Problem 10 - A Complete Resource Book in Chemistry for JEE Main

Question

Pentaamminenitrocobalt (III) cation possesses the property of (a) physiosorption (b) chirality (c) linkage isomerism (d) versatile reducing agent

Step-by-Step Solution

Answer

The correct property is (c) linkage isomerism.

Step 1: Understanding the Complex

The complex given is pentaamminenitrocobalt (III) cation. It consists of cobalt (III) as the central metal ion surrounded by five ammine ligands (NH3) and one nitro ligand (NO2). The complex has a positive charge due to the +3 oxidation state of cobalt.

Step 2: Analyze Possible Properties

We need to determine which property fits this complex best: physiosorption, chirality, linkage isomerism, or versatile reducing agent.

Step 3: Physiosorption Check

Physiosorption is the adsorption of species on the surface of a material through weak forces, such as Van der Waals interactions. This complex is in solution and does not exhibit this property.

Step 4: Chirality Check

A molecule is chiral if it is not superimposable on its mirror image. This complex is non-chiral as it has a symmetric arrangement of ligands around the central cobalt ion.

Step 5: Linkage Isomerism Check

Linkage isomerism occurs when a ligand can bind through different atoms. The nitro ligand can attach through either nitrogen (nitro) or oxygen (nitrito). This complex can show linkage isomerism due to the presence of the nitro ligand that can bind via N or O atoms.

Step 6: Versatile Reducing Agent Check

A reducing agent donates electrons to another species. This complex is not known to be a reducing agent as cobalt in the +3 oxidation state is less likely to donate electrons.

Key Concepts

Coordination Chemistry

Coordination chemistry revolves around the concept of coordination complexes. A coordination complex consists of a central metal atom or ion, surrounded by atoms, ions, or molecules known as ligands. These ligands bond to the metal through coordinate covalent bonds, which involve the donation of an electron pair from the ligand to the metal.

• The central metal is often a transition metal due to their capacity to accommodate various numbers of ligands thanks to their d orbitals.
• Ligands can be neutral molecules like water and ammonia, or they could be charged ions such as chloride or thiocyanate.

The geometric arrangement of ligands around the central metal ion defines the complex's structure. Common geometries include octahedral, tetrahedral, and square planar. In our exercise, the complex is pentaamminenitrocobalt (III), which means it has five ammine ligands and one nitro group. This indicates an octahedral geometry typical for six-coordinate complexes in coordination chemistry.
Understandably, this arrangement and the types of ligands influence the properties observed in the complex, including stability and reactivity.

Chirality in Complexes

Chirality is a fascinating aspect of complexes, heavily impacting their symmetry and optical activity. A chiral molecule cannot be superimposed on its mirror image, much like our left and right hands. For coordination complexes to be chiral, they generally lack a plane of symmetry or center of inversion within their structure.

• One common feature that can lead to chirality is the distribution of asymmetrical chelate rings or non-equivalent ligands.
• Chirality in coordination complexes is crucial in fields like pharmaceuticals, where the orientation of molecules can drastically affect medicinal properties.

However, in the case of pentaamminenitrocobalt (III), chirality does not arise. The arrangement of five ammine groups and one nitro ligand forms a symmetric setup around the cobalt center, meaning the complex has a plane of symmetry rendering it achiral. Thus, it lacks the optical activity characteristic of chiral compounds.

Oxidation States in Transition Metals

Oxidation states in transition metals are critical for understanding their chemical behavior and the types of reactions they undergo. Transition metals are unique for having multiple possible oxidation states due to the filling of d orbitals, contrasting the s and p orbitals common in main-group elements.

• The oxidation state of a metal in a complex affects its reactivity, magnetism, and the color of the compound.
• Transition metals typically show higher oxidation states than the main group because they can lose both s and d electrons during bonding.

For the pentaamminenitrocobalt (III) cation, cobalt exhibits a +3 oxidation state. This positive oxidation state results in a positively charged complex, impacting its solubility and interactions with other charged species. Importantly, the oxidation state helps determine whether the complex can participate in redox reactions. In this scenario, cobalt in the +3 oxidation state is stable and less inclined to act as a reducing agent, contrary to what might be observed in lower oxidation states.