KINETICS STUDY OF DEC01PLEXATION OF SOME VANADIUM (V), MOLYBDENLM )VI) AND TOOSTEN(VI) AMINOCARBOXYLATE COMPLEXES.

The kinetics of the de complexation by hydroxyl ions of some pervanadyl,
molybdate and tungstate amionocarboxyLate complexes have been studied spectrophotometrically
by means of a stopped flow technique. The chelate groups used were the
iminodiacetic acid (IDA), ethylenediarnine-N,N' -diacetic acid (EDDA), nitrilotriacetic
acid (NTA) and ethylene diamine-N,N,N' ,N'-tetraacetic acid (EDTA). The chelates
were 1:1 complexes except V(V)-IDA which was 1:2. The rate law for decomplexation can be expressed by:



(q=2 for the V(V) chelates and q=l for the No(VI) and W(VI) chelates).
Kc is the stability constant of an outer sphere complex preequilibrium between
the chelate and hydroxyl ions, Ka is the rate constant of the direct decomplexation by water and Kb that by OH The slow step of the reaction should be an interchange between OH (or H20) and the chelate group in the outer sphere complex. The differences in the reactivities of the complexes are discussed. The most important effect observed on Ka and Kb is that, for a given metal, the rate constants diminish by a factor 100 to 1000 when a ligand which has vacant chelating sites replaces a ligand in which all the chelating sites are occupied. This is interpreted as an inductive effect by the acetate group, which is not bonded to the metal, on the nitrogenmetal bond.