The magnetic moment of an octahedral homoleptic Mn(II) complex is 5.9 BM. The suitable ligand for this complex isa)COb)Ethylenediaminec)NCS–d)CN–Correct answer is option 'C'. Can you explain this answer?

Question

The magnetic moment of an octahedral homoleptic Mn(II) complex is 5.9 BM. The suitable ligand for this complex isa)COb)Ethylenediaminec)NCS&ndash;d)CN&ndash;Correct answer is option 'C'. Can you explain this answer?

Accepted Answer

Electronic configuration of Mn²⁺ is
Mn⁺² : 3d⁵

It has 5 unpaired electrons which corresponds to magnetic moment of

This shows that the homoleptic complex of Mn2+ has only weak field ligands and that is NCS^–. The remaining three ligands are strong field ligands.

Answer

Magnetic moment is 5.9 BM = √{n(n+2)}
n=5

EC of MN+2 = 3d5

i.e, 5 unpaired e

out of given ligands NCS- is a weak field ligand which cannot Pair up the e where rest are strong field ligand and they Pair up unpaired electrons and if it happens then BM will not be equal as given.
So, a/c question answer is C

Answer

Understanding the Magnetic Moment
The magnetic moment of a complex indicates the number of unpaired electrons present in the metal center. For transition metals, the formula used to estimate the magnetic moment (in Bohr Magnetons, BM) is:
Magnetic Moment = √(n(n + 2)), where n is the number of unpaired electrons.
In the case of Mn(II), the oxidation state corresponds to a d5 configuration, leading to five electrons in the d-orbitals.
Magnetic Moment Calculation
Given the magnetic moment of 5.9 BM, we can deduce the number of unpaired electrons:
- Plugging into the formula: 5.9 ≈ √(n(n + 2))
- Solving this indicates there are 4 unpaired electrons (n=4).
Nature of Ligands
The ligand's ability to influence the d-orbital splitting and the pairing of electrons is crucial:
- Strong Field Ligands: These can cause pairing of electrons, often leading to lower magnetic moments.
- Weak Field Ligands: They do not cause pairing, allowing more unpaired electrons.
Evaluating the Ligands
1. CO (Carbon monoxide): A strong field ligand, likely to cause electron pairing, reducing the number of unpaired electrons.
2. Ethylenediamine (en): Also a strong field ligand, expected to lead to pairing of electrons.
3. NCS– (Thiocyanate): A moderate field ligand, which can allow for some unpaired electrons.
4. CN– (Cyanide): A very strong field ligand, which causes significant pairing of electrons.
Conclusion
Given that the observed magnetic moment indicates a high number of unpaired electrons, the suitable ligand for the octahedral homoleptic Mn(II) complex is NCS–. This ligand maintains more unpaired electrons, allowing for a magnetic moment close to the observed 5.9 BM. Thus, option 'C' is correct.

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