Constructing Flexible Crystalline Porous Organic Salts via a Zwitterionic Strategy

Abstract

The unique ionic channels and highly polar pore structures have distinguished crystalline porous organic salts (CPOSs) from conventional porous frameworks in the past decade. Up to now, CPOSs were all constructed by a monoionic strategy, in which two types of building units individually bearing anionic or cationic groups were introduced, thus increasing complexity in the synthesis of CPOSs. In this study, by utilizing stereoisomeric compounds of TPE-NS-Z or TPE-NS-E bearing both anionic and cationic groups as a single building unit, the zwitterionic strategy was proven feasible in constructing CPOSs. Benefiting from the single building unit, the zwitterionic strategy simplified the preparation process and reduced the difficulty in studying the aggregation behavior of building units into CPOSs. And also, this novel strategy enabled precise control of the finally obtained CPOSs through fine-tuning of the initial building units. Surprisingly, the special parallel/vertical alternated stacking mode and unique ionic interaction networks in the crystal structure provided the flexible pore characteristic of CPOS-E, which further guaranteed the multitime controllable release of highly polar chemicals in different solvents.