RESUMEN
Oxidation states (OS) are the charges on atoms due to electrons gained or lost upon applying an ionic approximation to their bonds. As a fundamental property, OS has been widely used in charge-neutrality verification, crystal structure determination, and reaction estimation. Currently, only heuristic rules exist for guessing the oxidation states of a given compound with many exceptions. Recent work has developed machine learning models based on heuristic structural features for predicting the oxidation states of metal ions. However, composition-based oxidation state prediction still remains elusive so far, which has significant implications for the discovery of new materials for which the structures have not been determined. This work proposes a novel deep learning-based BERT transformer language model BERTOS for predicting the oxidation states for all elements of inorganic compounds given only their chemical composition. This model achieves 96.82% accuracy for all-element oxidation states prediction benchmarked on the cleaned ICSD dataset and achieves 97.61% accuracy for oxide materials. It is also demonstrated how it can be used to conduct large-scale screening of hypothetical material compositions for materials discovery.
RESUMEN
Superatoms are nanometer-sized molecules or particles that form ordered lattices, mimicking their atomic counterparts. Hierarchical assembly of superatoms gives rise to emergent properties in lattices of quantum dots, p-block clusters, and fullerenes. Here, we introduce a family of uranium-oxysulfate cluster anions whose hierarchical assembly in water is controlled by two parameters: acidity and the lanthanide or transition-metal countercation. In acid, larger LnIII (Ln = La-Ho) link hexamer (U6) oxoclusters into body-centered cubic frameworks, while smaller LnIII (Ln = Er-Lu and Y) promote linking of 14 U6 clusters into hollow superclusters (U84 superatoms). U84 assembles into superlattices including cubic-closest packed, body-centered cubic, and interpenetrating networks, bridged by interstitial countercations and U6 clusters. Divalent transition metals (TM = MnII and ZnII) charge-balance and promote the fusion of 10 U6 and 10 U monomers into a wheel-shaped cluster (U70). Dissolution of U70 in organic media reveals (by small-angle X-ray scattering) that differing supramolecular assemblies are accessed, controlled by TMII-linking of U70 clusters. Magnetic measurements of these assemblies reveal Curie-Weiss behavior at high temperatures, without pairing of the 5f2-electrons down to 2 K.
RESUMEN
Thermodynamic studies of actinide-containing metal-organic frameworks (An-MOFs), reported herein for the first time, are a step toward addressing challenges related to effective nuclear waste administration. In addition to An-MOF thermochemistry, enthalpies of formation were determined for the organic linkers, 2,2'-dimethylbiphenyl-4,4'-dicarboxylic acid (H2Me2BPDC) and biphenyl-4,4'-dicarboxylic acid (H2BPDC), which are commonly used building blocks for MOF preparation. The electronic structure of the first example of An-MOF with mixed-metal AnAn'-nodes was influenced through coordination of transition metals as shown by the density of states near the Fermi edge, changes in the Tauc plot, conductivity measurements, and theoretical calculations. The "structural memory" effect (i.e., solvent-directed crystalline-amorphous-crystalline structural dynamism) was demonstrated as a function of node coordination degree, which is the number of organic linkers per metal node. Remarkable three-month water stability was reported for Th-containing frameworks herein, and the mechanism is also considered for improvement of the behavior of a U-based framework in water. Mechanistic aspects of capping linker installation were highlighted through crystallographic characterization of the intermediate, and theoretical calculations of free energies of formation (ΔGf) for U- and Th-MOFs with 10- and 12-coordinated secondary building units (SBUs) were performed to elucidate experimentally observed transformations during the installation processes. Overall, these results are the first thermochemical, electronic, and mechanistic insights for a relatively young class of actinide-containing frameworks.
RESUMEN
Uranium(IV) 5f2 magnetism is dominated by a transition from a triplet to a singlet ground state at low temperatures. For the first time, we achieved magnetic ordering of U(IV) atoms in a complex fluoride through the incorporation of 3 d transition metal cations. This new route allowed us to obtain an unprecedented series of U(IV) ferrimagnetic materials of the new composition Cs2MU3F16 (M = Mn2+, Co2+, and Ni2+), which were comprehensively characterized with respect to their structural and magnetic properties. Magnetic susceptibility measurements revealed ferromagnetic-like phase transitions at temperatures of â¼14.0, 3.5, and 4.8 K for M = Mn2+, Co2+, and Ni2+, respectively. The transition is not observed when the magnetic M cations are replaced by a diamagnetic cation, Zn2+. Neutron diffraction measurements revealed the magnetic moments of 0.91(6)-1.97(3) µB on the U atoms, which are only partially compensated by antiparallel moments of 1.53(14)-3.26(5) µB on the 3 d cations. This arrangement promotes suppression of the transition to a diamagnetic ground state characteristic of U(IV), and in doing so, induces magnetic ordering on uranium via 3 d-5 f exchange coupling.
RESUMEN
Formation enthalpies and Gibbs energies of actinide and rare-earth containing SIMs with silicate and germanate frameworks are reported. Volume-based thermodynamics (VBT) techniques complemented by density functional theory (DFT) were adapted and applied to these complex structures. VBT and DFT results were in closest agreement for the smaller framework silicate structure, whereas DFT in general predicts less negative enthalpies across all SIMs, regardless of framework type. Both methods predict the rare-earth silicates to be the most stable of the comparable structures calculated, with VBT results being in good agreement with the limited experimental values available from drop solution calorimetry.
RESUMEN
The crystal chemistry and magnetic properties for two triple perovskites, Ba3Fe1.56Ir1.44O9 and Ba3NiIr2O9, grown as large, highly faceted single crystals from a molten strontium carbonate flux, are reported. Unlike the idealized A3MM2'O9 hexagonal symmetry characteristic of most triple perovskites, including Ba3NiIr2O9, Ba3Fe1.56Ir1.44O9 possesses significant site-disorder, resulting in a noncentrosymmetric polar structure with trigonal symmetry. The valence of iron and iridium in the heavily distorted Fe/Ir sites was determined to be Fe(III) and Ir(V) by X-ray absorption near edge spectroscopy (XANES). Density functional theory calculations were conducted to understand the effect of the trigonal distortion on the local Fe(III)O6 electronic structure, and the spin state of iron was determined to be S = 5/2 by Mössbauer spectroscopy. Conductivity measurements indicate thermally activated semiconducting behavior in the trigonal perovskite. Magnetic properties were measured and near room temperature magnetic ordering (TN = 270 K) was observed for Ba3Fe1.56Ir1.44O9.
RESUMEN
The lanthanide-containing ruthenium oxides Ln14Na3Ru6O36 (Ln = Pr, Nd) were prepared as single crystals from molten sodium hydroxide. The two compounds crystallize in the rhombohedral space group Rc with cell constants of a = 9.7380(2) and 9.6781(2) Angstrom and c = 55.5716(18) and 55.4156(18) Angstrom for Ln14Na3Ru6O36 (Ln = Pr, Nd), respectively. The structure of the two compounds is composed of two types of slabs that alternate in an AB fashion. Each slab consists of three layers and are arranged to yield a unit cell with a 12-layer structure. Both compounds exhibit magnetic behavior consistent with canted antiferromagnetism.
