As revealed by scanning electron microscopy, both materials were prepared as 1-10 μm large cubic crystals (Fig. and Fig. ). The structure of MFU-4 was elucidated in prior studies utilizing X-ray powder diffraction data and ab-initio structure determination methods (CCDC: 723714). Despite extensive efforts and modifications to the synthesis parameters (refer to Experimental section for details), we were unable to obtain single crystals exceeding 10 µm in size. Therefore, the structure of MFU-4-Br was elucidated by electron diffraction (Table -S7) and the phase purity of the bulk sample was confirmed by the Rietveld refinement (Fig. ). MFU-4-Br is isostructural to MFU-4. Selected structural parameters of both MOFs can be found in Table and Figure . When comparing the FTIR spectra of both MOFs, the characteristic Zn-X bands (X stands either for Cl or Br) were detected and the position of these bands agreed with their corresponding simulated IR spectra (Fig. and Fig. ). The material thermal stability was studied by TGA and variable temperature XRPD (Fig. and). The analyses revealed that both MOFs were stable up to more than 500 °C (under nitrogen atmosphere), and that the removal of the solvent from the pores did not affect the structure as confirmed by the variable temperature XRPD measurements (Fig. ). This means that the MOF voids could be emptied and made accessible for potential guest molecules. experimental FTIR data and simulated IR spectra, and (c) TGA curves of assynthetized and activated samples.