Reaction between [PdCl4]2- and 5,5-dimethyl-2-thioxoimidazolidin-4-one

The reaction between 5,5-dimethyl-2-thioxoimidazolidin-4-one (H(2)L) and [PdCl4](2-) has been studied in aqueous solution by potentiometric and spectrophotometric measurements. In the presence of the palladium salt, H(2)L is completely monodeprotonated (HL(-)); from spectrophotometric measurements, only two complexes having 1:1 and 1:2 Pd/ligand mol ratios have been identified. Potentiometric titrations, carried out on solutions with 1:1, 1:2, 1:3 and 1:4 metal/ligand mol ratios, show that these complexes must be formulated as Pd(HL)(2) and [Pd-2(HL)(2)(mu H2O)(mu-OH)](+). Ionization constants of the pure ligand and formation constants of the complexes give pH distribution curves of the various species and the spectra of the two complexes. From MeOH, S-coordinated Pd(H(2)L)(n)Cl-2 (n = 2-4) complexes have been separated in the solid state; from water, two complexes of formula Pd(H(2)L)(HL)Cl and Pd(HL)Cl have been obtained with HL(-) N,S-coordinated to the metal