Environmentally Friendly, Co-catalyst-Free Chemical Fixation of CO2at Mild Conditions Using Dual-Walled Nitrogen-Rich Three-Dimensional Porous Metal–Organic Frameworks

Highly porous, polyhedral metal–organic frameworks (MOFs) of Co(II)/Ni(II), {[M6(TATAB)4(DABCO)3(H2O)3]·12DMF·9H2O}n(where M = Co(II) (1)/Ni(II) (2), H3TATAB = 4,4′,4″-s-triazine-1,3,5-triyl-tri-p-aminobenzoic acid, and DABCO = 1,4-diazabicyclo[2.2.2]octane) have been synthesized solvothermally. Both MOFs 1and 2show 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 -NH- groups. Interestingly, MOF 1shows selective adsorption of CO2with high heat of adsorption (Qst) 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 1/2ideal candidate materials to carry out co-catalyst-free cycloaddition of CO2to epoxides. Consequently, MOFs 1/2act as excellent recyclable catalysts for cycloaddition of CO2to epoxides for high-yield synthesis of cyclic carbonates under co-catalyst-free mild conditions of 1 bar of CO2. Further, MOF 1was 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 CO2has been demonstrated.