Chemical conversion of CO2 into cyclic carbonates by two Metal–Organic frameworks

Abstract

Two metal–organic frameworks (MOFs), DDCu and DDMn have been synthesized from a tetracarboxylate ligand by solvothermal method. DDCu contained paddlewheel- [Cu2(COO)4] clusters with axial sites occupied by water molecules and comprised of two types of cages: smaller spherical cages of diameter 9.3 Å and larger ellipsoidal cages of dimensions of 12.4 × 17.7 Å2. While DDMn having bimetallic Mn2(COO)4 clusters with 1D rhombus channels of window size 10.16 × 8.97 Å2. Both the MOFs have open framework structure with solvent accessible void volume 66.5 % and 64.1 % based on the PLATON calculations. The MOFs have been characterized by a series of methods like Single crystal XRD, powder XRD, FT-IR, TGA and N2 adsorption study. Brunauer−Emmett−Teller (BET) surface area of the activated MOFs were 360 and 290 m2/g, respectively. The loosely bound water molecules could be removed to produce unsaturated metal coordination sites that rendered exciting heterogeneous catalytic properties at the metal center of DDCu and DDMn in the fixation of CO2 through the cycloaddition of CO2 with various epoxide. Under ambient conditions (25 °C and 1 atm. CO2 pressure), both the catalyst showed appreciable yields (96 and 91 %) and selectivity (>99 %) for cyclic carbonate formations. Both the catalysts showed very good recycling properties (at least five times).