Molecular and Crystal Structures of Plutonyl(VI) Nitrate Complexes with N-Alkylated 2-Pyrrolidone Derivatives: Cocrystallization Potentiality of UVI and PuVI

Plutonyl(VI) nitrate complexes with N -cyclohexyl-2-pyrrolidone (NCP) and N -neopentyl-2-pyrrolidone (NNpP) were prepared, and their molecular and crystal structures were determined by single crystal X-ray analysis. The obtained compounds have a similar composition, PuO 2 (NO 3 ) 2 (NRP) 2 (NRP = NCP, NNpP), which are analogous to the corresponding U VI complexes. Both PuO 2 (NO 3 ) 2 (NRP) 2 complexes show typical structural properties of actinyl(VI) nitrates, that is, hexagonal-bipyramidal geometry consisting of two NRP molecules and two NO 3 − ions located in trans positions in the equatorial plane of the PuO 2 2+ moiety, Pu═O ax = 1.73 Å, Pu−O NRP = 2.38 Å, Pu−O NO3 = 2.50 Å, and a bond angle between the Pu−O NRP bond and the carbonyl group of NRP ≈ 135°. PuO 2 (NO 3 ) 2 (NNpP) 2 is isostructural with the corresponding uranium compound, whereas PuO 2 (NO 3 ) 2 (NCP) 2 is not. These findings provide one of criteria in selection of suitable NRP as a precipitation agent for the spent nuclear fuel reprocessing based on the precipitation method from a viewpoint of crystal engineering.