Reduction of the complexes of zinc, copper and lead at the d.m.e. was reversible and the stability constants were determined from the shift in the half-wave potentials in the presence of mandelic acid. Four complexes were identified for zinc and copper with the overall stability constants 25, 125, 490 and 1380 and 100, 3.3 × 103, 9.6 × 103 and 1.6 × 104 respectively while three complexes were observed for lead with the stability constants 18, 215 and 294. In the case of indium, the reduction of the ‘simple’ ion is irreversible and that of the complex is reversible and hence the system was studied by the method of Momoki and Ogawa. Four complexes, with the stability constants 8.3 × 102, 4.0 × 109 were found to exist.
