Metal−organic frameworks (MOFs) and specifically the UiO family of MOFs have been extensively studied for the adsorption and degradation of chemical warfare agents (CWAs) and their simulants. We present a combined experimental and computational study of the adsorption of dimethyl methylphosphonate (DMMP), a CWA adsorption simulant, in functionalized UiO-67. We have used density functional theory (DFT) to design functionalized MOFs having a range of binding energies for DMMP. We have selected three different functionalized MOFs for experimental synthesis and characterization from a total of eight studied with DFT. These three MOFs were identified as having the weakest, intermediate, and strongest binding energies for DMMP of the set, as predicted by our DFT calculations. We find that the order of predicted binding energies agrees with data from temperature-programmed desorption experiments. Moreover, the values of the binding energies are also in good agreement. This serves as a proof of concept that ab initio calculations can guide experiments in designing MOFs that exhibit a higher affinity for CWAs and their simulants. One surprising outcome of this work is that reactions between DMMP and the three functionalized UiO-67 MOFs were not observed under ultrahigh-vacuum conditions for the exposure of DMMP of up to 9000 L. This lack of reactivity is attributed to the low levels of defects in the materials used.

Highly porous zirconium-based metal−organic frameworks (MOFs) have been widely studied as materials for sorption and destruction of chemical warfare agents (CWAs). It is important to understand the diffusion of CWAs, their reaction products, and environmental molecules through MOFs to utilize these materials for protection against CWA threats. As a first step toward this goal, we study adsorption and diffusion of acetone in pristine UiO-66. We have chosen to study UiO-66 because it has been demonstrated to be effective for destruction of CWAs and simulants; we use acetone because it is a prototypical polar organic molecule small enough to be expected to diffuse fairly rapidly through nondefective UiO-66. We specifically examine the impact of framework flexibility and hydrogen bonding between acetone and the OH groups on the nodes of the framework on the diffusivity of acetone. We find that inclusion of flexibility is essential for meaningful predictions of diffusion of acetone. We have identified the dynamics of the three linkers making up the triangular window between adjacent pores as the critical factor in controlling diffusion of acetone. We demonstrate from experiments and first-principles calculations that acetone readily hydrogen bonds to UiO-66 framework OH groups. We have modified the classical potential for UiO-66 to accurately model the framework−acetone hydrogen bonds, which are not accounted for in many MOF potentials. We find that hydrogen bonding decreases the diffusivity by about 1 order of magnitude at low loading and about a factor of 3 at high loading. Thus, proper accounting of hydrogen bonding and framework flexibility are both critical for obtaining physically realistic values of diffusivities for acetone and similar-sized polar molecules in UiO-66.

The UiO family of metal−organic frameworks (MOFs) has been extensively studied for several applications owing to their high stability rendered by their robust secondary building units. The efficient design and use of these materials require a fundamental understanding of their thermal stability and its impact on chemical and structural functionality. Herein, we provide a detailed characterization of the intrinsic thermal behavior of the UiO-67 and functional analogues, UiO-67-NH 2 and UiO-67-CH 3 . Using in situ temperature-programmed X-ray diffraction, we find that distortion of the carboxylate group on the organic linker leads to negative thermal expansion (NTE) of the UiO-67 MOFs during heating. This NTE behavior is correlated with rich and reversible thermal changes observed in the MOF infrared spectral signature as samples are heated to the sample activation temperature (473 K). We find that in the absence of oxygen, activated UiO-67 samples show higher thermal stability compared to ambient or inert environments, with temperature-programmed desorption revealing an overall stability trend: UiO-67 > UiO-67-CH 3 > UiO-67-NH 2 . Two stages of change are observed during thermal treatment above 473 K, which are directly related to deformation of the inorganic node and the isotropic NTE behavior of these materials. Ultimately, these results provide a real-time interpretation of the fundamental thermoresponsive behavior of UiO-67 MOFs and offer a foundation for accurate interpretation of MOF interactions with guest molecules and their temperature dependence.

Electron spin resonance (ESR) spectroscopic line shape analysis and continuous-wave (CW) progressive microwave power saturation experiments are used to probe the relaxation behavior and the relaxation times of charged excitations (hole and electron polarons) in meso-to-meso ethyne-bridged (porphinato)zinc(II) oligomers (PZnn compounds), which can serve as models for the relevant states generated upon spin injection. The observed ESR line shapes for the PZnn hole polaron ([PZnn](+•)) and electron polaron ([PZnn](-•)) states evolve from Gaussian to more Lorentzian as the oligomer length increases from 1.9 to 7.5 nm, with solution-phase [PZnn](+•) and [PZnn](-•) spin-spin (T2) and spin-lattice (T1) relaxation times at 298 K ranging, respectively, from 40 to 230 ns and 0.2 to 2.3 μs. Notably, these very long relaxation times are preserved in thick films of these species. Because the magnitudes of spin-spin and spin-lattice relaxation times are vital metrics for spin dephasing in quantum computing or for spin-polarized transport in magnetoresistive structures, these results, coupled with the established wire-like transport behavior across metal-dithiol-PZnn-metal junctions, present meso-to-meso ethyne-bridged multiporphyrin systems as leading candidates for ambient-temperature organic spintronic applications.

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