Cinnamic acid analogs having phenyl and/or heteroaromatic substituents attached to an acrylic acid framework form extended networks in the solid phase through various types of hydrogen bonds. In the acids strong O–H...O hydrogen bonds keep together dimers, trimers and other oligomers and this is the only organising force in solution. Beside this interaction in the solid state weak but crucially important (aromatic)C–H...O (N or F) hydrogen bonds command the formation of sheet like structures. A stack of these sheets then makes the 3D structure of the crystals. The nature of these short contacts has been studied by various forms of vibrational spectroscopy, solid-state and solution NMR and XRD methods as well as molecular modelling. These methods provided important geometric data about these interactions and made clear that even weak hydrogen bonds could have major structure-determining role.
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