Guest-responsive thermal expansion in the Zr-porphyrin metal-organic framework PCN-222

We use powder X-ray diffraction under variable temperature to study the thermal expansion of the metal- organic framework PCN-222 with varying amounts of guest content. The thermal expansion increases drastically in magnitude as the guest occupancy is reduced. Upon cooling, the thermal expansion along c changes sign from negative to positive and the volumetric expansivity nearly quadruples in magnitude. This seemingly results from a reorganisation of the guest molecules and so our results highlight the intriguing interplay between framework dynamics and guest occupancy in mesoporous metal-organic frameworks.