[CoF₆]^3- and [Co(en)₃]³⁺, which one complex is:

(i) Paramagnetic

(ii) More stable

(iii) Inner orbit complex and

(iv) High spin complex

(atomic no. of Co = 27)

Orbital of Co³⁺

Since (F) is a weak field ligand according to the spectrochemical series of ligands it acquires higher energy orbitals and thus results in no spin pairing of electrons in the lower d orbital and acquires one empty s orbital, three p orbitals and two empty d orbitals of higher energy, to give sp³d² hybridization.

Orbital of Co³⁺ undergoing hybridization

The given structure shows sp³d² hybridization, and as the compound has 3 unpaired electrons it is paramagnetic.

Due to acquiring of higher energy orbitals the stability of the compound decreases significantly.

Also the outer d-orbitals are used for bonding thus the compound is outer complex and is a high spin complex.

Hybridization of [CoF₆]^3-

Co³⁺ is the central atom with a fluoride ligand being the donor.

Electronic configuration = 2, 8, 7

= 4s², 3d⁷

Oxidised state = 4s⁰, 3d⁶

Orbital of Co³⁺

Since (en) is a strong field ligand according to the spectrochemical series of ligands it acquires lower energy orbitals and thus results in spin pairing of electrons in the lower d orbital and acquires one empty s orbital, three p orbitals and two empty d orbitals of lower energy, to give d²sp³d² hybridization.

Orbital of Co³⁺ undergoing hybridization

d²sp³ hybirdization

The given structure shows d²sp³ hybridization, and as the compound has 0 unpaired electrons it is diamagnetic.

Due to acquiring of lower energy orbitals the stability of the compound increases significantly.

Also the inner d-orbitals are used for bonding thus the compound is inner complex and is also a low spin complex.