Werner’s Theory
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| Werner’s Theory |
To overcome the drawback of chain theory Werner’s theory was proposed
in 1893. At that time, Pt and Co complexes were made.
Postulates of Werner’s theory:
1) Every metal has two types of valencies
·
Primary valency [P.V.]:
which is due to oxidation Stale. It is satisfied by an anion (dotted line).
·
Secondary valency [S.V.]:
which is due to coordination number. It is satisfied by a neutral molecule or
anionic specie (Solid line).
2) Atoms attached with secondary valencies are non-ionizable. [S.V.
= coordination number].
3) Every metal tries to satisfies both of its valencies.
4) Anionic ligand can play dual behavior i.e. it can satisfy both
primary and secondary valency. But, neutral ligand can satisfy only secondary
valency.
5) Every Metal have fix number of S.V.
6) The ligand which satisfy the S.V. are directed toward fixed
positions in space.
7) Geometry of complex is determined by number and arrangement of
ligands in space.
8) Primary valencies are non-directional
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Applications of Werner’s theory
Behavior of completes of cobalt can be studied by this theory.
The electrolytic solution was taken and conductance was measured.
- For first solution which
is CoCl3.6NH3 four free ions were detected which are 3Cl-
ions and one [Co(NH3)6]+3. The complex
will be [Co(NH3)6]Cl3.
- The molecule CoCl3.5NH3
has dual behavior. It has one non-ionizable chloride and three ionizable free
ions were detected. 2Cl- and one [Co(NH3)5Cl]+2.
The formula for complex is [Co(NH3)5Cl]Cl2.
- Similarly, for CoCl3.4NH3
two free ions were detected. One chloride and one [Co(NH3)4Cl2]+.
The complex formula is [Co(NH3)4Cl2]Cl.
- For CoCl3.3NH3
none free ions were detected and formula of complex is [Co(NH3)3Cl3].
Werner made a lot of complexes and explain their behavior. He
developed the concept of isomerism in coordination compounds. He works and separate
different enantiomers. Werner and his students works on stereochemistry of
coordination compounds. They made the complex “[Co(NH3)Cl(en)2]Cl2”
and made its enantiomers and diastereomers.
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