A new dynamic framework with direct in situ visualisation of breathing under CO2 gas pressure

Using in situ single-crystal X-ray diffraction analysis (SCD), direct structural evidence has been obtained for breathing behaviour of a new flexible MOF COB1. Desolvation of the as-synthesised material results in deformation of the coordination geometries due to flexibility of the bridging ligands, and the framework is capable of switching from a wide-pore to a narrow-pore form, with substantial reduction in guest-accessible volume. Upon exposure to CO2 gas the activated framework breathes and switches back to the wide-pore phase. This breathing behaviour is supported by gas sorption analysis, pressure-gradient differential scanning calorimetry, powder X-ray diffraction analysis and molecular modelling.