Environment-friendly, co-catalyst- and solvent-free fixation of CO2 using an ionic zinc(ii)-porphyrin complex immobilized in porous metal-organic frameworks

Herein an ionic Zn(ii)-porphyrin complex, [Zn(ii)NMeTPyP](4+)[I-](4) (Zn(ii)NMeTPyP = 5,10,15,20-tetrakis(1-methylpyridinium-4 '-yl) zinc(ii) porphyrin), was immobilized in a porous metal-organic framework, PCN-224. The resulting [Zn(ii)NMeTPyP](4+)[I-](4)@PCN-224 hybrid was thoroughly characterized by PXRD, UV-vis, FTIR, MP-AES, SEM-EDS and BET analysis. Further, DFT calculations confirmed the incorporation of the [Zn(ii)NMeTPyP](4+)[I-](4) complex in the 1D channels of PCN-224 owing to appropriate matching of the pore size with the size of the complex and stabilization via pi-pi interactions. Interestingly, the [Zn(ii)NMeTPyP](4+)[I-](4)@PCN-224 hybrid showed high affinity for CO2 with a high heat of adsorption (Q(st)) value of 40.5 kJ mol(-1) compared to the pristine MOF, PCN-224, with a Q(st) value of 36.8 kJ mol(-1). Remarkably, the hybrid material acts as an efficient environment-friendly, co-catalyst- and solvent-free heterogeneous catalyst for chemical fixation of CO2 to generate cyclic carbonates with high yield and selectivity due to synergistic cooperation between the complex and the framework.