Exploring the Dynamics of Zr-Based Metal-organic Frameworks Containing Mechanically Interlocked Molecular Shuttles
Zr(IV) metal-organic frameworks (MOFs) UiO-68 and PCN-57, containing linkers triphenylene dicarboxylate (TPDC) and tetramethyl-triphenylene dicarboxylate (TTDC), respectively, were doped with an H shaped, tetracarboxylate linker that contains a rotaxane molecular shuttle. The new MOFs, UWDM-8 and UWDM-9, contain a rotaxane crossbar spanning the tetrahedral cavities of the fcu topology while the octahedral cavities remain empty. 13C solid-state NMR (SSNMR) spectra and solution 1H NMR spectra verified that the rotaxanes were included as designed. Variable-temperature (VT) cross polarization (CP) magic-angle spinning (MAS) 13C SSNMR was used to explore the translational motion of the macrocyclic ring in both MOFs. The SSNMR results clearly show that the structure of the linker (TPDC vs. TTDC) effects the shuttling rate of the macrocyclic ring, although questions remain as to how rotation of the central phenylene unit of the strut might also affect the motion of the macrocycle.
- This article is part of the themed collection: Cooperative phenomena in framework materials