Dimerization of Thallium(I) Complexes with O,O’-Dialkyl Dithiophosphate in Organic Solvents

A number-average molecular weight measurement was tested as a direct and simple method for the confirmation of polymerization of the metal complex in organic solvent. This method was applied to the complexes of thallium(I), lead(II) and nickel(II) with O.O’-dialkyl dithiophosphates (alkyl groups=methyl, ethyl, propyl and butyl) in benzene, chloroform and acetonitrile. In the cases of lead(II) and nickel(II) complexes, the number-average molecular weight in any solvent did not depend on the concentration of these complexes, while it agreed with the molecular weight of each monomer of these complexes. On the other hand, the magnitude of the number-average molecular weight for thallium(I) complexes increased with increasing the concentration of the complex but did not go up to beyond twice the molecular weight of monomer in any solvent. The dimerization constants of thallium(I) complexes were obtained by analyzing the relationship between the number-average molecular weight and the concentration of the complex. The values of dimerization constants were little affected by the alkyl group in the ligand. But the values were affected by solvents and became smaller in the order: chloroform, benzene and acetonitrile.