Consider the following complexes. $\left[\mathrm{CoCl}\left(\mathrm{NH}_{3}\right)_{5}\right]^{2+}$, $\left[\mathrm{Co}(\mathrm{CN})_{6}\right]^{3-}$, (A) (B) $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{3+}$, $\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\right]^{2+}$ (C) (D) The correct order of A, B, C and D in terms of wavenumber of light absorbed is :

JEE Main · 2024 · 06 Apr 2024 · Shift 1 · Coordination Compounds

Consider the following complexes.

[CoCl (NH_{3})_{5}]^{2 +}

[Co (CN)_{6}]^{3 -}

,
(A)
(B)

[Co (NH_{3})_{5} (H_{2} O)]^{3 +}

[Cu (H_{2} O)_{4}]^{2 +}

Answer: (B)

The wavenumber of light absorbed increases with the crystal-field splitting

Δ_{o}

, which increases with the ligand field strength and metal oxidation state.
Ordering:

[Cu (H_{2} O)_{4}]^{2 +}

(D)

<

[CoCl (N H_{3})_{5}]^{2 +}

(A)

<

[Co (N H_{3})_{5} (H_{2} O)]^{3 +}

(C)

<

[Co (CN)_{6}]^{3 -}

(B).
Greater

Δ_{o}

means higher-energy (higher-wavenumber) absorption, so the order of increasing wavenumber is D

<

<

<

JEE Main · 2024 · 06 Apr 2024 · Shift 1 · Single correct option