μ-η:η-Peroxido-bis-[nitratodioxido-bis(pyrrolidin-2-one)uranium(VI)]

In the crystal structure of the title compound, [U(2)(NO(3))(2)O(4)(O(2))(C(4)H(7)NO)(4)], two UO(2) (2+) ions are connected by a μ-η(2):η(2)-O(2) unit. The O(2) unit shows 'side-on' coordination to both U atoms. An inversion center is located at the midpoint of the O-O bond in the O(2) unit, affording a centrosymmetrically expanded dimeric structure. The U-O(axial) bond lengths are 1.777 (4) Å and 1.784 (4) Å, indicating that the oxidation state of U is exclusively 6+, i.e., UO(2) (2+). Furthermore, the O-O distance is 1.492 (8) Å, which is typical of peroxide, O(2) (2-). The U atom is eight-coordinated in a hexa-gonal-bipyramidal geometry. The coordinating atoms of the nitrate and pyrrolidine-2-one ligands and the μ-η(2):η(2)-O(2) (2-) unit are located in the equatorial plane and form an irregular hexa-gon. An inter-molecular hydrogen bond is found between N-H of the pyrrolidine-2-one ligand and the coordinating O of the same ligand in a neighboring complex. A second inter-molecular hydrogen bond is found between the N-H of the other pyrrolidine-2-one ligand and one of the uranyl oxido atoms.