Modulated synthesis of Zr-fumarate MOF

We present the synthesis and characterization of a novel Zr-based metal–organic framework (MOF) which contains fumarate (fum) dianions as linkers: −OOC–CHCH–COO−. The synthesis of this MOF is possible only via modulation, i.e. by the addition of a monocarboxylic acid to the synthesis mixture. We have used formic acid as a modulator and have investigated its influence on the synthesis of the Zr-fumarate MOF in detail. The modulator improves the crystallinity of the material; varying its amounts, the crystal size and the degree of aggregation can be influenced. The novel MOF probably has a topology which is similar to that of UiO-66, but has a primitive cubic lattice instead of a face-centered one. A structural model in line with the experimental data is proposed. The Zr-fum MOF is further characterized by thermogravimetric analysis (TGA) and Ar sorption, showing that it can be activated and exhibits microporosity. The linker fumarate as well as the modulator formic acid used in the synthesis of Zr-fum MOF are both naturally occurring molecules; possible applications of the MOF may thus lie in the field of biomaterials. Therefore, the stability of Zr-fum MOF was tested in water-based salt solutions commonly used in biomedical research.

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► Formic acid acts as modulator in the synthesis of a new Zr-MOF.
► Improvement of crystallinity by modulation approach.
► In dependence on modulator concentration different crystallite sizes are accessible.
► The novel Zr-MOF is stable in several water-based salt solutions.