Tutorial 2 - Inorganic Mechanisms 2 PDF

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SHC4001 Inorganic Chemistry 3 – Tutorial 2

Inorganic Mechanisms 2 - Electron Transfer Reactions 1.

How can inner sphere electron transfer reactions be distinguished from outer sphere electron transfer reactions?

2.

Suggest giving reasons which electron transfer mechanism is operating in the following reactions

i) [Cr*(H2O)6]3+ + [Cr(H2O)6]2+ → [Cr*(H2O)6]2+ + [Cr(H2O)6]3+ k = 10-5 M-1 s-1 ii) [Cr*(H2O)5F]3+ + [Cr(H2O)6]2+ → [Cr*(H2O)6]2+ + [Cr(H2O)5F]3+ k = 0.02 M-1 s-1 iii) [Cr*(H2O)5Cl]3+ + [Cr(H2O)6]2+ → [Cr*(H2O)6]2+ + [Cr(H2O)5Cl]3+ k = 9.0 M-1 s-1 Explain why the rate constant for the reduction of [Co(NH3)5(OH)]2+ by

3.

[Cr(H2O)6]2+ is 107 times faster than that for [Co(NH3)5(H2O)]3+ and why the rate of reaction of [Co(NH3)5(H2O)]3+ is proportional to 1/[H +]. 4.

Explain the differences between the rate constants for the following outer sphere self-exchange electron transfer reactions

5.

i)

[Ru(H2O)6]2+ / [Ru(H2O)6]3+ k = 4 x 103 M-1 s-1

ii)

[Cr(H2O)6]2+ / [Cr(H2O)6]3+ k = 10-5 M-1 s-1

iii)

[Co(NH3)6]2+ / [Co(NH3)6]3+ k = 10-6 M-1 s-1

Give the oxidation states, d-electron counts and spin state (HS or LS) of the three following complexes and hence deduce which one is able to undergo an inner sphere reaction with [(NH3)5Co(NCS)]2+. [Cr(H2O)6]2+

[Fe(CN)6]4-

[Co(CN)5]3-

SHC4001 Inorganic Chemistry 3 – Tutorial 2

6.

The ambidentate ligand NCS- usually binds to hard metal ions through the N-atom. Suggest how the S-bound complex [(NH3)5Cr(SCN)]2+ could be prepared. Write out a reaction mechanism to explain your answer.

7.

Using the following electrochemical and self-exchange rate data calculate the rate of the oxidation at 298 K of [Cr(OH2)6]2+ (E = -0.41 V, kself = 1 x 10-5 dm3 mol-1 s-1) by a) [Fe(OH6)]3+ (E = +0.77 V, kself = 1.1 dm3 mol-1 s-1) and b) [Ru(bpy)3]3+ (E = +1.26 V, kself = 4 x 108 dm3 mol-1 s-1). Assume f12 = 1....