Coordination complexes, Formation of coordination complexes, Significance of Coordination chemistry, Important terminologies in coordination chemistry with examples, Types of ligands and types of complexes, Werner’s theory of coordination compounds with postulates, his experiments and observation, Limitations of Werner theory

1. By,
J.PADMAPRIYA, M.Sc.

2. CONTENTS:
Coordination complexes,
Important terminologies,
Types of ligands and complexes and
Werner’s Theory.

3. COORDINATION COMPLEXES
Derived from Latin words,
'complexus'
hold
'coordinate'
to arrange
How a coordination compound will form?
Covalent bond - mutual sharing of electrons b/w two atoms.
Coordinate covalent bond –
one atom acts as Lewis acid (e- pair acceptor)
another atom acts as Lewis base (e- pair donor)
Most of the transition / d-block elements form coordination
compounds.

4. Significance :
Play a vital role in the biological functions, and
Wide range of catalytic applications in chemical
industries.
Examples:
Haemoglobin – iron complex, oxygen transporter
of human.

5. Cobalamine – cobalt complex, an essential
vitamin.
Chlorophyll – Mg complex, helps in
photosynthesis.
Industries - Wilkinson's compound, Ziegler Natta
compound are used as catalysts.

10. Werner’s theory of coordination compounds
Alfred Werner – Swiss chemist
– 1st proposed this theory and
explained bonding in complexes.
Imaginary theory and did not
have any modern instrumental
techniques.
This study was made using
simple chemical reactions.
He got Nobel prize in 1913 for
his work. So he is called as
“Father of Coordination
Chemistry”.

11. Postulates:
There are 2 types of valencies :
Primary valency,
Secondary valency.
PRIMARY VALENCY SECONDARY VALENCY
Corresponds to oxidation state of
CMA.
Corresponds to Coordination
number of CMA.
Always satisfied by negative
ions.
Satisfied by negative or positive
or neutral ions called Ligands.
Shown by dotted lines. Shown in thick lines and in
square brackets.
Non – directional in nature. Directional in nature.
Ionisable valency. Non – ionisable valency.

12. In general, all the elements tend to satisfy both primary
and secondary valency.
But fulfillment of secondary valency is more essential.
Spatial arrangement :
no. of. ligands – 6 – Octahedral
no. of ligands – 4 – Tetrahedral or Square planar.
His experiment:
He has taken different coloured cobalt (III) chloride
with ammonia complexes and made to react with AgNO3
and tested conductivity.
A) CoCl3. 6NH3 - [Co(NH3) 6]Cl3
B) CoCl3. 5NH3 - [Co(NH3) 5 Cl]Cl2
C) CoCl3. 4NH3 - [Co(NH3) 4 Cl2]Cl
D) CoCl3. 3NH3 - [Co(NH3) 3Cl3].

15. Member Formula Complex
No.of.
Ions in
solution
Conductivity
(mho)
A CoCl3. 6NH3 [Co(NH3) 6]Cl3 4(3+1) ~409
B CoCl3. 5NH3 [Co(NH3) 5 Cl]Cl2 3(2+1) ~209
C CoCl3. 4NH3 [Co(NH3) 4 Cl2]Cl 2(1+1) ~97
D CoCl3. 3NH3 [Co(NH3) 3Cl3] 0 0
His Observation

17. Limitations:
It fails to explain the colour of the complexes.
It does not explain the magnetic and optical properties
of complexes.
This theory could not explain the directional
properties of various compounds.