Copper(II) Complexation with Thiosemicarbazide in Aqueous Solution

The complexation of copper(II) with thiosemicarbazide (Tsc) in aqueous solution at t = 25°С (in 0.1 М HClO4 and 1.0 М HCl) was studied by potentiometry and spectrophotometry. It was found that in 0.1 М HClO4 and 1.0 М HCl, stable thiosemicarbazide complexes CuTsc $$_{2}^{{2 + }}$$ formed at a ratio of СTsc/ $$C_{{{\text{Cu}}}}^{{2 + }}$$ ≥ 2.0. In hydrochloric acid, stepwise replacement of ligands occurs according to the equation [CuClx] $$^{{ + 2-x}}$$ + iTsc = [CuCl $${{_{x}}_{{-1}}}$$ Tsci] $$^{{ + 2-(x-1)}}$$ + xCl–, βi. The stability constants of thiosemicarbazide and chloro thiosemicarbazide copper(II) complexes calculated from spectrophotometric data are $$\log {{\beta }_{1}}$$ = 3.96 ± 0.10, $$\log {{\beta }_{2}}$$ = 8.01 ± 0.10 (0.1 М HClO4); $$\log {{\beta }_{1}}$$ = 4.19 ± 0.06, $$\log {{\beta }_{2}}$$ = 7.87 ± 0.08 (1.0 М HCl).