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 (H 2 Me 2 BPDC) and biphenyl-4,4′-dicarboxylic acid (H 2 BPDC), 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 (ΔG f ) 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.

Acquiring fundamental knowledge of properties of actinide‐based materials is a necessary step to create new possibilities for addressing the current challenges in the nuclear energy and nuclear waste sectors. In this report, we established a photophysics–electronics correlation for actinide‐containing metal‐organic frameworks (An‐MOFs) as a function of excitation wavelength, for the first time. A stepwise approach for dynamically modulating electronic properties was applied for the first time towards actinide‐based heterometallic MOFs through integration of photochromic linkers. Optical cycling, modeling of density of states near the Fermi edge, conductivity measurements, and photoisomerization kinetics were employed to shed light on the process of tailoring optoelectronic properties of An‐MOFs. Furthermore, the first photochromic MOF‐based field‐effect transistor, in which the field‐effect response could be changed through light exposure, was constructed. As a demonstration, the change in current upon light exposure was sufficient to operate a two‐LED fail‐safe indicator circuit.

High entropy alloys contain multiple elements in large proportions that make them prone to phase separation. These alloys generally have shallow enthalpy of mixing which makes the entropy contributions of similar magnitude. As a result, the phase stability of these alloys is equally dependent on enthalpy and entropy of mixing and understanding the individual contribution of thermodynamic properties is critical. In the overall vision of designing high entropy alloys, in this work, using density functional theory calculations, we elucidate the contributions of various entropies, i.e., vibrational, electronic and configurational towards the phase stability of binary alloys. We show that the contribution of electronic entropy is very small compared to the vibrational and configurational entropies, and does not play a significant role in the phase stability of alloys. The configurational and vibrational entropies can either destabilize or can collectively contribute to stabilize the solid solutions. As a result, even those systems that have negative mixing enthalpy can show phase instability, revealed as a miscibility gap; conversely, systems with positive mixing enthalpy can be phase stable due to entropic contributions. We suggest that including entropic contributions are critical in the development of theoretical framework for the computational prediction of stable, single-phase high entropy alloys that have shallow mixing enthalpies, unlike ordered intermetallics.

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Galvanic replacement reactions dictated by deliberately designed nanoparticulate templates have emerged as a robust and versatile approach that controllably transforms solid monometallic nanocrystals into a diverse set of architecturally more sophisticated multimetallic hollow nanostructures. The galvanic atomic exchange at the nanoparticle/liquid interfaces induces a series of intriguing structure-transforming processes that interplay over multiple time and length scales. Using colloidal Au-Cu alloy and intermetallic nanoparticles as structurally and compositionally fine-tunable bimetallic sacrificial templates, we show that atomically intermixed bimetallic nanocrystals undergo galvanic replacement-driven structural transformations remarkably more complicated than those of their monometallic counterparts. We interpret the versatile structure-transforming behaviors of the bimetallic nanocrystals in the context of a unified mechanistic picture that rigorously interprets the interplay of three key structure-evolutionary pathways: dealloying, Kirkendall diffusion, and Ostwald ripening. By deliberately tuning the compositional stoichiometry and atomic-level structural ordering of the Au-Cu bimetallic nanocrystals, we have been able to fine-maneuver the relative rates of dealloying and Kirkendall diffusion with respect to that of Ostwald ripening through which an entire family of architecturally distinct complex nanostructures are created in a selective and controllable manner upon galvanic replacement reactions. The insights gained from our systematic comparative studies form a central knowledge framework that allows us to fully understand how multiple classic effects and processes interplay within the confinement by a colloidal nanocrystal to synergistically guide the structural transformations of complex nanostructures at both the atomic and nanoparticulate levels.