Complexes of SSS′S′-ethanediylidenetetra[(thio)acetic acid] and related ligands with cobalt(II), nickel(II), and copper(II)

Abstract

The complexes of SSS′S′-ethanediylidenetetra[(thio)acetic acid](ETTA) have been studied in the solid state and in aqueous solution. The magnetic susceptibilities and electronic spectra of the complexes of ETTA with cobalt(II), nickel(II), and copper(II) are consistent with an octahedral metal ion. The solution studies were confined to the nickel(II) and copper(II) complexes of ETTA. The acid dissociation constants of ETTA at 25° in an aqueous solution (0·1M in sodium perchlorate) were found to be pK_1a 2·89, pK_2a 3·54, pK_3a 3·958, and pK_4a 4·572. Spectrophotometric measurements of the formation of the 1 : 1 complexes with nickel(II) and copper(II) gave values for the logarithms of the stability constants of 4·17 and 5·72 respectively. Preliminary studies on the solid complexes of other mercapto-carboxylic acids are reported.