Structure and Properties of a Mixed-Ligand Co-MOF That Was Synthesized in Situ from a Single Imidazole–Pyridyl–Tetrazole Trifunctional Ligand

Abstract

A mixed-ligand Co-MOF (SCNU-Z7) based on a new imidazole–pyridyl–tetrazole trifunctional ligand, 3-(imidazol-1-yl)-5-(tetrazol-5-yl) pyridine (HITP), was constructed using a solvothermal reaction. Single-crystal X-ray diffraction analysis revealed that in addition to HITP, the 5,5′-bis-(2H-tetrazol-5-yl)-[3,3′]bipyridinyl (H2BTBP) ligand obtained by the in situ reaction of HITP is also incorporated into the framework, thus generating a mixed-ligand metal–organic framework (MOF). SCNU-Z7 has a 3D porous framework with 1D channels along the c axis based on tetranuclear secondary building blocks and has a new highly (3,4,10)-connected network topology with the symbol (416·620·89)(43)2(44·62). SCNU-Z7 exhibits high stability in organic solvents but instability in water. Gas adsorption studies indicated that SCNU-Z7 can absorb CO2 more than N2. Magnetic studies indicate the existence of dominant antiferromagnetic interactions between Co(II) atoms. Due to porosity, Co(II) ions, nitrogen-rich conjugated aromatic rings, and uncoordinated nitrogen atoms in its framework, SCNU-Z7 can capture iodine in vapor with a capacity of 2.7 g/g. The strong interactions between the framework and the iodine molecules cause the amorphization of the framework, and approximately 60% of the adsorbed iodine molecules can be stably stored in the framework. This study provides a new possible route for obtaining mixed-ligand MOFs and provides a new example for stably capturing iodine in MOFs via amorphization.