Arrange the following complexes in increasing order of their magnetic moment
(A) $[Cr(H_2O)_6]^{3+}$
(B) $[Co(NH_3)_6]^{3+}$
(C) $[FeCl_6]^{4-}$
(D) $[Mn(CN)_6]^{3-}$
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (B), (D), (A), (C)
Detailed calculation of unpaired electrons and magnetic moment:
|
Complex |
Metal |
Oxidation state |
d-electron count |
Geometry |
Unpaired electrons |
Spin-only μ (B.M.) |
|
(B) [Co(NH₃)₆]³⁺ |
Co³⁺ |
+3 |
d⁶ |
Octahedral, strong field (NH₃) |
0 (low-spin) |
0 |
|
(D) [Mn(CN)₆]³⁻ |
Mn³⁺ |
+3 |
d⁴ |
Octahedral, strong field (CN⁻) |
2 (low-spin) |
2.83 |
|
(A) [Cr(H₂O)₆]³⁺ |
Cr³⁺ |
+3 |
d³ |
Octahedral |
3 |
3.87 |
|
(C) [FeCl₆]⁴⁻ |
Fe²⁺ |
+2 |
d⁶ |
Octahedral, very weak field (Cl⁻) |
4 (high-spin) |
4.90 |
Increasing order of magnetic moment:
0 < 2.83 < 3.87 < 4.90 B.M.
So: (B) < (D) < (A) < (C)