A proton-conductive metal-organic framework based on imidazole and sulphate ligands

A metal-organic framework (MOF) built from a combination of metal cations, neutral azole ligands and sulphate anions, [Cu₂(DHBDI)₃(SO₄)₂]_n (1, DHBDI = 1H,5H-benzo[1,2-d:4,5-d']diimidazole), was synthesized. MOF 1 exhibits good chemical stability in acids, bases and boiling water while showing high hydrophilicity. Meanwhile, MOF 1 exhibits a proton conductivity of 1.14 × 10^-3 S cm^-1 at 90 °C and 98% RH, among the best for MOF materials with uncoordinated N sites. Temperature-dependent conductivity measurements suggest a vehicle mechanism (E_a = 0.64 eV) for proton transport.

Enhanced proton conductivity of a MOF-808 framework through anchoring organic acids to the zirconium clusters by post-synthetic modification

Modified frameworks MOF-808-EDTA/OX show better proton-conduction behaviours, and conductivity is firstly tuned by modifying the metal clusters via a post-synthetic modification method.

Observation of Olefin/Paraffin Selectivity in Azo Compound and Its Application into a Metal-Organic Framework

Olefin/paraffin separation is an important and challenging issue because the two molecules have similar physicochemical properties. Although a couple of olefin adsorbents have been developed by introducing inorganic nanoparticles into metal-organic frameworks (MOFs), there has been no study on the development of an olefin adsorbent by introducing a certain organic functional group into a MOF. In this study, we posited that azo compounds could offer olefin/paraffin selectivity. We have revealed using first-principles calculations that the simplest aromatic azo compound (azobenzene, Azob) has an unusual propylene/propane selectivity due to special electrostatic interactions between Azob and propylene molecules. On the basis of this interesting discovery, we have synthesized a novel propylene adsorbent, MIL-101(Cr)_DAA, by grafting 4,4'-diaminoazobenzene (DAA) into open metal sites in a mesoporous MIL-101(Cr). Remarkably, MIL-101(Cr)_DAA exhibited enhanced propylene/propane selectivity as well as considerably higher propylene heat of adsorption compared to pristine MIL-101(Cr) while maintaining the high working capacity of MIL-101(Cr). This clearly indicates that azo compounds when introduced into MOFs can provide propylene selectivity. Moreover, MIL-101(Cr)_DAA showed good C₃H₆/C₃H₈ separation and easy regeneration performances from packed-bed breakthrough experiments and retained its propylene adsorption capacity even after exposure to air for 12 h. As far as we know, this is the first study that improves the olefin selectivity of MOF by postsynthetically introducing an organic functional group.

Water mediated proton conductance in a hydrogen-bonded Ni(ii)-bipyridine-glycoluril chloride self-assembled framework

Proton conducting properties have been investigated in a new Ni(ii)-based hydrogen-bonded porous framework synthesized using bipyridine-glycoluril (BPG) tecton.

Synthesis of an ultra-stable metal–organic framework for proton conduction

An ultra-stable metal organic framework material has been successfully synthesized for proton conduction.

One-Dimensional Anhydrous Proton Conducting Channel Formation at High Temperature in a Pt(II)-Based Metallo-Supramolecular Polymer and Imidazole System

One dimensional (1D) Pt(II)-based metallo-supramolecular polymer with carboxylic acids (polyPtC) was synthesized using a new asymmetrical ditopic ligand with a pyridine moiety bearing two carboxylic acids. The carboxylic acids in the polymer successfully served as apohosts for imidazole loaded in the polymer interlayer scaffold to generate highly ordered 1D imidazole channels through the metallo-supramolecular polymer chains. The 1D structure of imidazole loaded polymer (polyPtC-Im) was analyzed in detail by thermogravimetric analysis, powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and ultraviolet-visible and photoluminescence spectroscopic measurements. PolyPtC-Im exhibited proton conductivity of 1.5 × 10^-5 S cm^-1 at 120 °C under completely anhydrous conditions, which is 6 orders of magnitude higher than that of the pristine metallo-supramolecular polymer.

1000-fold enhancement in proton conductivity of a MOF using post-synthetically anchored proton transporters

Pyridinol, a coordinating zwitter-ionic species serves as stoichiometrically loadable and non-leachable proton carrier. The partial replacement of the pyridinol by stronger hydrogen bonding, coordinating guest, ethylene glycol (EG), offers 1000-fold enhancement in conductivity (10⁻⁶ to 10⁻³ Scm⁻¹) with record low activation energy (0.11 eV). Atomic modeling coupled with ¹³C-SSNMR provides insights into the potential proton conduction pathway functionalized with post-synthetically anchored dynamic proton transporting EG moieties.

Ionothermal synthesis and proton-conductive properties of NH2-MIL-53 MOF nanomaterials

Highly stable and proton-conductive NH₂-MIL-53 metal–organic framework nanomaterials have been successfully synthesized in an ionothermal system.

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

A systematic investigation on the influence of steric effects and the possibility to form host-guest interactions on the proton conductivity was carried out using imidazole loaded derivatives of Al-MIL-53 [Al(OH)(1,4-BDC-(CH₃)_x)] (x = 0, 1, 2) and CAU-11.

Incorporation of imidazole within the metal–organic framework UiO-67 for enhanced anhydrous proton conductivity

Imidazole@UiO-67 achieves a proton conductivity of over 10⁻³ S cm⁻¹ at 120 °C in a completely anhydrous environment.

Proton conductive watery channels constructed by Anderson polyanions and lanthanide coordination cations

An ionic network based on Anderson POM featuring water chains in 1D channels exhibits outstanding proton conductivity.

Post‐synthetic Modification of MOFs

Post‐synthetic modification is increasingly recognised as an important and versatile tool in the preparation of functionalised metal organic frameworks (MOFs). The process involves one or more reactions on a pre‐formed MOF, and it can be used to prepare MOFs that are not accessible by direct combination of metal and linker. This review explores the methods and strategies that have been developed for post‐synthetically modifying MOFs, concentrating on four classes of reaction: covalent transformations of the linker, coordination of a metal centre to a linker, modification of the inorganic part of the MOF and exchange of counter‐ions. Examples of the use of the modified MOFs are given, with a focus on their utility in catalysis.