Selective Separation of Water, Methanol, and Ethanol by a Porous Coordination Polymer Built with a Flexible Tetrahedral Ligand

A novel porous coordination polymer, Cu^II(mtpm)­Cl₂ [mtpm = tetrakis­(<i>m</i>-pyridyloxy methylene)­methane], has been synthesized, and its crystal structure has been determined. Its adsorption isotherms for water, methanol, and ethanol are totally different from each other. It adsorbs water at low humidity and shows gate-open behavior for methanol, but it does not adsorb ethanol. This compound has the capacity to separate both methanol and water from bioethanol, which is a mixture of water, methanol, and ethanol

Promotion of Low-Humidity Proton Conduction by Controlling Hydrophilicity in Layered Metal–Organic Frameworks

We controlled the hydrophilicity of metal–organic frameworks (MOFs) to achieve high proton conductivity and high adsorption of water under low humidity conditions, by employing novel class of MOFs, {NR₃(CH₂COOH)}­[MCr­(ox)₃]·<i>n</i>H₂O (abbreviated as <b>R-MCr</b>, where R = Me (methyl), Et (ethyl), or Bu (<i>n</i>-butyl), and M = Mn or Fe): <b>Me-FeCr</b>, <b>Et-MnCr</b>, <b>Bu-MnCr</b>, and <b>Bu-FeCr</b>. The cationic components have a carboxyl group that functions as the proton carrier. The hydrophilicity of the cationic ions was tuned by the NR₃ residue to decrease with increasing bulkiness of the residue: {NMe₃(CH₂COOH)}⁺ > {NEt₃(CH₂COOH)}⁺ > {NBu₃(CH₂COOH)}⁺. The proton conduction of the MOFs increased with increasing hydrophilicity of the cationic ions. The most hydrophilic sample, <b>Me-FeCr</b>, adsorbed a large number of water molecules and showed a high proton conductivity of ∼10^–4 S cm^–1, even at a low humidity of 65% relative humidity (RH), at ambient temperature. Notably, this is the highest conductivity among the previously reported proton-conducting MOFs that operate under low RH conditions

Promotion of Low-Humidity Proton Conduction by Controlling Hydrophilicity in Layered Metal–Organic Frameworks

We controlled the hydrophilicity of metal–organic frameworks (MOFs) to achieve high proton conductivity and high adsorption of water under low humidity conditions, by employing novel class of MOFs, {NR₃(CH₂COOH)}­[MCr­(ox)₃]·<i>n</i>H₂O (abbreviated as <b>R-MCr</b>, where R = Me (methyl), Et (ethyl), or Bu (<i>n</i>-butyl), and M = Mn or Fe): <b>Me-FeCr</b>, <b>Et-MnCr</b>, <b>Bu-MnCr</b>, and <b>Bu-FeCr</b>. The cationic components have a carboxyl group that functions as the proton carrier. The hydrophilicity of the cationic ions was tuned by the NR₃ residue to decrease with increasing bulkiness of the residue: {NMe₃(CH₂COOH)}⁺ > {NEt₃(CH₂COOH)}⁺ > {NBu₃(CH₂COOH)}⁺. The proton conduction of the MOFs increased with increasing hydrophilicity of the cationic ions. The most hydrophilic sample, <b>Me-FeCr</b>, adsorbed a large number of water molecules and showed a high proton conductivity of ∼10^–4 S cm^–1, even at a low humidity of 65% relative humidity (RH), at ambient temperature. Notably, this is the highest conductivity among the previously reported proton-conducting MOFs that operate under low RH conditions

Ammonia as Proton Conducting Medium Confined in Porous Materials

Molecular confinement within a limited space induces unique behaviour not seen in bulk systems. In particular, the proton diffusion in conducting medium under confined conditions is significantly affected by the surrounding environment.H2O, efficient conducting medium, confined in hydrophobic channels forms unique clusters allowing rapid diffusion, whereas confined NH3, having a similar degenerate system (Fig. 1a), has not been reported. Herein, we show NH3-mediated proton conduction in microporous metal–organic frameworks (MOFs), MIL-53(Al) functionalized with (-COOH)2, -NH2, -OH and -H. Anhydrous NH3 gas is trapped in the pore by proton donation of frameworks and forms hydrogen bonding networks exhibiting a remarkably enhanced proton conductivity. The crystallographic analysis and solid-state NMR clarify the veiled proton diffusion mechanism and unique dynamic behaviour of confined NH3.<br /