Porous crystals are strategic materials with industrial applications within petrochemistry, catalysis, gas storage, and selective separation. Their unique properties are based on the molecular-scale porous character. However, a principal limitation of zeolites and similar oxide-based materials is the relatively small size of the pores, typically in the range of medium-sized molecules, limiting their use in pharmaceutical and fine chemical applications. Metal organic frameworks (MOFs) provided a breakthrough in this respect. New MOFs appear at a high and an increasing pace, but the appearances of new, stable inorganic building bricks are rare. Here we present a new zirconium-based inorganic building brick that allows the synthesis of very high surface area MOFs with unprecedented stability. The high stability is based on the combination of strong Zr-O bonds and the ability of the inner Zr6-cluster to rearrange reversibly upon removal or addition of mu3-OH groups, without any changes in the connecting carboxylates. The weak thermal, chemical, and mechanical stability of most MOFs is probably the most important property that limits their use in large scale industrial applications. The Zr-MOFs presented in this work have the toughness needed for industrial applications; decomposition temperature above 500 degrees C and resistance to most chemicals, and they remain crystalline even after exposure to 10 tons/cm2 of external pressure.

We address the metal–organic frameworks UiO-6x (x = 6, 7, 8), their band gaps, and the changes in the band gaps upon perturbations in the metal–organic framework structures. Computational studies were performed with complementary experimental band gap measurements. Band gap modulations upon hydrogen substitutions by NH2 and NO2 on the organic linker, hydroxylation and dehydroxylation of the metal center, different linker lengths (x = 6, 7, 8), and Ti and Hf substitutions for Zr were analyzed in detail. The origin of the band gap changes was thoroughly investigated, and this work confirmed a reduction in the band gap upon NH2 and NO2 substitutions. Furthermore, this work explicitly illustrated that changes in the band gap were also observed by changing the coordination around the Zr atom, whereas isovalent substitutions on the metal center did not yield significant perturbations of the band gap.

Adsorption of H 2 S on the Ni 2 (dhtp)(H 2 O) 2 ·8H 2 O metal-organic framework (known as CPO-27-Ni or MOF-74-Ni) is characterized by in-situ technique (PXRD, FTIR, Raman and Uvvisible spectroscopy) and by first principles periodic boundary conditions calculations.Powder X-ray diffraction results show very high stability of CPO-27-Ni framework in presence of H 2 S. Nevertheless, as evidenced by change in color of the sample from pale yellow to dark green, the adsorption of H 2 S strongly affects the coordination of Ni sites. FTIR results show the reversible molecular adsorption of H 2 S. Experimental and computed energies of interaction reveal good agreement. Quantitative data considering energetic aspects (calorimetric measurements) are also included. This work highlights the fundamentals of H 2 S adsorption onto the CPO-27-Ni framework.

Adsorption equilibrium of CO 2 and CH 4 at three different temperatures was measured on three isoreticular Zr-MOFs: Zr(1,4-BDC) (UiO-66), Zr(4,4′-BPDC) UiO-67, and Zr(2,6-NDC) (DUT-52). Adsorption equilibrium data was measured at 298, 313, and 343 K up to 30 bar for CO 2 and 80 bar for CH 4 . The three adsorbents have increasing surface areas, pore volumes, and pore sizes in the order UiO-66 < DUT-52 < UiO-67. The maximum CO 2 and CH 4 loading and selectivity follow the same trend. The relatively low isosteric heats of adsorption of CO 2 for the three adsorbents indicate potential application at high partial pressures of CO 2 in so-called precombustion schemes. Since equilibrium selectivity was higher for UiO-67, adsorption kinetics of pure gases was also measured in this adsorbent. Diffusion of both molecules is very fast, allowing the use of equilibrium theory for estimation of process performance of this adsorbent.

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