The analysis of the mechanical properties was carried out by calculating the elastic tensor through finite distortions of the lattice. The calculated sets of elastic constants C ij (i and j correspond to directions) of the four new boron nitrides are given in Table . All C ij values are positive, indicating mechanically stable phases. For comparison, the elastic constants of template tet-C 5 and h-C 5 are also given. As expected, the carbon allotropes have the largest C ij values compared to the compounds of the B-N system. Elastic tensor analysis was performed to obtain the bulk (B v ), shear (G v ) and Young's (E v ) moduli and Poisson's ratio () by Voight's averaging using ELATE software . The calculated elastic moduli, whose values follow the trends observed for C ij , are shown in Table along with Vickers hardness values calculated using four contemporary models of hardness and fracture toughness evaluated using the Mazhnik-Oganov model .