MS32-P13 Playing hopscotch with pyridine@p-tert-butylcalixarene crystal structuresCalix[n]arenes have applications in the areas of host-guest chemistry, ion and molecular recognition, enzyme mimics, catalysis, interaction with biomolecules, ion extraction, and selective ion transport. However, crystallisation of these systems is still challenging owing to their conformational flexibility. Therefore, crystallisation conditions (supersaturation, temperature, additives) were screened to obtain crystal structures with varying architecture such as channels and spherical voids with different conformations of the host. The molecular recognition and self-assembly between host p-tert-butylcalixarene and guest pyridine led to kinetic trapping and crystallisation of the intermediate complexes, which were characterised by X-ray diffraction. The crystalline kinetic complex underwent slow spontaneous dissolution and subsequently recrystallises as thermodynamic inclusion complexes. Single-crystal X-ray diffraction revealed these first formed crystals to be the 15:1, 6:1 association complexes. These two crystal structures can transform into four different crystal structures depending on crystallisation conditions, forming 1:1, 1:1, 3:1, and 6:1 pyridine and p-tert-butylcalixarene complexes. The crystal structure of the host-guest system can be tuned by the supersaturation changes and hydrogen-bonding properties of used additives to form crystal structures with designed architecture.
 Vicens, J. & Harrowfield, J. (2007). Calixarenes in the Nanoworld. Springer.Keywords: host-guest, crystallisation, complexes