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.