In alkaline media Np(VI) is oxidised to heptavalent state by O3, oxygen compounds of hexa- and octavalent Xe, persulphate, periodate, hypochlorite, and hypobromite ions, bismuthates and, electrolytically, on platinum anode. The redox potential of the pair Np(VII)/Np(VI) in 1 M alkaline solutions is in the range of 0·40-0·76 V. To obtain Pu(VII) in diluted alkaline solutions O3 and S2O8 = ions can be used. In strong alkali Pu(VI) is also oxidized by hypochlorite, hypohromite and perxenate ions. The redox potential of the pair Pu(VII)/Pu(VI) in 1 M KOH is in the range of 0·76-1·24 V. Absorption spectra of alkaline solutions of Np(VII) and Pu(VII) are independent of the way they were taken and are practically unaffected by changing concentration of OH- ions over a broad range. The colour of solutions of Pu(VII) and Np(VII) in the visible part of the spectrum is in a satisfactory agreement with the Lambert-Beer law. Np(VII) and Pu(VII) can be converted in alkaline solutions to hexavalent state by means of numerous reducers. The stoichiometric evidence obtained for a number of reduction reactions confirms the monoelectronic metal transfer from hepta to hexavalent form. Compounds [Co(NH3)6].NpO5.3H2O, [Pt(NH3)5Cl]NpO5.H2O, Ba3(NpO5)2. nH2O, S3(NpO5)2.nH2O and Ba3(PuO5)2.nH2O. have been obtained in a solid state. Some of their properties have been studied. It has been found that Np(VII) and Pu(VII) exist in alkaline media as NpO53- and PuO53- anions. The latter are an anionic form of amphoteric hydroxides MeO2(OH)3.NpO2(OH)3.nH2 O has been obtained in a solid state. Some peculiar properties of heptavalent state of Np and Pu are discussed. © 1969.
