Four new Al-based microporous metal-organic framework compounds with MIL-53-type structure containing functionalized extended linker molecules

• Isoreticular MOFs were obtained using linkers with nitro, amino or sulfone groups.
• Naphthyl- and biphenyldicarboxylic acid derivatives were used as linker molecules.
• The permanently porous Al-MOFs are thermally stable at least up to 340 °C in air.
• The presence of the sulfone groups leads to an increase of CO2 adsorption capacity.

Al-based metal-organic framework (MOF) compounds containing nitro- and amino-substituted and sulfone-bridged groups were synthesized: [Al(OH)(NDC-(NO2)2)] (1), [Al(OH)(BPDC-NO2)] (2), [Al(OH)(BPDC-NH2)] (3) and [Al(OH)(BPDC-SO2)] (4), which are analogs of MIL-69/DUT-4 ([Al(OH)(NDC)]) or DUT-5 ([Al(OH)(BPDC)]) (NDC = 2,6-naphthalenedicarboxylate, BPDC = 4,4’-biphenyldicarboxylate). The compounds were synthesized under solvothermal conditions employing microwave-assisted heating and characterized by powder X-ray diffraction, thermogravimetric analysis and gas sorption measurements. They exhibit permanent porosity and are accessible to carbon dioxide, hydrogen and methane but do not show any framework flexibility like MIL-53. All compounds are highly stable as confirmed by temperature-dependent powder X-ray diffraction measurements (TD-PXRD) and framework decomposition takes place between 340 °C and 420 °C.

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