Synthesis, spectroscopic characterization, crystal structures, and theoretical studies of (E)-2-(2,4-dimethoxybenzylidene)thiosemicarbazone and (E)-2-(2,5-dimethoxybenzylidene)thiosemicarbazone

Two thiosemicarbazones, (E)-2-(2,4-dimethoxybenzylidene)thiosemicarbazone (24-MBTSC (1)) and (E)-2-(2,5-dimethoxybenzylidene)thiosemicarbazone (25-MBTSC (2)), derived from 2,4-dimethoxybenzaldehyde and 2,5-dimethoxybenzaldehyde, respectively, with thiosemicarbazide have been synthesized and their structures were characterized by elemental analyses, FT-IR, ¹H NMR spectroscopy, and X-ray single-crystal diffraction analysis. Molecular orbital calculations have been carried out for 1 and 2 by using an ab initio method (HF) and also density functional method (B3LYP) at 6-31G basis set. Compound 1 crystallizes in the monoclinic system, space group P2₁/c, with a = 8.1342(5) Å, b = 18.1406(10) Å, c = 8.2847(6) Å, β = 109.7258(17)°, V = 1150.75(12) ų, and Z = 4, whereas compound 2 crystallizes in the orthorhombic system, space group Pbca, with a = 11.0868(6) Å, b = 13.1332(6) Å, c = 15.9006(8) Å, V = 2315.2(2) ų, and Z = 8. The compounds 1 and 2 displays a trans-configuration about the C=N double bond.