Coordination Flexibility Aided CO2‐specific Gating in an Iron Isonicotinate MOF

Abstract Coordination flexibility assisted porosity has been introduced into an Iron‐isonicotinate metal‐organic framework (MOF), (Fe(4‐PyC) 2 ⋅ (OH). The framework showed CO 2 ‐specific gate opening behavior, which gets tuned as a function of temperature and pressure. The MOF′s physisorptive porosity towards CO 2 , CH 4 , and N 2 was investigated; it adsorbed only CO 2 via a gate opening phenomenon. The isonicotinate, representing a borderline soft base, is bound to the hard Fe 3+ centre through monodentate carboxylate and pyridyl nitrogen. This moderately weak binding enables isonicotinate to spin like a spindle under the CO 2 pressure opening the gate for a sharp increase in CO 2 uptake at 333 mmHg (At 298 K, the CO 2 uptake increases from 0.70 to 1.57 mmol/g). We investigated the MOF′s potential for CO 2 /N 2 and CO 2 /CH 4 gas separation aided by this gating. IAST model reveals that the CO 2 /N 2 selectivity jumps from 325 to 3131 when the gate opens, while the CO 2 /CH 4 selectivity increases three times. Interestingly, this Fe‐isonicotinate MOF did not follow the trend set by our earlier reported Hard‐Soft Gate Control (established for isostructural M 2+ ‐isonicotinate MOFs (M=Mg, Mn)). However, we account for this discrepancy using the different oxidation state of metals confirmed by X‐ray photoelectron spectroscopy and magnetism.