  Considering rhombohedral alpha-boron, rh-B12 as a matrix hosting
interstitials particularly triatomic linear ones as in B12C3 better known as
B4C, the subnitride B12N3 is proposed herein. The N3 triatomic linear alignment
labeled N2-N1-N2 resembles that found in the ionic sodium azide NaN3
characterized by a very short d(N1-N2)= 1.16 A. Within DFT-based calculations
B12N3 is found more cohesive than pristine B12 with larger inter-nitrogen
separation of d(N1-N2)= 1.38 A}. The N1-N2 elongation is explained from the
bonding of the two terminal N2 with one of the two B12 boron substructures
forming 3B-N2-N1-N2-3B-like complex. A resulting non-bonding charge density
localized on central N1 leads to the onset of a magnetic moment of 1 Bohr
Magneton in a half-metal ferromagnetic ground state illustrated by projections
of the magnetic charge density and the site and spin electronic density of
states DOS.
