Abstract:
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″-striazine-1,3,5-triyl-tri-p-aminobenzoic acid, and DABCO = 1,4-
diazabicyclo[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 CO2 with 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 1/2 ideal candidate materials to carry out co-catalyst-free
cycloaddition of CO2 to epoxides. Consequently, MOFs 1/2 act as
excellent recyclable catalysts for cycloaddition of CO2 to epoxides for high-yield synthesis of cyclic carbonates under co-catalystfree mild conditions of 1 bar of CO2. 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 CO2 has been demonstrated.
