Structural features of 1-furoylthioureas 3-monosubstituted and 3,3-disubstituted: Coordination to cadmium and analytical applications

The structural features of two series of 1-furoylthioureas 3-monosubstituted (Series 1) and 3,3-disubstituted (Series 2) 1-furoylthioureas and their CdCl₂ complexes are discussed. The coordination strength through the sulfur atom is determined by the ligand structure. In Series 1 ligands, the carbonyl group and the proton on N2 are engaged in a strong hydrogen bond interaction. This leads to an S-shaped conformation type of the C=O and C=S groups where these donor sites reach a maximum separation. In the absence of that hydrogen bridge in 3,3-disubstituted derivatives, the C=O and C=S groups can adopt a U-shaped conformation type. This feature is also observed for two novel crystal structures of 1-(2-furoyl)-3-(2-hydroxyethyl)thiourea and 1-furoyl-3-ethyl-3-phenylthiourea, as determined by X-ray diffractometry and reported here. Emphasis is placed on the relationship between structural features of these ligands and their behavior as cadmium ionophores in potentiometric and amperometric sensors.