Insight into coordination of dilead unit by molecules of 4-thiazolidinone-2-thione: Structural and computational studies

The reaction of Pb2+ ions with 4-thiazolidinone-2-thione (Hrd) yields to coordination of the uncommon dilead unit (Pb22+) by the N-deprotonated molecule of the ligand. The powder structure determination of the complex reveals an almost planar dimeric structure with the {N,S} coordination mode. The intermolecular distance of the Pb–Pb moiety (3.51(4) Å) is lower than the van der Waals parameter suggesting the formation of a bond. The structure in the solid state and DFT calculations of molecular orbitals and the presence of a bond critical point between the lead atoms clearly demonstrate the existence of a single bond within the Pb–Pb unit formed by the 6p orbital electrons. The lone pairs of the 6s orbitals do not participate in bonding with the ligand atoms and are likely bisdirected. FT-IR and FT-Raman spectra confirm the molecular structure since all the modes of the NH group disappear in the spectra of the complex, while the stretching mode of the CS bond shifts to lower values, as would be expected for this coordination fashion.