Question

Spin-only magnetic moments (in BM) of [NiCl$_2$(PPh$_3$)$_2$] and [Mn(NCS)$_6$]$^{4-}$, respectively, are

• A. 0.00 and 5.92
• B. 2.83 and 1.89
• C. 0.00 and 1.89
• D. 2.83 and 5.92

Hint:

For spin-only moment, use $\mu = \sqrt{n(n+2)}$. Weak field ligands lead to high-spin complexes with maximum unpaired electrons.

Answer 1

The Correct Option is D

Step 1: For [NiCl$_2$(PPh$_3$)$_2$].
Ni is in +2 oxidation state → 3d$^8$ configuration.
Cl$^-$ and PPh$_3$ are weak field ligands → complex is paramagnetic. Unpaired electrons = 2.
Spin-only magnetic moment, \[ \mu = \sqrt{n(n+2)} = \sqrt{2(2+2)} = \sqrt{8} = 2.83\ \text{BM.} \] Step 2: For [Mn(NCS)$_6$]$^{4-}$.
Mn is in +2 oxidation state → 3d$^5$ configuration.
All ligands are weak field (high-spin complex).
Unpaired electrons = 5. \[ \mu = \sqrt{5(5+2)} = \sqrt{35} = 5.92\ \text{BM.} \] Step 3: Conclusion.
Hence, magnetic moments are 2.83 BM and 5.92 BM, respectively.