Metastable Ionic Diodes Derived from an Amine‐Based Polymer of Intrinsic Microporosity

A highly rigid amine‐based polymer of intrinsic microporosity (PIM), prepared by a polymerization reaction involving the formation of Tröger’s base, is demonstrated to act as an ionic diode with electrolyte‐dependent bistable switchable states.     

Hexaphenylbenzene-based polymers of intrinsic microporosity

Microporous polymers derived from the 1,2- and 1,4-regioisomers of di(3',4'-dihydroxyphenyl)tetraphenylbenzene have very different properties with the former being composed predominantly of cyclic oligomers whereas the latter is of high molar mass suitable for the formation of robust solvent-cast films of high gas permeability.     

Highly Conductive Anion‐Exchange Membranes from Microporous Tröger's Base Polymers

The development of polymeric anion‐exchange membranes (AEMs) combining high ion conductivity and long‐term stability is a major challenge for materials chemistry. AEMs with regularly distributed fixed cationic groups, based on the formation of microporous polymers containing the V‐shape rigid Tröger's base units, are reported for the first time. Despite their simple preparation, which involves only two synthetic steps using commercially available precursors, the polymers provide AEMs with exceptional hydroxide conductivity at relatively low ion‐exchange capacity, as well as a high swelling resistance and chemical stability. An unprecedented hydroxide conductivity of 164.4 mS cm^?1 is obtained at a relatively a low ion‐exchange capacity of 0.82 mmol g^?1 under optimal operating conditions. The exceptional anion conductivity appears related to the intrinsic microporosity of the charged polymer matrix, which facilitates rapid anion transport.     

Novel polymers of intrinsic microporosity (PIMs) derived from 1,1-spiro-bis(1,2,3,4-tetrahydronaphthalene)-based monomers

The synthesis of novel monomers based upon the rigid 1,1′-spiro-bis(1,2,4,5-tetrahydro-6,7-dihydroxynaphthalene) framework is reported. These monomers can be used for the synthesis of polymers of intrinsic microporosity (PIMs) due to their reactive catechol units and nonlinear shape, which introduces the necessary sites of contortion into the resulting PIM.     

The immobilisation and reactivity of Fe(CN)63−/4− in an intrinsically microporous polyamine (PIM-EA-TB)

Protonation of the molecularly rigid polymer of intrinsic microporosity PIM-EA-TB can be coupled to immobilisation of Fe(CN)₆^3−/4− (as well as immobilisation of Prussian blue) into 1–2 nm diameter channels. The resulting films provide redox-active coatings on glassy carbon electrodes. Uptake, transport, and retention of Fe(CN)₆^3−/4− in the microporous polymer are strongly pH dependent requiring protonation of the PIM-EA-TB (pK_A ≈ 4). Both Fe(CN)₆⁴⁻ and Fe(CN)₆³⁻ can be immobilised, but Fe(CN)₆⁴⁻ appears to bind tighter to the polymer backbone presumably via bridging protons. Loss of Fe(CN)₆^3−/4− by leaching into the aqueous solution phase becomes significant only at pH > 9 and is likely to be associated with hydroxide anions directly entering the microporous structure to combine with protons. This and the interaction of Fe(CN)₆^3−/4− and protons within the molecularly rigid PIM-EA-TB host are suggested to be responsible for retention and relatively slow leaching processes. Electrocatalysis with immobilised Fe(CN)₆^3−/4− is demonstrated for the oxidation of ascorbic acid.

Graphical abstract

     

CO2 Separation by Imide/Imine Organic Cages

Two novel imide/imine-based organic cages have been prepared and studied as materials for the selective separation of CO₂ from N₂ and CH₄ under vacuum swing adsorption conditions. Gas adsorption on the new compounds showed selectivity for CO₂ over N₂ and CH₄. The cages were also tested as fillers in mixed-matrix membranes for gas separation. Dense and robust membranes were obtained by loading the cages in either Matrimid® or PEEK-WC polymers. Improved gas-transport properties and selectivity for CO₂ were achieved compared to the neat polymer membranes.     

