Two Co(II)-coordination polymers based on dicarboxylic acid and flexible bis(imidazole) linker for chemical fixation of CO2

• In this study, two Co(II)-coordination polymers have been synthesised and identified. The compounds were characterized by IR spectroscopy , elemental analysis , single and powder X-ray diffractions and thermal analysis . • These complexes were investigated as catalysts in chemical formation of CO 2 into cyclic carbonates. • All the complexes showed catalytic activity as catalyst for CO 2 fixation into cyclic carbonates. Two Co(II)-coordination polymers, [Co 3 (µ-tbipH) 2 (µ 4 -tbip) 2 (pbisoix)] n ( 1 ) and {[Co 3 (µ-tbipH) 2 (µ 4 -tbip) 2 (µ-pbisoix)]·2H 2 O} n ( 2 ) (tbip and tbipH: deprotonated and mono deprotonated 5-tert-butyl isophthalate, pbisoix: 1,4-bis(2-isopropylimidazol-1ylmethyl)benzene), were hydrothermally prepared using different metal salts and characterized by various techniques. The coordination polymers (CPs) exhibited structural diversity depending on the rotation of imidazole arms of the pbisoix ligands. X-ray results revealed that Co 2+ ions were coordinated by tbip and tbipH to generate [Co 3 (COO) 6 ] units in both CPs. These units linked by tbip ligand to create a 1D structure in CP- 1 and a 2D layer in CP- 2. In 2 , the pbisoix linkers acted as a bridging ligand, connecting the 2D layers and resulting in a 3D structure, whereas the pbisoix linkers displayed monodentate coordination in 1 . The catalytic activities of the CPs were investigated for the cycloaddition of CO 2 with epichlorohydrin (ECH) to form cyclic carbonates. The CPs showed high ECH conversion, with yields of 90.3 % and 60.0 %, respectively, into the cyclic carbonate (100 °C, 1.6 MPa, 2 h). The difference in the catalytic conversion yields between two CPs could be attributed to the presence of uncoordinated N atoms in the pbisoix linkers, which acted as Lewis basic sites, facilitating the efficient chemical fixation of CO 2 to form cyclic carbonates.