Understanding DABCO Nanorotor Dynamics in Isostructural Metal–Organic Frameworks

Flexible framework dynamics present
in the subset of metal–organic
frameworks known as soft porous crystals give rise to interesting
structural properties that are unique to this class of materials.
In this work, we use experiments and molecular simulation to understand
the highly dynamic nanorotor behavior of the 1,4-diazabicyclo[2.2.2]­octane
(DABCO) ligand in the pillared Zn-DMOF and Zn-DMOF-TM (TM = tetramethyl)
structures. While DABCO is known to be displaced in the presence of
water in the parent Zn-DMOF structure, the Zn-DMOF-TM variation is
highly stable even after adsorbing significant amounts of water vapor.
The dynamics of DABCO in the presence of water guest molecules is
therefore also explored in the Zn-DMOF-TM structure via in situ NMR
and IR experiments. This analysis shows that the rotational motion
of the DABCO linkers is dependent on water content, but not a likely
source of water instability because the dynamics are fast and largely
unaffected by the presence of methyl functional groups.