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 (MOF) PCN-222. The thermal expansion increases drastically in magnitude following more aggressive heating, which is rationalized by enhanced flexibility upon guest removal. Moreover, the thermal response strongly depends on the temperature: the volumetric expansivity nearly quadruples and the expansion along c changes sign upon cooling. Our results highlight the large flexibility of MOFs and the role of guest species.