Hollow Microcrystals of Copper Hexafluoroacetylacetonate-Pyridine Derivative Adducts via Supercritical CO₂ Recrystallization

© 2016 American Chemical Society. An innovative crystallization process, based on the use of the ecofriendly supercritical carbon dioxide (scCO2) solvent, is presented for the production of coordination compound macrocrystals of general formula [Cu(hfacac)2(dPy)2], with intriguing prismatic hollow structures and single polymorphic forms. In contrast, conventional solvents yielded compact microstructures. The studied pyridine derivatives (dPy) were 4-phenylpyridine, PhPy; 4-benzylylpyridine, BzPy; and 4-acetylpyridine, AcPy. In the specific case of the [Cu(hfacac)2(AcPy)2] adduct, the use of scCO2 as a solvent allowed obtaining a pure polymorph, while the conventional solvent trials yielded a mixture of two polymorphs. Four new crystalline structures have been resolved from single crystal X-ray diffraction. All the structures consist of mononuclear complexes connected through intermolecular interactions, including H⋯;H, H⋯;O, F⋯;F, C-F⋯;Caromatic, and/or C-F⋯;π interactions, generating bi-dimensional networks that determine their crystallization mode in scCO2.