Structural variations of uranium compounds with nitrate anions

The nitrate anion, NO 3 -, is known to be widely used in different stages of the PUREX (Plutonium and Uranium Recovery by Extraction) process [1].By changing nitrate concentration of the initial solution, one may control separation of actinides by various procedures.Three major coordination environments by ligands are observed for linear (UO 2 ) 2+ uranyl (Ur) ion in oxocompounds.It is typically coordinated by four, five or six ligands, arranged at the equatorial vertices of UrO 4 (square), UrO 5 (pentagonal bipyramid) or UrO 6 (hexagonal bipyramid), respectively.Nitrate groups in inorganic uranium compounds may either directly coordinate uranyl ion thus forming [(UO 2 )(NO 3 ) n X m ] or being bonded to interstitial cations only with formation of [(UO 2 )X m ](NO 3 ) n complexes, where X = O, Cl, Br.Four new uranyl-nitrate compounds were obtained from aqueous solutions: (CH 3 ) 2 (NH 2 ) 2 [(UO 2 ) 2 (NO 3 ) 2 (CrO 4 ) 2 (H 2 O)]H 2 O (1), (15-crown-5) 2 [(UO 2 ) 2 (H 2 O) 4 (O 2 )(NO 3 ) 2 ](H 2 O) 3.5 (2) , Cs 2 [(UO) 2 (NO 3 ) 4 (OH) 2 ] (3) and Rb 3 [(UO 2 )Cl 3 (NO 3 )](NO 3 ) (4).The structure of 1 is the first observation of one-dimensional unit (chain) with nitrate groups coordinating UrO 6 hexagonal pyramids and formation of [(UO2)2(NO3)2(CrO4)2(H2O)].Compound 2 is a rare example of organically templated uranyl compound containing peroxide component with neutral organic and inorganic constituents.Neutral 15-crown-5 and H2O molecules are packed around [(UO2)2(H2O)4(O2)(NO3)2] units providing structural stability exclusively via hydrogen and Van-der-Waals bonding.[(UO) 2 (NO 3 ) 4 (OH) 2 ] clusters in the structure of 3 were not previously observed in inorganic compounds without organic molecules.And the structure of 4 contains both, NO3-directly coordinating uranyl and nitrate bonded to Rb atoms only.The latter is reflected in the structural formula of 4. This work was