The gas-phase complexes AnO(2)(CH3CO2)(2)(-) are actinyl(V) cores, An(V)O(2)(+) (An = U, Np, Pu), coordinated by two acetate anion ligands. Whereas the addition of O-2 to (UO2)-O-V(CH3CO2)(2)(-) exothermically produces the superoxide complex (UO2)-O-VI(O-2)(CH3CO2)(2)(-), this oxidation does not occur for (NpO2)-O-V(CH3CO2)(2)(-) or (PuO2)-O-V(CH3CO2)(2)(-) because of the higher reduction potentials for Np-V and Pu-V. It is demonstrated that NO2 is a more effective electron-withdrawing oxidant than O-2, with the result that all three An(V)O(2)(CH3CO2)(2)(-) exothermically react with NO2 to form nitrite complexes, An(VI)O(2)(CH3CO2)2(NO2)-. The assignment of the NO2- anion ligand in these complexes, resulting in oxidation from An(V) to An(VI), is substantiated by the replacement of the acetate ligands in AnO(2)(CH3CO2)(2)(NO2)(-) and AnO(2)(CH3CO2)(3)(-) by nitrites, to produce the tris(nitrite) complexes AnO(2)(NO2)(3)(-). The key chemistry of oxidation of An(V) to An(VI) by the addition of neutral NO2 is established by the substitution of acetate by nitrite. The replacement of acetate ligands by NO2- is attributed to a metathesis reaction with nitrous acid to produce acetic acid and nitrite.