Synthesis and structural studies of 4-[(5-methoxy-1H-indole-3-yl)-methylene]-3-methyl-isoxazole-5-one by X-ray crystallography, NMR spectroscopy, and DFT calculations

A merocyanine dye with isoxazolone nucleus: 4-[(5-methoxy-1H-indole-3-yl)-methylene]-3-methylisoxazole-5-one (1) was synthesized and characterized by X-ray diffraction, H-1 NMR, C-13 NMR, IR. UV-Vis spectra and elemental analysis. The crystals are monoclinic, space group P2(1)/n, with a - 6.4195(16), b = 7.5759(19), c = 25.181(6) angstrom. V= 1217.9( 5) angstrom 3, and Z= 4 (at 298(2) K). Crystal stacking scheme indicates the hydrogen bonds and intermolecular face-to-face pi center dot center dot center dot pi aromatic stacking interactions generate a unique parallelogram-void supramolecular architecture in solid state of the dye (1). By DFT calculations, molecular electrostatic potential clearly shows that the formation of hydrogen-bonding interaction [N(2) H(2)center dot center dot center dot O(2) and C(1) H(1A)center dot center dot center dot N(1)] in the crystal structure is between the positive and negative regions. In addition, molecular geometry, tautomeric forms, H-1 NMR and C-13 NMR were calculated by DFT/GIAO (the gauge invariant atomic orbital) methods are in good agreement with the experimental values. The correlation value between experimental 13C chemical shifts and the calculated magnetic isotropic shielding tensors is 0.9989, and the absolute deviation is 0.2-4.4 based on B3LYP/6-31G*-PCM (the polarizable continuum model) level. (C) 2011 Elsevier B.V. All rights reserved.