Complexation of silver salts in pyridine

Abstract

The molar conductances of the silver halides AgCl and AgBr and pseudohalides AgCN and AgSCN in pyridine at 25°C have been analysed in terms of the Fuoss-Hsia equation involving equilibria between ions, ion pairs, triple ions and quadrupoles (dimers). For AgSCN, the molar conductivities exhibit the classic minimum which, according to the 1933 theory of Fuoss and Kraus, is due to the formation of triple ions. The analysis of the conductivity data, confirmed by emf data from the literature, show that the major complexes formed are ion pairs and asymmetric triple ions. For AgCl, AgBr and AgCN, a minimum in the molar conductivities is not observed although it is known from emf studies that asymmetric triple ions are important species in pyridine solutions. The molar conductivities for these salts can be accurately treated using the Fuoss-Hsia equation by the inclusion of quadrupole equilibria. Analyses in terms of Barthel's modification of the Bjerrum equation is consistent with the known behavior of silver salts in pyridine solution, ie AgCl, AgBr, AgCN and AgSCN form inner-sphere ( ie contact) complexes whereas the hard donors NO − 3, ClO − 4 and Pic − (picrate) form outer-sphere ( ie solvent separated) ion pairs.