Square tiling by square macrocycles at the liquid/solid interface: co-crystallisation with one- or two-dimensional order.

We have systematically investigated the self-assembled monolayers of seven bimolecular mixtures of square-shaped pyridinophanes and cyclophanes bearing alkoxy or alkoxycarbonyl substituents in the presence of the tropylium ion as a marker of pyridinophanes at liquid/graphite interfaces by means of scanning tunnelling microscopy (STM). The purpose of this work was to elucidate the mixing behaviour of these macrocycles highlighting the formation of one- or two-dimensionally ordered square tilings consisting of alternating alignments of different macrocycles as a result of attractive dipole-dipole or hydrogen-bonding interactions; four co-crystals differing in the dimensionality of the ordering of pyridinophane and cyclophane were observed. The different modes of interaction between the functional groups (ether or carbonyl group) in the side-chains of the pyridinophanes and cyclophanes lead to the formation of co-crystals with dimensionally different orderings of the two macrocycles. These observations revealed that a slight modification of the molecular structure may dramatically change the mixing behaviour and structures of the co-crystals.