Complex Formation Equilibria between Ag(I) and Thioureas in Propan-2-ol

Abstract

The complex formation equilibria between Ag(I) and thiourea (Tu), N methyl-Thiourea (MeTu), N,N′-dimethyl-Thiourea (Me2Tu), N,N,N′,N′ Tetramethyl-Thiourea (Me4Tu), N-ethyl-Thiourea (EtTu), N,N′ diethyl-Thiourea (Et2Tu), and N,N′-Ethylen-Thiourea (EnTu) in propan-2-ol as solvent medium have been investigated by potentiometry within the temperature range 10°C–40°C and self-determined ionic medium by (AgNO3) concentration range 6.36·10-6–3.83·10-5 m·dm−3 (no background electrolyte added). The experimental results can be interpreted with the stepwise formation of tris-coordinated complexes AgLn  (n=1–3; hereafter charge is omitted). The stability constants log βn and the standard thermodynamic changes in enthalpy (ΔHn°) and entropy (ΔSn°) for overall complex formation reactions AgI+nL=AgLn (n=1–3) have been evaluated. The reactions are exothermic in nature and entropy disfavored for all the investigated ligands. The standard enthalpy and entropy changes for the stepwise reactions AgLn-1+L=AgLn have been evaluated by difference ΔΔHn°=ΔHn°-ΔHn-1° and ΔΔSn°=ΔSn°-ΔSn-1°. The stepwise enthalpy are mutually linearly related to the corresponding entropy changes with isoequilibrium temperatures Tiso=285, 305, and 363 K for n=1, 2, or 3 respectively.