Meltable, Glass-Forming, Iron Zeolitic Imidazolate Frameworks

Abstract

We describe the first meltable iron-based zeolitic imidazolate framework (ZIF), denoted MUV-24. This material, elusive from direct synthesis, is obtained from the thermal treatment of [Fe 3 (im) 6 (Him) 2 ], which yields Fe(im) 2 upon loss of the neutral imidazole molecules. Different crystalline phase transformations are observed upon further heating, until the material melts at 482 °C. Vitrification upon cooling of the liquid phase gives rise to the first Fe-metal−organic framework glass. X-ray total scattering experiments show that the tetrahedral environment of the crystalline solids is maintained in the glass, whereas nanoindentation measurements reveal an increase in Young's modulus, in agreement with stiffening upon vitrification.

Implementing Mesoporosity in Zeolitic Imidazolate Frameworks through Clip-Off Chemistry in Heterometallic Iron–Zinc ZIF-8

“…Theoretical calculations predict smaller WBI, NAO, and IBSI values for the Fe–N bond (Table S7), as well as half bond breaking energy (Figure S28), confirming its weaker strength and therefore its more unstable nature, compared to the Zn–N bond. The higher polarity predicted in the electrostatic maps of Fe­(II)-containing ZIFs (Figure S26) further supports the lower air stability toward water or moisture. , Moreover, we have recently reported a new Fe-ZIF material ( MUV-24 ) that has a reduced melting temperature compared with the Zn analogue …”

Structural Chemistry of Zeolitic Imidazolate Frameworks

“…In view of the well-established porosity and structural tunability of ZIFs, it is conceptually possible to prepare ZIF glasses with permanent porosity through the thermally or pressure-induced amorphization of crystalline ZIFs. − This is possible since the transformation into denser and thermodynamically more stable phases is favored for the ZIFs in metastable phases. , In the presence of external stimuli, when the melting occurs prior to decomposition, glassification takes place, , where metal retains their tetrahedra coordination geometry with distortion during the amorphization. ,, This results in the creation of a new class of ZIF derivatives through the melt-quenching route. The most noticeable change in this process is the decrease in order and the retention of the pores and short-range interactions.…”

Microscopic mechanism of thermal amorphization of ZIF-4 and melting of ZIF-zni revealed via molecular dynamics and machine learning techniques

“…These may be induced by changes in temperature 16,17 and pressure, 18 mechanical grinding, 19 interaction with X-rays, 20 or even eliminating water from their structures. 21 Heat-induced amorphization was observed in a number of MOFs; 3,22–24 in this work we will concentrate our efforts on ZIF-4. This MOF is well-known for its applications in separating alkenes from alkanes among other gas mixtures, 25 and its synthesis has been scaled-up.…”