Question

Identify the diamagnetic octahedral complex ions from below ; 
A. [Mn(CN)\(_6\)]\(^{3-}\) 
B. [Co(NH\(_3\))\(_6\)]\(^{3+}\) 
C. [Fe(CN)\(_6\)]\(^{4-}\) 
D. [Co(H\(_2\)O)\(_3\)F\(_3\)] 
Choose the correct answer from the options given below :

• A. B and D Only
• B. A and D Only
• C. A and C Only
• D. B and C Only

Hint:

To determine the magnetic properties of a coordination complex, find the oxidation state of the central metal ion and its d electron configuration. Then, consider the strength of the ligands to determine the electron pairing in the octahedral field splitting. Strong field ligands (like CN\(^-\), NH\( _3 \)) cause pairing, while weak field ligands (like H\( _2 \)O, F\(^-\), Cl\(^-\)) generally do not. Diamagnetic complexes have all paired electrons, while paramagnetic complexes have unpaired electrons.

Answer 1

The Correct Option is D

To identify diamagnetic complexes, their electronic configurations and ligand field strengths must be analyzed.

1. [Mn(CN)₆]^3-:
   • Manganese (Mn) is in the +3 oxidation state, yielding a \(d^4\) configuration (Mn: [Ar] 3d⁵ 4s²; Mn³⁺: [Ar] 3d⁴).
   • CN^- is a strong field ligand that induces electron pairing in 3d orbitals.
   • However, a \(d^4\) configuration does not allow for complete electron pairing and thus diamagnetism.
2. [Co(NH₃)₆]³⁺:
   • Cobalt (Co) is in the +3 oxidation state, resulting in a \(d^6\) configuration (Co: [Ar] 3d⁷ 4s²; Co³⁺: [Ar] 3d⁶).
   • NH₃, a strong field ligand, causes pairing of d electrons.
   • This leads to a fully paired electronic configuration, rendering the complex diamagnetic.
3. [Fe(CN)₆]^4-:
   • Iron (Fe) is in the +2 oxidation state, yielding a \(d^6\) configuration (Fe: [Ar] 3d⁶ 4s²; Fe²⁺: [Ar] 3d⁶).
   • CN^-, a strong field ligand, also induces pairing of 3d electrons.
   • This results in a fully paired electronic configuration, making the complex diamagnetic.
4. [Co(H₂O)₃F₃]:
   • This complex features weak field ligands (H₂O and F^-), which do not cause electron pairing.
   • For Co³⁺ with a \(d^6\) configuration, unpaired electrons will exist under weak field conditions, resulting in a paramagnetic complex.

The diamagnetic complexes identified are [Co(NH₃)₆]³⁺ (B) and [Fe(CN)₆]^4- (C).

The correct selection is: B and C Only.