A Low‐Temperature Approach for the Phase‐Pure Synthesis of MIL‐140 Structured Metal–Organic Frameworks

Abstract

In as ystematic investigation,t he synthesis of metal-organicf rameworks (MOFs) with MIL-140 structure was studied. The precursors of this family of MOFs are the same as for the formation of the well-known UiO-typeM OFs although the synthesis temperature for MIL-140 is significantly higher. This study is focused on the formationo fZ rbased MIL-140M OFs with terephthalic acid (H 2 bdc), biphenyl-4,4'-dicarboxylic acid (H 2 bpdc), and4 ,4'-stilbenedicarboxylic acid (H 2 sdc)a nd the introduction of synthesis field diagrams to discover parameters for phase-pure products. In this context, aM IL-140n etwork with H 2 sdc as linkerm ole-cule is first reported. Additionally,a ni mportanta spect is the reduction of the synthesis temperature to make MIL-140 MOFsm ore accessible even though linkersw ith am ore delicate nature are used.T he solvothermal syntheses were conductedi nh ighly concentratedr eactionm ixtures whereby a targeted synthesis to yield the MIL-140p hase is possible. Furthermore, the effect of the often-used modulator approachi se xamined for these systems. Finally, the characteristics of the synthesized MOFs are compared with physisorption measurements, thermogravimetric analyses, and scanning electron microscopy.

In situ X-ray Diffraction Investigation of the Crystallisation of Perfluorinated Ce(IV)-based Metal-Organic Frameworks with UiO-66 and MIL-140 architectures

“…Another possibility could be that lowering the pH increases the possibility of linker protonation on the formed MOFs themselves, adding additional reversibility to the process and the thermodynamic F4_MIL-140A(Ce) to be formed, as suggested in a recent paper reporting a systematic investigation of the influence of several parameters on the crystallisation of phase pure MIL-140 type MOFs in DMF solvent. [16] However, the evidence in our hands does not indicate that a more acidic environment promotes such a dissolution-recrystallisation process.…”

In Situ X‐ray Diffraction Investigation of the Crystallisation of Perfluorinated CeIV‐Based Metal–Organic Frameworks with UiO‐66 and MIL‐140 Architectures**

“…This could be due to the role of HNO 3 in inhibiting deprotonation of AcOH and its coordination to Ce IV to form the hexanuclear [Ce 6 O 4 (OH) 4 (‐COO) 12 ] clusters needed for the F4_UiO‐66(Ce) phase. Another possibility could be that lowering the pH value increases the possibility of linker protonation on the formed MOFs themselves, adding additional reversibility to the process and allowing the thermodynamic product F4_MIL‐140A(Ce) to be formed, as suggested in a recent paper reporting a systematic investigation of the influence of several parameters on the crystallisation of phase‐pure MIL‐140 type MOFs in DMF [16] . However, the evidence in our hands does not indicate that a more acidic environment promotes such a dissolution–recrystallisation process.…”

“…It was recently shown that addition of 10 equivalents of AcOH to a DMF-based reaction mixture otherwise affording pure MIL-140A(Zr), a mixed MIL-140A/UiO-66 product is formed. [16] Further increasing the amount of acetic acid up to 30 equivalents appears to increase the MIL-140/UiO-66 ratio. These results may suggest that, at least in DMF solvent, the coordination modulator can in fact favour the thermodynamic product also in the MIL-140/UiO-66 system.…”

“…It was recently shown that addition of 10 equiv. of AcOH to a DMF‐based reaction mixture otherwise affording pure MIL‐140A(Zr), a mixed MIL‐140A/UiO‐66 product is formed [16] . Further increasing the amount of acetic acid up to 30 equiv.…”

Solvent-assisted linker exchange as a tool for the design of mixed-linker MIL-140D structured MOFs for highly selective detection of gaseous H2S

“…S1 †). 22 This MOF shows a high thermal and chemical stability which can be compared to the former reported MIL-140 MOFs. 18 A synthesis for an azo-based MIL-140D-H with H 2 abdc as linker is also described in literature (see ESI Table S1 †).…”