Aqueous thiocyanate complexes of neptunium(V)

Aqueous thiocyanate complexes of NpO2+ have been studied by spectrophotometry and potentiometry. The results obtained using both methods are in agreement. This suggests that the observed species are inner sphere complexes. For ionic strength 9, the value of the formation constants β1 to β5 are: 13.8-58.7-74.5-44.4 and 2.9. The occurence of NpO2(NCS)54- in the most concentrated thiocyanate aqueous solutions suggests that all the water molecules could be replaced in the first coordination sphere of Np(V). Spectrophotometric results allowed to follow the effect of the step by step substitution of water by SCN- ions, on the main absorption band of the NpO2+ spectra. (author)