OPEN Repository

Welcome to OPEN - the Repository of Open Scientific Publications, run by the Interdisciplinary Centre for Mathematical and Computational Modelling, University of Warsaw, previously operating as the CeON Repository. The Repository enables Polish researchers from all fields to openly share their articles, books, conference materials, reports, doctoral theses, and other scientific texts.

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Carboxylated Pillar[6]arene Emulates Pillar[5]arene in the Host–Guest Crystal Complexes and Shows Conformational Flexibility in the Solution/Gas Phase
(American Chemical Society, 2022-12-08) Butkiewicz, Helena; Kosiorek, Sandra; Sashuk, Volodymyr; Zimnicka, Magdalena; Danylyuk, Oksana; Instytut Chemii Fizycznej Polskiej Akademii Nauk; Instytut Chemii Organicznej Polskiej Akademii Nauk
Despite the thriving interest in the aqueous complexation properties of carboxylated pillar[6]arene, its solid state supramolecular chemistry has remained a mystery. Here, overcoming challenging crystallogenesis, we report the first crystallographic authentication of carboxylated pillar[6]arene in the form of two host−guest inclusion complexes with methyl viologen and pentamidine. The key to the successful crystallization of carboxylated pillar[6]arene is the mixed ionization state of its 12 carboxylic substituents. The deprotonation of several but not all substituents enables intermolecular hydrogen bonding and, as a result, “gluing” and crystallization of pillar[6]arene complexes with the aid of carboxylic-carboxylate, carboxylic-carboxylic, and amidinium-carboxylate supramolecular synthons. Single crystal X-ray diffraction analysis revealed that upon guest inclusion pillar[6]arene adopts a quasi-pentagonal shape rather than the expected hexagonal shape. The squeezed quasi-pentagonal conformation of the six-membered macrocycle is stabilized by two intramolecular hydrogen bonds between pillar[6]arene substituents. Moreover, the distinctive deviation of the macrocycle from hexagonal shape stays operative in the solution/gas phase as concluded from ion mobility mass spectrometry (IM-MS) studies and theoretical calculations. These results provide the first insight into how to gain control over the conformation of flexible pillar[6]arene with a view of solid state design of more advanced supramolecular host−guest structures.