Q47 · CSIR-NET Chemistry, December 2011

Paper: CSIR-NET December 2011 · Subject: Inorganic Chemistry · Chapter: Coordination Chemistry · Topic: Electron Transfer Redox · Marks: 2 · Difficulty: Medium

For the following outer sphere electron transfer reactions.
\[ \begin{array}{l} \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}+\left[\mathrm{Co}^{*}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+} \rightarrow \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}+\left[\mathrm{Co}^{*}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+} \\ \left[\mathrm{Ru}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}+\left[\mathrm{Ru}^{*}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+} \rightarrow \left[\mathrm{Ru}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}+\left[\mathrm{Ru}^{*}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+} \end{array} \]
due to
(a)A change from high spin to low spin in $\mathrm{Co}^{*}$ and high spin to low spin in Ru.
(b)A change from high spin to low spin in Co* and low spin to high spin $\mathrm{Ru}^{*}$.
(c)A change from low spin to high spin in $\mathrm{Co}^{*}$ and the low spin state remains unchanged in Ru.
(d)A change from low spin to high spin in $\mathrm{Co}^{*}$ and high spin to low spin in $\mathrm{Ru}^{*}$.
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
Co(II) high-spin (t₂g⁵e_g²) must reorganise to low-spin Co(III) (t₂g⁶): large inner-sphere reorganisation makes the exchange very slow. Both Ru(II) and Ru(III) are low-spin, so the Ru exchange is fast.

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