JEE Main · 2019 · 09 Jan 2019 · Shift 2 · Coordination Compounds

The complex that has highest crystal field splitting energy(

Δ

) is

(A) $[Co (NH_{3})_{5} (H_{2} O)] Cl_{3}$
(B) $K_{2} [CoCl_{4}]$
(C) $[Co (NH_{3})_{5} Cl] Cl_{2}$
(D) $K_{3} [Co (CN)_{6}]$ ✓ Correct

Answer: (D)

Solution

Crystal-field splitting

Δ

follows the spectrochemical series,

CN X^{-} > NH X_{3} > H X_{2} O > Cl X^{-}

, and octahedral fields split far more strongly than tetrahedral ones. Among the choices,

K X_{3} [Co (CN) X_{6}]

pairs the strongest-field ligand with an octahedral geometry, so it has the largest

Δ

of the set.

JEE Main · 2019 · 09 Jan 2019 · Shift 2 · Single correct option

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