Switching on the proton transport pathway of a lanthanide metal-organic framework by one-pot loading of tetraethylene glycol for high proton conductionElectronic supplementary information (ESI) available: Crystal data and structure refinement for SmHEDP-H2O; selected bond lengths and bond angles for SmHEDP-H2O; simulated and experimental powder XRD patterns of SmHEDP-H2O; TG and IR spectra of SmHEDP-H2O and SmHEDP-TEG; thermal ellipsoid plot (30% probability) and atomic labeling scheme of SmHEDP

A one-pot hydrothermal approach has been developed to introduce tetraethylene glycol (TEG) molecules into a two-dimensional (2D) layered lanthanide metal-organic framework ([Sm(H 5 C 2 P 2 O 7 )(H 2 O) 2 ]·Guest, denoted SmHEDP-Guest). Through the straightforward loading of TEG, the proton conductivity of SmHEDP-TEG (1.21 × 10 −3 S cm −1 ) is increased by 3 orders of magnitude compared with its analogue SmHEDP-H 2 O (1.22 × 10 −6 S cm −1 ) under 100% relative humidity at room temperature. More excitingly, SmHEDP-TEG exhibits very high proton conductivity of 9.17 × 10 −2 S cm −1 , even higher than commercial Nafion, when the temperature is increased to 333 K, which is significantly higher than SmHEDP-H 2 O (3.38 × 10 −5 S cm −1 ). The single crystal XRD reveals that the adjacent water molecules located in the channels of SmHEDP-H 2 O are isolated without hydrogen bonding interactions owing to their long distances. However, interestingly, the guest TEG molecules of SmHEDP-TEG behave as hydrogen bonded connected bridges, which switch on the proton transport pathway to promote proton hopping. This discovery may provide a facile strategy to design and synthesize more promising candidates for novel proton conductors. We enhance the proton conductivity of a lanthanide MOF compared to commercial Nafion by the one-pot loading of tetraethylene glycol.