Tailoring metal-organic framework catalysts by click chemistry.

We successively introduce new catalytic centers through click reaction into MOFs and modify their environment by addition of lipophilic groups. The resulting bifunctionalized MOF provides an optimized balance between basicity and lipophilicity and shows outstanding performance for the transesterification reaction.

Catalysis of transesterification by a nonfunctionalized metal-organic framework: acido-basicity at the external surface of ZIF-8 probed by FTIR and ab initio calculations.

The zeolite imidazolate framework ZIF-8 is shown for the first time to be able to catalyze transesterification of vegetable oil with significant activity. Rationalization of this behavior at the atomic scale is provided by combining CO adsorption monitored by FTIR and DFT calculations (clusters and periodic models). We demonstrate that the acido-basic sites are located at the external surface of the material or at defects, but not in the microporosity of ZIF-8. A great variety of sites are found the surface: OH and NH groups, hydrogenocarbonates, low-coordinated Zn atoms, and free N(-) moieties belonging to linkers. Their proportions depend on the operating conditions (temperature and pressure). The acido-basicity of the surface is then probed by adsorption of CO at low temperature. In parallel, the species present are mapped by DFT calculations combined with a thermodynamic model. An assignment of the CO region of the FTIR spectra can thus be proposed. The complex infrared spectrum is attributed to the coexistence of classical C-adducts of CO with acid sites and other modes on basic sites (O-adducts and side-on adducts). Adsorption energies and CO frequency shifts show that some strong Lewis sites exist (in particular Zn(II) species), as well as strong Brønsted acid sites (NH groups), together with basic sites (OH groups and N(-) moieties). By calculating the co-adsorption of a model ester (methyl acetate) and methanol, we show the prevailing role of Zn(II) species as acid sites, combined with N(-) moieties and OH groups as basic ones, in determining the catalytic properties of ZIF-8. This work opens new perspectives on the use of MOFs in catalysis and, more generally, on the properties of their external surface.

A zeolitic material with a three-dimensional pore system formed by straight 12- and 10-ring channels synthesized with an imidazolium derivative as structure-directing agent.

IM-20 is a novel microporous germanosilicate with an interesting zeolitic structure. It has been prepared via the fluoride route with 3-butyl-1-methyl-3H-imidazol-1-ium as the organic structure-directing agent and its structure solved from synchrotron powder X-ray diffraction data. The chemical formula per unit cell is Si(42.2)Ge(17.8)O(120) under its calcined form. IM-20 possesses a new framework topology, the 3D channel system being formed by straight intersecting 12- and 10-membered rings. Two types of d4r composite building units are present in IM-20, their average Si/Ge molar ratio being about 8.52 or 0.56. Surprisingly, the pure silica or silica-rich units are fluoride-free in the as-synthesized material.

Generic postfunctionalization route from amino-derived metal-organic frameworks.

This study deals with the development of a soft, generic, one-pot postfunctionalization method for metal-organic frameworks (MOFs) starting from compounds with an amino group on the linker. The first step consists of transforming the amino group into azide (N(3)) by an unconventional route using tBuONO and TMSN(3). In the same vessel, the desired functionalized MOF then is obtained by the Huisgen 1,3-dipolar cycloaddition of azides to alkynes, otherwise known as the "click" reaction. The method was applied to DMOF-NH(2) and MIL-68(In)-NH(2), which represent two distinct and important classes of MOF. For both, the functionalization was complete (>90% grafting) and the crystallinity was maintained. Thanks to the large diversity and availability of cyano- and acetylene-based chemicals, this method opens the door to tailor-made functionalized MOFs.

Adsorption of CO(2), CH(4), and N(2) on zeolitic imidazolate frameworks: experiments and simulations.

Experimental measurements and molecular simulations were conducted for two zeolitic imidazolate frameworks, ZIF-8 and ZIF-76. The transferability of the force field was tested by comparing molecular simulation results of gas adsorption with experimental data available in the literature for other ZIF materials (ZIF-69). Owing to the good agreement observed between simulation and experimental data, the simulation results can be used to identify preferential adsorption sites, which are located close to the organic linkers. Topological mapping of the potential-energy surfaces makes it possible to relate the preferential adsorption sites, Henry constant, and isosteric heats of adsorption at zero coverage to the nature of the host-guest interactions and the chemical nature of the organic linker. The role played by the topology of the solid and the organic linkers, instead of the metal sites, upon gas adsorption on zeolite-like metal-organic frameworks is discussed.

IM-19: a new flexible microporous gallium based-MOF framework with pressure- and temperature-dependent openings.

Five metal-organic frameworks (MOFs) based on the same three-dimensional gallium terephthalate network (IM-19) are described, and an incommensurate structure (for the as-synthesized form) as well as two remarkable guest-free polymorphs (open and closed) are highlighted.

Co-templating and modelling in the rational synthesis of zeolitic solids.

A 'co-templating' strategy supported by molecular modelling has been used to prepare, for the first time, silicoaluminophosphates with the SAV and KFI framework topologies, each of which has a three-dimensionally connected pore system with high specific volume.

Extra-large-pore zeolites with two-dimensional channels formed by 14 and 12 rings.

Stable zeolites that have larger pore apertures and a three-dimensional pore topology are of interest because they could be used to adsorb larger molecules, particularly for application in oil refining. Several large-pore zeolitic materials with channels formed by openings of more than 12 rings are known, but all of them have a one-dimensional channel system that limits their use in catalysis. We report the synthesis and some characterizations of IM-12, a thermally stable germanium-containing zeolite that contains the first two-dimensional channel system with extra-large pores formed by 14- and 12-ring channels.