pubs.acs.org
Strategic MOF Linker Methylation to Direct Pore Structure and Local Dynamics
The marvelous substrate recognition of enzyme hosts is attributed to induced-fit binding, in which the enzyme host maintains a delicate balance between preorganization and flexibility. For synthetic porous hosts such as MOFs, programmable control over the local and global flexibility modes is thus crucial for the optimization of host–guest interactions. Here we show that methylation adjacent to the pyrene-arene junction of the linker permits the synthesis of a derivative of NU-1000 in which aryl rotation is thermally inaccessible, but small-angle librations remain facile. Mechanochemically promoted Suzuki cross-coupling was able to overcome the twin challenges of poor solubility and steric congestion to access a linker that could not be prepared in solution. The incorporation of methyl groups in the linker controls the local dynamics of the MOF pore and permits a window that interconnects channels in the unsubstituted MOF to evolve into a separate micropore environment. In addition, we show how the different chemical shifts observed for nuclei that extend into distinct MOF pores permit experimental determination of rotational barriers via variable-temperature 13C solid-state NMR.
