Formation of halogenide complexes of cadmium or lead in dimethyl sulfoxide, N,N-dimethylformamide or propylene carbonate

The reason for the difference between the polarograms of Cd(2) observed in DMF (N,N-demethylformamide) or PC (propylene carbonate) and Pb(2) in PC was studied by potentiometric titration method, and the overall formation constants (beta-3, beta-4) were determined. Saturated cadmium or saturated lead amalgam was used for the reference electrode. Cadmium chlorate hexahydrate or lead chlorate trihydrate, each of which was vacuum dried for 48 hours, was used as the sale. The potentiometric titration experiments revealed that cadmium tetrachloride ions were the highest order complex in PC and DMF, but it was difficult to identify the formed complex in DMSO. Beside, the polarogram revealed that Cd(2) differed remarkably from the previously reported Pb(2), and that many reduction waves Cd(2) as observed in DMF and PC did not exist in DMSO. As a result of mathematical analysis, the logarithms of the overall formation constants for Pb(2) halogeno-complex coincided quite well with the previously reported polarographical constants for Pb(2). There is inversely proportional relationship between log(beta-4) and DN (donor number) for Cd(2) halogeno-complex. The order of the overall formation constants is as follows: Cl(-) ion is greater than Br(-) ion. Br(-) ion is greater than I(-) ion. Both are valid for all solvents. And the order of the constants for metalic ions is considered as Cd(2) greater than Cu(2) greater than Pb(2) greater than Co(2). (Iwakiri, K.)