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In molecular solids derived from Prussian blue, intermetallic charge transfer is fostered through a cyano bridge two metal ions. In this study, isostructural trivalent lanthanide and tetravalent actinide Prussian blue analogs' valence orbitals are probed by soft X-ray absorption measurements.

The electronic properties of actinide cations are of fundamental interest to describe intramolecular interactions and chemical bonding in the context of nuclear waste reprocessing or direct storage. The 5f and 6d orbitals are the first partially or totally vacant states in these elements, and the nature of the actinide ligand bonds is related to their ability to overlap with ligand orbitals. Because of its chemical and orbital selectivities, X-ray absorption spectroscopy (XAS) is an effective probe of actinide species frontier orbitals and for understanding actinide cation reactivity toward chelating ligands. The soft X-ray probes of the light elements provide better resolution than actinide L3-edges to obtain electronic information from the ligand. Thus coupling simulations to experimental soft X-ray spectral measurements and complementary quantum chemical calculations yields quantitative information on chemical bonding. In this study, soft X-ray XAS at the K-edges of C and N, and the L2,3-edges of Fe was used to investigate the electronic structures of the well-known ferrocyanide complexes K4Fe(II)(CN)6, thorium hexacyanoferrate Th(IV)Fe(II)(CN)6, and neodymium hexacyanoferrate KNd(III)Fe(II)(CN)6. The soft X-ray spectra were simulated based on quantum chemical calculations. Our results highlight the orbital overlapping effects and atomic effective charges in the Fe(II)(CN)6 building block. In addition to providing a detailed description of the electronic structure of the ferrocyanide complex (K4Fe(II)(CN)6), the results strongly contribute to confirming the actinide 5f and 6d orbital oddity in comparison to lanthanide 4f and 5d.

Radiometals are increasingly used in nuclear medicine for both diagnostic and therapeutic purposes. The DOTA ligand (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) is widely used as a chelating agent for various radionuclides, including 89Zr, with high thermodynamic stability constants and great in vivo stability. However, in contact with radioisotopes, chelating molecules are subjected to the effects of radiation, which can lead to structural degradation and induce alteration of their complexing properties. For the first time, the radiolytic stability of the Zr–DOTA complex in aqueous solution was studied and compared to the stability of the DOTA ligand. The identification of the major degradation products allows us to propose two different degradation schemes for the DOTA ligand and Zr–DOTA complex. DOTA is degraded preferentially by decarboxylation and cleavage of an acetate arm CH2–COOH, whereas in Zr–DOTA, DOTA tends to oxidize by the addition of the OH group in its structure. In addition, the degradation of the ligand, when involved in a Zr complex, is significantly less than when the ligand is free in solution, indicating that the metal protects the ligand from degradation. DFT calculations were performed to supplement the experimental data and give an improved understanding of the behaviour of DOTA and Zr–DOTA solutions after irradiation: the increase in stability upon complexation is attributed to the strengthening of the bonds in the presence of metal cations, which become less vulnerable to radical attack. Bond dissociation energies and Fukui indices are shown to be useful descriptors to estimate the most vulnerable sites of the ligand and to predict the protective effect of the complexation. [ABSTRACT FROM AUTHOR]

The photochromic cycloreversion reactions are theoretically examined in a model system of dithienylethenes. The study provides a basic insight for the photochromic molecular design.

The spin-orbit coupling (SOC) induced mixing between the low-lying singlet and triplet electronic excited states of M(H)(CO)3(H-DAB) (M = Mn, Re; H-DAB = 1,4-diaza-1,3-butadiene) was studied through SOC-CI computations, utilizing a one-electron effective spin-orbit operator at the metal center. In the manganese complex, the spin-orbit interactions between the low-lying singlet and triplet states range between 0 and 100/cm, while in the rhenium complex they are computed between 100 and 560/cm.

The use of tri-alkylcarbamides (TrAC) as novel extractants for the separation of uranium(VI) and plutonium(IV) by solvent extraction from spent nuclear fuels is investigated. The comparison between extraction properties of different tri-alkylcarbamides and tetra-alkylcarbamides indicates their higher ability to co-extract uranium(VI) and plutonium(IV). Moreover, tri-alkylcarbamides present very high separation factors SFU/Pu (up to 100) at lower nitric acid concentration showing that they are good candidates for U(VI)/Pu(IV) separation without redox chemistry. The addition of branched 2-ethylhexyl chains induces a decrease of distribution ratios and U/Pu separation factor. Due to the formation of intermolecular hydrogen bond between carbonyl and -NH functions, the viscosity of tri-alkylcarbamides is higher compared to tetra-alkylcarbamides. Nevertheless, the introduction of branched alkyl chains decreases the viscosity of the solvent and increases the limit organic concentration (LOC) for uranium(VI), preventing from third phase formation. [ABSTRACT FROM AUTHOR]

The relative order and nature of the low-lying excited states of Cr(CO)4-(bpy) on the basis of CASSCF/LS-CASPT2 calculations were investigated. The lowest singlet metal-to-ligand-charge-transfer excitation energies range from 12630 and 17580 cm. These states are probably responsible for the emission observed in this energy range. The excitation energies of the LSS of Cr(CO)4(bpy) and CR(CO)4(dab) were compared.

Among the fission products present in the spent nuclear fuel, technetium exhibits a singular behavior in reprocessing operations performed by solvent extraction. Indeed, this strong acid readily dissociates to form the oxo-anion TcO4− that may interfere with uranium(VI), plutonium(IV), and zirconium(IV) in the extraction cycles of the PUREX process. This paper focuses on the uranium-technetium complex with TBP and on its non-radioactive rhenium surrogate. Despite the large set of distribution data available for rhenium and technetium extraction with TBP, the structures of the co-extracted complexes remain largely unknown. However, it is important to understand clearly the extraction mechanism of technetium with TBP in the PUREX process to optimize the separation process and to model its behavior during the extraction steps. Based on distribution data available in the literature, a thermodynamic model was developed for the extraction of technetium with TBP for a large excess of uranium(VI) in organic phase. A good representation of uranium and technetium distribution data was thus obtained when considering the formation of (HTcO4)(TBP)n complexes, as well as mixed UO2(NO3)(TcO4)(HNO3)x(TBP)n, complexes. In the complex UO2(NO3)2(HNO3)x(TBP)n., one pertechnetate anion replaces one nitrate in the uranium coordination sphere. Combination of complementary spectroscopic techniques (FT-IR and X-ray absorption) supported by theoretical calculations (density functional theory) with organic phases containing a large excess of technetium(VII) or rhenium(VII) enabled full characterization of the limit mixed uranium−technetium species and also of mixed uranium-rhenium species. Details on the coordination of the uranium-technetium complex are provided with the help of DFT calculations and XAS measurements. [ABSTRACT FROM AUTHOR]