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 cation exhibits (c) linkage isomerism.

Step 1: Understanding the Compound

The compound in question is a complex ion, where cobalt is bonded to five ammine ligands (NH3) and one nitro group (NO2). This complex is represented as \([Co(NH_3)_5(NO_2)]^{2+}\).

Step 2: Identifying Properties of Ligands

The nitrite ion \((NO_2^-) \) is capable of bonding through either the nitrogen or an oxygen atom, which gives it the potential for linkage isomerism. This is because the nitro group can form different isomers depending on which atom it bonds through.

Step 3: Assessing Chirality

Chirality refers to an object's ability not to be superimposed on its mirror image. Complexes with coordination numbers like 6 (octahedral) could be chiral, but without additional asymmetric ligands or specific spatial arrangements, chirality in this complex is unlikely.

Step 4: Considering Physiological Sorption

Physiological sorption or physisorption involves weak van der Waals forces and typically relates to gas-solid interactions, not applicable to the cobalt complex in solution.

Step 5: Evaluating Reducing Properties

Versatile reducing agents readily donate electrons, typically containing metal ions capable of being oxidized to a lower oxidation state. Cobalt (III) in the complex is relatively stable, suggesting it's not a strong reducing agent.

Key Concepts

Complex Ions

In coordination chemistry, complex ions consist of a central metal atom surrounded by ligands. These ligands are ions or molecules that donate electron pairs to the metal, forming a stable entity. For the pentaamminenitrocobalt(III) cation, cobalt is the central metal atom bound to five ammine (NH₃) ligands and one nitro (NO₂) group.

• Central metal atom: Cobalt (III)
• Ligands: Five ammonia molecules and one nitro group
• Ion representation: \([Co(NH_3)_5(NO_2)]^{2+}\)

The stability and properties of complex ions depend on the nature of the metal ion and its oxidation state, as well as the type of ligands present. These ions are key players in various chemical processes, including catalysis and electrochemistry.

Coordination Chemistry

Coordination chemistry studies the structure and properties of complex ions. It focuses on how ligands bind to a central metal atom. The number of ligand binding sites on the metal is known as the coordination number, which often dictates the complex's geometry.

• Coordination Number: Six (five NH₃ and one NO₂)
• Geometry: Often octahedral for six-coordinated complexes

The exact shape of a complex affects its reactivity, color, and ability to participate in reactions like linkage isomerism, where a ligand can attach to the metal ion in several different ways.

Chiral Complexes

Chiral complexes in coordination chemistry have molecules that cannot be superimposed on their mirror images, much like left and right hands. This is usually due to specific spatial arrangements or the presence of asymmetric ligands.
Most octahedral complexes with octahedral geometry can exhibit chirality if they have specific arrangements of ligands.

• Asymmetry: Essential for chirality
• Mirror Image Non-superimposable: Key identifier of a chiral complex

In the case of pentaamminenitrocobalt(III) cation, chirality is less likely due to symmetric ligand arrangement without any asymmetric ligands involved.

Oxidation States

The oxidation state of a metal in a complex ion indicates how many electrons have been lost to reach the ion's current state. It helps determine the reactivity and stability of the complex. For cobalt in the pentaamminenitrocobalt(III) cation, the oxidation state is +3.

• Oxidation State: +3 for cobalt
• Stability: Relatively stable, less reactive
• Reducing Ability: Less effective due to its high oxidation state

Understanding oxidation states is crucial in predicting a complex ion's behavior in chemical reactions, such as its ability to act as a reducing agent.