Novel spirobisindanes for use as precursors to polymers of intrinsic microporosity

The synthesis of novel spirobisindane-based monomers for the preparation of polymers of intrinsic microporosity (PIMs) with bulky, rigid substituents is described. Polymers derived from monomers containing spiro-linked fluorene substituents display enhanced solubility and microporosity due to additional frustration of packing in the solid state.     

BN-Doped Metal–Organic Frameworks: Tailoring 2D and 3D Porous Architectures through Molecular Editing of Borazines

Building on the MOF approach to prepare porous materials, herein we report the engineering of porous BN-doped materials using tricarboxylic hexaarylborazine ligands, which are laterally decorated with functional groups at the full-carbon ‘inner shell’. Whilst an open porous 3D entangled structure could be obtained from the double interpenetration of two identical metal frameworks derived from the methyl substituted borazine, the chlorine-functionalised linker undergoes formation of a porous layered 2D honeycomb structure, as shown by single-crystal X-ray diffraction analysis. In this architecture, the borazine cores are rotated by 60° in alternating layers, thus generating large rhombohedral channels running perpendicular to the planes of the networks. An analogous unsubstituted full-carbon metal framework was synthesised for comparison. The resulting MOF revealed a crystalline 3D entangled porous structure, composed by three mutually interpenetrating networks, hence denser than those obtained from the borazine linkers. Their microporosity and CO₂ uptake were investigated, with the porous 3D BN-MOF entangled structure exhibiting a large apparent BET specific surface area (1091 m² g⁻¹) and significant CO₂ reversible adsorption (3.31 mmol g⁻¹) at 1 bar and 273 K.     

Crystal Structures of a Series of 1,1-Spiro-bis(1,2,3,4-tetrahydronaphthalene)-Based Derivatives

Abstract  

The structures of four spirobisnaphthalenes based monomers 1, 2, 3a and 3b are reported. Each compound represents a methoxylated precursor which after deprotection led to the formation of a monomer successfully used for the synthesis of Polymers of intrinsic microporosity. The spiro-centre represents the site of contortion that, since its rigidity, leads to inefficient packing in the solid state inducing microporosity in the final polymer. Compound 1 crystallized in the monoclinic P2/c space group with unit cell parameters a = 8.1659(19) ?, b = 7.5298(18) ?, c = 19.130(5) ?, β = 97.935(4)°, V = 1165.0(5) ?³, Z = 2, D = 1.210 Mg m⁻³. Compound 2 crystallized in the monoclinic P2₁/n space group with unit cell parameters a = 12.6940(9) ?, b = 7.7267(6) ?, c = 19.9754(15) ?, β = 97.220(1)°, V = 1943.7(3) ?³, Z = 4, D = 1.355 Mg m⁻³. Compound 3a crystallized in the monoclinic P2₁/c space group with unit cell parameters a = 16.8137(14) ?, b = 10.5577(9) ?, c = 31.344(3) ?, β = 103.618(1)°, V = 5407.5(8) ?³, Z = 8, D = 1.308 Mg m⁻³. Compound 3b crystallized in the monoclinic Pc space group with unit cell parameters a = 15.594 ?, b = 12.564 ?, c = 18.339 ?, β = 90.224(1)°, V = 3593.0 ?³, Z = 4, D = 1.236 Mg m⁻³.     

The Synthesis of Organic Molecules of Intrinsic Microporosity Designed to Frustrate Efficient Molecular Packing

Efficient reactions between fluorine‐functionalised biphenyl and terphenyl derivatives with catechol‐functionalised terminal groups provide a route to large, discrete organic molecules of intrinsic microporosity (OMIMs) that provide porous solids solely by their inefficient packing. By altering the size and substituent bulk of the terminal groups, a number of soluble compounds with apparent BET surface areas in excess of 600 m² g^?1 are produced. The efficiency of OMIM structural units for generating microporosity is in the order: propellane>triptycene>hexaphenylbenzene>spirobifluorene>naphthyl=phenyl. The introduction of bulky hydrocarbon substituents significantly enhances microporosity by further reducing packing efficiency. These results are consistent with findings from previously reported packing simulation studies. The introduction of methyl groups at the bridgehead position of triptycene units reduces intrinsic microporosity. This is presumably due to their internal position within the OMIM structure so that they occupy space, but unlike peripheral substituents they do not contribute to the generation of free volume by inefficient packing.