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 (Me 2 Tu), N,N,N′,N′ Tetramethyl-Thiourea (Me 4 Tu), N-ethyl-Thiourea (EtTu), N,N′ diethyl-Thiourea (Et 2 Tu), 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 (AgNO 3 ) 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 AgL n   ( n = 1 – 3 ; hereafter charge is omitted). The stability constants log β n and the standard thermodynamic changes in enthalpy ( Δ H n ° ) and entropy ( Δ S n ° ) for overall complex formation reactions A g I + n L = A g L n ( 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 A g L n - 1 + L = A g L n have been evaluated by difference Δ Δ H n ° = Δ H n ° - Δ H n - 1 ° and Δ Δ S n ° = Δ S n ° - Δ S n - 1 ° . The stepwise enthalpy are mutually linearly related to the corresponding entropy changes with isoequilibrium temperatures T i s o = 285 , 305, and 363 K for n = 1 , 2, or 3 respectively.