Mixed-Valence NpV/AnVI Molybdate Complexes with Single-Charge Outer-Sphere Cations

Five new mixed-valence NpV/AnVI molybdates of the composition [C(NH2)3]3[(NpVO2)(NpVIO2)(MoO4)3(H2O)]·H2O (1), [C(NH2)3]3[(NpVO2)(NpVIO2)(MoO4)3(H2O)]·3H2O (2), Na3[(NpVO2)(PuVIO2)(MoO4)3(H2O)]·nH2O (3), Na6[(NpVO2)2(UVIO2)(MoO4)5]·13H2O (4), and LiNa2[(NpVO2)(NpVIO2)2(MoO4)4(H2O)]·4H2O (5) have been synthesized and structurally characterized. The coordination polyhedra of the NpV and AnVI atoms in compounds 1-5 are pentagonal bipyramids. The basis of structures 1-3 is anionic layers of the composition [(NpVO2)(AnVIO2)(MoO4)3(H2O)]n3n-. Three crystallographically independent molybdate ions are tridentate-bridging ligands. The water molecule, which is a part of the anion layer, is coordinated to the NpV atom. The anionic layers in complexes 2 and 3 have the same structure, different from 1. The basis of structure 4 is anionic layers of the composition [(NpVO2)2(UVIO2)(MoO4)5]n6n-, the structure of which differs from the structure of anionic layers in 1-3. Complex 5 has a three-dimensional (3D) structure. The spectra of all compounds in the UV-visible and IR ranges were measured and analyzed.

Flux Crystal Growth of the Extended Structure Pu(V) Borate Na2(PuO2)(BO3)

As part of our exploration of plutonium-containing materials as potential nuclear waste forms, we report the first extended structure Pu(V) material and the first Pu(V) borate. Crystals of Na₂(PuO₂)(BO₃) were grown out of mixed hydroxide/boric acid flux and found to crystallize in the orthorhombic space group Cmcm with lattice parameters of a = 9.9067(4) Å, b = 6.5909(2) Å, and c = 6.9724(2) Å. Na₂(PuO₂)(BO₃) adopts a layered structure in which layers of PuO₂(BO₃)^2- are separated by sodium cations. Plutonium is found in a pentagonal bipyramidal coordination environment, with axial Pu(V)-O plutonyl bond lengths of 1.876(3) Å and equatorial Pu-O bond lengths ranging from 2.325(5) to 2.467(3) Å. We find that the Pu(V)-O plutonyl bond lengths are approximately 0.1 Å longer than the reported Pu(VI)-O plutonyl bond lengths and shorter by approximately 0.033 Å than the corresponding U(V) uranyl bond lengths. Raman spectroscopy on single crystals was used to determine the PuO₂⁺ plutonyl stretching and the equatorial breathing mode frequencies of the pentagonal bipyramidal coordination environment around plutonium. Density functional theory calculations were used to calculate the Raman spectrum to help identify the Raman bands at 690 and 630 cm^-1 as corresponding to the plutonyl(V) ν1 stretch and the equatorial PuO₅ breathing mode, respectively. UV-vis measurements on single crystals indicate semiconducting behavior with a band gap of ∼2.60 eV.