Optically active co-ordination compounds. Part XXIV. Tartrato-complexes of cobalt(III) and other transition metals

Abstract

(+)-Tartratotetra-amminecobalt(III) nitrate has been obtained with substantially higher optical activity than previously. The sign of the visible circular dichroism of this complex in aqueous solution undergoes a rapid and reversible change on acidification. Its magnitude is also greatly increased suggesting some form of specific aggregation is occurring. When set aside, aqueous solutions of the tetra-ammine yield an insoluble red-brown solid the analysis of which suggests that it is a polymeric tartratodiammine-cobalt(III) complex. Comparison is made with cobalt(II)(+)-tartrate and anhydrous copper(II)(+)-tartrate, both of which are insoluble in water and show strong circular dichroism. Polymeric structures here again seem likely. (+)-Tartratopenta-amminecobalt(III) nitrate is quite stable in aqueous solution and its circular dichroism does not change on acidification.