Oxidation of Actinyl(V) Complexes by the Addition of Nitrogen Dioxide Is Revealed via the Replacement of Acetate by Nitrite

The gas-phase complexes AnO2(CH3CO2)2 – are actinyl­(V) cores, AnVO2 + (An = U, Np, Pu), coordinated by two acetate anion ligands. Whereas the addition of O2 to UVO2(CH3CO2)2 – exothermically produces the superoxide complex UVIO2(O2)­(CH3CO2)2 –, this oxidation does not occur for NpVO2(CH3CO2)2 – or PuVO2(CH3CO2)2 – because of the higher reduction potentials for NpV and PuV. It is demonstrated that NO2 is a more effective electron-withdrawing oxidant than O2, with the result that all three AnVO2(CH3CO2)2 – exothermically react with NO2 to form nitrite complexes, AnVIO2(CH3CO2)2(NO2)−. The assignment of the NO2 – anion ligand in these complexes, resulting in oxidation from AnV to AnVI, is substantiated by the replacement of the acetate ligands in AnO2(CH3CO2)2(NO2)− and AnO2(CH3CO2)3 – by nitrites, to produce the tris­(nitrite) complexes AnO2(NO2)3 –. The key chemistry of oxidation of AnV to AnVI 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.