Rhombohedral B12 unit is viewed as a host matrix embedding linear tri-atomic arrangements of elements (E) resulting in a relatively large family of boron-rich compounds with B12{E-E-E} generic formulation. The present work focuses on boron subnitride, B13N2 that we express in present context as B12{N-B-N}. Within well established quantum density functional theory (DFT) a full study of its electronic properties is provided. Also linear triatomic arrangements in view of the existence in simple compounds such as sodium azide NaN3, i.e. NaI{N-N-N} and calcium cyanamide, CaII{N-C-N}, we devised ScIII{N-B-N} to establish comparison with B12{N-B-N}. ScBN2 is calculated to be cohesive and possessing N-B-N isolated from ScIII with dB-N = 1.33 Å. In B12{N-B-N} an elongated dB-N=1.43 Å is identified due to the bonding of N with one of the two B12 boron substructures, B1 with the formation of “3B…N-B-N…3B“-like complex accompanied by a magnetic instability. Spin polarized (SP) calculations led to the onset of magnetization on central boron with M=1uB in a stable half-ferromagnetic ground state observed from the electronic density of states (DOS). The results are backed with total energy and calculations in both non-spin-polarized (NSP) and spin-polarized stabilizing the latter configuration over a broad range of volumes from M(V) plots. Further illustrative results are given with the charge densities (total and magnetic) and electron localization function (ELF).