Q: Which of the following rate laws is characteristic of a dissociative ligand substitution mechanism?

$$\text{rate} = k_1$[\text{ML}_5\text{X}]$$

Q: Which of the following rate laws would indicate an associative mechanism for ligand substitution?

$$\text{rate} = k_1$[\text{ML}_5\text{X}][\text{Y}]$$

Question 1

Which of the following statements best describes the difference between a thermodynamically unstable complex and a kinetically labile complex?

Accepted Answer

A thermodynamically unstable complex has a large equilibrium constant for dissociation, while a kinetically labile complex has a low activation energy for substitution.

Question 2

Which of the following rate laws is characteristic of a dissociative ligand substitution mechanism?

Accepted Answer

$$	ext{rate} = k_1$[	ext{ML}_5	ext{X}]$$

Question 3

Which of the following factors would most likely increase the rate of ligand substitution in an octahedral complex via a dissociative mechanism?

Accepted Answer

Increasing the steric bulk of the ligands around the metal center.

Question 4

For the reaction $$[Co(NH_3$)_6]^{3+} + 6H_2O \rightarrow [Co(OH_2$)_6]^{3+} + 6NH_3$$, the half-life is several days. What does this indicate about the complex?

Accepted Answer

It is thermodynamically stable and kinetically inert.

Question 5

Which of the following best describes the associative mechanism of ligand substitution?

Accepted Answer

The entering ligand coordinates to the metal before the leaving group departs, forming a higher-coordinate intermediate.

Question 6

Which of the following is a key experimental signature of an interchange mechanism in ligand substitution?

Accepted Answer

A rate law that depends on both the complex and entering ligand, but no intermediate is observed.

Question 7

Which of the following d-electron configurations is most likely to result in an inert (slowly reacting) octahedral complex?

Accepted Answer

$$d^3 (e.g$$., Cr(III))

Question 8

The trans effect in square planar complexes is best described as:

Accepted Answer

The ability of a ligand to increase the rate of substitution of the ligand trans to it.

Question 9

Which of the following nucleophiles would you expect to substitute most rapidly into a Pt(II) square planar complex, based on the nucleophilicity parameter $$n_n$$?

Accepted Answer

$$(C_6H_5)_3P$$

Question 10

Which of the following is true regarding the volume of activation ($$\Delta V$$^{\ddagger}$$) for ligand substitution mechanisms?

Accepted Answer

A positive $$\Delta V$$^{\ddagger}$$ suggests a dissociative mechanism.

Question 11

Which of the following best explains why $$[Fe(phen)_3]^{2+} is $$particularly inert to ligand substitution?

Accepted Answer

It has a high ligand field stabilization energy (LFSE) due to chelation and low-spin $$d^6$$ configuration.

Question 12

Which of the following rate laws would indicate an associative mechanism for ligand substitution?

Accepted Answer

$$	ext{rate} = k_1$[	ext{ML}_5	ext{X}][	ext{Y}]$$

Question 13

Which of the following statements about outer-sphere electron transfer reactions is correct?

Accepted Answer

They involve electron tunneling without major disturbance of the coordination spheres.

Question 14

In the context of ligand substitution, what is the main kinetic consequence of increasing the electron density at the metal center (e.g., by using $$NH_3$$ ligands instead of $$H_2O$$)?

Accepted Answer

It increases the rate of ligand substitution by facilitating M-X bond cleavage.

Question 15

Which of the following is a correct expression for the Gibbs energy of activation?

Accepted Answer

$$\Delta G$$^{\ddagger}$$ = \Delta H$$^{\ddagger}$$ - T\Delta S$$^{\ddagger}$$

Question 16

Which of the following best describes the effect of bulky ligands on the mechanism of ligand substitution in octahedral complexes?

Accepted Answer

They favor dissociative activation by relieving steric strain in the transition state.

Question 17

Which of the following is a key difference between inner-sphere and outer-sphere electron transfer mechanisms?

Accepted Answer

Inner-sphere mechanisms involve a bridging ligand that may be exchanged during the reaction.

Question 18

Which of the following best explains why the rate of ligand substitution in $$[Co(NH_3$)_6]^{3+} is $$much slower than in $$[Ni(H_2O)_6]^{2+}$$?

Accepted Answer

$$[Co(NH_3$)_6]^{3+}$$ has a higher ligand field stabilization energy (LFSE).

Question 19

Which of the following is the correct relationship for the rate constant $$k in $$terms of activation parameters?

Accepted Answer

$$\ln\left(\frac{k}{T}\right) = -\frac{\Delta H$$^{\ddagger}$$}{RT} + \ln\left(\frac{k'}{h}\right) + \frac{\Delta S$$^{\ddagger}$$}{R}$$

Ligand Substitution and Electron Transfer in Coordination Complexes

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