Proton Conduction of Zn(II) Bisphosphonate Driven by the H-Bond Interaction of Water Molecules, [PO₃] Groups, and NH₃⁺

A metal phosphonate of [Zn3(HL)2(H2O)6]·3.27H2O (1) (H5L = 2-amino-1-hydroxypropane-1,1-diphosphonic acid) with a one-dimensional chain structure was synthesized. Complex 1 possesses NH3+, abundant water molecules, and a diversified hydrogen bond network structure, which contributes to achieve high proton conductivity. Proton-conduction studies indicate that complex 1 shows the highest proton conductivity of 6.38 × 10–3 S/cm at 363 K and 98% RH as well as outstanding cyclic stability for at least 18 h. Additionally, the Arrhenius activation energy (Ea) of 1 obtained at 291–363 K is 0.256 eV, suggesting that the proton conduction follows a typical Grotthuss mechanism. Analysis indicates that the prominent proton conductivity of 1 is driven by the H-bond interaction of water molecules, [PO3] groups, and NH3+.