The complex ion Fe(CN)6 is low spin.
Here's why:
- Strong Field Ligands: Cyanide (CN-) is a strong field ligand. Strong field ligands cause a large splitting of the d-orbitals in the metal ion. This large splitting results in pairing of electrons in the lower energy d-orbitals.
- Electron Configuration: Iron (Fe) in its +2 oxidation state has 6 d-electrons. In a low spin complex, these electrons will pair up in the lower energy d-orbitals before occupying the higher energy ones. This results in a diamagnetic complex.
- Diamagnetism: The low spin configuration of Fe(CN)6 makes it diamagnetic, meaning it is repelled by a magnetic field.
In contrast, high spin complexes:
- Have weak field ligands, which cause a smaller splitting of the d-orbitals.
- Have unpaired electrons in the higher energy d-orbitals, making them paramagnetic (attracted to a magnetic field).
Examples of high spin complexes:
- [Fe(H2O)6]2+
Examples of low spin complexes:
- [Fe(CN)6]4-
