Question

The geometry and magnetic properties of complexes can be explained by V.B. Theory. 

The octahedral complex [Co(NH₃]₆]³⁺ is diamagnetic while the octahedral complex [COF₆]^3-  is diamagnetic. Explain using VB. Theory,

Answer 1

In the complex, [Co(NH₃)₆]³⁺ the cobalt ion is in +3 oxidation state and has the electronic conguration 3a⁶ . It undergoes d²sp³ hybridisation as shown below:

Here, the six pairs of electrons, one from each NH₃ molecule, occupy the six hybrid orbitals. Thus, the complex has octahedral geometry and is diamagnetic be cause of the absence of an unpaired electron. 

In [CoF₆]^3- also he cobalt ion is in +3 oxidation state and has the electronic conguration 3d⁶ . Since F ion provides a weak ligand eld one 4s, three 4p and two 4d orbitaIs hybridise to yield six sp³d² hybrid or bitaIs pointing towards the six ends of an octahedron. The six Fions then donate a pair of electrons to each of these vacant orbitals to have an octahedral geometry. The presence of unpaired electrons in 3d orbit ais makes the complex paramagnetic.