CRYSTAL-STRUCTURE OF THE COMPLEX NEPTUNIUM(V) OXALATE (NH4)NPO2C2O4.NH2O

Results are presented of an x-ray structure study of (NH4)NpO2C2O4.2.67H2O. The NpO2 groups are joined by cation-cation interaction into rings bonded by oxalates into a three-dimensional framework. The Np has pentagonal bipyramidal coordination with four O atoms from oxalates and one O from a neighboring NpO2 in the equatorial positions. A large part of the waters of crystallization statistically populate positions in channels of the NpO2-oxalate framework. Comparison with a uranyl complex of similar geometry with cation-cation interaction indicates that the cation-cation bonds strengthen on going from UO22+ to NpO22+. The assumption made earlier on the basis of spectroscopic data about the nature of the NpO2+ coordination in (NH4)NpO2C2O4.nH2O is confirmed.