Exploring guest-induced breathing behaviour in a copper-based metal-organic framework using neutron diffraction

We have synthesised a new polycrystalline microporous MOF with the formula [Cu2(μ-ace)2(μ3-imp)2]n (where ace stands for acetate and imp for imidazo[4,5-b]pyridine), named as EHU-11-α. Upon adsorption of water or methanol vapour, PXRD data indicates a reversible transformation into a new crystal structure, EHU-11-β. Although this transformation involves the breaking and reformation of several bonds, both the space group and the coordination framework topology remain unchanged. In contrast, solvents without hydrogen-bonding groups do not induce any structural changes. This contrasting behaviour appears to be linked to a structural "breathing" mechanism driven by the unique hydrogen-bonding network formed by the adsorbed molecules within the host structure. Therefore, the main goal of this proposal is to obtain neutron diffraction data to determine the positions of water and methanol within the structure to better understand the hydrogen-bonding driven transformation mechanism.