Question

Given below are two statements:
Statement I: Among [Cu(NH₃)₄]²⁺, [Ni(en)₃]²⁺, [Ni(NH₃)₆]²⁺ and [Mn(H₂O)₆]²⁺, [Mn(H₂O)₆]²⁺ has the maximum number of unpaired electrons.
Statement II: The number of pairs among {[NiCl₄]²⁻, [Ni(CO)₄], {[NiCl₄]²⁻, [Ni(CN)₄]²⁻} and {[Ni(CO)₄], [Ni(CN)₄]²⁻} that contain only diamagnetic species is two.
In the light of the above statements, choose the correct answer from the options given below:}

• A. Statement I is false but Statement II is true
• B. Statement I is true but Statement II is false
• C. Both Statement I and Statement II are true
• D. Both Statement I and Statement II are false

Hint:

To determine the magnetic properties of coordination compounds, follow these steps:
1. Find the oxidation state of the central metal ion.
2. Write its d-electron configuration.
3. Consider the ligand type (strong/weak field) and coordination number to predict the geometry (octahedral, tetrahedral, square planar) and electron filling (high/low spin).
4. Count the number of unpaired electrons. Zero unpaired electrons = diamagnetic; one or more = paramagnetic.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:

We are given two statements related to coordination compounds. Statement I concerns the number of unpaired electrons (and hence magnetic behavior) of certain complexes. Statement II asks about identifying pairs consisting only of diamagnetic complexes.

Step 2: Detailed Explanation:

Analysis of Statement I:

We calculate the number of unpaired electrons in each complex.

[Cu(NH₃)₄]²⁺
Copper is in the +2 oxidation state. Cu²⁺ has the electronic configuration [Ar] 3d⁹. A d⁹ configuration always contains 1 unpaired electron, irrespective of geometry or ligand field strength.

[Ni(en)₃]²⁺
Nickel is in the +2 oxidation state with configuration [Ar] 3d⁸. Ethylenediamine (en) is a strong-field ligand and forms an octahedral complex. The electronic configuration is t₂g⁶ e_g², giving 2 unpaired electrons.

[Ni(NH₃)₆]²⁺
Nickel is again in the +2 oxidation state (3d⁸). NH₃ behaves as a weak-to-moderate field ligand for Ni²⁺, producing a high-spin octahedral complex. The configuration is t₂g⁶ e_g² with 2 unpaired electrons.

[Mn(H₂O)₆]²⁺
Manganese is in the +2 oxidation state with configuration [Ar] 3d⁵. H₂O is a weak-field ligand, so the complex is high-spin octahedral. The configuration is t₂g³ e_g² with 5 unpaired electrons.

Comparison:
Number of unpaired electrons = 1, 2, 2, and 5. The maximum is 5 for [Mn(H₂O)₆]²⁺.

Conclusion for Statement I:
Statement I is true.

Analysis of Statement II:

We now determine the magnetic nature of each complex.

[NiCl₄]²⁻
Nickel is in the +2 oxidation state (3d⁸). Cl⁻ is a weak-field ligand, giving a tetrahedral geometry. This results in 2 unpaired electrons. Hence, the complex is paramagnetic.

[Ni(CO)₄]
Nickel is in the 0 oxidation state. CO is a very strong-field ligand and causes complete pairing, giving a 3d¹⁰ configuration. There are no unpaired electrons. The complex is diamagnetic.

[Ni(CN)₄]²⁻
Nickel is in the +2 oxidation state (3d⁸). CN⁻ is a strong-field ligand and forms a square planar complex. All electrons are paired. The complex is diamagnetic.

Evaluation of Pairs:

Pair 1: [NiCl₄]²⁻ (paramagnetic) and [Ni(CO)₄] (diamagnetic) → Not all diamagnetic.

Pair 2: [NiCl₄]²⁻ (paramagnetic) and [Ni(CN)₄]²⁻ (diamagnetic) → Not all diamagnetic.

Pair 3: [Ni(CO)₄] (diamagnetic) and [Ni(CN)₄]²⁻ (diamagnetic) → Both diamagnetic.

Only one such pair exists.

Conclusion for Statement II:
Statement II is false.

Step 3: Final Answer:

Statement I is true and Statement II is false. Correct option: (B)