The magnetic moment of an octahedral homoleptic Mn(II) complex is 5.9 ...
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.
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The magnetic moment of an octahedral homoleptic Mn(II) complex is 5.9 ...
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
The magnetic moment of an octahedral homoleptic Mn(II) complex is 5.9 ...
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.