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-methyl-isoxazole-5-one (1) was synthesized and characterized by X-ray diffraction, 1H NMR, 13C NMR, IR, UV–Vis spectra and elemental analysis. The crystals are monoclinic, space group P21/n, with a = 6.4195(16), b = 7.5759(19), c = 25.181(6) Å, V = 1217.9(5) Å3, and Z = 4 (at 298(2) K). Crystal stacking scheme indicates the hydrogen bonds and intermolecular face-to-face π⋯π 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)⋯O(2) and C(1)H(1A)⋯N(1)] in the crystal structure is between the positive and negative regions. In addition, molecular geometry, tautomeric forms, 1H NMR and 13C 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.