Predicted crystal structures of superhard B–C–N compounds. (a) and (b) are the structures of sp³ BC₆N that originated from diamond structure,^[12] and (c) and (d) are low-density sp²-sp³ BC₂N structures that originated from C 222 1 -B₃N₅.^[11,14] (c) t-BC₆N-1 possesses novel 1D metallicity, and (d) o-BC₂N possesses both 1D and 2D metallicities. The gray shadows represent the conductive units. The C, B, and N atoms are painted in brown, green, and white colors, respectively.