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

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 [Co-6(mu(3)-OH)(6)]-based PL-MOFs (Co-6-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 [Co-6(mu(3)-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 [Co-6(mu(3)-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 m(2) 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 Co-6-MOF-3 without OMSs.

Automated summary

Pillar-layered metal-organic frameworks (PL-MOFs) have excellent structural tunability and framework stability, making them promising candidates for sorbents and catalysts. However, the fully occupied pillar ligands limit the involvement of open metal sites (OMSs) in CO2 adsorption and fixation. In this study, a strategy based on steric-hindrance effect on pillar linker was proposed to create OMSs on the metal cluster nodes of a 12-connected [Co-6(mu(3)-OH)(6)]-based PL-MOF. The newly synthesized PL-MOF, DZU-6, with accessible open Co(ii) sites showed improved CO2 adsorption and catalytic conversion compared to the isostructural Co-6-MOF-3 without OMSs.