Question

(a) Draw the two linkage isomers of \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{SCN}\right]^{2+}\). (b) Draw the two geometric isomers of \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3} \mathrm{Cl}_{3}\right]^{2+}\). (c) Two compounds with the formula \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{ClBr}\) can be prepared. Use structural formulas to show how they differ. What kind of isomerism does this illustrate?

Short answer

The two linkage isomers of \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{SCN}\right]^{2+}\) are: 1. N-Bound Isomer: \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left( \mathrm{NCS}\right) \right]^{2+}\) 2. S-Bound Isomer: \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left( \mathrm{SCN}\right) \right]^{2+}\) The two geometric isomers of \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3} \mathrm{Cl}_{3}\right]^{2+}\) are: 1. cis-Isomer: \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3}\left(\mathrm{Cl}\right)_{3}\right]^{2+}_\text{cis}\) 2. trans-Isomer: \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3}\left(\mathrm{Cl}\right)_{3}\right]^{2+}_\text{trans}\) The two compounds with the formula \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{ClBr}\) exhibit ionization isomerism: 1. Isomer 1: \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{Cl}\right)\right]^{+} \mathrm{Br}^{-}\) 2. Isomer 2: \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{Br}\right)\right]^{+} \mathrm{Cl}^{-}\)

Step-by-step solution

Part (a) Step 1: Understanding Linkage Isomerism

Linkage isomers are coordination complexes that have the same composition but the connectivity of one ligand is different. In this case, we are looking at isomers of \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{SCN}\right]^{2+}\) where the thiocyanate ligand (SCN-) can bind through either the sulfur (S) or nitrogen (N) atom to the central cobalt (Co) atom.

Part (a) Step 2: Drawing the Isomers

There are two linkage isomers for this complex: 1. N-Bound Isomer: The nitrogen atom in SCN- is bound to the cobalt atom. \[ \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left( \mathrm{NCS}\right) \right]^{2+} \] 2. S-Bound Isomer: The sulfur atom in SCN- is bound to the cobalt atom. \[ \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left( \mathrm{SCN}\right) \right]^{2+} \]

Part (b) Step 1: Understanding Geometric Isomerism

Geometric isomerism occurs in coordination complexes when the arrangement of the ligands around the coordination center is different. In this case, we are looking at the isomers of \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3} \mathrm{Cl}_{3}\right]^{2+}\). Geometric isomerism exists as cis- or trans-isomers based on the relative positions of the ligands.

Part (b) Step 2: Drawing the Isomers

There are two geometric isomers for this complex: 1. cis-Isomer: The three chlorine atoms are adjacent to each other. \[ \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3}\left(\mathrm{Cl}\right)_{3}\right]^{2+}_\text{cis} \] 2. trans-Isomer: The three chlorine atoms are opposite to each other. \[ \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3}\left(\mathrm{Cl}\right)_{3}\right]^{2+}_\text{trans} \]

Part (c) Step 1: Drawing the Structural Formulas

There are two compounds with the formula \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{ClBr}\): 1. Isomer 1 \[ \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{Cl}\right)\right]^{+} \mathrm{Br}^{-}\] 2. Isomer 2 \[ \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{Br}\right)\right]^{+} \mathrm{Cl}^{-}\]

Part (c) Step 2: Identifying Type of Isomerism

In these two compounds, the ligands are in different locations around the cobalt atoms. Specifically, the chlorine is a ligand in one compound, while bromine is a ligand in the other. This type of isomerism is called ionization isomerism.