Crystal structures, spectroscopic and theoretical study of novel Schiff bases of 2-(methylthiomethyl)anilines

• New Schiff bases derived from 2-(methylthiomethyl)anilines (CH3, CH3O, NO2).
• Solid structures present stabilizing intra- and intermolecular H-bonds in molecules.
• NMR shifts, geometric and electronic parameters were calculated by B3LYP/6-31G∗∗.
• Electronic nature of ring substituents tuned the Schiff bases properties.
• EHOMO–LUMO energy gaps suggest their application as organic semiconductors.

New Schiff bases derived from p-methoxysalicylaldehyde and 2-(methylthiomethyl)anilines (substituted with methyl, methoxy, nitro) were synthesized and characterized by elemental analyses, FT-IR, NMR, electronic spectra and quantum chemical calculations. X-ray crystallography of two compounds showed the solid structures are stabilized by intramolecular and intermolecular H-bonds. The effect of OH⋯N interaction between the phenolic hydrogen and imine nitrogen on the proton and carbon NMR shifts, and the role of CH⋯O and CH⋯S contacts are discussed. The bond lengths and angles, 1H and 13C NMR data, ELUMO–HOMO, dipole moments and polarizability of the compounds were predicted by density functional theory, DFT (B3LYP/6-31G∗∗) method. The experimental geometric parameters and the NMR shifts were compared with the calculated values, which gave good correlations. The electronic effects of aryl ring substituents (methyl, methoxy and nitro) on the properties of the resulting compounds, such as the color, NMR shifts, electronic spectra and the calculated energy band gaps, dipole moments and polarizability are discussed. Increase in electron density shifted the phenolic proton resonance to lower fields. The methoxy-substituted compound has a small dipole moment and subsequent large polarizability value. Highest polarity was indicated by the nitro compound which also showed high polarizability due to its larger size. The energy gaps obtained from ELUMO–HOMO calculations suggest these compounds may have applications as organic semiconducting materials.

Ball and stick representation of 1 shows intramolecular (green line) and intermolecular (red line) H-bonds which create pseudo six-membered chelates.Figure optionsDownload as PowerPoint slide