The only binary compounds of noble gases are fluorides and oxides of Kr, Xe and Rn because the ionisation energies of He, Ne and Ar are much higher than for Xe to allow the formation of similar compounds. The ionisation enthalpy of Kr is little lower than Xe and it forms $KrF _{ 2 }$
The ionisation enthalpy for Rn is less than that for Xe and it is expected to form compounds similar to Xe. However, Rn is a radioactive and its isotopes have short half-lives. Therefore, only $RnF _{ 2 }$ and a few complexes are known.