Bi. A tendency for a significant decrease in hardness with increasing atomic number of the pnictogen has been observed (from ~50 GPa for BN to ~13 GPa for BBi), however, all crb boron pnictides are hard phases with Vickers hardness exceeding (or equal to) that of cemented tungsten carbide, the conventional hard material. Dynamically, the new boron pnictides were found to be stable with positive phonon frequencies, except for X = Bi, which exhibits slightly negative acoustic phonons in the center of the Brillouin zone. The heat capacities of the crb BX calculated from the phonon frequencies were found to be slightly higher than those of the corresponding zincblende polymorphs, as expected for phases with increased openness of the crystal structures. From the analysis of the electronic band structures, it was found that the properties of the crb boron pnictides change from insulating to semiconducting along the series.