Designing Ordered Molecular Arrays in Two and Three Dimensions

Two- and three-dimensional assemblies — self-assembled monolayers (SAMs) and hydrogen-bonded co-crystals, respectively — show substantial changes in their supramolecular structures with seemingly minor changes in the structures of their molecular/atomic constituents. The structure of SAMs obtained by adsorption of alkanethiols onto silver and copper are indistinguishable, although the atomic radii of silver and copper are different. The structure of the SAM on silver is different from that on gold, although the atomic radii of these metals are essentially the same. A macroscopic property of the SAMs, wetting, is not affected by these structural differences. Co-crystals formed from derivatives of barbiturates and melamines form hydrogen-bonded tapes in the solid state. These tapes provide a template for studying the packing forces within crystals. The three-dimensional arrangement of the tapes in the crystals changes markedly in response to subtle differences in the steric and electronic structures of the molecular constituents.