Constructing [Co6(μ3-OH)6]-based pillar-layered MOF with open metal sites via steric-hindrance effect on ligand for CO2 adsorption and fixation

Abstract

With excellent structural tunability and well framework stability, pillar-layered metal-organic frameworks (PL-MOFs) are promising candidates as sorbents and catalysts. Yet, the open metal sites (OMSs) in PL-MOFs are usually fully occupied by the pillar ligands, mostly limiting their involvement in CO2 adsorption and fixation. Herein, in consideration of the 12-connected [Co6(μ3-OH)6]-based PL-MOFs (Co6-MOF-3), a strategy based on steric-hindrance effect on pillar linker is proposed to create OMSs on their metal cluster nodes. The 4,4′-(9,10-anthracenediyl)bis-Pyridine (ABPY) that possessed anthracene groups was selected as the pillar linker, and a new [Co6(μ3-OH)6]-based PL-MOF (DZU-6) with accessible open Co(ii) sites was successfully synthesized. Single crystal structure of DZU-6 analysis reveals that ABPY ligands which were firstly linked to the metal clusters prevented the other ABPY ligands from coordinating with the nodes due to the steric-hindrance effect on ligands, resulting that four sites on [Co6(μ3-OH)6] were occupied by the terminal solvent molecules. The coordinated solvent molecules in DZU-6 could be removed easily, meanwhile the porosity was preserved (BET surface 2566 m2 g−1). Importantly, CO2 adsorption and catalytic cycloaddition conversion of DZU-6 were performed that the CO2 uptake improved 40% and the catalytic conversion yield increased over 50% compared with isostructural Co6-MOF-3 without OMSs.