Structures and vibrational spectra of indolecarboxylic acids. Part II. 5-Methoxyindole-2-carboxylic acidq

The crystal and molecular structure of 5-methoxyindole-2-carboxylic acid (5-MeOICA) are determined by single crystal X-ray diffraction analysis, infrared spectra and density functional (B3LYP) calculations. The title compound crystallizes in the monoclinic system, space group C2=c; with a ¼ 13:079ð3Þ; b ¼ 7:696ð2Þ; c ¼ 35:185ð7Þ A; b ¼ 91:1ð1Þ8; V ¼ 3541:0ð1Þ A3 and z ¼ 16: There are two independent molecules of 5-MeOICA in the asymmetric unit cell. The molecular ribbons, constituted by two independent molecular chains, are held together by intermolecular O–H· · ·O and N–H· · ·O hydrogen bond interactions. The carboxylic O atom is the acceptor of two hydrogen bonds. In molecular ribbon, the relative orientation of the A and B carboxylic groups is nearly perpendicular, which leads to formation of the zig-zag pattern of H-bonds. The molecular layers, separated by about 3.344 A ° , are arranged in stacks. Interestingly, the layers in the adjacent stacks are oriented in a herringbone-like pattern. The B3LYP-calculated bond lengths and angles are in good agreement with experimental data. Examination of the infrared spectrum of 5- MeOICA supports the conclusions from the X-ray diffraction studies. The characteristic bands at 3336, 1695 and 1206 cm21 have been assigned to the stretching vibrations of the N–H, CyO and C–O groups, respectively. q 2003 Elsevier B.V. All rights reserved.