Question

In which of the following octahedral complexes of Cobalt $\left( {at.no.27} \right)$ will the magnitude of ${\Delta _0}$ be the highest?
A.${\left[ {Co{{\left( {{C_2}{O_4}} \right)}_3}} \right]^{3 - }}$
B.${\left[ {Co{{\left( {{H_2}O} \right)}_6}} \right]^{3 + }}$
C.${\left[ {Co{{\left( {N{H_3}} \right)}_6}} \right]^{3 + }}$
D.${\left[ {Co{{\left( {CN} \right)}_6}} \right]^{3 - }}$

Answer 1

Octahedral complexes are the complex compounds that have the coordination number of six. The crystal field splitting energy ${\Delta _0}$ will be high for the complexes that have high splitting power according to the spectrochemical series. Cyanide is the strong ligand that has high splitting power that leads to high crystal field splitting energy ${\Delta _0}$ .

Complete answer:
Complex compounds are also known as coordination compounds that are special types of compounds which can retain their identity even dissolved in water or any other organic solvents. Octahedral complexes are the complex compounds that have the coordination number of six. Cobalt forms an octahedral complex with the ligands like oxalate, water, ammonia and cyanide.
In octahedral complexes, splitting of d-orbitals takes place into ${t_{2g}}$ and ${e_g}$ orbitals. The energy required for splitting of d-orbitals is known as crystal field splitting energy and represented by ${\Delta _0}$.
According to spectrochemical series, the ligands were arranged in the order of splitting power. Cyanide is the ligand with high splitting energy. Thus, in the given options cobalt with cyanide ligands have high crystal field splitting energy.
${\left[ {Co{{\left( {CN} \right)}_6}} \right]^{3 - }}$ has a high ${\Delta _0}$.
So, option (D) is the correct answer.

Note:
In spectrochemical series, the ligands that has high splitting power are considered as strong ligands and the examples were cyanide and leads to the high value of ${\Delta _0}$ Weak ligands like water and ammonia have low splitting power leads to the low value of ${\Delta _0}$ .