Flexible and Rigid Amine‐Functionalized Microporous Frameworks Based on Different Secondary Building Units: Supramolecular Isomerism, Selective CO₂ Capture, and Catalysis

Abstract

We report the synthesis, structural characterization, and porous properties of two isomeric supramolecular complexes of ([Cd(NH2 bdc)(bphz)0.5 ]⋅DMF⋅H2 O}n (NH2 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 Cd2 (COO)4 secondary building unit (SBU), is flexible in nature, whereas the other isomer has a rigid framework based on a μ-oxo-bridged Cd2 (μ-OCO)2 SBU. Both frameworks are two-fold interpenetrated and the pore surface is decorated with pendant -NH2 and NN functional groups. Both the frameworks are nonporous to N2 , revealed by the type II adsorption profiles. However, at 195 K, the first isomer shows an unusual double-step hysteretic CO2 adsorption profile, whereas the second isomer shows a typical type I CO2 profile. Moreover, at 195 K, both frameworks show excellent selectivity for CO2 among other gases (N2 , O2 , H2 , and Ar), which has been correlated to the specific interaction of CO2 with the -NH2 and NN functionalized pore surface. DFT calculations for the oxo-bridged isomer unveiled that the -NH2 group is the primary binding site for CO2 . The high heat of CO2 adsorption (ΔHads =37.7 kJ mol(-1) ) in the oxo-bridged isomer is realized by NH2 ⋅⋅⋅CO2 /aromatic π⋅⋅⋅CO2 and cooperative CO2 ⋅⋅⋅CO2 interactions. Further, postsynthetic modification of the -NH2 group into -NHCOCH3 in the second isomer leads to a reduced CO2 uptake with lower binding energy, which establishes the critical role of the -NH2 group for CO2 capture. The presence of basic -NH2 sites in the oxo-bridged isomer was further exploited for efficient catalytic activity in a Knoevenagel condensation reaction.

Effect of the structural constituents of metal organic frameworks on carbon dioxide capture

“…A competitive CO 2 adsorption was also observed for this material in the low pressure range (0 to 0.3 bar) which is advantageous for postcombustion capture [167]. again azobenzene molecule was used to make one of the ligands [174]. In this case, the organic linkers include =N-N= and -NH 2 functional groups and results in two isomeric two-fold interpenetrated frameworks with pore sizes of 4x4 Å for one and 3x5 Å for M A N U S C R I P T…”

“…The heat of adsorption values for these MOFs were estimated to be not higher than 40 kJ/mol indicating moderate interactions with adsorbate gas molecules of CO 2 . A few different types of interactions were detected by DFT calculations in isomer 2: one as expected between -NH 2 and CO 2 , another due to the π interactions or aromatic ring of the ligand with CO 2 , and hydrogen bonding between oxygens of CO 2 and hydrogens of aromatic rings [174].…”

Crystal Structures, Gas Adsorption, and Electrochemical Properties of Electroactive Coordination Polymers Based on the Tetrathiafulvalene-Tetrabenzoate Ligand

“…arises from sliding of the 3D pillared layer-type nets, which opens up additional void space for CO 2 molecules to diffuse in. 66 It is most likely that this structural rearrangement causes a barrier for gas to diffuse out of the pores. 67 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 18 Figure 10.…”

Solvent-Dependent Structural Variation of Zinc(II) Coordination Polymers and Their Catalytic Activity in the Knoevenagel Condensation Reaction

“…[63][64][65][66][67][68][69][70][71][72][73][74][75][76] This condensation is generally catalyzed by bases or Lewis acids and widely studied in homogeneous systems. 90,91 Only a few studies have employed heterogeneous catalysts including metal organic frameworks.…”

“…49 Recently, we have reported various coordination polymers which are catalytically active for the oxidation of alkanes, alcohols or olefins. [50][51][52][53][54][55][56][57][58][59][60][61] Acidic and basic polymers can exhibit high catalytic activity in condensation reactions like the Pechmann, 62 Knoevenagel, [63][64][65][66][67][68][69][70][71][72][73][74][75][76] and Prins reactions. 77 Coordination polymers can work as catalysts through two different components, viz.…”