A Comprehensive Potentiometric Study of the Tartrate Complexes of Trivalent Arsenic, Antimony, and Bismuth in Aqueous Solution.

The tartrate complexes of trivalent arsenic, antimony, and bismuth were studied potentiometrically. The existing, fragmentary data on the antimony/l-(+)-tartrate system were confirmed. Nine complexes of arsenic and bismuth with optically active, racemic, and meso-tartrate, as well as complexes of antimony with meso-tartrate, were newly identified, and their formation constants computed. Difficulties arising from the poor stability of the arsenic complexes and precipitation in the Sb(III)/meso-tartrate system were overcome by titrating at very high concentrations [As(III) systems] and using an auxiliary ligand [Sb(III) in the presence of catechol]. All data were obtained at 25.0 °C and at constant ionic strength [0.1 mol L-1 for Sb(III) and Bi(III) complexes and 1 mol L-1 for As(III) complexes]. Speciation diagrams of all systems at millimolar concentrations were computed on the basis of the newly obtained constants and the results discussed.