CO₂-Specific Gate Opening Transforms a Dense Cation-Filled Zinc-Aminotriazolato-Oxalate Framework into an Ultramicroporous MOF

CALF-20, a zinc-triazolato-oxalate MOF, [Zn2(tz)2(Ox)]·solvent, is an industrially practiced ultramicroporous MOF sorbent. In CALF-20, some interesting structural transformations occur during its humid CO2 capture. Even though its structure is simple, the design of superior sorbents based on its structure is still not straightforward. Hence, a broader investigation of these Zn-triazolato-oxalate frameworks with a new outlook is necessary. Herein, we report a Zn-aminotriazolato-oxalate MOF (IISERP-MOF35, [(CH3)2NH2]2[Zn5(Atz)4(Ox)4]·2H2O), which has a unique framework that does not resemble the ubiquitous layered-pillared topology prevalent among CALF-20 and related zinc-triazolato-oxalate systems. The IISERP-MOF35’s CO2-specific gate opening at lower partial pressures makes it intriguing. Comparing it to our earlier reported flexible Zn-aminotriazolato-oxalate MOF (IISERP-MOF32), [Zn2(Atz)2(Ox)]·solvent, which had a CALF-20-like layered-pillared topology, reveals valuable structure–property insights. Despite its markedly different structures and compositions, this new dense 3D framework has the same structural feature as that in the layered-pillared IISERP-MOF32, which is responsible for the gate opening. Further comparison with the existing frameworks in this system advocates that the structural motif identified here could help in the futuristic design of creating open frameworks predesigned for guest-assisted flexibility.