Consider the following reaction and statements : [ Co ( NH 3 ) 4 Br 2 ] + + Br − → [ Co ( NH 3 ) 3 Br 3 ] + NH 3 (I) Two isomers are produced if the reactant complex ion is a cis-isomer.

Question

Consider the following reaction and statements : $[Co (NH_{3})_{4} Br_{2}]^{+} + Br^{-} \to [Co (NH_{3})_{3} Br_{3}] + NH_{3}$

(I) Two isomers are produced if the reactant complex ion is a cis-isomer.

(II) Two isomers are produced if the reactant complex ion is a trans-isomer.

(III) Only one isomer is produced if the reactant complex ion is a trans-isomer.

(IV) Only one isomer is produced if the reactant complex ion is a cis-isomer.

The correct statements are :

TestHub · Accepted Answer

Concepts: Isomerism in coordination compounds, specifically geometric isomerism (cis/trans) and substitution reactions.

Explanation:

The reaction is a substitution reaction where an NH₃ ligand is replaced by a Br⁻ ligand.

Reactant: $[C o (N H_{3})_{4} B r_{2}]^{+}$ (octahedral complex, $M A_{4} B_{2}$ type)

Product: $[C o (N H_{3})_{3} B r_{3}]$ (octahedral complex, $M A_{3} B_{3}$ type)

1. If the reactant is cis- $[C o (N H_{3})_{4} B r_{2}]^{+}$ :

The two Br ligands are adjacent. When one NH₃ is replaced by Br⁻, two possible isomers of $[C o (N H_{3})_{3} B r_{3}]$ can be formed:

a) One where the three Br ligands are facial (fac-isomer).

b) One where the three Br ligands are meridional (mer-isomer).

Thus, two isomers are produced. Statement (I) is correct.

2. If the reactant is trans- $[C o (N H_{3})_{4} B r_{2}]^{+}$ :

The two Br ligands are opposite. When one NH₃ is replaced by Br⁻, only one isomer of $[C o (N H_{3})_{3} B r_{3}]$ can be formed, which is the mer-isomer. The three Br ligands will be in a plane, forming a meridian.

Thus, only one isomer is produced. Statement (III) is correct.

Therefore, statements (I) and (III) are correct.

The final answer is $A$

Chemistry - Coordination Chemistry Question with Solution | TestHub

Options:

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