Irving-Williams series
The Irving -Williams series was named after chemists Harry Munroe Napier Irving Hetherington (1905-1993) and Robert Joseph Paton Williams ( b. 1926 ). They published in 1948 in the scientific journal Nature an article about research on trends in the stabilities of complexes of divalent ions of transition metals of the fourth period. With the use of various ligands always resulted in an increase of the stability of manganese to iron, cobalt and nickel to copper, and then a drop of zinc. This " stability trend series" was named after them as Irving -Williams series.
The series
Ba ( II) < Sr ( II) < Ca ( II) < Mg ( II) < Mn (II) < Fe (II) < Co (II) < Ni (II)
Explanation
I ) If we consider one period, the screening of the 3d orbitals with increasing atomic number decreases. The metal ion radius decreases, so that the Lewis acidity is increased and thus the ML- bond is strengthened.
Ii ) Additional stabilization we obtained from the ligand field stabilization energy and other electrons in the t2g band.
Iii ) Due to the Jahn -Teller distortion undergoes Cu ( II) an amazingly high stabilization.