Studies on the Irreversible Polarographic Wave of Nickel thiocyante Complex

The polarographic reduction wave of nickel thiocyanate complex has been studied for the purpose of clarifying the reduction mechanism of the complex. The current-voltage curves of the complex were measured in media of KSCN-KCl and KSCN-KNO3. In the medium of KSCN-KCl, the reduction wave involved the kinetic current as well as the diffusion current, when the concentration of potassium thiocyanate was less than 0.2 M. The relation of log I⁄(Il−I) and V held a straight line, but its slope was not in accord with the value expected from the reversible reduction. From these experimental results and the polarograms obtained with the Kalousek’s method, the reduction of the complex was confirmed to proceed irreversibly at the dropping mercury electrode. The redaction mechanism of the complex and the number of thiocyanate ions coordinated to the centered metal ion in the supporting electrolytes containing various concentrations of potassium thiocyanate were estimated from these experimental results, when the theoretical consequence for the activation-controlled reduction of the complex ion reported in the previous paper was applied.