Hydrogen bonding patterns and crystal packing in azobenzene-carboxylic acids

X-ray structures of four substituted azobenzene-carboxylic acids have been determined. The crystal packing of the compounds has been analyzed in terms of three main features: parallel placement of the long molecular axes, lateral contacts of (offset) face to face and face to edge types among aromatic rings and hydrogen bonding between carboxy and/or alcoholic hydroxy groups. Hydrogen bonding patterns of the dimer, catemer and expanded dimer types have been found, as well as supramolecular architectures such as chains, rows, sheets and networks.