Crystal field theory (CFT) considers ligands as point charges and focuses on the electrostatic interaction between metal and ligand.
CFT is successful in explaining:
II. Formation and structures of complexes
III. Colour (due to d-d transition)
IV. Magnetic properties (due to electron pairing/unpairing in d orbitals)
It does not explain I (ligands as point charges is an assumption, not an outcome)
It also fails to explain V (covalent character), which is covered by Molecular Orbital Theory
Werner’s coordination theory in 1893 was the first attempt to explain the bonding in coordination complexes. It must be remembered that this theory was put forward before the electron had been discovered by J.J. Thomson in 1897, and before the electronic theory of valency. Werner did not have any of the modern instrumental techniques and all his studies were made using simple experimental techniques. Werner was able to explain the nature of bonding in complexes and he concluded that in complexes, the metal shows two different sorts of valency: primary and secondary. Primary valences are normally ionisable whereas secondary valences are non-ionisable.
The logic gate equivalent to the combination of logic gates shown in the figure is