Proton Transportation Behavior in Lanthanide Tartrate Metal-Organic Frameworks

A series of lanthanide tartrate metal-organic frameworks (MOFs) were synthesized and structurally characterized. These include the three-dimensional (3D) frameworks {[Ln(C₄H₄O₆)(H₂O)₃]Cl·2H₂O}_n (C₄H₄O₆), tartrate; Ln = La (1), Nd (2), and Pr (3) and the 2D framework {[Ce₂(C₄H₄O₆)₃(H₂O)₅]·2.5H₂O}_n (4). Using compounds 3 and 4 as representatives, proton conductivities of the two different kinds of MOFs were measured. The extensive hydrogen bonding interactions involving the tartrate ligands, the aqua ligands, and the water molecules inside and outside the porous structures are believed to be responsible for the observed proton conduction, likely via the Grotthuss mechanism in both cases.