Stability of metal complexes with reference to thenature of metal ion :

The Irving-William series:

This series is obtained from a plot of long Kf against Z for the first-row transition elements. For any one set of ligands, i.e., no change in ligand type, the series shows a regular increase in stability constants from Sc to Cu, and a decrease to zinc. 

Ba²⁺ < Sr²⁺ < Ca²⁺< Mg²⁺ < Mn²⁺ < Fe²⁺ < Co²⁺ < Ni²⁺ < Cu²⁺ > Zn²⁺ 

This series can be understood as a consequence of electrostatic effects, of the first part of this series. Ligand-field interactions explain the increase in the value of K_f for Fe (II), d⁶; Co (II), d⁷; Ni (II), d⁸; and Cu (II), d⁹ – Cu (II) obtains increased stability from Jahn-Teller distortion when compared to Ni (II) complexes.
Stability of metal complexes with reference to the nature of  ligand:

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For detail study Click on these links: 
1- http://web.uvic.ca/~djberg/Chem324/Chem324-14.pdf
2 -http://bit.ly/10OzNcK (Important Link)