CO<sub>2</sub>‑Specific\nGate Opening Transforms\na Dense Cation-Filled Zinc-Aminotriazolato-Oxalate Framework into\nan Ultramicroporous MOF

CALF-20, a zinc-triazolato-oxalate MOF, [Zn<sub>2</sub>(tz)<sub>2</sub>(Ox)]·solvent, is an industrially practiced\nultramicroporous\nMOF sorbent. In CALF-20, some interesting structural transformations\noccur during its humid CO<sub>2</sub> capture. Even though its structure\nis simple, the design of superior sorbents based on its structure\nis still not straightforward. Hence, a broader investigation of these\nZn-triazolato-oxalate frameworks with a new outlook is necessary.\nHerein, we report a Zn-aminotriazolato-oxalate MOF (<b>IISERP-MOF35</b>, [(CH<sub>3</sub>)<sub>2</sub>NH<sub>2</sub>]<sub>2</sub>[Zn<sub>5</sub>(Atz)<sub>4</sub>(Ox)<sub>4</sub>]·2H<sub>2</sub>O),\nwhich has a unique framework that does not resemble the ubiquitous\nlayered-pillared topology prevalent among CALF-20 and related zinc-triazolato-oxalate\nsystems. The <b>IISERP-MOF35</b>’s CO<sub>2</sub>-specific\ngate opening at lower partial pressures makes it intriguing. Comparing\nit to our earlier reported flexible Zn-aminotriazolato-oxalate MOF\n(IISERP-MOF32), [Zn<sub>2</sub>(Atz)<sub>2</sub>(Ox)]·solvent,\nwhich had a CALF-20-like layered-pillared topology, reveals valuable\nstructure–property insights. Despite its markedly different\nstructures and compositions, this new dense 3D framework has the same\nstructural feature as that in the layered-pillared IISERP-MOF32, which\nis responsible for the gate opening. Further comparison with the existing\nframeworks in this system advocates that the structural motif identified\nhere could help in the futuristic design of creating open frameworks\npredesigned for guest-assisted flexibility.