| Abstract
| - Volumes of activation for the formation and homolysis of the transient complexes (hedta)FeIII−CO22- and (hedta)FeIII−CH3- (HOCH2CH2N(CH2CO2-)CH2CH2N(CH2CO2-)2 = hedta) were determined using high-pressure pulse-radiolysis techniques. A comparison of the results with those for analogous complexes with other central transition-metal cations (Mn+) and ligands (L) points out that (i) the reaction of MnLm with aliphatic radicals (R•) proceedsvia an interchange ligand substitution mechanism, i.e. MnLm + R• → Lm-1Mn+1−R + L, (ii) the homolysis of themetal−carbon bonds naturally follows the same mechanism, and (iii) the volume of activation for the homolysisreaction depends strongly on the nature of the central cation, i.e. larger for Mn+1 = CrIII, CoIII, NiIII and smallerfor FeIII. The volume of activation for the reaction (hedta)FeIII−CO22- + CO2•- + 2H+ → FeII(hedta)(H2O)- +CO + CO2 was measured, and the results enable a tentative proposal for the nature of the transition state of thisinteresting reaction.
- The reactions of radicals with transition-metal complexes involve an interchange ligand substitution mechanism. The overall volume of reaction, ΔV°(K1), depends strongly on the nature of the central cation.
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