Arrange the following Cobalt complexes in the order of increasing Crystal Field Stabilization Energy (CFSE) value. Complexes: $\left[\mathrm{CoF}_{6}\right]^{3-},\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+},\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}$ and $\left[\mathrm{Co}(\mathrm{en})_{3}\right]^{3+}$ A B C D Choose the correct option:

JEE Main · 2021 · 26 Aug 2021 · Shift 2 · Coordination Compounds

Arrange the following Cobalt complexes in the order of increasing Crystal Field Stabilization Energy (CFSE) value.
Complexes:

[CoF_{6}]^{3 -}, [Co (H_{2} O)_{6}]^{2 +}, [Co (NH_{3})_{6}]^{3 +}

and

[Co (en)_{3}]^{3 +}

A
B
C
D

Choose the correct option:

(A)B $<$ A $<$ C $<$ D✓ Correct
(B)A $<$ B $<$ C $<$ D
(C)B $<$ C $<$ D $<$ A
(D)C $<$ D $<$ B $<$ A

Answer: (A)

Solution

The crystal field stabilisation energy of these cobalt complexes follows the magnitude of

Δ_{0}

, which grows with the charge on the metal ion and with the position of the ligand in the spectrochemical series,

F^{-} < H_{2} O < N H_{3} < en

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

is the only

C o^{2 +}

species and carries a weak-field ligand, so its splitting is the smallest. The other three hold

C o^{3 +}

, and among them the field strength rises from fluoride through ammonia to the chelating ethylenediamine, which binds most strongly. The increasing order is

[Co (H_{2} O)_{6}]^{2 +} < [Co F_{6}]^{3 -} < [Co (N H_{3})_{6}]^{3 +} < [Co (en)_{3}]^{3 +}

JEE Main · 2021 · 26 Aug 2021 · Shift 2 · Single correct option

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JEE Main · 2021 · 26 Aug 2021 · Shift 2 · Coordination Compounds

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