Statement I: Both [Co(NH3)6]^3+ and [CoF6]^3– complexes are octahedra

Question

Given below are two statements : 

Statement I: Both \([Co(NH_3)_6] ^{3+}\) and \([CoF_6] ^{3-}\) complexes are octahedral but differ in their magnetic behaviour. 

Statement II: \([Co(NH_3)_6] ^{3+}\) is diamagnetic whereas \([CoF_6]^{3-}\) is paramagnetic. 

In the light of the above statements, choose the correct answer from the options given below: 

(1) Both Statement I and Statement II are true 

(2) Both Statement I and Statement II are false 

(3) Statement I is true but Statement II is false 

(4) Statement I is false but Statement II is true

Answer 1

Correct option is (1) Both Statement I and Statement II are true 

In \( [Co(NH_3)6]3+, Co^3\)  

Electronic configuration of \(Co^{3+} :\) 

In presence of \(NH_3\) ligand, pairing of electrons takes place and it becomes diamagnetic complex ion. In presence of \(NH_3\) ligand :

\(\therefore \) \([Co (NH_3)_6]^{3+} \) is octahedral with \(d^2sp^3\) hybridisation and it is diamagnetic in nature.

In case of \([CoF_6]^{3-}\), Co is in +3 oxidation state and it is having \(3d^6\) configuration. In presence of weak field \(F ^-\) ligand, pairing does not take place.

In presence of \(F^-\) ligands : 

\(\therefore\) In \([CoF_6]^{3-},\) \(Co ^{3+}\) is \(sp^3 d^2\) hybridised with four unpaired electrons, so it is paramagnetic in nature.