High Proton Conductivity of Zinc Oxalate Coordination Polymers Mediated by a Hydrogen Bond with Pyridinium

A novel metal–organic framework, (Hpy)₂[Zn₂(ox)₃]·<i>n</i>H₂O (<i>n</i> = 0, 1), having a pyridinium cation, was newly synthesized, and the crystal structures were determined. The hydrated compound shows a high proton conductivity of 2.2 × 10^–3 S cm^–1 at 298 K and 98% relative humidity. Single crystal XRD analysis revealed a rotational displacement factor for the hydrated pyridinium ring and elongated water site that is thought to cause the high proton conductivity

High Proton Conductivity of Zinc Oxalate Coordination Polymers Mediated by a Hydrogen Bond with Pyridinium

A novel metal–organic framework, (Hpy)₂[Zn₂(ox)₃]·<i>n</i>H₂O (<i>n</i> = 0, 1), having a pyridinium cation, was newly synthesized, and the crystal structures were determined. The hydrated compound shows a high proton conductivity of 2.2 × 10^–3 S cm^–1 at 298 K and 98% relative humidity. Single crystal XRD analysis revealed a rotational displacement factor for the hydrated pyridinium ring and elongated water site that is thought to cause the high proton conductivity

High Proton Conductivity of Zinc Oxalate Coordination Polymers Mediated by a Hydrogen Bond with Pyridinium

A novel metal–organic framework, (Hpy)₂[Zn₂(ox)₃]·<i>n</i>H₂O (<i>n</i> = 0, 1), having a pyridinium cation, was newly synthesized, and the crystal structures were determined. The hydrated compound shows a high proton conductivity of 2.2 × 10^–3 S cm^–1 at 298 K and 98% relative humidity. Single crystal XRD analysis revealed a rotational displacement factor for the hydrated pyridinium ring and elongated water site that is thought to cause the high proton conductivity

Supramolecular Thermo-Electrochemical Cells: Enhanced Thermoelectric Performance by Host–Guest Complexation and Salt-Induced Crystallization

Thermo-electrochemical cells have potential to generate thermoelectric voltage 1 order higher than that given by semiconductor materials. To overcome the current issues in thermoelectric energy conversion, it is of paramount importance to grow and fulfill the full potential of thermo-electrochemical cells. Here we report a rational supramolecular methodology that yielded the highest Seebeck coefficient of ca. 2.0 mV K^–1 around ambient temperatures. This is based on the encapsulation of triiodide ions in α-cyclodextrin, whose equilibrium is shifted to the complexation at lower temperatures, whereas it is inverted at elevated temperatures. This temperature-dependent host–guest interaction provides a concentration gradient of redox ion pairs between two electrodes, leading to the eminent performance of the thermo-electrochemical cells. The figure of merit for this system, <i>zT</i> reached a high value of 5 × 10^–3. The introduction of host–guest chemistry to thermoelectric cells thus provides a new perspective in thermoelectric energy conversion

Proton Conductivity Control by Ion Substitution in a Highly Proton-Conductive Metal–Organic Framework

Proton conductivity through two-dimensional (2-D) hydrogen-bonding networks within a layered metal–organic framework (MOF) (NH₄)₂(H₂adp)­[Zn₂(ox)₃]·3H₂O (H₂adp = adipic acid; ox = oxalate) has been successfully controlled by cation substitution. We synthesized a cation-substituted MOF, K₂(H₂adp)­[Zn₂(ox)₃]·3H₂O, where the ammonium ions in a well-defined hydrogen-bonding network are substituted with non-hydrogen-bonding potassium ions, without any apparent change in the crystal structure. We successfully controlled the proton conductivity by cleavage of the hydrogen bonds in a proton-conducting pathway, showing that the 2-D hydrogen-bonding networks in the MOF truly contribute to the high proton conductivity. This is the first example of the control of proton conductivity by ion substitution in a well-defined hydrogen-bonding network within a MOF

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

3D Coordination Polymer of Cd(II) with an Imidazolium-Based Linker Showing Parallel Polycatenation Forming Channels with Aligned Imidazolium Groups

A novel entangled architecture formed on solvothermal reaction of a imidazolium based bent ligand with Cd­(NO₃)₂, showing 1D channels decorated with imidazolium groups, is reported. The polymer, {[Cd₂(L)₃(DMF)­(NO₃)]­(DMF)₃(H₂O)₈}_<i>n</i> (<b>1</b>) (where H₂L = 1,3-bis­(4-carboxyphenyl)­imidazolium, DMF = dimethylformamide), shows an interesting 6,3-connected polycatenated structure with channels along the crystallographic <i>b</i>-axis occupied with large number of DMF and water molecules. On removal of these solvent molecules the compound maintains its overall structure. Proton conductivity investigation affords a proton conductivity of 1.3 × 10^–5 Scm^–1 at 25 °C and 98% RH when water molecules are introduced into the empty channels

Control of Crystalline Proton-Conducting Pathways by Water-Induced Transformations of Hydrogen-Bonding Networks in a Metal–Organic Framework

