Within a similar approach, we propose herein two novel carbon allotropes, tetragonal C 9 and C 12 , both characterized by sp 3 carbon in original architectures comprising corner and edge sharing tetrahedra. The purpose of this paper is to present their crystal structures and to demonstrate ultrahardness, while also presenting high phonon optical mode frequencies of  > 40 THz like in diamond and C 4 , a large electronic band gap, and a temperature evolution of the heat capacity close to that of diamond.