Question

Identify the correct increasing order of crystal field stabilization energy value for the given complexes.

• A. $\left[Ir\left(NH_{3}\right)_{6}\right]^{3+} < \left[Rh\left(NH_{3}\right)_{6}\right]^{3+} < \left[Co\left(NH_{3}\right)_{6}\right]^{3+}$
• B. $\left[Rh\left(NH_{3}\right)_{6}\right]^{3+} < \left[Co\left(NH_{3}\right)_{6}\right]^{3+} < \left[Ir\left(NH_{3}\right)_{6}\right]^{3+}$
• C. $\left[Co\left(NH_{3}\right)_{6}\right]^{3+} < \left[Ir\left(NH_{3}\right)_{6}\right]^{3+} < \left[Rh\left(NH_{3}\right)_{6}\right]^{3+}$
• D. $\left[Co\left(NH_{3}\right)_{6}\right]^{3+} < \left[Rh\left(NH_{3}\right)_{6}\right]^{3+}< \left[Ir\left(NH_{3}\right)_{6}\right]^{3+}$

Answer 1

Answer: (D)

The elements in the $2^{nd}$ and $3^{rd}$ transition series (the $4d$ and $5d$ elements) have large splitting than those in $3d$ series. So, the order of $CFSE$ is
$[Co(NH_{3})_{6}]^{3+} < \, [Rh(NH_{3})_{6}]^{3+} < \, [Ir(NH_{3})_{6}]^{3+}$