The density changes drastically along the series: (C 5 ) = 3.25 > (C 6 ) = 3.12 > (C 7 ) = 2.84 g/cm 3 as a result of the increase in volume caused by the introduction of a larger number of Simulated X-ray diffraction patterns of three new tetragonal carbon allotropes are shown in Fig. . It is evident that they all exhibit distinct topologies that differ significantly from diamond.