MIL‐53 and its Isoreticular Analogues: a Review of the Chemistry and Structure of a Prototypical Flexible Metal‐Organic Framework

Abstract

We present a review of the structural chemistry of metal-organic framework materials with the MIL-53 type structure. This family of materials is well-known for its structural flexibility, and also the wide variety of metal cations and functional ligands that can be included. This gives rise to a set of multivariate materials and isoreticular analogues, to which isoreticular functionalisation can also be applied. Starting from the parent structure, containing infinite chains of octahedral trivalent metal cations cross-linked by benzene-1,4-dicarboxylate, we illustrate the compositional variety possible: this includes materials that contain tetravalent and divalent cations, mixtures of metal cations, functionalised ligands, expanded structures from extended linkers and inclusion of pendant ligands. We emphasise the crystal chemistry of this group of materials, but will give some examples of properties, particularly those associated with the structural breathing effect of relevance to molecular sieving, and also discuss emerging practical applications.

Overcoming Crystallinity Limitations of Aluminium Metal‐Organic Frameworks by Oxalic Acid Modulated Synthesis

“…Moreover, their exceptional chemical stability in both aqueous and organic media makes this class of materials ideal for applications that are unsuitable for most MOFs, such as moisture harvesting, adsorption‐driven heat exchange, and water remediation . Unfortunately, the synthesis of highly crystalline Al‐MOFs is a long‐standing challenge as most of these can only be obtained as nanocrystalline powders and such limitations are known to have detrimental effects on MOFs’ porosity and sorption capacity . Importantly, increasing the achievable crystal size of MOFs enables the detailed description of their structural features by single‐crystal X‐ray diffraction (SCXRD) and the investigation of functional properties of interest, such as mechanical response and electronic behavior .…”

The Zeolitic Imidazolate Framework ZIF‐4 under Low Hydrostatic Pressures

“…The situation becomes even more challenging when probing the response of so‐called flexible MOFs to hydrostatic pressures, where phase transitions can occur at pressures p < 0.1 GPa , . Flexible MOFs represent a subclass of MOFs, which undergo a phase transition when exposed to an external trigger such as hydrostatic pressure, temperature or gas sorption , , . Concerning pressure‐induced flexibility, the materials of the iconic MIL‐53 and MIL‐47 families [MIL = Matériaux de l′Institut Lavoisier, M (OH)bdc, M = Al/Cr or V, respectively] are the most thoroughly investigated materials.…”

“…Concerning pressure‐induced flexibility, the materials of the iconic MIL‐53 and MIL‐47 families [MIL = Matériaux de l′Institut Lavoisier, M (OH)bdc, M = Al/Cr or V, respectively] are the most thoroughly investigated materials. In these series, a wine‐rack type structure with sra topology is built from infinite metal‐hydroxide or metal‐oxide chains, which are crosslinked through dicarboxylate linkers such as bdc 2– or fumarate , . An overview of the different flexible MOFs that exhibit a phase transition as function of pressure is given in references, .…”

“…[20,21] Flexible MOFs represent a subclass of MOFs, which undergo a phase transition when exposed to an external trigger such as hydrostatic pressure, temperature or gas sorption. [20,22,23] Concerning pressure-induced flexibility, the materials of the iconic MIL-53 and MIL-47 families [MIL = Matériaux de lЈInstitut Lavoisier, M(OH)bdc, M = Al/Cr or V, respectively] are the most thoroughly investigated materials. In these series, a wine-rack type structure with sra topology is built from infinite metal-hydroxide or metal-oxide chains, which are crosslinked through dicarboxylate linkers such as bdc 2or fumarate.…”

Overcoming Crystallinity Limitations of Aluminium Metal–Organic Frameworks by Oxalic Acid Modulated Synthesis

“…Moreover, their exceptional chemical stability [9,10] in both aqueous and organic media makes this class of materials ideal fora pplications that are unsuitable for most MOFs, such as moisture harvesting, [11,12] adsorption-drivenh eat exchange, [13][14][15] and water remediation. [16] Unfortunately,t he synthesis of highlyc rystalline Al-MOFs is al ong-standing challenge as most of these can only be obtained as nanocrystalline powders [9,17,18] and such limitations are known to have detrimental effects on MOFs' porosity and sorption capacity. [19][20][21] Importantly,i ncreasing the achievable crystal size of MOFs enables the detailedd escription of their structural features by single-crystal X-ray diffraction (SCXRD) and the investigation of functional properties of interest,s uch as mechanical response [22][23][24][25] and electronic behavior.…”