A designed zwitterionic group APS (amino-1-propanesulfonate) is grafted onto the metal-carboxylate framework to investigate its strategic and promising function for the melting of metal-carboxylate MOFs and glass formation. Such APS groups on 1,4-dicarboxybenzene ligand (BDC) composite with Bro̷nsted acids to form a binary ionic liquid subsystem within the UiO-66, one well-known nonmeltable MOF in coordination chemistry community, and thus readily lead to the melt at moderate temperature (<160 °C) and melt-quenched glass formation. The synergic effects of suppressed charge transition from ligand to metal ion, protonation of carboxylate COO– and multiple H-bonding interactions well account for the weakened coordination bond and unmeltable-to-meltable transform of the metal-carboxylate framework. The structure before and after vitrification and melt mechanism are systemically investigated through experiment and computer calculation study. High anhydrous proton conduction (10 °C, ∼10–3 S cm–1) and meltability enable the materials to be facilely fabricated into a high-performance supercapacitor with a stable electrolyte–electrode interface via a melt-infiltration method. We hope this work would point an expressway of exploring various meltable MOFs materials with different zwitterions and carboxylate ligands. It may mean the numerous function materials of MOFs with easy processability toward large areas without grain boundary and structure fragility is desirable in future.
Li et al. (Sat,) studied this question.