Highly porous metal-organic frameworks (MOFs), which have undergone exciting developments over the past few decades, show promise for a wide range of applications. However, many studies indicate that they suffer from significant stability issues, especially with respect to their interactions with water, which severely limits their practical potential. Here we demonstrate how the presence of 'sacrificial' bonds in the coordination environment of its metal centres (referred to as hemilability) endows a dehydrated copper-based MOF with good hydrolytic stability. On exposure to water, in contrast to the indiscriminate breaking of coordination bonds that typically results in structure degradation, it is non-structural weak interactions between the MOF's copper paddlewheel clusters that are broken and the framework recovers its as-synthesized, hydrated structure. This MOF retained its structural integrity even after contact with water for one year, whereas HKUST-1, a compositionally similar material that lacks these sacrificial bonds, loses its crystallinity in less than a day under the same conditions.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The structural instability in a humid environment of the majority of metal− organic frameworks (MOFs) is a challenging obstacle for their industrial-scale development.Recently, two water-resistant MOFs have been synthetized, STAM-1 and STAM-17-OEt. They both contain copper paddle wheels, like the well-known water-sensitive HKUST-1, but different organic linkers. The crystal lattice of both the MOFs undergoes a phase transition upon interaction with water molecules. Their unusual flexibility allows the controlled breaking of some interpaddle wheel Cu−O interactions in the so-called crumple zones, with a mechanism called hemilability, which is considered to have a crucial role for the stability toward water. In this work, we present a detailed investigation on the different effects of water exposure on the local and long-range structures of HKUST-1, STAM-1, and STAM-17-OEt. Electron paramagnetic resonance (EPR) spectroscopy has allowed us to characterize the different phases occurring during hydration of each MOF. In particular, we have identified and portrayed the moment of the adsorption of the first water molecule on each copper ion and shown that such soft hydration lead to a similar reversible evolution in all of the three MOFs. This aspect unveiled that the bulk water stability of the MOFs studied is unimportant at this early stage, whereas with a higher degree of hydration (more than few hours in our experimental conditions), we observe the three MOFs embarked on different paths, here carefully described. The evolution of HKUST-1 is not reversible because of its well-known tendency to hydrolysis, but, in contrast, we proved the reversibility of the water effects in STAM-1 and STAM-17-OEt even at the atomic scale level. Furthermore, for the first time, we report a Raman characterization of both STAM-1 and STAM-17-OEt, for each phase of the hydration. The data also include X-ray diffraction, nuclear magnetic resonance measurements, and Brunauer−Emmett−Teller surface area calculations of all the samples.

Metal-organic frameworks (MOFs) are ac lass of porous materials that show promise in the removal of toxic industrial chemicals (TICs) from contaminated airstreams, though their development for this application has so far been hindered by issues of water stability and the wide availability and low cost of traditionally used activated carbons.H ere as eries of three MOF-activated carbon composite materials with different MOF to carbon ratios are prepared by growing STAM-17-OEt crystals inside the commercially available BPL activated carbon. The composite materials displaye xcellent water stability and increased uptake of ammonia gas when compared to unimpregnated carbon. Suchp roperties make these composites very promising in the fields of air purification and personal protective equipment.

NMR spectroscopy of paramagnetic materials (pNMR) has the potential to provide great structural insight, but many challenges remain in interpreting the spectra in detail. This work presents a study of a series of structurally analogous metal-organic frameworks (MOFs) based on 5-substituted isophthalate linkers and Cu(II) paddlewheel dimers, of interest owing to their "crumple zone" structural rearrangement on dehydration/rehydration. 13 C MAS NMR spectra of the MOFs reveal a wide variation in the observed resonance position for chemically similar C species in the different MOFs but, despite this, resonances are overlapped in several cases. However, by considering a combination of the integration of quantitative spectra, the resonance position as a function of temperature and T1 relaxation measurements, the spectra can be fully assigned. It is also demonstrated that the prototypical MOF in this series, STAM-1, displays a similar crumple zone rearrangement on dehydration to the well-characterised 5ethoxyisophthalate MOF (STAM-17-OEt) although, while the materials have similar local C environments, dehydrated STAM-1 exhibits less long-range order.

MOF crystal-glass composites (MOF CGCs) are materials with crystalline MOFs embedded within a MOF glass. Here we develop two novel MOF CGCs, and explore the gas uptake and guest-size limitations within these materials.

Melt-quenched metal−organic framework (MOF) glasses have gained significant interest as the first new category of glass reported in 50 years. In this work, an amine-functionalized zeolitic imidazolate framework (ZIF), denoted ZIF-UC-6, was prepared and demonstrated to undergo both melting and glass formation. The presence of an amine group resulted in a lower melting temperature compared to other ZIFs, while also allowing material properties to be tuned by post-synthetic modification (PSM). As a prototypical example, the ZIF glass surface was functionalized with octyl isocyanate, changing its behavior from hydrophilic to hydrophobic. PSM therefore provides a promising strategy for tuning the surface properties of MOF glasses.

A lower temperature route to metal–organic framework crystal–glass composites is presented. Specifically, the annealing pre-formed ZIF-62 glass with a crystalline MOF above Tg will enable formation of a greatly expanded range of materials.