Coordination Compounds

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  • Topic: Ligand, Coordination chemistry, Coordination complex
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PAC-II COMPLEXOMETRIC TITRATION

Course Contents:

C OMPLEXOMETRIC
TITRATION
T ITRATION

Complexation, Chelation.
Werner’s co-ordination number, Titrants
Stability of complexes, titration curves.
Types of complexometric titrations.
Methods of detecting end point,
Standardization.
 Application of complexometric titrations.






COMPLEXOMETRIC TITRATIONS

COMPLEXOMETRIC TITRATIONS

What is Complexometric Titration (CT)????
What
What is a complex metal ion?
A complex is a molecule or ion formed by
the reaction of two or more ions or
molecules capable of independent
existence.

What is COMPLEXATION?????
Chemical reaction that takes place between the metal
ion and a molecular or ionic entity (known as ligand).

 Also known as Chilometric titration, Chilometry, Chilatometric, EDTA titrations.
 It is a form of volumetric analysis in which the formation of a colored complex is used to indicate the end point of a titration.  The technique involves titrating metal ions with a complexing agent or chelating agent (Ligand) and is commonly referred to as complexometric titration.

 This method represents the analytical application of a
complexation reaction.
 The endpoint is usually measured with an indicator ligand that forms a colored complex with the free metal ion.
CT are useful for determination of mixture of different metal ions in solution.

COMPLEXOMETRIC TITRATIONS

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COMPLEXOMETRIC TITRATIONS

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PAC-II COMPLEXOMETRIC TITRATION

LIGANDS:

Metal
ion
( analyte ;
cation)

Metal ion
indicators

Chilon
Complexing
agent

pM indicators

( Chelating agent
L igand/Sequestering agent)

Chelate
Complex ion
Metal co -ordination compound
/Metal complex/Chelate
compound

 Ligands or complexing or chelating agents are
electron donating entity, which has the ability to
bind to the metal ion and produce a complex
ion.
 The molecules or ions which displace the solvent
molecules are called Ligands.
 They are usually anions or polar molecules.

COMPLEXOMETRIC TITRATIONS

EXA
E XA MP LES O F CO MP LEX IO N FO RMA T IO N

COMPLEXOMETRIC TITRATIONS

EXA
E XA MP LES O F CO MP LEX IO N FO RMA TIO N
i.

[Fe(H2O)6]3+
Hexaaquairon(III) ion/
Iron(III) hexahydrated
complex ion.
ii. [AlF6]3Hexafluoroaluminate (III)
ion
iii. [Co(NH3)6]2+
Cobalt(II) hexaammino
complex ion OR
Hexaamminocobalt(II) ion
iv. [Cu(NH3)4(H2O)2]2+
Tetra ammine copper(II)

Hexaaqua cobalt (III) ion

Tetra amminediaqua copper(II)

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COMPLEXOMETRIC TITRATIONS

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COMPLEXOMETRIC TITRATIONS

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PAC-II COMPLEXOMETRIC TITRATION

Bidentate and Multidentate Ligands:

Classification of Ligands :
Unidentate Ligands: Ligands that are bound to
metal ion only at one place are called unidentate
ligands (one toothed).
Ex: water, ammonia, halide ions, cyanide ions

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COMPLEXOMETRIC TITRATIONS

Ligands that contain more than one donar group
and capable of binding with metal ions as
multidentate ligands or chelating agents.
They include:
 bidentate ligands (2 donar atoms),
 tridentate ligands (3 donar atoms),
 quadridentate ligands (4 donar atoms) Eg:
chlorophyll
 Hexadentate ligands (6 donar atoms) Eg: Ethylene
diamine tetra acetic acid (EDTA

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COMPLEXOMETRIC TITRATIONS

E xamples Of M ultidentate L igands
Multidentate Ligands
SOME BIDENTATE LIGANDS
Ethylenediammine (en)

acetylacetonate ion (acac)

Phenanthroline (phen)

Oxalate ion (ox)

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COMPLEXOMETRIC TITRATIONS

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COMPLEXOMETRIC TITRATIONS

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PAC-II COMPLEXOMETRIC TITRATION

BONDING IN METAL COMPLEXES
 A central metal atom bonded to a
group of molecules or ions is a metal
complex.
 If the complex bears a charge, it is a
complex ion.
 Compounds containing complexes are
known as coordination compounds.
 The bonds are either ordinary covalent
bonds or co-ordinate bonds.
 Ordinary covalent bonds in which the
metal and the ligand...
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