Effect of fluorine substitution on the crystal structures and vibrational properties of phenylthiourea isomers

The 1-(2-chlorobenzoyl)-3-(isomeric fluorophenyl)thiourea derivatives (1-3) were prepared by the reaction of 2-chlorobenzoyl isothiocyanate produced in situ with isomeric fluoroanilines in excellent yields. The novel compounds are characterized by multinuclear (1H and 13C) NMR, GC-MS, elemental analyses and FTIR spectroscopy techniques. Structural and conformational properties of compounds 1-3 are analyzed using a combined approach including X-ray diffraction, vibrational spectra (solid FTIR and FT-Raman) and theoretical calculation methods. The crystal structures have been determined by X-ray diffraction methods. The three species crystallize in the monoclinic C2/c space group with and Z = 8 molecules per unit cell. The carbonyl and thiourea groups are almost planar and the conformation adopted by the CS and the CO double bonds is antiperiplanar. The crystal lattices show the presence of centro-symmetric dimeric units held by N−H···S hydrogen bonds stacked along the [0 1 0] plane. The effect of fluorine substitution on the vibrational properties and on the conformational space has been determined by quantum chemical calculations (B3LYP functional in connection with the 6-311+G* basis sets) and vibrational spectroscopy.