Furan derivatives of substituted phenylthiourea: spectral studies, semi-empirical quantum-chemical calculations and X-ray structure analyses

Fifty new derivatives of 1-(furan-2-carbonyl)- and 1-(furan-3-carbonyl)-3-phenyl substituted thiourea have been synthesised and identified. Intramolecular hydrogen bonds were investigated in detail, using IR spectroscopy. The three-level Fermi resonance effect in the IR spectra was analysed after deconvolution and band separation. Semi-empirical quantum-chemical calculations (AM1 and PM3) support the results of the IR spectroscopic studies. X-ray single crystal diffraction analyses of four selected compounds, namely 1-(furan-3-carbonyl)-3-(2-trifluoromethyl-phenyl)-thiourea (1e), 1-(2-methyl-furan-3-carbonyl)-3-(2-trifluoromethyl-phenyl)-thiourea (2e), 1-(2,6-dichloro-phenyl)-3-(2-methyl-furan-3-carbonyl)-thiourea (2n) and 1-(4-methoxyphenyl)-3-(3-methyl-2-furan-carbonyl)-thiourea (3e), corroborated the molecular and crystal structure of these compounds. Relatively strong intramolecular hydrogen bonds of the N-H⋯OC type as well as intermolecular two-centred and bifurcated three-centred hydrogen bonds were observed, confirming the results of the IR spectral study and the semi-empirical quantum-chemical calculations. A variety of intermolecular interactions, yielding the supramolecular architectures in the four crystalline compounds, are discussed in detail.