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

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. Hy drogen bonding with co-crystallized water molecules as well as van der Waal s interactions between terminal aromatic moieties lead to specific packing patterns, namely: (i) a membrane-like architecture of associated molecular tapes in 1 . 2H(2)O, (ii) coupled right-handed and left-handed helices in 2 . H2O and (iii) a stepped arrangement provided by a back-to-back pairing i n (3)(2) . H2O. Molecular modelling of individual molecules in vacuo shows that the most stable conformers of 1-3 intrinsically display attractive int eractions between the terminal aromatic groups, which stabilize a pseudocav ity suitable for incorporation of a guest compound.