These types of ligand are located in low to medium of the spectrochemical series.

It is a pure σ-donor, in the middle of the spectrochemical series, and shows intermediate hard-soft behaviour.

Pi-donor ligands are low in the spectrochemical series.

It has also been observed that the stretching frequency correlates with the position of the equatorial ligands in the spectrochemical series.

This ordering of ligands is almost invariable for all metal ions and is called spectrochemical series.

The spectrochemical series is an empirically-derived list of ligands ordered by the size of the splitting Δ that they produce.

Ligands also affect the magnitude of Δ splitting of the d-orbitals according to their field strength as described by the spectrochemical series.

A partial spectrochemical series listing of ligands from small Δ to large Δ is given below.

However, keep in mind that "the spectrochemical series is essentially backwards from what it should be for a reasonable prediction based on the assumptions of crystal field theory."

Among all NMR active nuclei, Co has the largest chemical shift range and the chemical shift can be correlated with the spectrochemical series.

A spectrochemical series is a list of ligands ordered on ligand strength and a list of metal ions based on oxidation number, group and its identity.

Ligands which cause a large splitting Δ of the d-orbitals are referred to as strong-field ligands, such as CN and CO from the spectrochemical series.

There are three factors that affect the Δ: the period of the metal center, the charge of the metal center, and the field strength of the complex's ligands as described by the spectrochemical series.

Ligands arranged on the left end of this spectrochemical series are generally regarded as weaker ligands and cannot cause forcible pairing of electrons within 3d level and thus form outer orbital octahedral complexes.

The cluster chlorides and carbonyls of transition metals will be briefly discussed here as they represent opposite ends of the spectrochemical series and show important features of the differences between transition metal clusters with different ligands.

Although parts of this series may seem quite similar to the spectrochemical series of ligands - for example, cyanide, ethylenediamine, and fluoride seem to occupy similar positions in the two - others such as chloride, iodide and bromide, amongst others, occupy very different positions.