For the octahedral complexes of in (thiocyanato-S) and in ligand environments, calculate the differe — Coordination Compounds Chemistry Question
Question
For the octahedral complexes of $Fe^{3+}$ in $SCN^-$ (thiocyanato-S) and in $CN^-$ ligand environments, calculate the difference between the spin-only magnetic moments in Bohr magnetons (approximated to the nearest integer). [Atomic number of Fe = 26]
💡 Solution & Explanation
The electronic configuration of $Fe^{3+}$ is $[Ar] 3d^5$. The ligand $SCN^-$ is a weak field ligand, forming a high-spin inner/outer complex with $5$ unpaired electrons. Its spin-only magnetic moment $\mu = \sqrt{n(n+2)} = \sqrt{5(7)} = \sqrt{35} \approx 5.92 \text{ BM}$. The ligand $CN^-$ is a strong field ligand, forcing pairing to form a low-spin $d^2sp^3$ complex with only $1$ unpaired electron. Its magnetic moment $\mu = \sqrt{1(3)} = \sqrt{3} \approx 1.73 \text{ BM}$. The difference is $5.92 - 1.73 = 4.19 \text{ BM}$, which rounds to $4$.