The electronic structures of 4f(3)/5f(3) Cp''3M and Cp''3M·alkylisocyanide complexes, where Cp'' is 1,3-bis-(trimethylsilyl)cyclopentadienyl, are explored with a focus on the splitting of the f-orbitals, which provides information about the strengths of the metal-ligand interactions. While the f-orbital splitting in many lanthanide complexes has been reported in detail, experimental determination of the f-orbital splitting in actinide complexes remains rare in systems other than halide and oxide compounds, since the experimental approach, crystal field analysis, is generally significantly more difficult for actinide complexes than for lanthanide complexes. In this study, a set of analogous neodymium(iii) and uranium(iii) tris-cyclopentadienyl complexes and their isocyanide adducts was characterized by electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility. The crystal field model was parameterized by combined fitting of EPR and susceptibility data, yielding an accurate description of f-orbital splitting. The isocyanide derivatives were also studied using density functional theory, resulting in f-orbital splitting that is consistent with crystal field fitting, and by multi-reference wavefunction calculations that support the electronic structure analysis derived from the crystal-field calculations. The results highlight that the 5f-orbitals, but not the 4f-orbitals, are significantly involved in bonding to the isocyanide ligands. The main interaction between isocyanide ligand and the metal center is a σ-bond, with additional 5f to π* donation for the uranium complexes. While interaction with the isocyanide π*-orbitals lowers the energies of the 5fxz(2) and 5fyz(2)-orbitals, spin-orbit coupling greatly reduces the population of 5fxz(2) and 5fyz(2) in the ground state.

Nuclear weapons testing generates large volumes of glassy materials that influence the transport of dispersed actinides in the environment and may carry information on the composition of the detonated device. We determine the oxidation state of U and Fe (which is known to buffer the oxidation state of actinide elements and to affect the redox state of groundwater) in samples of melt glass collected from three U.S. nuclear weapons tests. For selected samples, we also determine the coordination geometry of U and Fe, and we report the oxidation state of Pu from one melt glass sample. We find significant variations among the melt glass samples and, in particular, find a clear deviation in one sample from the expected buffering effect of Fe(II)/Fe(III) on the oxidation state of uranium. In the first direct measurement of Pu oxidation state in a nuclear test melt glass, we obtain a result consistent with existing literature that proposes Pu is primarily present as Pu(IV) in post-detonation material. In addition, our measurements imply that highly mobile U(VI) may be produced in significant quantities when melt glass is quenched rapidly following a nuclear detonation, though these products may remain immobile in the vitrified matrices. The observed differences in chemical state among the three samples show that redox conditions can vary dramatically across different nuclear test conditions. The local soil composition, associated device materials, and the rate of quenching are all likely to affect the final redox state of the glass. The resulting variations in glass chemistry are significant for understanding and interpreting debris chemistry and the later environmental mobility of dispersed material.

A non-oxido V(v) complex with glutaroimide-dioxime (H₃L), a ligand for recovering uranium from seawater, was synthesized from aqueous solution as Na[V(L)₂]·2H₂O, and the structure determined by X-ray diffraction. It is the first non-oxido V(v) complex that has been directly synthesized in and crystallized from aqueous solution. The distorted octahedral structure contains two fully deprotonated ligands (L^3-) coordinating to V⁵⁺, each in a tridentate mode via the imide N (R _V-N = 1.96 Å) and oxime O atoms (R _V-O = 1.87-1.90 Å). Using ¹⁷O-labelled vanadate as the starting material, concurrent ¹⁷O/⁵¹V/¹H/¹³C NMR, in conjunction with ESI-MS, unprecedentedly demonstrated the stepwise displacement of the oxido V[double bond, length as m-dash]O bonds by glutaroimide-dioxime and verified the existence of the "bare" V⁵⁺/glutaroimide-dioxime complex, [V(L)₂]^-, in aqueous solution. In addition, the crystal structure of an intermediate 1 : 1 V(v)/glutaroimide-dioxime complex, [VO₂(HL)]^-, in which the oxido bonds of vanadate are only partially displaced, corroborates the observations by NMR and ESI-MS. Results from this work provide important insights into the strong sorption of vanadium on poly(amidoxime) sorbents in the recovery of uranium from seawater. Also, because vanadium plays important roles in biological systems, the syntheses of the oxido and non-oxido V⁵⁺ complexes and the unprecedented demonstration of the displacement of the oxido V[double bond, length as m-dash]O bonds help with the on-going efforts to develop new vanadium compounds that could be of importance in biological applications.