Role of the relative molecular length of the components in ternary inclusion crystals in the chiral recognition and assembly of supramolecular helical architectures

The systematic investigation of supramolecular host systems consisting of a primary amine/carboxylic acids has been performed upon changing the molecular length of the component. The combinations of enantiopure erythro-2-amino-1,2-diphenylethanol (1) and achiral benzoic acid derivatives (2a-e) were found to be effective for the inclusion of 1-phenylethanol derivatives (3a-d) with chiral recognition. X-ray crystallographic analyses revealed that a one-dimensional (1D) helical columnar architecture was commonly constructed in the ternary inclusion crystals. However, there were two types of arrangements of the columns, anti-parallel and parallel, depending on the relative molecular length of 2/3. Similarity in molecular lengths between 2 and 3 resulted in an anti-parallel alignment of the columns, while a parallel alignment was achieved when one of the two components was much longer than the other; the 1D helical columns tend to align in an anti-parallel manner to cancel their dipole; however, the alignment switches to a parallel manner to avoid the formation of large voids between the columns.