Using N,N'?Dimethylpiperazine as structure directing agent, a 3D open?framework neodymium oxalate [Nd(H₂O)(C₂O₄)₂](C₆N₂H₁₆)_0.5?2H₂O (compound 1) was synthesized under hydrothermal condition. The single crystal X?ray diffraction reveals that the structure is composed of alternating single?capped tetragonal antiprism NdO₉ and oxalic acid units connected to each other. The structure contains three?dimensional 12?membered ring channels, in which water molecules and protonated Me₂ppz cations are located in the channels along the b and a axes, respectively. The presence of guest water molecules provides the structural basis for proton conductivity. The results of hydrothermal and acid?base stability tests show that the structure of compound 1 had excellent stability. AC impedance tests show that compound 1 has a high proton conductivity, which is 2.81×10^-4 S/cm at 348 K and 98% RH.

Proton conductive materials are an important part of sensors and fuel cells. In recent years, the research of crystalline proton conducting materials has mainly focused on metal organic framework material(MOF). Lanthanide metal organic framework (Ln?MOF) is an important member of the MOF family, and it is easy to form a stable and diverse framework owing to the strong coordination ability, Lewis acidity and complex functionality of lanthanide ions. At present, people are beginning to focus on its research in the field of proton conduction. This article reviews the research progress in proton conduction of Ln?MOF materials with different functional acid groups (carboxylate, phosphonate or sulfonate groups, etc.) introduced into the main frame. The challenges faced by Ln?MOF materials in the study of proton conduction were prospected.