In other words, the Irving–Williams series is almost exclusively independent of the nature of the incoming ligand, L. The main application of the series is to empirically suggest an order of stability within first row transition metal complexes (where the transition metal is in oxidation state II).
Another application of the Irving–Williams series is to use it as a correlation "ruler" in comparing the first stability constant for replacement of water in the aqueous ion by a ligand.
A recent study of metal-thiolate complexes indicates that an interplay between covalent and electrostatic contributions in metal–ligand binding energies might result in the Irving–Williams series.
When the stability constants are quantitatively adjusted for these values they follow the trend that is predicted, in the absence of crystal field effects, between manganese and zinc.
However, in a recent study published in the journal Nature, researchers have reported a protein-design approach to overcome the Irving-Williams series restriction, allowing proteins to bind other metals over copper ions vice versa to Irving–Williams series.