Question

$[ \text{Co(NH}_3)_6 ]^{3+}$ and $[ \text{CoF}_6 ]^{3-}$ are respectively known as:

• A. Spin free Complex, Spin paired Complex
• B. Spin paired Complex, Spin free Complex
• C. Outer orbital Complex, Inner orbital Complex
• D. Inner orbital Complex, Spin paired Complex

Answer 1

Answer: (B)

Spin paired Complex, Spin free Complex

Answer 2

[Co(NH$_3$)$_6$]$^{3+}$:} In this complex, cobalt is in the $+3$ oxidation state with an electronic configuration of [Ar]3$d^6$. Since ammonia (NH$_3$) is a weak field ligand, it causes a small splitting of d-orbitals in the octahedral field, leading to a spin paired (low-spin) configuration. Therefore, [Co(NH$_3$)$_6$]$^{3+}$ is a spin paired complex.
[CoF$_6$]$^{3-}$: In this complex, cobalt is also in the $+3$ oxidation state with an electronic configuration of [Ar]3$d^6$. Fluoride (F$^-$) is a weak field ligand, causing less splitting of d-orbitals in the octahedral field, resulting in a spin free (high-spin) complex configuration. Therefore, [CoF$_6$]$^{3-}$ is a spin free complex.
Conclusion: [Co(NH$_3$)$_6$]$^{3+}$ is a spin paired complex and [CoF$_6$]$^{3-}$ is a spin free complex.