Green synthesis of a new Al-MOF based on the aliphatic linker mesaconic acid: Structure, properties and in situ crystallisation studies of Al-MIL-68-Mes

A new aluminium metal‐organic framework (MOF), based on the short aliphatic linker molecule mesaconic acid (H2Mes; methylfumaric acid) is reported. Al‐MIL‐68‐Mes with composition [Al(OH)(O2C‐C3H4‐CO2)]⋅n H2O is obtained after short reaction times of 45 minutes under mild, aqueous synthesis conditions (95 °C). It exhibits a kagome‐like framework structure with large hexagonal, and small trigonal channels (diameters of ≈6 and ≈2 Å, respectively) and a specific surface area of SBET ≈1040 m2 g−1 (VMIC=0.42 cm3 g−1). A sigmoidal vapour sorption isotherm for water, and uptakes of water and methanol above 30 wt. % were observed. Al‐MIL‐68‐Mes is stable against water ad‐/desorption and its thermal stability is 350 °C in air. The proton conductivity for the hydrated MOF showed values up to 1.1×10−5 S cm at 130 °C and 100 % relative humidity, which exceeds the values observed for the non‐hydrated compound by up to four orders of magnitude. Using synchrotron radiation the crystallisation of the MOF by in situ PXRD was also studied at temperatures from 80 to 100 °C. Kinetic evaluation revealed that the induction periods and crystallization times vary depending on the synthesis batch, but the rate limiting steps are consistently observed.