We report the synthesis, structural characterization, and porous properties of two isomeric supramolecular complexes of ([Cd(NH
2?bdc)(bphz)
0.5]?DMF?H
2O}
n (NH
2?bdc=2‐aminobenzenedicarboxylic acid, bphz=1,2‐bis(4‐pyridylmethylene)hydrazine) composed of a mixed‐ligand system. The first isomer, with a paddle‐wheel‐type Cd
2(COO)
4 secondary building unit (SBU), is flexible in nature, whereas the other isomer has a rigid framework based on a μ‐oxo‐bridged Cd
2(μ‐OCO)
2 SBU. Both frameworks are two‐fold interpenetrated and the pore surface is decorated with pendant ?NH
2 and ?N?N? functional groups. Both the frameworks are nonporous to N
2, revealed by the type II adsorption profiles. However, at 195 K, the first isomer shows an unusual double‐step hysteretic CO
2 adsorption profile, whereas the second isomer shows a typical type I CO
2 profile. Moreover, at 195 K, both frameworks show excellent selectivity for CO
2 among other gases (N
2, O
2, H
2, and Ar), which has been correlated to the specific interaction of CO
2 with the ?NH
2 and ?N?N? functionalized pore surface. DFT calculations for the oxo‐bridged isomer unveiled that the ?NH
2 group is the primary binding site for CO
2. The high heat of CO
2 adsorption (Δ
Hads=37.7 kJ mol
?1) in the oxo‐bridged isomer is realized by NH
2???CO
2/aromatic π???CO
2 and cooperative CO
2???CO
2 interactions. Further, postsynthetic modification of the ?NH
2 group into ?NHCOCH
3 in the second isomer leads to a reduced CO
2 uptake with lower binding energy, which establishes the critical role of the ?NH
2 group for CO
2 capture. The presence of basic ?NH
2 sites in the oxo‐bridged isomer was further exploited for efficient catalytic activity in a Knoevenagel condensation reaction.
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