Identification of a new supramolecular synthon in o-anisaldehydes: molecular self-assembly into tapes and staircases

We have shown through a rational design, synthesis and X-ray structural analyses of a set of aldehydes that o-methoxybenzaldehydes tend to associate in a centrosymmetric fashion, akin to the carboxylic acids, to give rise to a dimer motif II, which derives stabilization from four C-H⋯O hydrogen bonds in addition to a dipole-dipole interaction. That the synthon II is credible to be structure determining is revealed from the crystal structures of aldehydes 1-4 that are devoid of any other competing weak interactions. The aldehydes 1-4 are found to undergo self-assembly into 1-dimensional molecular tapes and staircases. We have shown that the steric factors as in aldehyde 5 and the presence of a functional group such as Br in 6 perturb the expected crystal packing based on synthon II.