Elucidating the role of non-covalent interactions in unexpectedly high and selective CO2 uptake and catalytic conversion of porphyrin-based ionic organic polymers

Abstract

Here, we present viologen-porphyrin based ionic covalent organic polymers (H2-ICOP and Zn-ICOP) with multiple CO2-philic sites. The specific surface areas of H2-ICOP and Zn-ICOP were found to be 9 m(2) g(-1) and 20 m(2) g(-1), respectively. CO2 uptake analyses reveal that H2-ICOP exhibits very high CO2 capture uptake (62.9 mg g(-1)), which is one of the highest values among previously reported ICOPs. The results indicate very efficient non-covalent interactions between H2-ICOP and CO2. The possible non-covalent interactions of hydrogen (O-CO2...H-N), tetrel (C-CO2...N, C-CO2...Cl-), pnicogen (O-CO2...N+), and spodium bonds (O-CO2...Zn) between CO2 and H2-ICOP and Zn-ICOP are investigated via symmetry adapted perturbation theory (SAPT) analysis and electrostatic potential maps (MEP). The strength of non-covalent interactions in H2-ICOP and Zn-ICOP is decreasing in the following order Delta E-C...(N) > Delta E-C...(-)(Cl) > Delta E-O...(+)(N) and Delta E-Zn...(O) > Delta E-C...(-)(Cl) > Delta E-C...(N) > Delta E-O...(+)(N), respectively. The major CO2 uptake contribution comes from C-CO2...N tetrel bonding (-22.02 kJ mol(-1)) interactions for H2-ICOP, whereas O-CO2...Zn spodium bonding (-21.065 kJ mol(-1)) interactions for Zn-ICOP. H2-ICOP has more CO2-philic moieties with powerful non-covalent interactions compared to Zn-ICOP, which is in good agreement with the experimental results. Furthermore, the CO2 catalytic conversion performances of Zn-ICOP and H2-ICOP gave good yields of 83% and 54%, respectively. Surprisingly, Zn-ICOP, despite having significantly lower CO2 uptake capacity, displayed better catalytic activity than H2-ICOP, owing to a higher number of counter anions (Cl-) on its surface, which shows the crucial role of the counter anion (Cl-) in the mechanism of this catalytic reaction.