Designing linear hydrogen-bonded arrays by using substituted charge-transfer complexes. The crystal structure of the 1:1 adduct of indole-2-carboxylic acid with 3,5-dinitrobenzoic acid

Five adducts consisting of carboxylic acid-substituted indoles with nitro-substituted benzoic acids have been synthesized and tested for second-order non-linear optical properties. These were indole-2-carboxylic acid with 2,4-dinitrobenzoic acid (1), 3,5-dinitrobenzoic acid (2), and 2,4,6-trinitrobenzoic acid (3), and indole-3-acetic acid with 3,5-dinitrobenzoic acid (4), and 2,4,6-trinitrobenzoic acid (5). Compound (2) produced clear, yellow crystals (space group P1̄ with a 6-8400(7), b 15-150(2), c 16-097(2) Å, α 84-911(9), β87-088(10), γ 77-865(9)°, Z 4) which allowed the structure to be determined by X-ray diffraction. Of the five adducts, compounds (3) and (5) gave second harmonic intensities of 0.15 and 0.16 times respectively that of a urea standard