Inherent Proton Conduction in a 2D Coordination Framework

We synthesized a coordination polymer consisting of Zn2+, 1,2,4-triazole, and orthophosphates, and demonstrated for the first time intrinsic proton conduction by a coordination network. The compound has a two-dimensional layered structure with extended hydrogen bonds between the layers. It shows intrinsic proton conductivity along the direction parallel to the layers, as elucidated by impedance studies of powder and single crystals. From the low activation energy for proton hopping, the conduction mechanism was found to be of the Grotthuss fashion. The hopping is promoted by rotation of phosphate ligands, which are aligned on the layers at appropriate intervals

Reversible Solid-to-Liquid Phase Transition of Coordination Polymer Crystals

The solid-to-liquid phase transition, a fundamental process commonly observed for various types of substances with significant potential for application, has been given little attention in the field of coordination polymers (CPs) despite the rich functionality of these compounds. In this article, we report the reversible solid-to-liquid phase transition of crystalline CPs. These CPs are composed of zinc ions, phosphate, and azoles, and a well-balanced composition, ionicity, and bond strength afford “melting” CPs. We examined the structure of one such melting framework in the liquid and glass states and found that the coordination bonds are not fully preserved in the liquid state but are re-formed in the glass state. As a demonstration, we fabricated, via phase transition, a thin film with an aligned crystal orientation and a monolith crystal of the CP

Coordination-Network-Based Ionic Plastic Crystal for Anhydrous Proton Conductivity

An ionic coordination network consisting of protonated imidazole and anionic one-dimensional chains of Zn²⁺ phosphate was synthesized. The compound possesses highly mobile ions in the crystal lattice and behaves as an ionic plastic crystal. The dynamic behavior provides a proton conductivity of 2.6 × 10^–4 S cm^–1 at 130 °C without humidity

Fast Conduction of Organic Cations in Metal Sulfate Frameworks

We demonstrated a new method of synthesizing crystalline organic cation conductors. The conductivities of various organic cations involved in a one-dimensional zinc sulfate framework were studied. The optimized structure (EMIm)₂[Zn­(SO₄)₂] exhibited an ionic conductivity of 3.8 × 10^–3 S cm^–1 at 210 °C, which is comparable to that of highly conductive organic ionic plastic crystals. The high ionic conductivity is attributable to the defect structures of the organic cations in the inorganic frameworks. The pulsed-field gradient solid-state NMR technique revealed that the self-diffusion coefficient of organic cations in the zinc sulfate at 80 °C is comparable to that of the popular ionic liquid EMIm-BF₄ at 30 °C, which indicates that liquid-like fast transporting of organic cation is achieved in the robust crystal structure

Reversible Solid-to-Liquid Phase Transition of Coordination Polymer Crystals

The solid-to-liquid phase transition, a fundamental process commonly observed for various types of substances with significant potential for application, has been given little attention in the field of coordination polymers (CPs) despite the rich functionality of these compounds. In this article, we report the reversible solid-to-liquid phase transition of crystalline CPs. These CPs are composed of zinc ions, phosphate, and azoles, and a well-balanced composition, ionicity, and bond strength afford “melting” CPs. We examined the structure of one such melting framework in the liquid and glass states and found that the coordination bonds are not fully preserved in the liquid state but are re-formed in the glass state. As a demonstration, we fabricated, via phase transition, a thin film with an aligned crystal orientation and a monolith crystal of the CP

Inherent Proton Conduction in a 2D Coordination Framework

We synthesized a coordination polymer consisting of Zn²⁺, 1,2,4-triazole, and orthophosphates, and demonstrated for the first time intrinsic proton conduction by a coordination network. The compound has a two-dimensional layered structure with extended hydrogen bonds between the layers. It shows intrinsic proton conductivity along the direction parallel to the layers, as elucidated by impedance studies of powder and single crystals. From the low activation energy for proton hopping, the conduction mechanism was found to be of the Grotthuss fashion. The hopping is promoted by rotation of phosphate ligands, which are aligned on the layers at appropriate intervals

Fast Conduction of Organic Cations in Metal Sulfate Frameworks

We demonstrated a new method of synthesizing crystalline organic cation conductors. The conductivities of various organic cations involved in a one-dimensional zinc sulfate framework were studied. The optimized structure (EMIm)₂[Zn­(SO₄)₂] exhibited an ionic conductivity of 3.8 × 10^–3 S cm^–1 at 210 °C, which is comparable to that of highly conductive organic ionic plastic crystals. The high ionic conductivity is attributable to the defect structures of the organic cations in the inorganic frameworks. The pulsed-field gradient solid-state NMR technique revealed that the self-diffusion coefficient of organic cations in the zinc sulfate at 80 °C is comparable to that of the popular ionic liquid EMIm-BF₄ at 30 °C, which indicates that liquid-like fast transporting of organic cation is achieved in the robust crystal structure

Postsynthesis Modification of a Porous Coordination Polymer by LiCl To Enhance H⁺ Transport

A Ca²⁺ porous coordination polymer with 1D channels was functionalized by the postsynthesis addition of LiCl to enhance the H⁺ conductivity. The compound showed over 10^–2 S cm^–1 at 25 °C and 20% relative humidity. Pulse-field gradient NMR elucidated that the fast H⁺ conductivity was achieved by the support of Li⁺ ion movements in the channel

Postsynthesis Modification of a Porous Coordination Polymer by LiCl To Enhance H⁺ Transport

A Ca²⁺ porous coordination polymer with 1D channels was functionalized by the postsynthesis addition of LiCl to enhance the H⁺ conductivity. The compound showed over 10^–2 S cm^–1 at 25 °C and 20% relative humidity. Pulse-field gradient NMR elucidated that the fast H⁺ conductivity was achieved by the support of Li⁺ ion movements in the channel

Encapsulating Mobile Proton Carriers into Structural Defects in Coordination Polymer Crystals: High Anhydrous Proton Conduction and Fuel Cell Application

We describe the encapsulation of mobile proton carriers into defect sites in nonporous coordination polymers (CPs). The proton carriers were encapsulated with high mobility and provided high proton conductivity at 150 °C under anhydrous conditions. The high proton conductivity and nonporous nature of the CP allowed its application as an electrolyte in a fuel cell. The defects and mobile proton carriers were investigated using solid-state NMR, XAFS, XRD, and ICP-AES/EA. On the basis of these analyses, we concluded that the defect sites provide space for mobile uncoordinated H3PO4, H2PO4–, and H2O. These mobile carriers play a key role in expanding the proton-hopping path and promoting the mobility of protons in the coordination framework, leading to high proton conductivity and fuel cell power generation