Actinyl Electronic Structure Probed by XAS: The Role of Many-Body Effects.

A detailed analysis of the wave functions for the M5 to 5f excitations in the linear actinyls, UO22+, NpO22+, and PuO22+, and the theoretical X-ray absorption spectra obtained with these wave functions in comparison with experimental M5-edge high-resolution X-ray absorption near-edge structure (HR-XANES) spectra is presented. The wave functions include full treatment of scalar and spin-orbit relativistic effects through the use of a Dirac-Coulomb Hamiltonian; many-body effects are included in determining the wave functions. The character of the excited states and of the active spaces to describe the wave functions for these states are investigated and analyzed. It is shown that the excited states cannot, in general, be described with a single configuration but have an essential multiconfiguration character. The characterization of the properties of the excited states and the X-ray absorption spectra was achieved through the use of novel methods.

U(V) Stabilization via Aliovalent Incorporation of Ln(III) into Oxo-salt Framework.

Pentavalent uranium compounds are key components of uranium's redox chemistry and play important roles in environmental transport. Despite this, well-characterized U(V) compounds are scarce primarily because of their instability with respect to disproportionation to U(IV) and U(VI). In this work, we provide an alternate route to incorporation of U(V) into a crystalline lattice where different oxidation states of uranium can be stabilized through the incorporation of secondary cations with different sizes and charges. We show that iriginite-based crystalline layers allow for systematically replacing U(VI) with U(V) through aliovalent substitution of 2+ alkaline-earth or 3+ rare-earth cations as dopant ions under high-temperature conditions, specifically Ca(UVIO2)W4O14 and Ln(UVO2)W4O14 (Ln=Nd, Sm, Eu, Gd, Yb). Evidence for the existence of U(V) and U(VI) is supported by single-crystal X-ray diffraction, high energy resolution X-ray absorption near edge structure, X-ray photoelectron spectroscopy, and optical absorption spectroscopy. In contrast with other reported U(V) materials, the U(V) single crystals obtained using this route are relatively large (several centimeters) and easily reproducible, and thus provide a substantial improvement in the facile synthesis and stabilization of U(V).

Unveiling Hidden Shake-Up Features in the Uranyl M4-Edge Spectrum.

The M4,5-edge high energy resolution X-ray absorption near-edge structure (HR-XANES) spectra of actinyls offer valuable insights into the electronic structure and bonding properties of heavy-element complexes. To conduct a comprehensive spectral analysis, it is essential to employ computational methods that accurately account for relativistic effects and electron correlation. In this work, we utilize variational relativistic multireference configurational interaction methods to compute and analyze the X-ray M4-edge absorption spectrum of uranyl. By employing these advanced computational techniques, we achieve excellent agreement between the calculated spectral features and experimental observations. Moreover, the calculations unveil significant shake-up features, which arise from the intricate interplay between strongly correlated 3d core-electron and ligand excitations. This research provides important theoretical insights into the spectral characteristics of heavy-element complexes. Furthermore, it establishes the foundation for utilizing M4,5-edge spectroscopy as a means to investigate the chemical activities of such complexes. By leveraging this technique, we can gain a deeper understanding of the bonding behavior and reactivity of heavy-element compounds.

Sc, Zr, Hf, and Mn Metal Nanoparticles: Reactive Starting Materials for Synthesis Near Room Temperature.

Zerovalent scandium, zirconium, hafnium, and manganese nanoparticles are prepared by reduction of ScCl3, ZrCl4, HfCl4, and MnCl2 with lithium or sodium naphthalenide in a one-pot, liquid-phase synthesis. Small-sized monocrystalline nanoparticles are obtained with diameters of 2.4 ± 0.2 nm (Sc), 4.0 ± 0.9 nm (Zr), 8.0 ± 3.9 nm (Hf) and 2.4 ± 0.3 nm (Mn). Thereof, Zr(0) and Hf(0) nanoparticles with such size are shown for the first time. To probe the reactivity and reactions of the as-prepared Sc(0), Zr(0), Hf(0), and Mn(0) nanoparticles, they are exemplarily reacted in the liquid phase (e.g., THF, toluene, ionic liquids) with different sterically demanding, monodentate to multidentate ligands, mainly comprising O-H and N-H acidic alcohols and amines. These include isopropanol (HOiPr), 1,1'-bi-2-naphthol (H2binol), N,N'-bis(salicylidene)ethylenediamine (H2salen), 2-mercaptopyridine (2-Hmpy), 2,6-diisopropylaniline (H2dipa), carbazole (Hcz), triphenylphosphane (PPh3), N,N,N',N'-tetramethylethylenediamine (tmeda), 2,2'-bipyridine (bipy), N,N'-diphenylformamidine (Hdpfa), N,N'-(2,6-diisopropylphenyl)-2,4-pentanediimine ((dipp)2nacnacH), 2,2'-dipydridylamine (Hdpa), and 2,6-bis(2-benzimidazolyl)pyridine (H2bbp). As a result, 22 new compounds are obtained, which frequently exhibit a metal center coordinated only by the sterically demanding ligand. Options and restrictions for the liquid-phase syntheses of novel coordination compounds using the oxidation of base-metal nanoparticles near room temperature are evaluated.

Electronic Structure of Actinyls: Orbital Properties.

A detailed analysis is presented for the covalent character of the orbitals in the actinyls: UO22+, NpO22+, and PuO22+. Both the initial, or ground state, GS, configuration and the excited configurations where a 3d electron is excited into the open valence, nominally the 5f shell, are considered. The orbitals are determined as fully relativistic, four component Dirac-Coulomb Hartree-Fock solutions. Several measures, which go beyond the commonly used population analyses, are used to characterize the covalent character of an orbital in order to obtain reliable estimates of the covalency. Although there are differences in the covalent character of the orbitals for the initial and excited configurations of the different actinyls, there is a surprising similarity in the covalent character for all of the states considered. This is true both between the initial and excited configurations as well as between the different actinyls. The analysis emphasizes the 5f covalent character in the closed shell bonding orbitals and the open shell antibonding orbitals since the focus is on characterizing orbitals needed in a many-body treatment of the actinyl wave functions. However, estimates are also made of the participation of the actinide 6d in the covalent bonding.