Polynuclear thiolate complexes in solution. Solution equilibria studies of silver(I) complexes of 3-(dimethylamino)propane-1-thiol and 3-aminopropane-1-thiol and comparative study with 4-mercapto-1-methylpiperidine

Abstract

The complexation of Ag^l by the ligands 3-(dimethylamino)propane-1-thiol and 3-aminopropane-1-thiol has been studied first in strong acidic solutions and then at increasing pH values, up to pH ⩽ 8, at 25 °C in 0.1 mol dm^–3 NaNO₃(10% v/v MeOH). The extended-variation method and other graphical methods based on the ‘core + links’ hypothesis have been used and give results in accord with the final equilibrium model obtained by means of the program SUPERQUAD. Species [Ag_p(AH)_q]^p+, AH denoting the monoprotonated ligand, in a strong acidic medium have the same stoicheiometric coefficients and comparable formation constants with both ligands; p,q values are 6,3; 6,4; 8,6; 7,6; 10,9; and 12,12. The species 5,6 is already present at low pH with H₂N(CH₂)₃SH. More basic solutions contain species with p,q values 5,6; 4,6; and 1,3 in the case of Me₂N(CH₂)₃SH and 5,6; 5,7; 4,6; 2,4; and 1,3 in that of H₂N(CH₂)₃SH. These results together with those obtained with 4-mercapto-1-methylpiperidine indicate that the species existing in a strong acidic medium are independent of the aliphatic chain of the ligand, whereas at higher pH values the nuclearity and the number of species present depend on the nature of the γ-mercaptoamine.