Synthesis and structural characterization. gis-ZIF-1 was synthesized with Zn(CF3SO3)2, imidazole ligands (Im, hereafter), and ethylenediamine (EDA) in N,N-diethylformamide (DEF) solution via solvothermal reaction (Figure ). Single-crystal X-ray diffraction (SCXRD) revealed that gis-ZIF-1 is one of Zn(Im)2 polymorphs with gis topology (Figure , 2B). The gis topology is one of zeolitic topologies, composed of one type of tetrahedral vertices and two types of edges, where the network includes two types of CBUs, four-membered rings (4MRs) and helical chains (Figure ).