Predicted crystal structures of superhard B–C/N–O compounds. (a–c) Hypothetical diamond-like B₂CO structures with covalent sp³ B–C and B–O bonds.^[20,21] (d–f) Hypothetical B₃NO structures with covalent B–B, B–N, and B–O bonds.^[23] All structures are isoelectronic with diamond, indicating their semiconducting characteristics. Their hardness value is approximately 50 GPa. The B, C, N, and O atoms are painted in green, brown, white, and red colors, respectively.