What is spectrochemical series?

The spectrochemical series is a list of ligands arranged in order of their ability to cause a split in the energy levels of a transition metal complex. This splitting is known as the crystal field splitting and is responsible for the colors observed in many transition metal complexes.

The ligands at the top of the spectrochemical series are known as strong field ligands, as they cause a large splitting of the energy levels. These ligands typically have multiple lone pairs of electrons available for bonding, such as cyanide, carbon monoxide, and phosphine ligands.

On the other hand, ligands at the bottom of the spectrochemical series are known as weak field ligands, as they cause a small splitting of the energy levels. These ligands typically have less ability to donate lone pairs of electrons for bonding, such as water, ammonia, and chloride ligands.

The spectrochemical series is important in predicting the colors of transition metal complexes, as complexes with strong field ligands tend to absorb higher energy light (such as blue or violet) and appear to be a complementary color (such as yellow or orange), while complexes with weak field ligands tend to absorb lower energy light (such as red or green) and appear to be the same color.