Synthesis, characterization, and theoretical analysis of a plutonyl phosphine oxide complex

Stabilization of Pu(IV) in PuBr4(OPCy3)2 and Comparisons with Structurally Similar ThX4(OPR3)2 (R = Cy, Ph) Molecules

The pursuit of a trivalent plutonium halide phosphine oxide compound, e.g., "PuBr3(OPR)3," instead led to the isolation of the tetravalent trans-PuIVBr4(OPCy3)2, PuBr/Cy, compound by spontaneous oxidation of PuIII. The donating nature of phosphine oxides has allowed the isolation and characterization of PuBr/Cy by crystallographic, multinuclear NMR, solid state, and solution phase UV-vis-NIR spectroscopic techniques. The presence of a putative plutonyl(VI) complex formulated as "trans-PuVIO2Br2(OPCy3)2" was also observed spectroscopically and tentatively by single-crystal X-ray diffraction as a cocrystal of PuBr/Cy. A series of trans-ThX4(OPCy3)2 (X = Cl, ThCl/Cy; Br, ThBr/Cy; I, ThI/Cy) complexes were synthesized for comparison to PuBr/Cy. The triphenylphosphine oxide, OPPh3, complexes, trans-AnI4(OPPh3)2 (An = Th, ThI/Ph; U, UI/Ph), were also synthesized for comparison, completing the series trans-UX4(OPPh3)2 (X = Cl, Br, I), UX/Ph. To enable the synthesis of ThI/Cy and ThI/Ph, a new nonaqueous thorium iodide starting material, ThI4(Et2O)2, was synthesized. The syntheses of organic solvent soluble ThI4L2 (L = Et2O, OPCy3, and OPPh3) are the first examples of crystallographically characterized neutral thorium tetraiodide materials beyond binary ThI4. To show the viability of ThI4(Et2O)2 as a starting material for organothorium chemistry, (C5Me4H)3ThI was synthesized and crystallographically characterized.

Slow magnetic relaxation in a homoaxially phosphine oxide coordinated pentagonal bipyramidal Dy(III) complex

We report the synthesis of [(L)Dy^III(Cy₃PO)₂]·[BPh₄] (1-Dy) (where H₂L = 2,6-diacetylpyridine bis-benzoylhydrazone and Cy = cyclohexyl) which crystallized in the triclinic, P1̄ space group. The local geometry around Dy(III) in 1-Dy was found to be pentagonal bipyramidal (pseudo-D_5h). The AC magnetic susceptibility measurements performed on 1-Dy and on its diluted 1-Y(Dy) samples showed a typical single-molecule magnet signature revealed by the appearance of AC-frequency dependent out-of-phase susceptibility signals in the absence of a static magnetic field. The out-of-phase AC susceptibility signals were well resolved on the application of a small magnetic field (H_DC = 500 Oe) and yielded an energy barrier for magnetization flipping of U_eff/k_B = 50 K for the diluted derivative. The magnetic studies on 1-Dy and 1-Y(Dy) and data analysis further confirm that Raman and QTM under-barrier magnetic relaxations play a crucial role in lowering U_eff despite the almost axial nature of the Dy(III) ion in 1-Dy. We have rationalized these observations through detailed ab initio calculations performed on the X-ray crystal structure of 1-Dy.

Transuranium Sulfide via the Boron Chalcogen Mixture Method and Reversible Water Uptake in the NaCuTS3 Family

The behavior of 5f electrons in soft ligand environments makes actinides, and especially transuranium chalcogenides, an intriguing class of materials for fundamental studies. Due to the affinity of actinides for oxygen, however, it is a challenge to synthesize actinide chalcogenides using non-metallic reagents. Using the boron chalcogen mixture method, we achieved the synthesis of the transuranium sulfide NaCuNpS₃ starting from the oxide reagent, NpO₂. Via the same synthetic route, the isostructural composition of NaCuUS₃ was synthesized and the material contrasted with NaCuNpS₃. Single crystals of the U-analogue, NaCuUS₃, were found to undergo an unexpected reversible hydration process to form NaCuUS₃·xH₂O (x ≈ 1.5). A large combination of techniques was used to fully characterize the structure, hydration process, and electronic structures, specifically a combination of single crystal, powder, high temperature powder X-ray diffraction, extended X-ray absorption fine structure, infrared, and inductively coupled plasma spectroscopies, thermogravimetric analysis, and density functional theory calculations. The outcome of these analyses enabled us to determine the composition of NaCuUS₃·xH₂O and obtain a structural model that demonstrated the retention of the local structure within the [CuUS₃]^- layers throughout the hydration-dehydration process. Band structure, density of states, and Bader charge calculations for NaCuUS₃, NaCuUS₃·xH₂O, and NaCuNpS₃ along with X-ray absorption near edge structure, UV-vis-NIR, and work function measurements on ACuUS₃ (A = Na, K, and Rb) and NaCuUS₃·xH₂O samples were carried out to demonstrate that electronic properties arise from the [CuTS₃]^- layers and show surprisingly little dependence on the interlayer distance.