Highly porous, polyhedral metal−organic frameworks (MOFs) of Co(II)/Ni(II), {[M 6 (TATAB) 4 (DABCO) 3 (H 2 O) 3 ]•12DMF• 9H 2 O} n (where M = Co(II) (1)/Ni(II) ( 2), H 3 TATAB = 4,4′,4″-striazine-1,3,5-triyl-tri-p-aminobenzoic acid, and DABCO = 1,4diazabicyclo[2.2.2]octane) have been synthesized solvothermally. Both MOFs 1 and 2 show a 2-fold interpenetrated 3D framework structure composed of dual-walled cages of dimension ∼ 30 Å functionalized with a high density of Lewis acidic Co(II)/Ni(II) metal sites and basic -NHgroups. Interestingly, MOF 1 shows selective adsorption of CO 2 with high heat of adsorption (Q st ) value of 39.7 kJ/mol that is further supported by theoretical studies with computed binding energy (BE) of 41.17 kJ/mol. The presence of the high density of both Lewis acidic and basic sites make MOFs 1/2 ideal candidate materials to carry out co-catalyst-free cycloaddition of CO 2 to epoxides. Consequently, MOFs 1/2 act as excellent recyclable catalysts for cycloaddition of CO 2 to epoxides for high-yield synthesis of cyclic carbonates under co-catalystfree mild conditions of 1 bar of CO 2 . Further, MOF 1 was recycled for five successive cycles without substantial loss in catalytic activity. Herein, rational design of rare examples of 3D polyhedral MOFs composed of Lewis acidic and basic sites exhibiting efficient co-catalyst-free conversion of CO 2 has been demonstrated.
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A bifunctional, microporous Zn metal-organic framework, [Zn (NH BDC) (dpNDI)] (MOF1) (where, NH BDC=2-aminoterephthalic acid, dpNDI=N,N'-di(4-pyridyl)-1,4,5,8-naphthalenediimide) has been synthesized solvothermally. MOF1 shows an interesting two-fold interpenetrated, 3D pillar-layered framework structure composed of two types of 1D channels with dimensions of approximately 2.99×3.58 Å and 4.58×5.38 Å decorated with pendent -NH groups. Owing to the presence of a basic functionalized pore surface, MOF1 exhibits selective adsorption of CO with high value of heat of adsorption (Q =46.5 kJ mol ) which is further supported by theoretically calculated binding energy of 48.4 kJ mol . Interestingly, the value of Q observed for MOF1 is about 10 kJ mol higher than that of analogues MOF with the benzene-1,4-dicarboxylic acid (BDC) ligand, which establishes the critical role of the -NH group for CO capture. Moreover, MOF1 exhibits highly selective and sensitive sensing of the nitroaromatic compound (NAC), 2,4,6-trinitrophenol (TNP) over other competing NACs through a luminescence quenching mechanism. The observed selectivity for TNP over other nitrophenols has been correlated to stronger hydrogen bonding interaction of TNP with the basic -NH group of MOF1, which is revealed from DFT calculations. To the best of our knowledge, MOF1 is the first example of an interpenetrated Zn -MOF exhibiting selective adsorption of CO as well as efficient aqueous-phase sensing of TNP; investigated through combined experimental and theoretical studies.
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