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ABSTRACT: 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.
Dalton Transactions 01/2012; 41(14):3945-8. · 3.84 Impact Factor
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ABSTRACT: 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.
Journal of the American Chemical Society 09/2010; 132(35):12365-77. · 9.91 Impact Factor
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ABSTRACT: 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.
Journal of the American Chemical Society 03/2010; 132(13):4518-9. · 9.91 Impact Factor
