Hexanitratoprotactinates(V), MIPa(NO3)6(MI= Cs, NMe4, and NEt4), have been prepared by reaction of the hexachloroprotactinates(V) with liquid dinitrogen pentoxide at room temperature. The niobium(V) and tantalum(V) hexachloro-analogues form oxytetranitrato-complexes, NMe4MVO(NO3)4(MV= Nb and Ta), under similar conditions. Protactinium() halides react with fuming nitric acid, yielding the hydrated oxynitrate PaO(NO3)3,xH2O (1 < x < 4) which is probably polymeric. Dinitrogen tetroxide reacts with protactinium(V) halides in anhydrous methyl cyanide to give the dimeric, solvated oxynitrate Pa2O(NO3)8,2MeCN, whereas liquid dinitrogen pentoxide converts the pentahalides and freshly prepared hydroxide, but not the pentoxide, into the acid hexanitrato-complex HPa(NO3)6. Some chemical properties and the infrared spectra of the compounds are reported.