Question

Arrange following complex ions in increasing order of crystal field splitting energy $(\Delta_0)$
$[CrCl_6]^{3-}, [Cr(CN)_6]^{3-}, [Cr(NH_3)_6]^{3+}$

• A. $[Cr(NH_3)_6]^{3+} < [CrCl_6]^{3-} < [Cr(CN)_6]^{3+}$
• B. $[CrCl_6]^{3-} < [Cr(NH_3)_6]^{3+} < [Cr(CN)_6]^{3-}$
• C. $[CrCl_6]^{3-} < [Cr(CN)_6]^{3-} < [Cr(NH_3)_6]^{3+}$
• D. $[Cr(NH_3)_6]^{3+} < [Cr(CN)_6]^{3-} < [CrCl_6]^{3-}$

Answer 1

Answer: (B)

$Cl^-$ is a weak field ligand while $CN^-$ is a strong field ligand.
Hence, the order of crystal field splitting energy $(\Delta_0)$ is
$[CrCl_6]^{3-} < [Cr(NH_3)_6]^{3+} < [Cr(CN)_6]^{3-}$