Sources of symmetry in ‘Blind Tests’ crystal structures

Molecules create crystals via intermolecular interactions that embody long-range order. Previously, close approaches between the aromatic rings of halobenzene molecules, designated ‘Symthons’, were found to be highly effective in creating long-range order in their crystal structures. Here, analysis of 42 ‘blind test’ crystal structures extends the application of ‘Symthons’ to fused rings, heterocycles and five-membered rings. This concept is further adapted to identify hydrogen-bonded approaches which create symmetry. Most of the 42 crystal structures contain at least one Symthon, some of which create long-range order. Other aromatic approaches and hydrogen bonds help to create symmetrical interactions, providing an alternative route to long-range order. In this dataset, hydrogen bonds were both less frequent and less effective at creating long-range order. However, hydrogen bonds were more effective at linking different molecules in salts, hydrates and cocrystals. Implications for nucleation, supramolecular synthons and graph sets are discussed briefly.