Further insights into intermediate- and mixed-valency in neptunium oxoanion compounds: structure and absorption spectroscopy of K2[(NpO2)3B10O16(OH)2(NO3)2]

The reaction of Np(V) chloride with molten boric acid results in the disproportionation of Np(V) into Np(IV) and Np(VI), and the crystallization of K(2)[(NpO(2))(3)B(10)O(16)(OH)(2)(NO(3))(2)]. UV-vis-NIR spectroscopy demonstrates that in addition to the Np(VI) and Np(V) found in the crystal structure, Np(IV) is also present.