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1. Terahertz Dynamics at the Actinide Frontier: Linking Low-Frequency Vibrations, Electronic Structure, and Bonding in Molecular Uranium Complexes

   https://doi.org/10.1039/D6SC02116F  

   Pittalis, Michele; Shiels, Dominic; Stoll, William B; Alvarez, Alejandro; Kölbel, Johanna; Brennessel, William W; Lewis, Rob; Matson, Ellen; Ruggiero, Michael T (January 2026, Chemical Science)

   Understanding the nature of uranium–ligand bonding in molecular complexes is a central challenge in modern actinide chemistry. Here, we introduce low-frequency vibrational spectroscopy as a powerful new probe of bonding in uranium-containing molecular crystals by combining terahertz and low-frequency Raman spectroscopy with periodic solid-state density functional theory. Using U(VI)(OtBu)6 and its one-electron-reduced analogue [Cp*2Co][U(V)(OtBu)6] as model systems, we show that uranium–oxygen bonding is encoded across the low-frequency spectrum through strongly mixed metal–ligand and ligand–lattice motions that cannot be interpreted using conventional gas-phase or high-frequency vibrational pictures alone. Local mode analysis isolates the intrinsic U–O stretching coordinates and reveals a clear weakening of the U–O bond upon reduction from U(VI) to U(V), while quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses connect these vibrational changes to differences in electron density, orbital mixing, and covalency. Periodic calculations further show that crystal packing stiffens collective low-frequency motions in the neutral U(VI) lattice without significantly perturbing the underlying U–O bonding core, whereas the more charge-sensitive U(V) complex is strongly influenced by its ionic environment and associated non-covalent intermolecular interactions. These results establish, for the first time, a computationally validated correlation between low-frequency vibrational dynamics, local U–O force constants, and simulated bonding descriptors in molecular uranium complexes, and demonstrate this combined experimental and computational approach as a new route for interrogating electronic structure in heavy-element coordination complexes. 

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2. 4d crystal melting, toric Calabi-Yau 4-folds and brane brick models

   https://doi.org/10.1007/JHEP03(2024)091  

   Franco, Sebastián (March 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> We introduce a class of 4-dimensional crystal melting models that count the BPS bound state of branes on toric Calabi-Yau 4-folds. The crystalline structure is determined by the brane brick model associated to the Calabi-Yau 4-fold under consideration or, equivalently, its dual periodic quiver. The crystals provide a discretized version of the underlying toric geometries. We introduce various techniques to visualize crystals and their melting configurations, including 3-dimensional slicing and Hasse diagrams. We illustrate the construction with the D0-D8 system on$${\mathbb{C}}$$⁴. Finally, we outline how our proposal generalizes to arbitrary toric CY 4-folds and general brane configurations. 

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3. Uranium: The Nuclear Fuel Cycle and Beyond

   https://doi.org/10.3390/ijms23094655  

   Costa Peluzo, Bárbara Maria; Kraka, Elfi (May 2022, International Journal of Molecular Sciences)

   This review summarizes the recent developments regarding the use of uranium as nuclear fuel, including recycling and health aspects, elucidated from a chemical point of view, i.e., emphasizing the rich uranium coordination chemistry, which has also raised interest in using uranium compounds in synthesis and catalysis. A number of novel uranium coordination features are addressed, such the emerging number of U(II) complexes and uranium nitride complexes as a promising class of materials for more efficient and safer nuclear fuels. The current discussion about uranium triple bonds is addressed by quantum chemical investigations using local vibrational mode force constants as quantitative bond strength descriptors based on vibrational spectroscopy. The local mode analysis of selected uranium nitrides, N≡U≡N, U≡N, N≡U=NH and N≡U=O, could confirm and quantify, for the first time, that these molecules exhibit a UN triple bond as hypothesized in the literature. We hope that this review will inspire the community interested in uranium chemistry and will serve as an incubator for fruitful collaborations between theory and experimentation in exploring the wealth of uranium chemistry. 

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4. Advanced 2D XRF imaging of uranium oxidation states using HERFD at the U M ₄ edge

   https://doi.org/10.1039/d4cc06211f  

   Bazarkina, Elena F; Lau, Kimberly V; Chappaz, Anthony; Bastrakov, Evgeny; Etschmann, Barbara; Brugger, Joël; Marshall, Madeline; Meyer, Frances M; Boreham, Christopher J; Amidani, Lucia; et al (February 2025, Chemical Communications)

   Identification of U(iv), U(v) and U(vi) oxidation states in rocks can be achieved with HERFD-XRF imaging at the uranium M₄edge. 

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5. Introduction of Local Resonators to a Nonlinear Metamaterial With Topological Features

   https://doi.org/10.1115/1.4064726  

   LeGrande, Joshua; Malla, Arun; Bukhari, Mohammad; Barry, Oumar (July 2024, Journal of Computational and Nonlinear Dynamics)

   Abstract Recent work in nonlinear topological metamaterials has revealed many useful properties such as amplitude dependent localized vibration modes and nonreciprocal wave propagation. However, thus far, there have not been any studies to include the use of local resonators in these systems. This work seeks to fill that gap through investigating a nonlinear quasi-periodic metamaterial with periodic local resonator attachments. We model a one-dimensional metamaterial lattice as a spring-mass chain with coupled local resonators. Quasi-periodic modulation in the nonlinear connecting springs is utilized to achieve topological features. For comparison, a similar system without local resonators is also modeled. Both analytical and numerical methods are used to study this system. The dispersion relation of the infinite chain of the proposed system is determined analytically through the perturbation method of multiple scales. This analytical solution is compared to the finite chain response, estimated using the method of harmonic balance and solved numerically. The resulting band structures and mode shapes are used to study the effects of quasi-periodic parameters and excitation amplitude on the system behavior both with and without the presence of local resonators. Specifically, the impact of local resonators on topological features such as edge modes is established, demonstrating the appearance of a trivial bandgap and multiple localized edge states for both main cells and local resonators. These results highlight the interplay between local resonance and nonlinearity in a topological metamaterial demonstrating for the first time the presence of an amplitude invariant bandgap alongside amplitude dependent topological bandgaps. 

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