Among the interhalogen compounds of the general type $\mathrm{X}{\mathrm{X}}_7^{\prime }$, the only one known is

Only the large iodine atom can accommodate seven small fluorine atoms. Hence $\mathrm{IF}{}_7$ is the sole known $\mathrm{X}{\mathrm{X}}_7^{\prime }$ compound, while $\mathrm{ClF}{}_7$, $\mathrm{BrF}{}_7$ and $\mathrm{ICl}{}_7$ are not known.