The inert pair effect on heavy noble gases: insights from radon tetroxide.

A quantum chemical survey of radon and xenon tetroxides (NgO 4 , Ng = Xe, Rn) is reported herein. The intermediate species, which are formed in their explosive decomposition back to their elemental states (Ng and O 2 ), were also studied and their energetics were compared. While T d symmetric RnO 4 has a minimum energy structure, its standard enthalpy of formation is 88.6 kJ mol -1 higher than for XeO 4 . The reason for this higher instability lies in what is known as the inert pair effect. This work establishes that the high-valent chemical trends of the sixth period of groups 13-15 are indeed extended to group 18.