Irving-Williams series

Irving-Wiliams Series
This series refers to the relative stabilities of complexes formed by a metal ion. It is independent of ligand choice (in most cases)

The Series
Ba(II)Zn(II)

Explanation
i) As we go across the periodic table effective nuclear charge increases as the 3d orbitals are poorly shielding. Also the metal ionic radius contracts, resulting in an increase in Lewis Acidity and thus a stronger M-L co-ordinate bond.

ii) We get additional stabilisation from the Ligand Field Stabilisation Energy (cf Ligand Field Theory) and electrons enter the t2g band.

iii) Cu(II) is often surprisingly high due to extra stabilisation offered by the Jahn-Teller effect