For the C2 hydrocarbons a lower TPV is observed indicating partial contraction of the sample during adsorption. Following the trends for the rigidification of flexible MOFs a reasonable hypothesis is that larger crystals collapse completely while smaller crystals resist the contractive adsorption stress and maintain the pore volume of the sample. For ethane the TPV is decreased to 2.52 cm 3 •g -1 and then further falls by 20 % to 2.01 cm 3 •g -1 after a third cycle indicating a transition into a less porous structure. For ethylene the TPV is further decreased to 2.30 cm 3 •g -1 and after three cycles decreases by 44 % to 1.28 cm 3 •g -1 . This result is in agreement with other findings showing a higher isosteric heat of adsorption with increasing carbon chain length due to stronger Van-der-Waals interactions and additional π-π interactions when double bonds are introduced but the chain length remains the same. This lower TPV also correlates with the mean crystal size decreasing from 8.3 µm to 7.8 µm as well as the visible changes in the crystals morphology (Figure ).