Microporous mixed-metal mixed-ligand metal organic framework for selective CO 2 capture

A microporous mixed-ligand-based metal–organic framework has been synthesized using two different dicarboxylic acid-based ligands (4,4′-biphenyldicarboxylate (BPDC) and imino diacetate (IMDA)) and two different metal ions (Ce 3+ and Na + ), namely Ce 3 Na 3 (BPDC) 3 (IMDA) 3 ·(DMF) 2 (H 2 O) 9 . The framework built from Ce–Na–carboxylate layers and BPDC pillars consists of 2D slit-shaped pores occupied by extra-framework Na + ions. The desolvated framework is permanently porous with a BET surface area of ∼771 m 2 g −1 and displays moderate CO 2 uptake of 2.0 mmol g −1 with a CO 2 /N 2 selectivity ( S ) of 68 at room temperature and 1 bar. A modest heat of adsorption (23 kJ mol −1 ) and smooth diffusion kinetics are observed, as reflected in the facile CO 2 cycling. Using GCMC methods, the CO 2 adsorption isotherm at 298 K was simulated, which matches the experimental isotherm well. The CO 2 positions observed from the simulations showed that Na + ions in the channels serve as favorable adsorption sites for the oxygen atoms in CO 2 pointing toward the Na + ions (OCO⋯Na + = 3.34–5.87 Å), while some CO 2 molecules sit flat on the phenyl rings of the BPDC at a CO 2 ⋯centroid distance of 3.6–3.7 Å.