The nitridoborate nitrides Mg3[BN2]N and Ca3[BN2]N – electronic structure and chemical bonding
Résumé
The nitridoborates Mg3[BN2]N (P63/mmc) and Ca3[BN2]N (P4/mmm) are electron-precise compounds with discrete linear [BN2]3− and isolated N3− anions. Electronic structure calculations reveal pronounced B–N bonding within the [BN2]3− units with more covalent Mg–N vs. Ca–N bonding. Total energy calculation for hexagonal normal-pressure Mg3[BN2]N, orthorhombic high-pressure Mg3[BN2]N and a hypothetical Ca3[BN2]N-type tetragonal Mg3[BN2]N modification revealed that the hexagonal modification is the ground state structure. The band structure for orthorhombic high-pressure Mg3[BN2]N indicates a substantial metallization (delocalization in the high-pressure regime). This peculiar result calls for a reinvestigation of high-pressure Mg3[BN2]N under different high-pressure high-temperature conditions along with physical property studies.