Unprecedented role of water in self-assembly of potential molecular tweezers

Abstract

The X-ray structures of three potential molecular tweezers, C₂₀H₂₄N₂O₅ (1), C₂₀H₂₀N₆O₁₃ (2) and C₂₈H₃₂N₂O₁₃ (3), differing only by the substituents on the terminal aromatic moieties, display three as yet unreported arrays. Hydrogen bonding with co-crystallized water molecules as well as van der Waals interactions between terminal aromatic moieties lead to specific packing patterns, namely: (i) a membrane-like architecture of associated molecular tapes in 1·2H₂O, (ii) coupled right-handed and left-handed helices in 2·H₂O and (iii) a stepped arrangement provided by a back-to-back pairing in (3)₂·H₂O. Molecular modelling of individual molecules in vacuo shows that the most stable conformers of 1–3 intrinsically display attractive interactions between the terminal aromatic groups, which stabilize a pseudocavity suitable for incorporation of a guest compound.