Optically active co-ordination compounds. Part VI. Stereoselective effects in alkaline tartrato-complexes of transition metals
The marked difference in the colours of alkaline solutions of copper(II) racemate and copper(II)(+)-tartrate [or of copper(II)(–)-tartrate] arise from differences between both d-d and charge transfer absorption bands. The effect becomes apparent when the molar proportions [Cu2+] : [tartrate] : [OH–] are 1 : 1 : 2 +x, and are most marked for x 1. An explanation involving polymerisation is given; the polymers formed in the (+)-tartrate system differ in stoicheiometry from those formed in the (±)-system.
Similar stereoselective effects have been discovered for vanadyl tartrate, the effects becoming noticeable when [VO2+] : [tartrate] : [OH–] is 1 : 1 : 2 +x, being most marked for x 1. Anomalous results on the circular dichroism of vanadyl tartrate species have been disproved. Polymer formation is again invoked to explain the stereoselective effect, and the likely intervention of polymers in other systems containing tartrate as ligand is discussed.