Solvent-Assisted Modification to Enhance Proton Conductivity and Water Stability in Metal Phosphonates
Zhenni Que, Yingxiang Ye, Yisi Yang, Fahui Xiang, Shimin Chen, Jiali Huang, Yunbin Li, Chulong Liu, Shengchang Xiang, Zhangjing Zhang
Abstract
Although proton-conductive metal phosphonates with well-defined structure offer a favorable platform for exploring their structure–property relationship, investigating of the synergic effect of phosphonate groups and functional moieties on proton conduction is rare. In this work, we have synthesized two new copper phosphonates, [Cu(4-cppH)(4,4′-bipy)(H2O)3] (FJU-80) and [Cu(4-cppH)(4,4′-bipy)]·H2O·DMF (FJU-81), by the method of solvent-assisted modification, giving a 1D metal coordination polymer and a 3D metal open framework, respectively. Single-crystal X-ray diffraction shows that FJU-80 is full of hydrogen-bonding sites contributed from the improved synergic effect of phosphonate groups, carboxylate groups, and coordinated water molecules, thereby facilitating continuous hydrogen-bonding networks, whereas FJU-81 only has discrete hydrogen-bonding fragments. Powder X-ray diffraction and impedance analyses confirm that FJU-80 possesses higher water stability as well as improved proton conductivity, indicating that solvent-assisted modification is effective in increasing the hydrogen-bonding sites from phosphonate groups and functional moieties and then realizing facile proton transfer.