Bis{N-[bis(pyrrolidin-1-yl)phosphoryl]-2,2,2-trichloroacetamide}dinitratodioxidouranium(VI)

The crystal structure of the title compound, [U(NO3)2O2(C10H17Cl3N3O2P)2], is composed of centrosymmetric [UO2(L)2(NO3)2] molecules {L is N-[bis(pyrrolidin-1-yl)phosphoryl]-2,2,2-trichloroacetamide, C10H17Cl3N3O2P}. The UVI ion, located on an inversion center, is eight-coordinated with axial oxido ligands and six equatorial oxygen atoms of the phosphoryl and nitrate groups in a slightly distorted hexagonal-bipyramidal geometry. One of the pyrrolidine fragments in the ligand is disordered over two conformation (occupancy ratio 0.58:0.42). Intramolecular N—H⋯O hydrogen bonds between the amine and nitrate groups are found.


Related literature
For the synthesis and coordination properties of the ligand L, see: Znovjyak et al. (2009). For a structural investigation of L, see: Gholivand et al. (2006). For the synthesis and structural investigation of a uranium(IV)-containing complex with a similar ligand, see: Amirkhanov et al. (1997).
Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Burnett & Johnson, 1996;Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999). The crystal structure of 1 is made of centrosymmetric molecules UO 2 (L) 2 (NO 3 ) 2 and uranium is located on an inversion center. The analysis of the bond lengths and angles of 1 indicates that the coordination polyhedra of the uranium ions are slightly distorted hexagonal bipyramids. The axial vertices are occupied by two oxido ligands while six oxygen atoms of monodentate coordinated L ligands and bidentate coordinated nitrate groups lie in the equatorial plane. The nitrate groups additionally form intramolecular hydrogen bonding with the hydrogen atoms of the N-H groups of the L ligands (Table   1). In the crystal structure of the complex, the phosphoryl and carbonyl groups are in the trans position to each other which was early observed in the structure of the free L (Gholivand et al., 2006) and similar complex with uranium ion (Amirkhanov et al., 1997). It was shown that 2,2,2-trichloro-N-[di(1-pyrrolidinyl)phosphoryl]acetamide aggregates into non-centrosymmetric dimers (L) 2 , therefore in the following will be given two values of bond lengths due to comparison of non-coordinated and coordinated L.

Experimental
The synthesis of L was carried out according to the procedure described previously (Znovjyak et al., 2009).

Refinement
All H atoms were placed at calculated positions and treated as riding on their parent atoms [C-H = 0.93 Å and U iso (H) = 1.2U eq (C), N-H = 0.86 Å and U iso (H) = 1.2U eq (N)]. In one pyrrolidine group, atoms C3-C6 were treated as disordered between two orientations A and B, respectively, with the occupancies to 0.58 and 0.42.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.