What are inner and outer orbital complexes ?

Explanation

In octahedral complexes the central metal atom or iòn either uses the inner i.e. (n-1)d-orbitals or outer i.e., nd orbitals for the hybridisation. Accordingly the complexes are termed as inner or outer complexes respectively.
(i) Inner orbital complexes : When the complex formed involves the inner i.e., (n-1) d-orbitals for the hybridisation, the hybridisation involved is termed as `d^2-sp^3` hybridisation and the complex is called inner orbital complex. In such complexes, the electrons of the central metal atom or ion pair up if needed. Therefore, the resulting complex will either be diamagnetic (if no unpaired electron is there) or weakly paramagnetic (if lesser number of unpaired electrons are there). Such complexes are also known as low spin complexes or hyperligated complexes.
(ii) Outer orbital complexes : When the complex formed involves the outer i.e., nd orbitals for the hybridisation, the hybridisation involved is termed as `sp^3d^2` of hybridisation and the complex is called outer orbital complex. In such complexes, the Electrons of the central metal atom or ion do not pair up. Therefore, the resulting complex will generally be paramagnetic due to the presence of unpaired electrons. Such complexes are also known as high spin complexes or hypoligated complexes.