Molecular cocrystals of carboxylic acids.: XXXIII -: The crystal structure of the 1:1 adduct of indole-2-carboxylic acid with 5-nitroquinoline

The molecular adducts of indole-3-acetic acid (iaa) and indole-2-carboxylic acid (ica) with 5-nitroquinoline (nq), [(iaa)(nq)(2)] (1) and [(ica)(nq)] (2), have been prepared and characterized by X-ray diffraction and spectroscopic methods. Both examples involve charge transfer as well as a network of hydrogen-bonding interactions. Thin films of compound (2), and other similar adduct complexes of ica, can be prepared by thermal evaporation techniques and in this form exhibit a weak second-order non-linear optical signal. However, these films display poor optical quality and, without improvement, are not suitable for any potential non-linear optical applications.