The flexibility of modified-linker MIL-53 materials

Abstract

The flexibility of eight aluminum hydroxo terephthalates [Al(OH)(BDC-X)]·n(guest) (BDC = 1,4-benzene-dicarboxylate; X = -H, -CH3, -Cl, -Br, -NH2, -NO2, -(OH)2, -CO2H) crystallising in the MIL-53-type structure was investigated upon thermal dehydration of as-made samples, superhydration and methanol adsorption/desorption using in situ powder X-ray diffraction (PXRD). Profile fitting was used to determine lattice parameters as a function of time and/or temperature to describe their structural evolution. It has thus been shown that while methanol vapour adsorption induces an opening of all the modified frameworks, except the -NH2 material, superhydration only leads to open structures for Al-MIL-53-NO2, -Br and -(OH)2. All the MIL-53 solids, except Al-MIL-53-(OH)2 are present in the open structures upon thermal dehydration. In addition to the exploration of the breathing behavior of this MIL-53 series, the issue of disorder in the distribution of the functional groups between the organic linkers was explored. As a typical illustration, density functional theory calculations were carried out on different structures of Al-MIL-53-Cl, in which the distribution of -Cl within two adjacent BDC linkers is varied. The results show that the most energetically stable configuration leads to the best agreement with the experimental PXRD pattern. This observation supports that the distribution of the selected linker substituent in the functionalised solid is governed by energetics and that there is a preference for an ordering of this arrangement.

Iodine sequestration by thiol-modified MIL-53(Al)

“…The powder XRD patterns show considerable peak broadening, suggesting either small crystallites or microstrain due to some inherent disorder in the structure (such as static disordered of ligand substituent positions), but this is typical for linkermodified MIL-53 materials for which full structure refinement has rarely been proved possible. 9 The incorporation of the intact ligand was confirmed by sulfur K-edge XANES spectroscopy, Figure ), 27 but this behaviour is similar to that seen in the other forms of MIL-53 with modified linkers, such as the case of dihydroxy-or bromo-, where a very small nitrogen uptake was ascribed to the bulky substituents. 6 Thus for the dithiolated material we conclude the material exists in a closed structure and presents a non-breathing framework.…”

“…4 The potentially most versatile method of modification of MIL-53 materials, however, is the addition of functional groups to the aromatic ring of the terephthalate linker: this has been widely studied for a range of substituents and a common strategy is to premake substituted 1,4-benzenedicarboxylic acid that is then used as a reagent for the crystallisation of MIL-53. 5,6 This has been used with great effect to modify the response of the MIL-53 towards guest molecules and their thermally induced breathing behaviour, 7,8,9 or to introduce reactive functionalities that can be used for further chemical modification. 19 Others have shown that post-synthetic modification allows thiol groups to be added to a pre-made MOF: in the case of MIL-101(Cr) this allowed formation of an Hg 2+ adsorbent.…”

Unraveling the origin of the “Turn-On” effect of Al-MIL-53-NO2 during H2S detection

“…1a, all the peaks are consistent with those as reported in the previous references, where Al-MIL-53-NO 2 has a monoclinic crystal structure. 35,39,40 The main peak was located at ∼8.5°, which is ascribed to the (100) plane. 39 The crystals and morphologies were also characterized by scanning electron microscopy (SEM).…”

Structure property relationships affecting the proton conductivity in imidazole loaded Al-MOFs

“…26 The 3D framework of MIL-53 is built up of infinite chains of trans corner-sharing AlO 4 (µ-OH) 2 polyhedra, which are connected by 1,4-benzenedicarboxylate (BDC 2− ) molecules, to form onedimensional rhombic-shaped channels. 21,27,28 Bureekaew et al synthesised MIL-53 frameworks using 1,4-H 2 NDC and 1,4-H 2 BDC as linker molecules and subsequently impregnated the frameworks with HIm molecules. 26 The different steric influences of the linker molecules leads to different pore shapes and host-guest interactions, which was demonstrated via solid-state 2 H-NMR spectroscopy.…”