Temperature-, molar ratio- and counterion-effects on the crystal growth of bipyridinium-bis(alkylcarboxylic acid)–crown ether pseudorotaxanes

Abstract

Five new dicarboxylic acid-functionalized pseudorotaxanes, comprised of a bis(1,5-naphtho)-38-crown-10 ring-component and a N,N′-di(n-carboxyalkyl)-4,4′-bipyridinium dihexafluorophosphate (n = 4 or 5, alkyl = butyl or pentyl) rod-component, have been synthesized and characterized by UV-Vis and ¹H-NMR spectroscopic, ESI-MS and/or X-ray crystallographic methods. Depending on the temperature of crystallization and the molar ratio between the N,N′-di(4-carboxybutyl)-4,4′-bipyridinium rod and the crown ether, three different polymorphs were obtained. In the case of the N,N′-di(5-carboxypentyl)-4,4′-bipyridinium rod, two different pseudorotaxane-structures were obtained at different temperatures and in the presence of one or two different counterions. The latter one is an unprecedented example of a pseudorotaxane in which the bipyridinium rod is not sandwiched in-between the crown ether ring’s two naphthalene units, as expected, but forms intermolecular π–π interactions with neighboring pseudorotaxanes.