Question

While finding the spin-only magnetic moment of a coordination complex, we count the number of unpaired electrons on the central metal atom. What about unpaired electrons on the ligand? Say in the case of O₂

or NO? Won’t they contribute to the magnetic moment?

Answer 1

In coordination complexes, only the central metal ion's unpaired electrons are commonly considered for the spin-only magnetic moment, as the ligands' electrons often pair up or do not affect the metal's configuration when they form coordinate bonds, affecting the complex's overall magnetism.

Step-by-step explanation:

While calculating the spin-only magnetic moment of a coordination complex, it's important to consider only the unpaired electrons of the central metal ion because the bonding within the complex significantly affects the magnetic properties.

Ligands like O₂ and NO, which may possess unpaired electrons, can contribute to the overall magnetism of a molecule in a free state. However, when they act as ligands, the interaction with the metal center often results in a different electronic arrangement, either causing pairing of their unpaired electrons or not affecting the central metal's electron configuration as they form coordinate bonds.

It is the unpaired electrons of the central metal ion that are mainly responsible for the observed paramagnetism or diamagnetism. For example, a molecule such as [Fe(CN)6] containing no unpaired electrons is diamagnetic, showing that ligand electrons do not contribute to its magnetic moment in the complex form.