1. THERMODYNAMIC & KINETIC ASPECTS OF METAL COMPLEXES
Inorganic Chemistry
B.Sc. III
Presentation By:
Sitanshu Kumar

2. STABILITY Discussed under two main types:- Thermodynamic Stability
Kinetic Stability
Generally we talk about THERMODYNAMIC STABILITY, unless KINETIC or RATE OF FORMATION word is mentioned.

3. Refers to the faster rate of formation of the particular species.
POINTS OF DIFFERENCE
Thermodynamic Stability
Relates to the time period of existence of a species in a particular form.
Kinetic Stability
Refers to the faster rate of formation of the particular species.

4. STABILITY CONSTANTS
Higher the value of equilibrium constant for a reaction, more stable is the product formed.
TYPES:
Stepwise stability constant
Overall stability constant

5. FORMATION OF MLn COMPLEX
Two different ways:
Stepwise formation
M + L------> ML ; K1 = [ML]/[M][L]
ML + L ----> ML2 ; K2 = [ML2]/[ML][L] .
MLn-1 + L -----> MLn ; Kn = [MLn]/ [MLn-1][L]
K1, K2, Kn are known as stepwise stability constants.

6. 2. Overall formation:
M + L------> ML ; β1 = [ML]/[M][L]
M + 2L ----> ML2 ; β2 = [ML2]/[M][L]2 .
M + nL -----> MLn ; βn = [MLn]/[M][L]n
β1, β2, βn are known as overall stability constants.

7. Proceeding with rate constants, we get,
β1 = K1
β2 = K1 . K2
βn = K1 . K2 . K3 ………. Kn
Taking log, we get,
log βn = log K1 + log K2 + log K3 +……. log Kn.
Complex is stable if log β >= 8.

8. INERTNESS & LABILITY OF COMPLEXES
Lability refers to reactivity and Inertness refers to non- reactivity of the complex.
In other words, complex with ability to exchange its ligand(s) present inside co-ordination sphere is labile otherwise inert.
Inert complexes have substitution reaction half life period larger than a minute & opposite for labile complexes.

9. FACTORS AFFECTING STABILITY OF COMPLEXES
Nature of Metal Ion:
+ve Charge on metal ion ↑, stability of complex↑
Size of metal ion ↓, stability of complex ↑
Charge:size ratio ↑, stability of complex ↑
more electronegative metal ions form complexes with ligand having donor atom of high electronegativity & vice versa.

10. 2. Nature of ligand:
-ve charge on ligand ↑, stability of complex ↑
Size of ligand ↓, stability of complex ↑
Basic strength of ligand ↑, stability of complex↑
Presence of chelating ligand makes the complex more stable.
Ligand bulkiness↓ , stability of complex↑, because of less stearic hindrance.

11. SUBSTITUTION REACTIONS IN SQUARE PLANAR COMPLEXES
• Associative - A (2 steps) MLnX + Y→ MLnXY→ MLnY + X • Dissociative - D (2 steps) MLnX + Y→ MLn + X + Y→ MLnY + X • Interchange (1 continuous process) MLnX + Y→ Y--MLn --X→ MLnY + X

12. rate of substitution of ligands opposite to it.
TRANS EFFECT
Definition
The trans effect is best defined as the effect of a coordinated ligand upon the
rate of substitution of ligands opposite to it. Or
The ability of a ligand in a square planar complex to direct the replacement if the ligand trans to it.
The trans effect is given as the following series:
CN- > NO2- > I- = SCN- > Br- > Cl- > py > NH3 > H2O

13. Substitution reactions in square-planar complexes the trans effect
In the above reaction, “T” is the ligand having good trans effect ; L’s are the inert ligands & “X” is the labile ligand.

14. MECHANISM OF Nu- SUBSTITUTION REACTION

15. THEORIES EXPLAINING TRANS EFFECT (∏-bonding)
p-backbonding to a
metal is weakened
when it is trans to
another good
p-backbonding ligand.
metal is strengthened
when it is trans to a
good s-donating ligand
that can’t p-backbond .

16. Polarization theory:- This theory explains the weakening of metal-leaving group bond due to the more polarizable nature of Trans ligand, resulting in cleavage of the former bond and thus SUBSTITUTION. !!!!!!THANK YOU!!!!!!
∂+ T ∂- X
∂+ M ∂-