Outer orbital complexes-definition-octahedral complex

What is outer-orbital complexes in chemistry ?

Octahedral complexes  which is formed through sp³d² hybridization, show that, 3d-orbitals of central metal ion remain unchanged.

In this case, outer 4d-orbtals are involved in hybridization and form octahedral complexes. 

Such a complex in which the central metal ion utilizes outer nd-orbitals is called outer-orbital complex.

For example, hexaaquo nickel(II)ion,[ Ni ( H₂O )₆ ]²⁺ and  hexaamine zinc(II)ion, [ Zn( NH3)₆ ]²⁺ are two outer-orbital complex .

According to valence bond theory, the formation of [ Ni ( H₂O )₆ ]²⁺ complex ion is shown below.

The outer-orbital complex has a large number of unpaired electrons than their number in inner orbital complex of the same metal ion due to unchanged of 

configuration of metal ion on complexation .Such a complex is also called high spin complex.

Why are octahedral complexes of Co²⁺,Ni²⁺,Cu²⁺ and Zn²⁺ ions always outer-orbital  ?

According to valence bond theory, it has been seen that, the octahedral complexes of Co²⁺,Ni²⁺,Cu²⁺ and Zn²⁺ ions are always outer-orbital .

This can be explained on the basis of their electronic arrangement . From their electronic arrangement it has been found that no ions among them have two vacant 3d-orbitals.

Because, all the above said ions contain seven or more electrons in their inner 3d-orbital.Hence, in the formation of octahedral complexes, they can’t attain d²sp³ hybridization.

That is, the metal ions, Co²⁺,Ni²⁺,Cu²⁺ and Zn²⁺ show sp3d² hybridization by using their outervacant 4d-orbital.

Consequently, all the octahedral complexes of Co²⁺,Ni²⁺,Cu²⁺ and Zn²⁺ ions are always outer-orbital.

The electronic arrangement and hybridization of the Co²⁺,Ni²⁺,Cu²⁺ and Zn²⁺ ions are shown below.

The electronic arrangement and hybridization of Cu²⁺ and Zn²⁺ ions are same. 




Summary :


What is outer-orbital complexes in chemistry ?
Why are octahedral complexes of Co²⁺,Ni²⁺,Cu²⁺ and Zn²⁺ ions always outer-orbital  ?

Why are all square planar complexes always inner-orbital complexes ? 

Chelate complex definition example and pi acid ligands.