Consider two redox pairs: (1) Cr(II)/Ru(III) (2) Cr(II)/Co(III) The rate of acceleration in going from a outer-sphere to a inner-sphere mechanism is lower for (1) relative to (2). Its correct explanation is
(a)HOMO/LUMO are $\sigma^{*}$ and $\sigma^{*}$ respectively.
(b)HOMO/LUMO are $\sigma^{*}$ and $\pi^{*}$ respectively.
(c)HOMO/LUMO are $\pi^{*}$ and $\sigma^{*}$ and respectively.
(d)HOMO/LUMO are $\pi^{*}$ and $\pi^{*}$ respectively.
Answer
Answer: B ✓ checked by 4AB · confidence medium
The source book printed A; on checking, B is correct — see the explanation.
Explanation
Cr(II) donates from σ* (e_g). Ru(III) accepts into π* (t₂g), while Co(III) accepts into σ*. A bridging ligand helps σ*→σ* transfer most, so pair (1), with HOMO σ* and LUMO π*, gains less from the inner-sphere path (b).