The novel MOF hcp UiO-66 is synthesized using the ionic liquid ([PBuMEE]2[BDC]) as a linker precursor.

The paper describes a method to induce the formation of MIL-68(Al) rather than MIL-53(Al) using a formic acid modulated synthesis approach.

Using ionic liquids (ILs) as linker precursors, the well‐known metal‐organic framework (MOF) UiO‐66 (Universitetet i Oslo) and the recently reported MOF hcp UiO‐66 (hexagonal closed packed) have been successfully synthesized and characterized. The advantage of the applied novel synthesis approach is an economically and environmentally benign work‐up procedure, due to the better solubility of the IL. Additionally, the reactivity of the terephthalate anions is increased compared to terephthalic acid, resulting in faster MOF formation with an increased amount of defects in the MOF structure. In order to explore to the influence of defects on the catalytic performance, the cyclisation of citronellal to isopulegol was employed as test reaction. The activity of hcp UiO‐66 and fcc UiO‐66 (face centered cubic) is improved compared to other MOF or zeolite based catalysts, while the selectivity is similar.

While it is well-known that the particle size of solvothermally synthesized metal–organic frameworks (MOFs) can be controlled by tuning the solvent composition, which affects the solubility of the linker and metal salt educts, the exact relationship between linker solubility, initial chemical coordination steps occurring in solution, and the resulting MOFs’ particle size has not yet been investigated. Here, we have studied the solvothermal synthesis of MIL-53­(Al) in DMF and water/DMF mixtures with in situ Raman spectroscopy, which reveals the formation of intermediate prenucleation building unit (PNBU) species that consist of one linker molecule and one metal atom and self-assemble in solution to form MIL-53­(Al). The concentration of PNBUs in solution prior to particle precipitation is dependent on the synthesis solvent ratio used and influences the MIL-53 particle size. Synthesis in pure DMF results in a high concentration of PNBUs in solution prior to MOF supersaturation and precipitation. This results in a large burst of MOF nucleation and the formation of nanosized MIL-53­(Al) particles. Adding water to the DMF solution leads to reduced PNBU accumulation in solution prior to MOF precipitation due to the reduced linker solubility. The reduced accumulation of PNBUs prior to particle precipitation causes reduced nucleation and favors particle growth. The MIL-53­(Al) particle size, in contrast, is independent of the MOF phase growth rate, which is highly dependent on the synthesis temperature.

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