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Modulators are widely used in the synthesis of metal‐organic frameworks (MOFs) for improving the porosity and morphology. For aluminum MOFs modulation has been seldom reported and as is shown here for the example of the aluminum furandicarboxylate MOF MIL‐160 the positive effects of modulators are small and disadvantageous effects will be more likely. Formic acid as modulator can slightly increase the BET surface area and pore volume of MIL‐160 up to a modulator:linker ratio of 1.25 : 1. Acetic acid only shows some increase in both surface area and pore volume at the smallest tested ratio of 0.125 : 1. The stronger acids oxalic acid and hydrochloric acid with the also more aluminum‐coordinating anions have no positive porosity effect and decrease surface area and pore volume already at small amounts. At a 1 : 1 modulator:linker ratio for oxalic acid and at 0.75 : 1 for hydrochloric acid no porous MOF is formed anymore from the analysis by powder X‐ray diffraction and nitrogen sorption. Further, thermogravimetric analysis and scanning electron microscopy suggests that none of the tested modulators has any noticeable positive effect on the introduction of linker defects or the improvement of crystallinity or crystal size. [ABSTRACT FROM AUTHOR]

We report a systematic study on the possibility of forming mixed-linker metal–organic frameworks (MOFs) spanning between the aluminum MOFs CAU-23 and MIL-160 with their 2,5-thiophenedicarboxylate (TDC) and 2,5-furandicarboxylate (FDC) linkers, respectively. The planned synthesis of a mixed-linker MOF, combining TDC and FDC in the framework turned out to yield a rather largely intricate mixture of CAU-23 and MIL-160. This is due to the different opening angles of 150° for TDC versus 120° for FDC and the concomitant cis–trans versus cis-only OH-bridges in the infinite secondary building unit {Al(μ-OH)(O2C–)} chains. At the same time, the CAU-23 phase is accompanied by the polymorphic MIL-53-TDC phase with trans-only OH-bridges. The measurement of water vapor sorption isotherms was the method of choice to confirm the formation of mixed MOFs instead of mixed-linker phases. Thereby, the water sorption isotherms indicate the simultaneous formation of both MOF phases, albeit they do not exclude mixed-linker MOFs which may have formed at low levels of substitution. The differentiation via powder X-ray diffractometry (PXRD), IR-spectroscopy and nitrogen sorption was either not conclusive enough or impossible, due to similarities of the neat MOF phases. The synthesized MOF mixtures within the TDC : FDC ratios of 38 : 62 up to 82 : 18 exhibit two or three uptake steps in the water sorption isotherm, with the first two corresponding to an overlay from the individual water sorption isotherm of CAU-23 and MIL-160 and a third one from the additional MIL-53-TDC. [ABSTRACT FROM AUTHOR]