Molecular Cocrystals of Carboxylic Acids. I. The Crystal Structures of the Adducts of Indole-3-acetic-Acid With Pyridin-2(1H)-one, 3,5-Dinitrobenzoic Acid and 1,3,5-Trinitrobenzene

Three molecular cocrystal adducts of the plant hormone indole-3-acetic acid (iaa) have been prepared and their structures determined by X-ray diffraction. They are indole-3-acetic acid-bis[pyridin-2(1H)-one] (1), indole-3-acetic acid-3,5-dinitrobenzoic acid (2) and indole-3-acetic acid-1,3,5-trinitrobenzene (3). Complexes (2) and (3), which may be prepared in a solid-state reaction, are orange and are structurally similar, having significant pi-pi indole-benzene ring interactions. However, the colourless complex (1) shows no pi-pi ring interactions. In complex (2), the 3,5-dinitrobenzoic acid molecules form hydrogen-bonded cyclic dimers (O...O, 2.64 angstrom), while in (3) the indole-3-acetic acid molecules form dimers (O...O, 2.66 angstrom). This feature contrasts with the structure of adduct (1) in which the pyridin-2(1H)-one molecules exist as dimers [N...O, 2.79, 2.74 angstrom] analogous to those found in the parent compound