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

Controlling aspects of the mu(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)] . 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.

Automated summary

Controlling the mu(2)-X- bridging anion in Ga-MIL-53 [GaX(bdc)] (X-=(OH)(-) or F-, bdc=1, 4-benzenedicarboxylate) can direct the temperature at which breathing transitions of this framework occur. Substituting (OH)(-) with F- stabilizes the large pore (lp) form and decreases the onset temperature of lp to narrow pore (np) transition. In situ diffraction studies provide a plausible crystal structure and reveal a lower temperature pathway for the transition.