The self-exchange reaction of hexaamminecobalt complexes shown in (a.) is very s

Question

The self-exchange reaction of hexaamminecobalt complexes shown in (a.) is very slow, with a second-order rate constant of 10^-6M^-1s^-1. The analogous self-exchange rate constant for the hexaammineruthenium complexes shown in (b.) is, at 10^3 M^-1s^-1, faster by a factor of 109. Explain why these two electron-transfer rates are so different. Note: Co-N bond lengths are 2.11 A for Co(ll) and 1.94 A for Co(lll). Ru-N bond lengths are 2.14 A for Ru(ll), and 2.10 A for Ru(lll). [*Co(NH_3)_6]^3+ + [Co(NH_3)_6]^2+ rightarrow [*Co(NH_3)_6]^2+ + [Co(NH_3)_6]^3+ [*Ru(NH_3)_6]^3+ + [Ru(NH_3)_6]^2+ rightarrow [*Ru(NH_3)_6]^2+ + [Ru(NH_3)_6]^3+

Explanation / Answer

bond length change and change in electron arrangement attributes towards the rate constant of the self exchange reaction.

as we can see that the bond length change in cobalt complex is more, which results in more change in electron arrangement that is why the reaction is slow. whereas, in Ru complex the bond length change is less, resulting in faster reaction.

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