The correct order of energy of absorption for the following metal complexes is A: $\left[\mathrm{Ni}(\mathrm{en})_{3}\right]^{2+}$, B:$\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}$, C:$\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$

(A) $\mathrm{C}<\mathrm{B}<\mathrm{A}$

(B) B $<\mathrm{C}<\mathrm{A}$

(C) $\mathrm{C}<\mathrm{A}<\mathrm{B}$

JEE Main · 2022 · 25 Jul 2022 · Shift 2 · Coordination Compounds

The correct order of energy of absorption for the following metal complexes is
A:

[Ni (en)_{3}]^{2 +}

, B:

[Ni (NH_{3})_{6}]^{2 +}

, C:

[Ni (H_{2} O)_{6}]^{2 +}

Answer: (A)

The energy of absorption in coordination complexes depends on the crystal field splitting (

Δ

), which is determined by ligand field strength according to the spectrochemical series.

Ligand strength order: en (ethylenediamine) >

NH_{3}

H_{2} O

Stronger ligands cause larger splitting and require higher energy for d-d transitions:

A:

[Ni (en)_{3}]^{2 +}

- strongest ligand (en) → highest

Δ

→ highest absorption energy

B:

[Ni (NH_{3})_{6}]^{2 +}

- intermediate ligand → intermediate energy

C:

[Ni (H_{2} O)_{6}]^{2 +}

- weakest ligand → lowest energy

Order:

C < B < A

JEE Main · 2022 · 25 Jul 2022 · Shift 2 · Single correct option