Ligands containing elements of Group VIB. Part I. The silver complexes of substituted phenylthioacetic acids

Abstract

The stability constants of the neutral and protonated silver complexes of 20 substituted phenylselenoacetic acids of general formula R·C6H4·Se·CH2·CO2H have been measured at 20° in a sodium acetate–acetic acid buffer solution of µ= 0·10M(0·20M for the protonated complexes), using a silver–silver chloride indicator electrode. For comparison the silver complex of phenoxyacetic acid has been found to have the value log K1= 0·58. Comparison of these results with those for the analogous sulphur complexes shows selenium to be decidedly more class (b) or ‘soft’ than sulphur. Trends in the stability constants of the complexes are considered in terms of the Hammett σ-functions for the substituents, and the slopes (ρ) of graphs of log K values against σ-values are used to consider the extent of dπ-bonding present in the complexes. It is concluded that dπ-bonding may be present but can only play a relatively minor role in the stability trends found.