The document discusses the naphelauxetic effect, which is a decrease in the Racah parameter value when a complex is formed. It then discusses various factors that affect the stability of complexes, including thermodynamic stability measured by formation constants, the nature of the central metal ion and ligands, the chelate effect, and kinetic stability. Thermodynamic stability depends on free energy change and favors complexes with higher formation constants, while kinetic stability refers to how rapidly a complex breaks down in solution.

1. Naphelauxetic effect: Decrease in Racah parameter value (a measure of inter electronic repulsion when a complex is
formed).
Naphelauxetic effect

2. (NET 2021)

3. Stability of complexes and reaction mechanism

4. Stability
(aq. Soln.)
Thermodynamic
Stability
Kinetic Stability

5. Thermodynamic stability
 Existence of a complex under equilibrium condition.
 It is a measure of tendency of metal ion to form a particular complex ion.
 It is given by formation constant.

6.  If Kf value is higher, the product will be in higher amount, that is, ligand bind to the metal ion
more strongly than the water.
 If Kf value is lower, the product will be in lower amount, that is, ligand will not bind metal more
strongly than water.

7. 𝛥G=-RTlnKf
 Positive value of Kf will give negative value of 𝛥G.
 Negative value of Kf will give positive value of 𝛥G.

8. Stepwise formation constant of complex

9. Overall formation constant of complex

10. Relationship between stepwise formation and overall
formation constant

11. K1 > K2 > K3 > K4……..Kn-1 > Kn

12. K1 > K2 > K3 > K4……..Kn-1 > Kn
 Increase in number of ligands in coordination sphere causes to decrease the number of replaceable water
molecule
 Steric hinderance increases
 Electrostatic factor (in charged ligand)

15. Factors affecting stability of complexes
 Nature of the central metal ion
Nature of the ligand
The chelate effect
 Macrocyclic effect
Resonance effect
Steric effcet

16. Nature of the central metal ion
a) Charge on metal cation : Higher oxidation state, more stable complex.
Exception: The ligand which has vacant π* orbital like CO (Carbonyl), PMe3 (Trimethyl phosphene), CN- (good σ donor).

17. b) Charge on the central metal ion
Stability of complex increase with decrease in size of metal (if oxidation state is the same).
Nature of the central metal ion
Ni
2+ Co2+
Mn2+
Mg2+ Ca2+
Sr2+
Ba2+
Irving - Williams series

18. Nature of Ligands
Higher the ability to donate lone pair of electron, the higher will be the stability
NH3 >H2O >F-
Covalent character higher, stability will be higher
AgI2
- > AgBr2
- > AgCl2
- > AgF2
-
Vacant 𝜋-orbital ligand will form stable complex

19. Chelate effect
𝛥G= 𝛥H-T𝛥S
𝛥G=-RTlnKf
Resonance effect

20. Steric hinderance effect

21. Kinetic stability

22. Stability
(aq. Soln.)
Thermodynamic
Stability
Kinetic Stability
Kinetic stability
Stable Unstable Labile Inert
𝛥G= 𝛥H-T𝛥S

23. Kinetic stability