Complexation of Np(V) and Pu(VI) with 2-(2-Morpholino-2-oxoethoxy)acetic Acid in Comparison with N,N-Dimethyl-diglycolamic Acid.

The complexation of Np(V)/Pu(VI) with 2-(2-morpholino-2-oxoethoxy)acetic acid (HMOROGA, HLI) is studied, and the case for its analogue, N,N-dimethyl-diglycolamic acid (DMOGA, HL), is revisited with respect to the arguable stability constants and optical properties of the complexes likely due to the relatively low percentage of the 1:2 complexes in the previous works. Among the complex species, the 1:2 complexes of Np(V) with both HMOROGA and DMOGA are identified in aqueous solutions for the first time. The relationship between the optical properties and possibly alternative arrangement of the ligands in the equatorial plane of actinyl ions (Np(V)/Pu(VI)) in the 1:2 complexes is discussed by taking into account the clear difference in symmetry. The obtained stability constants indicate that DMOGA is a slightly stronger ligand for Np(V)/Pu(VI) than HMOROGA. In addition, single crystals of NpO2(H2O)2LI(c) with good quality suitable for single-crystal X-ray diffraction experiments were obtained, and the structure was analyzed.