MULTIDENTATE LIGAND KINETICS .12. ETHYLENEDIAMINETETRAACETATE ION REACTION WITH MONO- AND BIS(DIETHYLENETRIAMINE)NICKEL(2) COMPLEXES

The stepwise process by which one multidentate ligand displaces another from a metal ion is observed in the reactions of Ni(dien)22+ and Ni(dien)2 + with EDTA. The bis-dien complex does not react directly with EDTA but must completely lose one dien first. The mono-dien complex reacts rapidly with EDTA to give Ni(dien)EDTA2− and this complex under¬goes successive unwrapping of dien and increasing coordination to EDTA. Two successive first-order steps are observed before NiEDTA2− and dien are produced. Excess Ni(dien)2 + can slow the reaction with EDTA owing to the formation of a bridged EDTA species, [Ni(dien)EDTA(dien)Ni]. Difference spectral studies indicate another possible bridged species, [Ni(dien)(EDTA)Ni(EDTA)(dien)Ni]2−. © 1968, American Chemical Society. All rights reserved.