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 triphenylene dicarboxylate (TPDC) and tetramethyl-triphenylene dicarboxylate (TTDC) linkers, respectively, were doped with an H-shaped tetracarboxylate linker that contains a [2]rotaxane molecular shuttle. The new MOFs, UWDM-8 and UWDM-9, contain a [2]rotaxane crossbar spanning the tetrahedral cavities of the fcu topology while the octahedral cavities remain empty. C-13 solid-state NMR (SSNMR) spectra and solution H-1 NMR spectra verified that the [2]rotaxanes were included as designed. Variable-temperature (VT) cross polarization (CP) magic-angle spinning (MAS) C-13 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 (TPDCvs.TTDC) affects 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.

Automated summary

Two Zr(IV) metal-organic frameworks (MOFs) were studied, incorporating a new H-shaped tetracarboxylate linker with [2]rotaxane molecular shuttles. Solid-state NMR and solution NMR spectra confirmed the successful incorporation of the [2]rotaxanes, while the study found that the structure of the linker affects the shuttling rate of the macrocyclic ring.