The photochemistry of complex ions: photochemical and thermal decomposition of the trioxalatocobaltate III complex

Abstract

The photochemistry of the trioxalatocobaltate III complex was studied. It was shown that both the peak in the ultra-violet region (attributed to electron transfer) and that in the blue (attributed to d->d transitions) are photochemically active. Primary quantum efficiencies were found for various lines to be: 313 m μ , 0.365; 365 m μ , 0.345; 405 m μ , 0.085; 435 m μ , 0.06. The quantum efficiency of cobaltous ion formation is twice the primary quantum efficiency. No temperature dependence was detected. Ethyl alcohol (up to 75%) and acetone (up to 60%) did not effect the photochemical quantum yield. The radical C 2 O 4 - is postulated as intermediate capable of reducing mercuric chloride in the course of the reaction. The reaction scheme consists of photo-excitation, primary dark back-reaction, dissociation of excited complex and non-rate-determining oxidation of the C 2 O 4 - ion. The thermal reaction was also studied. It was found that the reaction rate could be presented by -d[Co Ox 3- 3 ]/d t = k 1 [Co Ox 3- 3 ]+ k 2 [H + ][Co Ox 3- 3 ] k 1 and k 2 were evaluated as 1.62 x 10 18 exp ( - 33 600/ RT ) s -1 and 1.77 x 10 19 exp ( - 32500/ RT ) s -1 (mol./l.) -1 respectively. Both the neutral and acid reactions were, however, postulated to proceed through a pseudomonomolecular mechanism involving water molecules with the [H + ] ion effecting the level of the transition state. Activation energies are discussed and finally the suitability of the trioxalatocobaltate III complex for chemical actionometry is analyzed.

Photoelectron Detachment and Solvated Electron Dynamics of the Cobalt(III) and Iron(III) Oxalato Complexes

“…Numerous researchers have investigated the photochemical mechanism of ferrioxalate − and cobaltoxalate − systems by various techniques. The flash photolysis studies of ferrioxalate and cobaltoxalate complexes had been summarized by Stasicka et al and further discussed by Poznyak et al Although it has been a tendency to assume that a similar mechanism is operative for both complexes, the value of this assumption has not been confirmed because their photochemical mechanisms have not been clearly defined.…”

Photochemistry and electron-transfer mechanism of transition metal oxalato complexes excited in the charge transfer band

“…By using the quantum yield of solvated electron generated in ferrocyanide, which is reported to be Ϸ1 (45), we determined the quantum yield for the photoelectron detachment from trisoxalato cobaltate (III) to be Ϸ0.10. The quantum yield of Co(II)(ox) formation has been measured to be 0.7 (46); therefore, the photoelectron detachment is a low quantum yield side reaction. Similar results have been observed for ferrioxalate (29).…”

Szilard-Chalmers Reaction of Anionic Cobalt Complex Ions on Ion-Exchange Resins

“…It can be inferred that this discrepancy might be due to [Vol. 39,No. 12 usually can be classified as the separable species,6) the anionic intermediates may be considerably stable and resistant to aquation or elution and thus the separable yield will be considerably low.…”

“…Chem., 56, 1097 (1952 [Vol. 39,No. 12 determined in this work in order to determine the interrelation of this value with the stability of complex and specific activity.10) Since the dependence of the yield on the nature of the complexes i. e. on their relative stability is one of the main concerns of this paper, and since the tendency that the higher the stability the lower the separable yield is what we have already observed with the two cationic cobalt complexes, [Co-(NtH3)6]s+ and [Co en3]3+,1,6) a theoretical consideration was attempted also in this paper as a first approach to a more rigorous treatment.…”