Problem 6 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The one that can exhibit highest paramagnetic behaviour among the following is: gly \(=\) glycinato; bpy \(=2,2\) '-bipyridine (a) \(\left[\mathrm{Pd}(\mathrm{gly})_{2}\right]\) (b) \(\left[\mathrm{Fe}(\mathrm{en})(\mathrm{bpy})\left(\mathrm{NH}_{3}\right)_{2}\right]^{2+}\) (c) \(\left[\mathrm{Co}(\mathrm{OX})_{2}(\mathrm{OH})_{2}\right]^{-}\left(\Delta_{0}>\mathrm{P}\right)\) (d) \(\left[\mathrm{Ti}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}\)

Step-by-Step Solution

Answer

Compound (b) [Fe(en)(bpy)(NH_3)_2]^{2+} has the highest paramagnetic behaviour.

Step 1: Understanding Paramagnetic Behaviour

Paramagnetism is related to the presence of unpaired electrons in a compound. The more unpaired electrons present, the higher the paramagnetic behaviour. To determine which compound has the highest paramagnetic behaviour, we must consider the electron configurations of each central metal ion.

Step 2: Assessing Compound (a): [Pd(gly)_2]

Palladium ( ext{Pd}) generally loses its two s electrons when it forms a complex. In the ext{Pd}^{2+} oxidation state, all the d electrons are paired, leading to a diamagnetic character. Hence, it exhibits no paramagnetic behaviour.

Step 3: Assessing Compound (b): [Fe(en)(bpy)(NH_3)_2]^{2+}

Iron ( ext{Fe}) in this complex is in the +2 oxidation state. Typically, ext{Fe}^{2+} has six d electrons. If it is a high-spin complex, it will have four unpaired electrons, showing strong paramagnetic behaviour. However, we must verify the coordination environment to confirm.

Step 4: Assessing Compound (c): [Co(OX)_2(OH)_2]^{-} (Δ_{0}>P)

Cobalt ( ext{Co}) in this complex is likely in the +3 oxidation state, giving it six d electrons in a low-spin arrangement ( ext{Δ_{0}>P}). Given a low-spin configuration, all electrons are paired, leading to a diamagnetic or weakly paramagnetic character.

Step 5: Assessing Compound (d): [Ti(NH_3)_6]^{3+}

Titanium ( ext{Ti}) in this complex is in the +3 oxidation state, giving it one d electron. With one unpaired electron, it displays paramagnetic behaviour, though not as strong as multiple unpaired electrons.

Step 6: Comparing Unpaired Electrons

Comparing the complexes, compound (b) [Fe(en)(bpy)(NH_3)_2]^{2+} can potentially be high-spin with four unpaired electrons if formed as such, thus exhibiting strong paramagnetic behaviour. Compounds (a), (c), and (d) have either paired electrons or fewer unpaired electrons.

Key Concepts

Coordination Chemistry

Coordination chemistry is a fascinating field that studies the interactions between metal ions and ligands. These interactions form structures known as coordination complexes, where a central metal ion binds to surrounding molecules or ions, called ligands.
Coordination chemistry is not only crucial for understanding various biological processes and industrial applications,
but it also aids in comprehending the magnetic properties of materials, such as paramagnetism.
Some key features of coordination complexes include:

• Coordination Number: This is the number of ligand donor atoms bonded to the central metal ion. Each ligand contributes a set of electrons, typically through lone pairs.
• Geometric Structure: The arrangement of ligands around the central metal ion can vary greatly, influencing the properties of the complex. Common geometries include octahedral, tetrahedral, and square planar.
• Ligand Field Theory: This theory explains how ligands affect the d-orbitals of the central metal ion, leading to variations in electronic configurations and the behaviour of unpaired electrons.

Understanding coordination chemistry is essential for appreciating the complex nature of paramagnetism in transition metal complexes, as seen in the given exercise.

Electron Configuration

Electron configuration is pivotal in predicting the properties of elements and their compounds,
including their magnetic behavior. It involves the distribution of electrons among the available orbitals around a nucleus.
For transition metals, the d-orbitals play a crucial role in determining the overall electron configuration.
Key considerations when understanding electron configurations of transition metals include:

• Oxidation States: Transition metals often exhibit various oxidation states, affecting their electron configurations. Each oxidation state involves a different number of electrons in the d-orbitals.
• Spin States: There are high-spin and low-spin configurations, which depend on the energy gap between the d-orbitals and the distribution of electrons among them.
• Unpaired Electrons: Paramagnetism arises from unpaired electrons in the d-orbitals, making understanding their configuration vital in predicting magnetic behaviors.

By mastering electron configurations, you will have better insights into the magnetic properties of transition metal complexes.

Transition Metal Complexes

Transition metal complexes are unique due to their ability to exhibit a variety of magnetic and electronic properties,
thanks to their partially filled d-orbitals.
Each transition metal can form complexes with different ligands, taking on distinct geometries and properties.
Some key attributes of transition metal complexes include:

• Varying Magnetic Properties: Depending on the number of unpaired electrons and the type of ligands, these complexes can be diamagnetic or paramagnetic. Paramagnetism, in particular, involves unpaired electrons contributing to the overall magnetic properties.
• Colorful Nature: These complexes with unpaired electrons often exhibit vivid colors. This is due to d-d transitions, where electrons move between d-orbitals of different energy levels, absorbing light in the process.
• Catalytic Abilities: Many transition metal complexes act as catalysts due to their ability to change oxidation states easily, facilitating various chemical reactions.

Understanding transition metal complexes is essential when evaluating their paramagnetic behavior, as demonstrated in the example exercise. By examining the electronic arrangement and ligand interactions, one can predict which complexes will have higher paramagnetic properties.