The Formation Constants and the Rate Constants of the Electrode Processes of Thiocyanato-Indium(III) Complexes with the Dropping Mercury Electrode

The formation constants,Kj=[In(SCN)j(3−j)+]/[In3+][SCN−]j (j=1, 2, 3, 4), have been determined to be 50, 200, 120 and 1670 respectively. The electrode reaction proceeds as follows:(1) At a higher ligand concentration ;In(SCN)P(3−P)+ \ightleftarrows InSCN2++ (p−1) SCN− (fast) (p=2, 3 and 4)InSCN2++ 3e− + Hg → In(Hg) + SCN− (rate constant (k1)B)(2) At a lower ligand concentration:InSCN2+\ightleftarrows Inaq3+ + SCN− (fast)Inaq3+ + 3e− + Hg→ In(Hg) (rate constant (k0)BThe rate constants, (k0)B and (k1)B at the standard potential are (0.64±0.16)×10−4cm./ sec. and (1.5±0.2)×10−4 (cm./sec.)/(mol./l.) respectively. The rate constant, k0f,h, at 0 V. vs. NHE was 4.77×10−12 cm./sec.