Quantum chemical calculations suggest that group 4 tetra-azides M(N[3])[4], where M = Ti, Zr, Hf, and Th, are stable species. They present a unique structural feature; namely, the M−N−N−N fragments are linear. These species are energetically more stable than the corresponding isomers with general formula η[5]-N[5] −M−η[7]-N[7], and the Th species, Th(N[3])[4], is the most stable of all. Possible mixed nitride azides NMN[3] were also investigated.