Molecular and supramolecular properties of nitroaromatic thiosemicarbazones: Synthesis, spectroscopy, X-ray structure elucidation and DFT calculations

The reactions of 6-nitropiperonal with H2N-NH-C(S)-NHR, R = Me, Et, Ph or H, afforded four nitro aromatic thiosemicarbazones 1-4, respectively. 1-4 were characterized by elemental analysis (CHN), FTIR, and H-1 and C-13{H-1} NMR spectroscopy. In addition, the crystal structures of 2 and 3 were determined by single -crystal X-ray diffraction. Our X-ray structural results have shown that the nitropiperonal and thiosemicarbazone moieties exhibit an almost coplanar arrangement for both 2 and 3. Moreover, they establish 2-D networks along the [111] base vector by means of classical and nonclassical hydrogen bonds. Electronic and spectroscopic properties of 1-4 were investigated at the DFT B3LYP/6-311G** level of calculation. The C=S group of 1-4 constitutes a nucleophilic region, whereas the NO2 group defines an electrophilic centre, as expected. Furthermore, a DFF vibrational analysis of 4 allowed a reliable assignment of the thiosemicarbazone-based vibrations. Also, a good agreement between theoretical and experimental C-13 chemical shift values was obtained for 1-4. (C) 2016 Elsevier B.V. All rights reserved.