5. slow +Y(fast)
[L5MX] [L5M] [L5MY]
5-coordinate complex
slow X -X(fast)
[L5MX]+Y [L5M ] [L5MY] + X
Y
7-coordinate complex
slow X -X(fast)
[L5MX]+Y [L5M ] [L5MY] + X
Y
7-coordinate transition state
Associative :
Dissociative :
Interchange :
6. Note :
There will be some cases in which it is difficult to find which
mechanism is followed to give the product i.e., in cases when there is
* solvent interaction
*ion pair interaction etc…
7. STOP THE DRIP TO
SAVE THE DROP
-An initiative to be taken up by everyearthling
8.
9. DEFINITIONS
The ability of a complex to engage in reaction that results in
replacing one or more ligands in it’s coordination sphere
(by other ligands) is called lability and the complexes in which the
ligands are rapidly replaced by others are called labile complexes.
The inability of a complex to engage in such reaction is termed
as inertness and the complexes which exhibit such property are
called labile complexes.
10. > H.TAUBE has described the complexes as labile if they have
half life(t1/2) of reaction under 30 sec while the reactions having
half life greater than 30 sec are termed as inert.
t1/2 < 30 sec LABILE complex
t1/2 >= 30 sec INERT complex
11. The terms inert and labile are kinetic terms because they reflect the rate with
which the reaction proceeds and these kinetic terms should not be confused
With thermodynamic terms stable and unstable which refer to tendency of
species to exist(governed by equilibrium constants.)
Consider the reaction: M + nL ⇌ MLn ; βn =[MLn]/[M][L]n
where βn is formation constant of the complex.
The higher values of βn indicate it’s higher thermodynamic stability of the
complex. Thus it gives measure of the extent to which the reaction proceeds
but it cannot say anything about the speed with which equilibrium is attained.
12. Examples:
* [Hg(CN)4]-2 + 4 14CN- ⇌ [Hg14(CN)4]-2 + 4CN-
log βn =42 ; t1/2= very small
*[Cr(CN)6]-3 + 6 14CN- ⇌ [Cr14(CN)6]-3 + 6 CN-
log βn =37 ; t1/2= 24 days
Thermodynamically
Stable and kinetically
Unstable
Thermodynamically
Stable and kinetically
stable
13. * The inertness or lability depends upon the activation energy i.e., high
Activation energy imparts inertness while low activation energy
imparts lability.Thus inertness or lability is determined by ∆G‡
(free energy of activation).
∆G‡ = ∆H‡ - T ∆S‡
The stability of a complex is determined by free energy change(∆G0)in a
reaction.
∆G0 = ∆H0- T ∆S0
• ∆G‡ depends on reaction pathway while ∆G0 depends upon the difference
in free energy of reactants and products.
14. VBT interpretation of lability and
inertness in octahedral complexes :
• Outer and inner orbital complexes and their stability
• Kinetic behavior of outer orbital complexes
• Kinetic behavior of inner orbital complexes
18. CFT interpretation of lability and
inertness in octahedral complexes :
CFAE = loss of cfse in forming the activated complex
= cfse of the starting complex – cfse of the activated complex
cfse of activated complex ???
19.
20.
21. Generalisations:
• Both the high spin and low spin complexes of d0,d1,d2,d7,d9,d10 and
high spin complexes of d4,d5,d6 are generally labile.
• Both high spin and low spin complexes of d3,d8 and low spin
complexes of d4,d5,d6 are generally inert.