Question

Why $[\mathrm{Co}{\left(\mathrm{CN}\right)}_6{]}^{3-}$ is diamagnetic but $[\mathrm{Mn}{\left(\mathrm{CN}\right)}_6{]}^{3-}$ is paramagnetic?

Answer 1

Magnetic Nature

• Materials having unpaired electrons are paramagnetic and attracted to a magnetic field.
• Examples of paramagnetic: Aluminum, Gold, and Copper.
• Materials containing paired electrons are diamagnetic and repel a magnetic field.

$\mathbf{[}\mathbf{Co}{\mathbf{\left(}\mathbf{CN}\mathbf{\right)}}_{\mathbf{6}}{\mathbf{]}}^{\mathbf{3}\mathbf{-}}$

• In $[\mathrm{Co}{\left(\mathrm{CN}\right)}_6{]}^{3-}$, $\mathrm{Co}$ has $+3$ oxidation state.
• The electronic configuration of ${\mathrm{Co}}^{3+}$ is $\left[\mathrm{Ar}\right]3d^6$.
• ${\mathrm{CN}}^{-}$ is a strong field ligand that causes inner $d$-orbital pairing.
• The electronic configuration is as follows:

• $[\mathrm{Co}{\left(\mathrm{CN}\right)}_6{]}^{3-}$ is diamagnetic because it has no unpaired electron.

$\mathbf{[}\mathbf{Mn}{\mathbf{\left(}\mathbf{CN}\mathbf{\right)}}_{\mathbf{6}}{\mathbf{]}}^{\mathbf{3}\mathbf{-}}$

• In $[\mathrm{Mn}{\left(\mathrm{CN}\right)}_6{]}^{3-}$, $\mathrm{Mn}$ has $+3$ oxidation state.
• The electronic configuration of ${\mathrm{Mn}}^{3+}$ is $\left[\mathrm{Ar}\right]3d^4$.
• ${\mathrm{CN}}^{-}$ is a strong field ligand that causes inner $d$-orbital pairing.
• The electronic configuration is as follows:

• $[\mathrm{Mn}{\left(\mathrm{CN}\right)}_6{]}^{3-}$ is paramagnetic because it has two unpaired electrons because pairing of electrons is not needed for the availability of orbitals.