Mercury(II) bistrifluoromethylnitroxide has been prepared by reaction of mercury with an excess of liquid bistrifluoromethylnitroxide radical. It is a white crystalline solid which dissociates to mercury and the free radical at 85°. It reacts at room temperature with typical compounds containing B–Cl, C–halogen, Si–Cl, Ge–Cl, and P–Cl bonds to give the corresponding bistrifluoromethylnitroxide derivative in high yield. Boron tri(bistrifluoromethylnitroxide) yields a 1 : 1 adduct with caesium fluoride.