Breathing Behaviour Modification of Gallium MIL‐53 Metal–Organic Frameworks Induced by the Bridging Framework Inorganic Anion

Abstract Controlling aspects of the μ 2 ‐X − bridging anion in the metal–organic framework Ga‐MIL‐53 [GaX(bdc)] (X − =(OH) − or F − , bdc=1, 4‐benzenedicarboxylate) is shown to direct the temperature at which thermally induced breathing transitions of this framework occur. In situ single crystal X‐ray diffraction studies reveal that substituting 20 % of (OH) − in [Ga(OH)(bdc)] ( 1 ) for F − to produce [Ga(OH) 0.8 F 0.2 (bdc)] ( 2 ) stabilises the large pore (lp) form relative to the narrow pore (np) form, causing a well‐defined decrease in the onset of the lp to np transition at higher temperatures, and the adsorption/desorption of nitrogen at lower temperatures through np to lp to intermediate (int) pore transitions. These in situ diffraction studies have also yielded a more plausible crystal structure of the int‐[GaX(bdc)] ⋅ H 2 O phases and shown that increasing the heating rate to a flash heating regime can enable the int‐[GaX(bdc)] ⋅ H 2 O to lp‐[GaX(bdc)] transition to occur at a lower temperature than np‐[GaX(bdc)] via an unreported pathway.