Radon oxides are among the few other reported compounds of radon; only the trioxide () has been confirmed. The higher fluorides and have been claimed, and are calculated to be stable, but it is doubtful whether they have yet been synthesized. They may have been observed in experiments where unknown radon-containing products distilled together with xenon hexafluoride: these may have been , , or both. Trace-scale heating of radon with xenon, fluorine, bromine pentafluoride, and either sodium fluoride or nickel fluoride was claimed to produce a higher fluoride as well which hydrolysed to form . While it has been suggested that these claims were really due to radon precipitating out as the solid complex the fact that radon coprecipitates from aqueous solution with has been taken as confirmation that was formed, which has been supported by further studies of the hydrolysed solution. That [RnO3F− did not form in other experiments may have been due to the high concentration of fluoride used. Electromigration studies also suggest the presence of cationic and anionic [HRnO4− forms of radon in weakly acidic aqueous solution (pH > 5), the procedure having previously been validated by examination of the homologous xenon trioxide.