Hubert Chevreau

Iron(III) metal–organic frameworks as solid Lewis acids for the isomerization of α-pinene oxide

A series of Fe3+-containing porous metal–organic frameworks (MOFs), including the commercial iron trimesate Basolite F-300 or Fe(BTC) (BTC: 1,3,5-benzenetricarboxylate) and the synthetic iron terephthalate MIL-88B (Fe3O(BDC)3X, X = Cl, OH, BDC = 1,4-benzenedicarboxylate), iron naphthalenedicarboxylate MIL-88C (Fe3O(NDC)3X, X = Cl, OH, NDC = 1,6-naphthalenedicarboxylate), iron trimesate MIL-100 (Fe3O(BTC)2X, X = Cl, OH) and iron azobenzenetetracarboxylate soc-MOF(Fe) or MIL-127 (Fe6O2(Tazb)3X2, X = Cl, OH, Tazb = 3,3′,5,5′-azobenzenetetracarboxylate; MIL stands for Materials from Institut Lavoisier), have been tested for the rearrangement of α-pinene oxide to camphonelal and isopinocamphone in the absence of solvent. Conversions of about 10% with 50% selectivity towards camphonelal were obtained. This catalytic performance has been compared with that of the copper trimesate Basolite C-300 or HKUST-1 of formula Cu3(BTC)2 and the aluminium terephthalate Basolite A-100 or MIL-53(Al) of formula Al(OH)(BDC) as well as with some homogeneous (ZnCl2, Cu(NO3)2, Al(NO3)3) and heterogeneous (Fe3+-exchanged Y-zeolite) Lewis acids. Fe(BTC) also exhibits catalytic activity for the rearrangement of other epoxides (styrene, cyclohexene and norbornene oxides) under solventless conditions. Some partial deactivation of the Fe(BTC) with a slight degradation of the structure has nevertheless been observed.

In situ energy-dispersive X-ray diffraction for the synthesis optimization and scale-up of the porous zirconium terephthalate UiO-66.

The synthesis optimization and scale-up of the benchmarked microporous zirconium terephthalate UiO-66(Zr) were investigated by evaluating the impact of several parameters (zirconium precursors, acidic conditions, addition of water, and temperature) over the kinetics of crystallization by time-resolved in situ energy-dispersive X-ray diffraction. Both the addition of hydrochloric acid and water were found to speed up the reaction. The use of the less acidic ZrOCl2·8H2O as the precursor seemed to be a suitable alternative to ZrCl4·xH2O, avoiding possible reproducibility issues as a consequence of the high hygroscopic character of ZrCl4. ZrOCl2·8H2O allowed the formation of smaller good quality UiO-66(Zr) submicronic particles, paving the way for their use within the nanotechnology domain, in addition to higher reaction yields, which makes this synthesis route suitable for the preparation of UiO-66(Zr) at a larger scale. In a final step, UiO-66(Zr) was prepared using conventional reflux conditions at the 0.5 kg scale, leading to a rather high space-time yield of 490 kg m(-3) day(-1), while keeping physicochemical properties similar to those obtained from smaller scale solvothermally prepared batches.

Tuning the breathing behaviour of MIL-53 by cation mixing

A mixed cation MIL-53(Cr-Fe) MOF has been obtained by direct synthesis. Multiple experimental techniques have demonstrated the presence of a genuine mixed phase, leading to a breathing behaviour different from either of the single cation analogues.

A lithium–organic framework with coordinatively unsaturated metal sites that reversibly binds water

The synthesis and characterisation of a three-dimensional lithium-organic framework MIL-145 is described, which upon thermal treatment yields a second open framework, MIL-146, that contains four and three-coordinate lithium centres: the coordinatively unsaturated trigonal planar lithium centres are able to reversibly bind water with crystallinity maintained, while the dehydrated phase shows preferential adsorption of CO(2) over N(2).

Investigating the Case of Titanium(IV) Carboxyphenolate Photoactive Coordination Polymers

The reactivity of 2,5-dihydroxyterephthalic acid (H4DOBDC) with titanium(IV) precursors was thoroughly investigated for the synthesis of metal-organic frameworks under solvothermal conditions. Four crystalline phases were isolated whose structures were studied by a combination of single-crystal or powder X-ray diffraction and solid-state NMR. The strong coordination ability of the phenolate moieties was found to favor the formation of isolated TiO6 octahedra bearing solely organic ligands in the resulting structures, unless hydrothermal conditions and precondensed inorganic precursors are used. It is worth noting that these solids strongly absorb visible light, as a consequence of the ligand-to-metal charge transfer (LMCT) arising from Ti-phenolate bonds. Preliminary photocatalytic tests suggest that one compound, namely, MIL-167, presents a higher activity for hydrogen evolution than the titanium carboxylate MIL-125-NH2 but that such an effect cannot be directly correlated with its improved light absorption feature.

Synthesis of the biocompatible and highly stable MIL-127(Fe): from large scale synthesis to particle size control

Controlled-sized crystals, from the nano to the microscale, of the biocompatible and highly stable porous iron(III) 3,3,′5,5′-azobenzenetetracarboxylate MIL-127(Fe) MOF have been successfully prepared with very high space-time-yields using different synthetic routes.