This document discusses coordination chemistry, including the concepts of labile and inert complexes, factors that affect stability and lability, and theories of the trans effect. It also briefly outlines the structures of chlorophyll, hemoglobin, and vitamin B12. Labile complexes rapidly exchange ligands while inert complexes exchange ligands slowly. Stability is influenced by factors like the metal ion size and charge, as well as ligand properties. The polarization and pi-bonding theories explain the trans effect, in which ligands trans to certain others make that site more reactive.

1. COORDINATION CHEMISTRY-III
R.Mamani
Assistant Professor
Department of Chemistry
Bon Secours College for Women
Thanjavur

2. INTRODUCTION:
 LABILE AND INERT COMPLEX.
 FACTORS AFFECTING LABILITY.
STABILITY OF COMPLEX.
KINETIC STABILITY.
THERMODYNAMIC STABILITY.
FACTORS AFFECTING STABILITY.
TRANS EFFECT.
POLARISATION THEORY.
PI-BONDING THEORY.
STRUCTURE OF CHLOROPHYLL.
STRUCTURE OF HAEMOGLOBIN.
STRUCTURE OF VITAMIN B12.

3. Labile and inertness:
 Complexes in which exchange of one
or more ligands are rapidly exchanged
are called labile complexes.
 If the rate of ligand exchange is slow
then the complex is said to be inert.
 Lability is not related to the
thermodynamic stability of a complex.
 A stable complex may be labile or inert
.so as the unstable complex.

4. Factors affecting lability of complex:
 size of the central metal ion
smaller the size of the metal ion
greater will be the inertness because the
ligands are held tightly by the metal ion.
 charge of the central metal ion
Greater the charge on the metal
ion greater will be the inertness of the
complex.since the M-L bonds are
stronger.
1. Size of the central metal ion
2. Charge of the central metal ion

5. Stability of coordination compounds:
 Thermodynamic equilibrium
constant.
 stability depend upon the
interaction between metal and ligand.
 If interaction strong
thermodynamic stability strong.
 Reaction between metal ion and
ligand is based on lewis acid and lewis
base.
 The greater the value of stability
constant more stable is the complex.

6. Stability of complex:
There are two types of stability of complex
1. Thermodynamic stability
2. kinetic stability
THERMODYNAMIC STABILITY:
• Thermodynamic stability so called stability of
the complex.
• Thermodynamically complexes divided into two
types
1. Stable complex.
2. Unstable complex.

7. KINETIC STABILITY:
 It refers to the speed with
which the transformations leading
to equilibrium will occur.
 Under this the rates of that the
substitutions;racemisations and
their mechanisms.
 The factors which are affecting
the rates of the reactions are also
studied.

9. Stability constant / formation constant:
 According to the formation of a complex in
aqueous solution proceeds through the step
wise process.

10. Factors affecting stability of complex:
Size of the metal ion.
Charge of the metal ion.
Ligand field stabilization
energy.
John teller effect.
Acid base theory.
Basicity of the ligands.
Ph of the solution.
Denticity of the ligand.
Denticity of the chelate
ligand.
Size of ligand.
Macrocyclic effect.

11. Trans effect:
 Simply the trans effect is the
labilization (making more reactive ) of
ligands that are trans to certain other
ligands .
 which can thus be regarded as trans
directing ligands.
 The trans effect which is often called as
the kinetic trans effect.
 It refers to the observation that certain
ligands increases the rate of ligand.
 This substitution when positioned trans
to the seperating ligands.

12. Theories of trans effect:
 Two general theory of trans
effect are given below:
 POLARISATION THEORY.
 PI-BONDING THEORY.

13. POLARISATION THEORY:
 It was given by A.A.GRINBERG(1935).
 It is electrostatic in nature.
 According to this theory. The ligand
by the electrostatic effect.
 This polarisation theory weakens the
bond trans to it.
 This polarisation theory facilitates
the substitution in that position.

14. Success of polarization theory:
 Although subject to some criticism of
that theory.
 The polarization theory appears to
account nicely for the behavior of the
ligand like hydride methide phenyl and
chloride.
 In these the ligands pi-bonding is
expected to be of the minor importance.

15. Pi-bonding theory:
 This theory was given by chat in 1995
and orgel in 1956.
 According to this theory vacant pi
and pi* orbitals of the metal (pi and
pi*) to form M-L pi bond.
 In these cases a reduction of the
electron density on the metal.as a
result of the back donation and that
donation from the donation from M-L.

18. Typesof chlorophyll:

19. Structure of hemoglobin:
 it facilitates oxygen transport.
 it facilitates carbondioxide.
It has a important role as a buffer
solution.

20. Structure of vitaminb12:
 The chemical structure of the molecule
was determined by crowfoce hodgkin and
her team in 1956.
It was based on the crystallographic
data.