Problem 114 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the list I and II, pick the correct matching from the codes given below List I List II (a) \(\left[\mathrm{Ag}(\mathrm{CN})_{2}\right]\) 1\. square planar and \(1.73 \mathrm{BM}\) (b) \(\left[\mathrm{Cu}\left(\mathrm{CN}_{4}\right)\right]^{3}\) 2\. linear and zero (c) \(\left[\mathrm{Cu}(\mathrm{CN})_{6}\right]^{3-}\) 3\. octahedral and zero (d) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}\) 4\. tetrahedral and zero (e) \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4} \quad\) 5. octahedral and \(1.73 \mathrm{BM}\) (a) \(a-4, b-2, c-5, d-3, e-1\) (b) \(a-4, b-5, c-2, d-1, e-3\) (c) a-2, b-4, c-5, d-1, e-3 (d) a-5, b-4, c-1, d-3, e-2

Step-by-Step Solution

Answer

Option (c): a-2, b-4, c-5, d-1, e-3 matches the descriptions correctly.

Step 1: Identify Coordination Geometry

Examine each complex ion to determine its coordination geometry based on the number and type of ligands. Use this to simplify matching each compound in List I with the corresponding property in List II.

Step 2: Match [Ag(CN)2]-

The complex \[\mathrm{Ag}(\mathrm{CN})_2\]\ is linearly coordinated due to the linear alignment of two ligands with silver. This suggests it matches with 'linear and zero,' corresponding to option 2 in List II.

Step 3: Match [Cu(CN)4]3-

The complex ion \[\mathrm{Cu}(\mathrm{CN})_4\]^{3-}\ has a tetrahedral geometry due to four ligands surrounding the copper ion. This configuration suggests zero magnetic moment, matching option 4.

Step 4: Match [Cu(CN)6]3-

The complex \[\mathrm{Cu}(\mathrm{CN})_6\]^{3-}\ is octahedral with six ligands around the central metal. Given this structure and electronic configuration, it will have a zero magnetic moment, matching option 3.

Step 5: Match [Cu(NH3)4]2+

The complex \[\mathrm{Cu}(\mathrm{NH}_3)_4\]^{2+}\ is square planar typically for copper complexes and due to d9 configuration, it has a measurable magnetic moment, which could be 1.73 BM, matching option 1.

Step 6: Match [Fe(CN)6]4-

The complex \[\mathrm{Fe}(\mathrm{CN})_6\]^{4-}\ being an iron complex with six ligands usually forms an octahedral structure. This configuration could make it either low or high spin, and historically, its measured moment can match 1.73 BM, corresponding to option 5.

Step 7: Cross-Checking Results

Cross-verify the assigned matches with all given options: the solutions find only option (c) aligns: a-2, b-4, c-5, d-1, e-3. This seems consistent with determined coordination geometries and associated magnetic properties.

Key Concepts

Coordination Geometry

Understanding coordination geometry is key in predicting the shape and certain properties of complex ions. Coordination geometry refers to the spatial arrangement of ligands around the central metal atom or ion.

This arrangement can significantly impact the stability and reactivity of a complex. Here are some common coordination geometries:

• **Linear**: as seen with the \[\mathrm{Ag}(\mathrm{CN})_2^{-}\] complex, where a metal is bonded to two ligands in a straight line.
• **Tetrahedral**: observed in a complex like \\[\mathrm{Cu}(\mathrm{CN})_4^{3-}\], with four ligands in a shape similar to a pyramid.
• **Octahedral**: typical in structures like \\[\mathrm{Fe}(\mathrm{CN})_6^{4-}\], where six ligands form an octahedral shape around the metal ion.
• **Square Planar**: often found in complexes of metals like copper, where four ligands form a square around the central ion, as in \\[\mathrm{Cu}(\mathrm{NH}_3)_4^{2+}\].

Predicting the geometry helps in envisaging how a complex might behave chemically and physically.

Complex Ions

Complex ions are entities formed from a central metal atom or ion surrounded by one or more ligands. These compounds play crucial roles in various chemical processes.

A key component of complex ions is the metal center, which has empty orbitals ready to accept electrons from ligands. The ligands act as Lewis bases, donating electron pairs into the metal's orbitals. This results in a coordination bond, enabling the formation of the complex.

For example, in \\[\mathrm{Cu}(\mathrm{NH}_3)_4^{2+}\], copper acts as the central metal and ammonia molecules are the ligands. This intricate interaction defines the properties such as color, magnetic behavior, and reactivity of the complex. Complex ions can exist in different geometries, as the d-block elements offer a flexible bonding environment.

Magnetic Properties

The magnetic properties of coordination compounds arise from the presence or absence of unpaired electrons in the metal's d-orbitals. These properties vary due to the different electronic arrangements in the compounds.

A complex with no unpaired electrons is termed diamagnetic. For instance, the octahedral \\[\mathrm{Cu}(\mathrm{CN})_6^{3-}\] has a zero magnetic moment.

However, if a complex contains unpaired electrons, it can be paramagnetic and exhibit a magnetic moment. An example is \\[\mathrm{Cu}(\mathrm{NH}_3)_4^{2+}\] with a possible magnetic moment of 1.73 BM, due to its square planar configuration and d9 electronic configuration. Knowing the magnetic properties helps in understanding the compound's electronic configuration and predicting its reactivity.

Ligands

Ligands are ions or molecules that donate electron pairs to the central metal atom or ion in a coordination complex. Their nature and the way they bond play a critical role in the characteristics of the complex.

Ligands can be classified based on several factors:

• **Charge**: Neutral (e.g., \'\(\mathrm{NH}_3\)) or negatively charged (e.g., \'\(\mathrm{CN}^-\)).
• **Dentate**: Monodentate (offering a single pair of electrons to the metal like \'\(\mathrm{CN}^-\)) or polydentate (offering multiple electron pairs such as EDTA).
• **Field Strength**: Depending on the ligand's ability to split the d-orbitals of the central atom more effectively, leading to strong or weak field ligands.

In complexes like \\[\mathrm{Ag}(\mathrm{CN})_2^{-}\], the ligands lead to a linear structure because of their strong field nature, resulting in zero magnetic moment.

Electronic Configuration

Electronic configuration concerns the arrangement of electrons in an atom's d-orbitals, impacting the overall properties of a coordination compound. It dictates the geometry and magnetic nature of the complex.

Understanding this helps in predicting how the complex will interact chemically. Take \\[\mathrm{Cu}(\mathrm{NH}_3)_4^{2+}\] as an example. Here, copper in a +2 oxidation state has a d9 configuration, resulting in a square planar structure.

Configurations can broadly influence whether a complex is high-spin or low-spin. In some octahedral complexes like \\[\mathrm{Fe}(\mathrm{CN})_6^{4-}\], the electronic configuration can produce either low or high spin states, impacting the complex's magnetic properties and reactivity.