Chemical Fixation of CO₂ Under Solvent and Co-Catalyst-free Conditions Using a Highly Porous Two-fold Interpenetrated Cu(II)-Metal–Organic Framework

Abstract

A highly porous metal–organic framework (MOF) based on the Cu(II) ion, {[Cu6(TATAB)4(DABCO)3(H2O)3]·24DMF}n (Cu(II)-MOF) (where H3TATAB = 4,4′,4″-s-triazine-1,3,5-triyl-tri-p-aminobenzoic acid and DABCO = 1,4-diazabicyclo[2.2.2]octane) was prepared and structurally characterized. The Cu(II)-MOF features a 2-fold interpenetrated three-dimensional, dual-walled cage with a dimension of ∼29.8 Å composed of a high density of Lewis acidic (LA) Cu(II) ions and basic -NH sites. The MOF possesses a high surface area of 2043.7 m2/g and exhibits selective adsorption of CO2 with a high heat of interaction (Qst) energy of 41.9 kJ mol–1. Owing to the synergetic participation of LA and basic sites, the Cu(II)-MOF acts as an efficient heterogeneous catalyst for co-catalyst- and solvent-free chemical fixation of CO2 into cyclic carbonates. In-depth theoretical calculations were carried out using density functional theory (DFT) to elucidate the detailed mechanistic path involved in the successful co-catalyst-free conversion of CO2 into cyclic carbonates by the Cu(II)-MOF, and the results were found to be in clear agreement with the experimental findings. Further, Cu(II)-MOF exhibits recyclable catalytic activity and can be reused for several cycles without significant loss of catalytic activity. Herein, we report the rational design of a highly porous Cu(II)-MOF for the co-catalyst- and solvent-free fixation of CO2 into cyclic carbonates under environmentally friendly conditions.