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

Controlling aspects of the μ2-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)0.8F0.2(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)] ⋅ H2O phases and shown that increasing the heating rate to a flash heating regime can enable the int-[GaX(bdc)] ⋅ H2O to lp-[GaX(bdc)] transition to occur at a lower temperature than np-[GaX(bdc)] via an unreported pathway.