Structure-defined metal–organic frameworks (MOFs) are of interest because rational design and construction allow us to develop good proton conductors or possibly control the proton conductivity in solids. We prepared a highly proton-conductive MOF (NH₄)₂(adp)­[Zn₂(ox)₃]·<i>n</i>H₂O (abbreviated to <b>1·</b><i><b>n</b></i><b>H</b>_<b>2</b><b>O</b>, adp: adipic acid, ox: oxalate, <i>n</i> = 0, 2, 3) having definite crystal structures and showing reversible structural transformations among the anhydrate (<b>1</b>), dihydrate (<b>1·2H</b>_<b>2</b><b>O</b>), and trihydrate (<b>1·3H</b>_<b>2</b><b>O</b>) phases. The crystal structures of all of these phases were determined by X-ray crystallography. Hydrogen-bonding networks consisting of ammonium ions, water molecules, and carboxylic acid groups of the adipic acids were formed inside the two-dimensional interlayer space in hydrated <b>1·2H</b>_<b>2</b><b>O</b> and <b>1·3H</b>_<b>2</b><b>O</b>. The crystal system of <b>1</b> or <b>1·2H</b>_<b>2</b><b>O</b> (<i>P</i>2₁/<i>c</i>, No. 14) was changed into that of <b>1·3H</b>_<b>2</b><b>O</b> (<i>P</i>1̅, No. 2), depending on water content because of rearrangement of guests and acidic molecules. Water molecules play a key role in proton conduction as conducting media and serve as triggers to change the proton conductivity through reforming hydrogen-bonding networks by water adsorption/desorption processes. Proton conductivity was consecutively controlled in the range from ∼10^–12 S cm^–1 (<b>1</b>) to ∼10^–2 S cm^–1 (<b>1·3H</b>_<b>2</b><b>O</b>) by the humidity. The relationships among the structures of conducting pathways, adsorption behavior, and proton conductivity were investigated. To the best of our knowledge, this is the first example of the control of a crystalline proton-conducting pathway by guest adsorption/desorption to control proton conductivity using MOFs

Facile “Modular Assembly” for Fast Construction of a Highly Oriented Crystalline MOF Nanofilm

The preparation of crystalline, ordered thin films of metal–organic frameworks (MOFs) will be a critical process for MOF-based nanodevices in the future. MOF thin films with perfect orientation and excellent crystallinity were formed with novel nanosheet-structured components, Cu–TCPP [TCPP = 5,10,15,20-tetrakis­(4-carboxyphenyl)­porphyrin], by a new “modular assembly” strategy. The modular assembly process involves two steps: a “modularization” step is used to synthesize highly crystalline “modules” with a nanosized structure that can be conveniently assembled into a thin film in the following “assembly” step. With this method, MOF thin films can easily be set up on different substrates at very high speed with controllable thickness. This new approach also enabled us to prepare highly oriented crystalline thin films of MOFs that cannot be prepared in thin-film form by traditional techniques

Control of Crystalline Proton-Conducting Pathways by Water-Induced Transformations of Hydrogen-Bonding Networks in a Metal–Organic Framework

Structure-defined metal–organic frameworks (MOFs) are of interest because rational design and construction allow us to develop good proton conductors or possibly control the proton conductivity in solids. We prepared a highly proton-conductive MOF (NH₄)₂(adp)­[Zn₂(ox)₃]·<i>n</i>H₂O (abbreviated to <b>1·</b><i><b>n</b></i><b>H</b>_<b>2</b><b>O</b>, adp: adipic acid, ox: oxalate, <i>n</i> = 0, 2, 3) having definite crystal structures and showing reversible structural transformations among the anhydrate (<b>1</b>), dihydrate (<b>1·2H</b>_<b>2</b><b>O</b>), and trihydrate (<b>1·3H</b>_<b>2</b><b>O</b>) phases. The crystal structures of all of these phases were determined by X-ray crystallography. Hydrogen-bonding networks consisting of ammonium ions, water molecules, and carboxylic acid groups of the adipic acids were formed inside the two-dimensional interlayer space in hydrated <b>1·2H</b>_<b>2</b><b>O</b> and <b>1·3H</b>_<b>2</b><b>O</b>. The crystal system of <b>1</b> or <b>1·2H</b>_<b>2</b><b>O</b> (<i>P</i>2₁/<i>c</i>, No. 14) was changed into that of <b>1·3H</b>_<b>2</b><b>O</b> (<i>P</i>1̅, No. 2), depending on water content because of rearrangement of guests and acidic molecules. Water molecules play a key role in proton conduction as conducting media and serve as triggers to change the proton conductivity through reforming hydrogen-bonding networks by water adsorption/desorption processes. Proton conductivity was consecutively controlled in the range from ∼10^–12 S cm^–1 (<b>1</b>) to ∼10^–2 S cm^–1 (<b>1·3H</b>_<b>2</b><b>O</b>) by the humidity. The relationships among the structures of conducting pathways, adsorption behavior, and proton conductivity were investigated. To the best of our knowledge, this is the first example of the control of a crystalline proton-conducting pathway by guest adsorption/desorption to control proton conductivity using MOFs