A flexible copper MOF as a carboxylate-specific crystalline sponge for structure solution using X-ray and electron diffraction

A new metal-organic framework (MOF) comprising copper and 2,3-dihydroxyterephthalate (2,3-dhtp) has been prepared using solvothermal synthesis. The solid (chemical formula of the as-made material): Cu₁₂(dhtp)₄(H₂dhtp)₃(CH₃CO₂)₂ 2DMF·10H₂O is flexible in that its pore size adapts to match the size of guest molecules that are adsorbed. Carboxylate-containing molecules of different sizes (acetate, benzoic acid and ibuprofen) can be accommodated within the pores of the material and are coordinated to a dimeric copper unit. The localisation of the adsorbate guest molecule, the mode of binding and relatively low symmetry of the MOF allows the system to be used as a crystalline sponge. The crystal structure determination of the as-synthesised acetate-bound MOF was accomplished using single-crystal X-ray diffraction using a synchrotron source, while the benzoate- and ibuprofen-bound structures were solved using electron diffraction. A more practical adsorbent can be formulated by growing the MOF on a cotton fabric substrate, and this is shown to adsorb ibuprofen in a similar manner to the powdered MOF.