JEE Mains · Chemistry · STD 12 - 5. Co-ordination chemistry

The correct order of the following complexes in terms of their crystal field stabilization energies is _______.

A \(\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+} \lt \left[\mathrm{Co}(\mathrm{en})_3\right]^{3+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}\)
B \(\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+} \lt \left[\mathrm{Co}(\mathrm{en})_3\right]^{3+}\)
C \(\left[\mathrm{Co}(\mathrm{en})_3\right]^{3+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+}\)
D \(\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} \lt \left[\mathrm{Co}(\mathrm{en})_3\right]^{3+}\)

Verified Solution

Answer & Solution

Correct Answer

(D) \(\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} \lt \left[\mathrm{Co}(\mathrm{en})_3\right]^{3+}\)

Step-by-step Solution

Detailed explanation

Crystal field splitting energy \((\Delta) \propto\) charge or oxidation state of central metal atom. Crystal field splitting energy \((\Delta) \propto\) Field strength of ligand (and chelation) Crystal field stabilisation energy (CFSE)…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

Same subject

Match List\(-I\) with List\(-II\)

	List\(-I\)		List\(-II\)
\((a)\)	Sucrose	\((i)\)	\(\beta\) -D-Galactose and \(\beta\) -D-Glucose
\((b)\)	Lactose	\((ii)\)	\(\alpha\) -D-Glucose and \(\beta\) -D-Fructose
\((c)\)	Maltose	\((iii)\)	\(\alpha\) -D-Glucose and \(\alpha\) -D-Glucose

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