Problem 132 - A Complete Resource Book in Chemistry for JEE Main

Question

$$ \begin{aligned} &\text { Match the following }\\\ &\begin{array}{ll} \hline \text { Column-I } & \text { Column-II } \\ \hline \text { (a) }\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right] & \text { (p) Geometrical isomers } \\ \mathrm{Cl}_{2} & \\ \text { (b) }\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right] & \text { (q) Paramagnetic } \\ \text { (c) }\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5} \mathrm{Cl}\right] \mathrm{Cl} & \text { (r) Diamagnetic } \\ \text { (d) }\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right] \mathrm{Cl}_{2} & \text { (s) } \begin{array}{l} \text { Metal ion with }+2 \\ \text { oxidation state } \end{array} \\ & \text { (t) } s p^{3} \mathrm{~d}^{2} \text { hybridization } \\ & \text { of central metal atom } \end{array} \end{aligned} $$

Step-by-Step Solution

Answer

a - q, b - p, c - r (if apply external ligand set), or default retains to s (ox state +3), d - s (Ni for +2 oxidation)

Step 1: Analyze the First Complex - (a)

Consider the complex \( ext{[Co(NH}_3 ext{)}_4( ext{H}_2 ext{O)}_2 ext{]Cl}_2\). This is an octahedral complex where Co has an oxidation state of +2. Co(II) is known to be paramagnetic due to the presence of unpaired electrons. Therefore, (a) matches with (q).

Step 2: Analyze the Second Complex - (b)

The complex \( ext{[Pt(NH}_3 ext{)}_2 ext{Cl}_2 ext{]}\) is a square planar complex. It shows geometrical isomerism because it can exist as cis and trans isomers. Therefore, (b) matches with (p).

Step 3: Analyze the Third Complex - (c)

The complex \( ext{[Co(H}_2 ext{O)}_5 ext{Cl]Cl}\) contains Co in the +3 oxidation state. In the absence of strong field ligands like ammonia (NH₃), Co(III) tends to be low spin and potentially diamagnetic. However, Co in a +3 state isn't necessarily diamagnetic or paramagnetic unless confirmed by ligand type and external configurations. Hence, for safety of elements, it is closer to (r) diamagnetism.

Step 4: Analyze the Fourth Complex - (d)

In the complex \( ext{[Ni(H}_2 ext{O)}_6 ext{]Cl}_2\), Ni is in a +2 oxidation state since each chloride ion (Cl-) provides a -1 charge. Furthermore, \( ext{Ni}^{2+}\) generally uses \(dsp^2\) hybridization for square planar complexes and \(sp^3d^2\) for octahedral, however, this complex is demonstrated with \( ext{sp}^3\) hybrid orbitals, not the provided \(sp^3d^2\), making it having the tendency to be intrinsically close to concept of geometries. Hence, related directly to Column II combination as hybridization was not matching.

Key Concepts

Geometrical Isomerism

In coordination chemistry, geometrical isomerism occurs in complex compounds, particularly those with certain shapes like square planar or octahedral. Geometrical isomers have the same formula but differ in the spatial arrangement of ligands.

• Common in square planar complexes like \([\text{Pt(NH}_3)_2\text{Cl}_2]\).
• Can exist as cis-isomers, where identical ligands are adjacent, or trans-isomers, where they are opposite one another.
• This type of isomerism is not possible in tetrahedral complexes due to symmetry.

Geometrical isomerism is significant for its impact on the physical and chemical properties of a compound. For example, the cis and trans forms can have vastly different activities in biological systems.

Paramagnetism

Paramagnetism is a type of magnetism occurring in materials with unpaired electrons. In coordination chemistry, many metal complexes exhibit paramagnetism due to these unpaired electrons in the d-orbitals.

• Transition metals like Co(II) often exhibit paramagnetism.
• The paramagnetic nature depends on the oxidation state and ligand field.
• Complexes with unpaired d-electrons align with an external magnetic field, making them paramagnetic.

For example, \([\text{Co(NH}_3)_4(\text{H}_2O)_2]\text{Cl}_2\) shows paramagnetic properties due to unpaired electrons present in the Co(II). Understanding this concept is crucial for identifying the magnetic behavior of a coordination compound.

Hybridization

Hybridization in coordination compounds involves the mixing of atomic orbitals to form new hybrid orbitals, which then accommodate ligand electrons. The type of hybridization affects the shape and bonding of the metal complex.

• Common types include \(sp^3\), \(dsp^2\), and \(sp^3d^2\).
• The geometry (e.g., octahedral, square planar) influences the hybridization types.
• Metal complexes like \(\text{Ni(H}_2\text{O)}_6\text{Cl}_2\) show octahedral geometry typically involving \(sp^3d^2\) hybridization.

The hybridization concept helps in predicting the geometry of the complex, understanding how ligands are bonded, and analyzing the physical properties like stability and reactivity.

Oxidation State

The oxidation state in coordination chemistry indicates the total number of electrons that an atom uses to form bonds with ligands. It is crucial for understanding the electron configuration and reactivity of a complex.

• Determined by considering the charge of the complex and the known charges of the ligands.
• For example, in \([\text{Co(NH}_3)_4(\text{H}_2O)_2]\text{Cl}_2\), Co has an oxidation state of +2.
• Transition metals can exhibit multiple oxidation states, affecting their magnetic and spectral behavior.

Recognizing the oxidation state aids in predicting the magnetic properties (paramagnetic or diamagnetic) and potential reactivity of coordination compounds.

Complex Ions

Complex ions consist of a central metal ion bonded to surrounding ligands. These entities play a key role in the field of coordination chemistry due to their versatile bonding and reactions.

• Comprised of a transition metal and coordinated ligands, such as ammonia or water.
• The overall charge of a complex ion depends on the charges of the metal and ligands.
• Examples include complexes like \([\text{Co(H}_2\text{O)}_5\text{Cl}]\text{Cl}\), where ligands determine the chemistry and functionality.

Studying complex ions can help understand the color, solubility, and catalytic activity of compounds, making this concept valuable in industrial and biological applications.