Werner turned
his attention towards the geometrical arrangements of the coordinated groups
around the central cation and explained successfully the cause of optical and
geometrical isomerism of these compounds. Some examples are given below:
Octahedral complexes:
[CoCl2(NH3)4]Cl: Werner
said that theoretically there are three structure possible for this complex.
These are planar, trigonal prism, octahedral. The number of possible isomer
is 3 for planar, 3 for trigonal prism and 2 for
octahedral structure.
Various possible isomers for the planar, trigonal prism and octahedral
structures of the complex ion [CoCl3(NH3)4]
since only two isomers of the compound could be isolated, werner concluded that
geometrical arrangement of the coordinated group around the central atom in
this compound was octahedral. In the case of several other complexes in which
the coordination number of the central atom was six, werner was able to
conclude that in all these cases the six coordinated complex have octahedral
geometry.
Square Planar and Tetrahedral:
He studied
the geometry of the complexes in which the coordination number of the central
metal atom is 4. He proposed that there are two possible structures.
[PtCl2(NH3)2] complex:
In this complex the coordination number of the metal is 4, werner
found that it existed in two isomeric forms, cis and trans. This shows that all
the four ligands lie in the same plane. Therefore the structure should be a
square planar or tetrahedral
.
Cis
and trans isomers of [PtCl2(NH3)2]
complex
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