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.

No abstract

For the first time, we report the ability to control radionuclide species release kinetics in metal–organic frameworks (MOFs) as a function of postsynthetic capping linker installation, which is essential for understanding MOF potential as viable radionuclide wasteform materials or versatile platforms for sensing, leaching, and radionuclide sequestration. The radiation damage of prepared frameworks under γ radiation has also been studied. We envision that the presented studies are the first steps toward utilization of the reported scaffolds for more efficient nuclear waste administration.

Tuning metal oxidation states in metal–organic framework (MOF) nodes by switching between two discrete linker photoisomers via an external stimulus was probed for the first time. On the examples of three novel photochromic copper-based frameworks, we demonstrated the capability of switching between +2 and +1 oxidation states, on demand. In addition to crystallographic methods used for material characterization, the role of the photochromic moieties for tuning the oxidation state was probed via conductivity measurements, cyclic voltammetry, and electron paramagnetic resonance, X-ray photoelectron, and diffuse reflectance spectroscopies. We confirmed the reversible photoswitching activity including photoisomerization rate determination of spiropyran- and diarylethene-containing linkers in extended frameworks, resulting in changes in metal oxidation states as a function of alternating excitation wavelengths. To elucidate the switching process between two states, the photoisomerization quantum yield of photochromic MOFs was determined for the first time. Overall, the introduced noninvasive concept of metal oxidation state modulation on the examples of stimuli-responsive MOFs foreshadows a new pathway for alternation of material properties toward targeted applications.

The effect of donor (D)–acceptor (A) alignment on the materials electronic structure was probed for the first time using novel purely organic porous crystalline materials with covalently bound two‐ and three‐dimensional acceptors. The first studies towards estimation of charge transfer rates as a function of acceptor stacking are in line with the experimentally observed drastic, eight‐fold conductivity enhancement. The first evaluation of redox behavior of buckyball‐ or tetracyanoquinodimethane‐integrated crystalline was conducted. In parallel with tailoring the D‐A alignment responsible for “static” changes in materials properties, an external stimulus was applied for “dynamic” control of the electronic profiles. Overall, the presented D–A strategic design, with stimuli‐controlled electronic behavior, redox activity, and modularity could be used as a blueprint for the development of electroactive and conductive multidimensional and multifunctional crystalline porous materials.