Coordinatively unsaturated 5-nitroisophthalate based cobalt(ii) coordination polymers: efficient catalytic CO2 fixation and Hantzsch condensation

Abstract

Two 5-nitroisophthalate (NIPA) based cobalt(II) coordination polymers [Co(4-ABPT)(NIPA)(H₂O)₃], SSICG-6 (4-ABPT = 3,5-di(pyridine-4-yl)-4H-1,2,4-triazol-4-amine, SSICG stands for solid-state and inorganic chemistry group) and [Co(4-ABPT)(NIPA)(H₂O)], SSICG-7, have been synthesized using a mixed ligand approach. Strategic utilization of H₂NIPA enables tunability in framework formation and generates coordinated water containing coordination polymers. The –NO₂ group in H₂NIPA is unlikely to bind directly with metal ions but draws solvent molecules near the metal center via H-bonding. The coordinated water molecules in SSICG-6 and 7 are reversible in nature, resulting in unsaturated metal centers that serve as excellent heterogeneous catalysts in CO₂ cycloaddition and tone-pot Hantzsch condensation reactions. The near quantitative conversion of epichlorohydrin into its corresponding carbonate compound was successfully accomplished, employing SSICG-6 as a catalyst under solvent-free conditions. The unique coordination characteristics of SSICG-6 enhance its catalytic efficiency for larger substrates in CO₂ cycloaddition reactions compared to other one-dimensional polymers.