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Chapter 27: Problem 13

Discuss the mechanism for the base hydrolysis of octahedral ammine complexes of \(\mathrm{Co}^{3+}\).

Short Answer

Expert verified
In the base hydrolysis of octahedral ammine complexes, a hydroxide ion acts as a nucleophile and displaces one of the ammine ligands in the cobalt complex. This forms a new octahedral complex where one of the ammonia ligands is replaced with a hydroxide ion.

Step by step solution

01

- Understanding the Reaction

Octahedral ammine complexes of \(\mathrm{Co}^{3+}\) for example, can be represented as \([Co(NH_3)_6]^{3+}\). In base hydrolysis, a base, such as hydroxide ion \(\mathrm{OH^-}\), reacts with the complex to displace one or more of the ammine ligands. This results in the formation of a new complex, along with water and ammonia.
02

- Identifying the reactants and products

During base hydrolysis, the base (hydroxide ion) reacts with the complex. In the case of \([Co(NH_3)_6]^{3+}\), the reaction can be represented as follows:\n\([Co(NH_3)_6]^{3+} + OH^- → [Co(NH_3)_5OH]^{2+} + NH_3\)\nThe reactants are therefore the complex \([Co(NH_3)_6]^{3+}\) and hydroxide ion, and the products are the complex \([Co(NH_3)_5OH]^{2+}\), ammonia and water.
03

- Describing the Reaction Pathway

The reaction begins with the nucleophilic attack of the hydroxide ion on the cobalt center of \([Co(NH_3)_6]^{3+}\). This results in the formation of a transition state, where the hydroxide ion has partially bonded to the cobalt. Since cobalt is in a high oxidation state, it prefers a smaller coordination number and displaces one of the ammonia ligands from the complex. This leaves the cobalt bound to five ammonia ligands and one hydroxide ion, forming the complex \([Co(NH_3)_5OH]^{2+}\). The displaced \(\mathrm{NH_3}\) leaves as a free molecule.
04

- Role of Base Hydrolysis

Base hydrolysis plays a critical role in this reaction. The hydroxide ion, a strong base, acts as a nucleophile and attacks the cobalt center. This causes one of the bonded ammonia molecules in the ammine complex to be displaced. The reaction is facilitated as the hydroxide ion provides the nucleophilic attack necessary to displace the ammonia ligand and reduce the coordination number of the cobalt center.

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Most popular questions from this chapter

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