to the prediction of a novel alkaline earth nitride BeN4 containing a square planar N42− ring. This compound has a particular chemical bonding pattern giving it potential as a high-energy-density material. The P4/ nmm phase of BeN4 may be stable under ambient conditions, with a bandgap of 3.72 eV. It is predicted to have high thermodynamic and kinetic stability due to transfer of the outer-shell s electrons of the Be atom to the N4 cluster, with the outer-shell 2 p orbital accommodating the lone-pair electrons of N42−. The total of six π electrons is the most striking feature, indicating that the square planar N42− exhibits aromaticity. Under ambient conditions, BeN4 has a high energy density (3.924 kJ/g relative to Be3N2 and N2 gas), and its synthesis might be possible at pressures above 31.6 GPa.