Nanoporous organic layered crystals of double-headed bis(trifluorolactate)s. Hydrogen-bonded systematic crystal structures controlled by the symmetries of molecular components

Abstract

Systematic crystal engineering using the one-dimensional hydrogen bonding motif of chiral trifluorolactates is described. A series of double-headed (S,S)- or (R,S)-bis(trifluorolactate)s with polymethylene chains, CF₃CH(OH)CO₂(CH₂)_nOCOCH(OH)CF₃ (n = 4–10), formed isostructural layered crystals of undulated supramolecular sheets with fluorinated one-dimensional channel structures. Guest inclusion of some of the nanoporous crystals was observed by X-ray, ¹H NMR, and TG analyses. The crystal structure determination showed a structural alternation connected to the chain length (even–odd effect) and the relative stereochemistry of the two chiral centres. The periodic structural alternation could be explained by the symmetry of the two types of molecular component. That is, the crystal structures are systematically controlled by the symmetries of the molecular components, leading to a rational adjustment of the pore size with varying length of the polymethylene chain.