Structural design of porous coordination networks from tetrahedral building units

Abstract

Ligand design is of vital importance in the preparation of metal–organic frameworks (MOFs), and the rigid tetrahedral ligands are especially interesting due to their fully extended nature and diverse symmetric elements. In this work, a synthetically accessible silicon-centered tetrahedral ligand was prepared from inexpensive starting materials and eight MOFs were obtained from different solvothermal reactions. All the MOFs were structurally characterized and are inherently porous with solvent accessible volume up to 73.10%; while at least two of them possess a permanent inner porosity after the removal of any guest molecules in the framework. Among all these MOFs, seven of them possess a new structure, one of them possesses a novel topology, and two of them show properties potentially useful for gas storage applications. In particular, PCN-512 has a H₂ uptake of 1.39 wt% at 77 K and 1.08 bar. This makes it a promising material for industrial gas storage applications because of both its low synthetic cost and its relatively large gas capacity. PCN-515 contains three distinctive rarely-seen secondary building units (SBUs) in the same framework, which makes it an unprecedented 4,4,4,4,4,5,7-connected network.