![[FeCl4]2− (I), [CoCl4]2− (II) and [NiCl4]2− (III) are paramagnetic tetrahedral complexes. Q.23 The order of values of spin-only magnetic moment is (A) III > II > I (B) III > I > II (C) II > I > III (D) I > II > III](https://www.letstalkacademy.com/wp-content/uploads/2026/01/slide_23-7.jpg)
[FeCl4]2− (I), [CoCl4]2− (II) and [NiCl4]2− (III) are paramagnetic tetrahedral complexes.
Q.23 The order of values of spin-only magnetic moment is
Concept Used
Spin-only magnetic moment depends on the number of unpaired electrons and is given by:
μ = √n(n + 2) BM
Tetrahedral complexes with weak field ligands like Cl− are always high spin.
Step-by-Step Solution
(I) [FeCl4]2−
- Oxidation state of Fe = +2
- Electronic configuration = d6
- Unpaired electrons = 4
- Magnetic moment = √24
(II) [CoCl4]2−
- Oxidation state of Co = +2
- Electronic configuration = d7
- Unpaired electrons = 3
- Magnetic moment = √15
(III) [NiCl4]2−
- Oxidation state of Ni = +2
- Electronic configuration = d8
- Unpaired electrons = 2
- Magnetic moment = √8
Comparison Table
| Complex | d-electrons | Unpaired electrons |
|---|---|---|
| [FeCl4]2− | d6 | 4 |
| [CoCl4]2− | d7 | 3 |
| [NiCl4]2− | d8 | 2 |
Final Answer
The correct order of spin-only magnetic moment is:
I > II > III
Correct Option: (D)
Conclusion
In tetrahedral complexes with weak field ligands, all complexes are high spin and
magnetic moment decreases as the number of unpaired electrons decreases.
