Thermodynamic Characteristics of Silver(I) Complex Formation with Selected N- and N,N'-Substituted Thioureas in Aqueous Solution

Silver(I) complex formation with thiourea (Tu), N -phenylthiourea (Phtu), N , N '-diphenylthiourea (Bphtu), N -acetylthiourea (Aсtu), and thiosemicarbazide (Tsc) in aqueous solution at temperatures in the range 278.2–328.2 K at the ionic strength I = 0.11 mol/L (0.1 NaNO 3 + 0.01 HNO 3 ) was studied potentiometrically. The reactions yield various complexes by the scheme Ag + + i L = where i = 1–3, at = (1–5) × 10 –5 mol/L. The thermodynamic characteristics (logβ i , Δ r G 0 , Δ r H 0 , and Δ r S 0 ) for these reactions were determined. The highest rise in exothermicity (Δ r H 0 ) was observed for the second complex formation step: AgL + + L = The exception is the reaction with thiosemicarbazide. The stabilities of monocoordinated complexes vary in the order Aсtu < Tsc < Bphtu < Phtu < Tu, in good match with the protonation constants of the respective ligands. For the and complexes of Phtu and Bphtu, this trend is spoiled because of the influence of phenyl substituents on the complex-forming properties of these thiourea derivatives.