International audienceWe report here a simple method for controlling the crystal size and morphology of zeolitic imidazolate framework-8 (ZIF-8) nanocrystals in methanol solution. ZIF-8 crystals were prepared by mixing 2-methylimidazole (Hmim) with various zinc salts for 1 h and using a Hmim/Zn(+2) salt molar ratio of 8/1. All products prepared were assigned to a sodalite-type structure and both particle size and morphology were found to be dependent on the reactivity of the Zn(+2) salt. Small ZIF-8 crystals with diameters varying between ca. 50 and 200 nm were obtained with reactive zinc salts like Zn(acac)2, Zn(NO3)2, ZnSO4 or Zn(ClO4)2 as demonstrated by SEM, TEM and DLS analyses. The use of ZnCl2, Zn(OAc)2 or ZnI2 afforded crystals with sizes varying between ca. 350 and 650 nm. Finally, the low reactive ZnBr2 salt was found to generate microsized crystals. Taking ZIF-8 crystals prepared from Zn(NO3)2, Zn(OAc)2 and ZnBr2 as representatives and through thermogravimetric analysis and BET measurements, we also demonstrated that changes in particle size induced changes in stability and adsorption properties. The small sized ZIF-8 crystals produced from Zn(NO3)2 were found to exhibit the highest surface area (1700 m2 g−1) and the best catalytic activity in Knoevenagel and Friedländer reactions

International audienceCu2+-doped zeolitic imidazolate framework (ZIF) crystals were efficiently prepared by reaction of Cu(NO3)2, Zn(NO3)2, and 2-methylimidazole in methanol at room temperature. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction showed that the Cu/ZIF-8 particles were nanosized (between ca. 120 and 170 nm) and that the body-centered cubic crystal lattice of the parent ZIF-8 framework is continuously maintained, regardless of the doping percentage. Moreover, thermogravimetric analyses and specific BET surface area measurements demonstrated that the doping does not alter the high stability of ZIF-8 crystals and that the porosity only decreases at a high doping percentage (25% in Cu2+). The Cu/ZIF-8 material showed excellent catalytic activity in the [3 + 2] cycloaddition of organic azides with alkynes and in Friedländer and Combes condensations due to the high catalyst surface area and the high dispersion of Cu/ZIF-8 particles. Notably, the Cu/ZIF-8 particles not only exhibit excellent performance but also show great stability in the reaction, allowing their reuse up to ten times in condensation reactions. Our findings explored a simple and powerful way to incorporate metal ions into the backbones of open framework materials without losing their properties

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