Tomoya Itakura

Inherent Proton Conduction in a 2D Coordination Framework

We synthesized a coordination polymer consisting of Zn(2+), 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.

Coordination-network-based ionic plastic crystal for anhydrous proton conductivity.

An ionic coordination network consisting of protonated imidazole and anionic one-dimensional chains of Zn(2+) 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.

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

A Ca(2+) 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.

Glass Formation of a Coordination Polymer Crystal for Enhanced Proton Conductivity and Material Flexibility

The glassy state of a two-dimensional (2D) Cd(2+) coordination polymer crystal was prepared by a solvent-free mechanical milling process. The glassy state retains the 2D structure of the crystalline material, albeit with significant distortion, as characterized by synchrotron X-ray analyses and solid-state multinuclear NMR spectroscopy. It transforms to its original crystal structure upon heating. Thus, reversible crystal-to-glass transformation is possible using our new processes. The glass state displays superior properties compared to the crystalline state; specifically, it shows anhydrous proton conductivity and a dielectric constant two orders of magnitude greater than the crystalline material. It also shows material flexibility and transparency.

Template-directed proton conduction pathways in a coordination framework

We present a strategy for creating coordination frameworks exhibiting proton conduction with thermal stability. The coordination framework, where template cations link 1-D chains via hydrogen bonds, has dynamic hydrogen bond networks where protons move without water support. Solid-state NMR and X-ray studies visualized the proton hopping mechanism, and revealed that the templates provide the bridging of the 1-D chains to attain proton conduction. The templates also enable the proton conductive networks to be maintained at 190 °C through multiple interactions between the templates and the 1-D chains.

Enhanced and Optically Switchable Proton Conductivity in a Melting Coordination Polymer Crystal

The melting behavior of a coordination polymer (CP) crystal was utilized to achieve enhanced and optically switchable proton conductivity in the solid state. The strong acid molecules (triflic acid) were doped in one-dimensional (1D) CP, [Zn(HPO4 )(H2 PO4 )2 ](ImH2 )2 (ImH2 =monoprotonated imidazole) in the melt state, and overall enhancement in the proton conductivity was obtained. The enhanced proton conductivity is assigned to increased number of mobile protons and defects created by acid doping. Optical control over proton conductivity in the CP is achieved by doping of the photo acid molecule pyranine into the melted CP. The pyranine reversibly generates the mobile acidic protons and local defects in the glassy state of CP resulting in the bulk switchable conductivity mediated by light irradiation. Utilization of CP crystal in liquid state enables to be a novel route to incorporate functional molecules and defects, and it provides a tool to control the bulk properties of the CP material.

Coordination polymer glass for bio-inspired photoelectric conversion application

Sanjog S. Nagarkar1, Satoshi Horike1, Tomoya Itakura2, Benjamin Le Ouay3, Aude Demessence4, Masahiko Tsujimoto1, Susumu Kitagawa1 1Institute For Integrated Cell-Material Sciences (WPI-ICeMS), Kyoto University, Kyoto, Japan, 2DENSO Corporation, Aichi, Japan, 3Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan, 4Institut de Recherches sur la Catalyse et l’ Environnement de Lyon, Université Claude Bernard Lyon 1, Villeurbanne, FRANCE, Lyon, France E-mail: nagarkar.sanjog.82c@st.kyoto-u.ac.jp