Electron Transfer Kinetic Studies Of Isomeric Cobalt (iii) Complexes - Linkage Isomers And Geometric Isomers

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Doctor of Philosophy (Ph.D.)




A kinetic study of the electron transfer reaction from chromium (II) to N(,1)-bonded (5-methyltetrazolato)cobalt (III) has been performed by stopped-flow spectrophotometry. Two rate constants have been obtained, one dependent(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)and one independent(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)of the hydrogen ion concentration. The magnitudes of the rate constants together with the results of the product study indicate that both paths are inner sphere with different points of attack by chromium (II) on the tetrazole ring.The electron transfer reaction of the N(,2)-bonded (5-phenyltetrazolato) cobalt (III) complex has also been studied with chromium (II) as reductant and again two different rate constants resulted, one acid dependent (k(,2) = 0.015 (+OR-) 0.001 s('-1), 25(DEGREES)C, I = 1.0 M) and one acid independent (k(,0) = 0.064 (+OR-) 0.010 M('-1) s('-1), 25(DEGREES)C, I = 1.0 M). Using the reported K(,a) for this complex and k(,2) = k(,2)'K(,a), the second order rate constant for the acid dependent step was calculated. (k(,2)' = 0.41 (+OR-) 0.04 M('-1) s('-1), 25(DEGREES)C, I = 1.0 M). It was concluded that the k(,2) path was inner sphere and the k(,0) path was outer sphere according to the magnitudes of the rate constants and the results of the product study and stoichiometry studies which were performed.The three geometrical isomers of bisdiethylenetriamine-cobalt (III) were also submitted to electron transfer reactions from bivalent chromium. The outer sphere rate constants decreased as the reduction potentials decreased for the three isomers, in the order mer > u-facial > s-facial. Addition of the sulfate ion increased the rates of electron transfer in all three cases, but the extent of rate enhancement decreased in the order s-facial > u-facial > mer.


Chemistry, Inorganic; Chemistry, Organic

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