The thermodynamically stable metal organic framework UiO-66-NH2 has experimentally been demonstrated as an ideal platform to isolate metal clusters within its nanocages; however, the electronic structures and the dynamics of the encapsulated metal clusters are still unclear. Ab initio molecular dynamics simulations combined with density functional theory-based methods were employed to search the stable structures of Pd n @UiO-66-NH2 composites, and their electronic properties were analyzed in detail. We found that the thermodynamics of the composites are highly correlated with charge transfer between the Pd n cluster and the UiO-66-NH2 framework, as well as the deformation energy of the framework. In addition, both ab initio molecular dynamics simulations and density functional theory calculations show that the small Pd clusters can easily diffuse into the tetrahedral cage of UiO-66-NH2 from the octahedral cage through the window connecting these two types of cages, with a small energy barrier.

There has been considerable interest in adsorptive separation of C2H2/CH4 and CO2/CH4 gas mixtures due to its industrial significance and scientific challenge. In this work, we have designed and synthesized a bent diisophthalate ligand functionalized with aminopyrimidine groups, and constructed via a solvothermal reaction, a porous copper-based framework. Single-crystal X-ray diffraction studies show that the framework is a three-dimensional network containing three different types of polyhedral nanocages, which are stacked together to form two distinct types of one-dimensional channels along the crystallographic c axis. The compound after activation shows exceptionally high C2H2 and CO2 uptakes of 211 and 120 cm(3) (STP) g(-1) at 295 K and 1 atm, as well as impressive adsorption selectivities towards C2H2 and CO2 over CH4. High C2H2 and CO2 uptake capacities as well as significant adsorption selectivities of C2H2 and CO2 over CH4 imply potential applications in the adsorptive separation and purification of C2H2/CH4 and CO2/CH4 gas mixtures, which have been verified by column breakthrough experiments. Several important binding sites for C2H2 and CO2 in ZJNU-54 were revealed by quantum chemical calculations, demonstrating that the organic linkers in ZJNU-54 form unique structures that facilitate the adsorption of C2H2, while the amine groups and the Lewis basic pyrimidine-ring nitrogen sites in the organic linker improve the adsorption energies for CO2, finally leading to the increase of adsorption capacities for these two gas molecules. This work provides an efficient strategy for incorporating specific functional groups into cage-based MOFs for generating new adsorbents for highly selective gas storage and separation.

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The zeolitic imidazolate frameworks (ZIFs) are chemically and thermally stable microporous materials that are being considered as ideal supports for the uniform encapsulation of noble metal nanoparticles. Our theoretical investigations started from the adsorption of the molecular precursor Au(CO)Cl in both ZIF-8 and ZIF-90; surprisingly, pore-B, with the diameter less than 2.2 Å in the two ZIFs, dramatically expanded as an energetically most favorable site for the location of Au(CO)Cl, whereas the well-known pore-A, with a diameter of about 3.5 Å, is less favorable. Then, ab initio molecular dynamics simulations showed that the confined Au n cluster has a transition from two-dimensional to three-dimensional structures when n is larger than 12 in both ZIFs. Interestingly, the aldehyde groups in ZIF-90 were computed to be the main binding sites for Au clusters, whereas the imidazole rings were identified as the binding sites in ZIF-8. Compared to ZIF-90, the binding of Au clusters in ZIF-8 was stronger, accompanied by transfer of larger electrons from the frameworks to the confined Au clusters. Finally, the computed energy barriers for the CO oxidation using Au clusters confined in ZIFs as catalysts were found to be smaller than those for isolated Au clusters.

Construction of coupling site with electrophilic and nucleophilic centers is the key to enhance ORR in acidic electrolyte.