Problem 129 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following Column-I Column-II \begin{tabular}{ll} Column-I & Column-II \\ \hline \(\begin{array}{ll}\text { (a) }\left[\mathrm{Co}\left(\mathrm{NO}_{2}\right)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\left(\mathrm{NH}_{3}\right)_{2}\right] & \text { (p) } & \text { Number of } \\ \mathrm{NO}_{3} & \text { stereoisomers } \\ & =6\end{array}\) \\ \(\begin{array}{ll}\text { (b) }\left[\mathrm{Ni}(\mathrm{en})_{3}\right] \mathrm{Br}_{3} & \text { (q) Linkage } \\ \text { isomerism }\end{array}\) \\ (c) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3}(\mathrm{py})_{3}\right] \mathrm{Br}_{2}\) & (r) Ionization isomerism \\ (d) \(\left[\mathrm{Pt}(\mathrm{en})(\mathrm{SCN})_{2}\right]\left(\mathrm{NO}_{3}\right)_{2}\) & (s) Optical isomerism \\ (t) Geometrical \\ & isomerism \\ \hline \end{tabular}

Step-by-Step Solution

Answer

(a) matches with (q), (b) with (s), (c) with (t), and (d) with (r).

Step 1: Analyze Complex (a)

The complex \(\left[\mathrm{Co}\left(\mathrm{NO}_{2}\right)_{2}\left(\mathrm{H}_{2}\mathrm{O}\right)_{2}\left(\mathrm{NH}_{3}\right)_{2}\right]\) contains two bidentate ligands \(\mathrm{NO}_{2}\left(\mathrm{nitrito}\right)\), which can exhibit linkage isomerism because this ligand can bind through the nitrogen or the oxygen atom. Therefore, the correct match for complex (a) is linkage isomerism, matching with Column-II option (q).

Step 2: Analyze Complex (b)

The complex \(\left[\mathrm{Ni}(\mathrm{en})_{3}\right]\mathrm{Br}_{3}\) is an octahedral complex with \(en\) (ethylenediamine) as a bidentate ligand, which can exhibit optical isomerism due to the presence of non-superimposable mirror images. Thus, complex (b) matches with option (s) in Column-II.

Step 3: Analyze Complex (c)

The complex \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3}(\mathrm{py})_{3}\right]\mathrm{Br}_{2}\) is an octahedral complex with different monodentate ligands. It can exhibit geometrical isomerism, allowing for different spatial arrangements. Therefore, complex (c) matches with option (t) from Column-II.

Step 4: Analyze Complex (d)

The complex \(\left[\mathrm{Pt}(\mathrm{en})(\mathrm{SCN})_{2}\right](\mathrm{NO}_{3})_{2}\) has \(SCN^{-}\) ligands that can exhibit linkage isomerism (binding through sulfur or nitrogen) or ionization isomerism due to the exchange of \(NO_3^-\) groups. Given Column-II options and typical considerations, ionization isomerism is more typical here, matching with option (r).

Step 5: Final Matching

Compile the results from each analysis step into the final matches: - (a) matches with (q): Linkage isomerism, - (b) matches with (s): Optical isomerism, - (c) matches with (t): Geometrical isomerism, - (d) matches with (r): Ionization isomerism.

Key Concepts

Linkage Isomerism

Linkage isomerism occurs in coordination compounds when a ligand can bind to the central atom in multiple ways. In such cases, different atoms in the same ligand can attach to the metal center, forming distinct isomers. This isomerism is typically observed in ligands like nitrite (NO\(^-\)\(_2\)) and thiocyanate (SCN\(^-\)).

For example, in nitrite, the nitrogen atom can bind to the metal, forming a nitro linkage, or the oxygen atom can bind, forming a nitrito linkage. This leads to different coordination modes:

• Nitro: The nitrogen atom is the donor.
• Nitrito: The oxygen atom is the donor.

Linkage isomers can have different physical and chemical properties, despite having the same molecular formula. These differences arise because the method of attachment can affect the overall geometry and polarity of the molecule.

Optical Isomerism

Optical isomerism is a type of stereoisomerism where compounds can have non-superimposable mirror images, similar to how your left and right hands are mirror images but cannot perfectly overlap. These mirror-image forms are known as enantiomers.

In coordination chemistry, optical isomerism occurs when chiral ligands or arrangements cause a spatial setup that does not have a plane of symmetry. A common scenario involves complexes with polydentate ligands like ethylenediamine (en), which can wrap around the central atom in a specific orientation.

Enantiomers have identical physical properties, such as melting and boiling points, but they interact differently with polarized light and other chiral environments. When placed in polarized light, one enantiomer will rotate the plane of light in one direction, while the other will rotate it in the opposite direction, thus exhibiting optical activity.

Geometrical Isomerism

Geometrical isomerism, also known as cis-trans isomerism, involves the different spatial arrangements of ligands around the central metal atom in a coordination complex. This type of isomerism is prevalent in coordination compounds with square planar or octahedral geometries.

In simple terms, geometrical isomers differ in the relative positions of their ligands:

• Cis: Similar ligands are adjacent to each other.
• Trans: Similar ligands are opposite each other.

The differences in spatial arrangement can lead to varied physical and chemical properties. For example, a cis isomer might be more reactive or have a higher solubility than its trans counterpart. Understanding these isomeric forms is crucial in designing coordination compounds with specific functions, as the properties can drastically influence their effectiveness in applications like catalysis or pharmacology.

Ionization Isomerism

Ionization isomerism occurs when a coordinated compound undergoes a switch between ions inside and outside the coordination sphere. This means that ligands can exchange places with ions outside the complex's coordination shell, altering the compound's properties.

This type of isomerism is distinguished by varying ions in the solution when dissolved. For example, a compound with the formula \([\text{Pt}(\text{en})(\text{SCN})_2](\text{NO}_3)_2\) might appear differently as \([\text{Pt}(\text{en})(\text{NO}_3)(\text{SCN})](\text{SCN})\), with nitrate and thiocyanate ions swapping places between the ligand sphere and the outer ionic field.

Such isomerism affects not only solubility but also conductivity and the response of the compound in different environments, making them interesting targets for study and application in fields such as coordination chemistry and bioinorganic chemistry.