Applying the ligand electrochemical parameter approach to sandwich complexes and standardizing to the Fe[(III)/Fe-II couple, we obtained E(L)(L) values for over 200 pi-ligands. Linear correlations exist between formal potential (E degrees) and the Sigma E(L)(L) for each metal couple. In this fashion, pre report correlation data for many first row transition metal couples. The correlations between the E(L)(L) of the substituted pi-ligand and the Hammett substituent constants (sigma(p)) are also explored.