The structures and stabilities of the M6N8 clusters (M = Si, Ge, Sn, Ti) have been theoretically studied at DFT and ab initio levels of theory. Two new isomers have been considered: cage-like molecules and propeller-like molecules. It is shown that only for M = Si are both isomers true minima on the potential energy surface. The thermodynamics of the dissociation process 1/6M(6)N(8) -> 1/3M(3)N(4) is discussed. For each M3N4 molecule, four structures with different multiplicity are considered. The thermodynamic analysis shows that independently of the multiplicity of M3N4 nitrides all M6N8 clusters are stable in the gas phase in a wide temperature raw and could be potential intermediates in chemical vapor deposition of the nitride materials.