Question

Predict the order of ${\Delta }_o$ for the following compounds:-
(i) $\left[Cr\right(H_{2}O{)}_6{]}^{3+}$
(ii) $\left[Cr\right(CN{)}_2(H_{2}O{)}_4{]}^{-}$
(iii) $\left[Cr\right(CN{)}_4(H_{2}O{)}_2{]}^{-}$
(iv) $\left[Cr\right(CN{)}_6{]}^{3-}$

• A. ${\Delta }_o\left(i\right)<{\Delta }_o\left(ii\right)<{\Delta }_o\left(iii\right)<{\Delta }_o\left(iv\right)$
• B. ${\Delta }_o\left(i\right)>{\Delta }_o\left(ii\right)>{\Delta }_o\left(iii\right)>{\Delta }_o\left(iv\right)$
• C. ${\Delta }_o\left(ii\right)={\Delta }_o\left(iii\right)<{\Delta }_o\left(i\right)<{\Delta }_o\left(iv\right)$
• D. ${\Delta }_o\left(ii\right)<{\Delta }_o\left(iii\right)<{\Delta }_o\left(iv\right)<{\Delta }_o\left(i\right)$

Answer 1

The correct option is A ${\Delta }_o\left(i\right)<{\Delta }_o\left(ii\right)<{\Delta }_o\left(iii\right)<{\Delta }_o\left(iv\right)$

Stronger the ligand, more is the crystal field energy. Here $C{N}^{-}$ is stronger ligand than $H_{2}O$, so the appropriate order of ${\Delta }_o$ is
${\Delta }_o\left(i\right)<{\Delta }_o\left(ii\right)<{\Delta }_o\left(iii\right)<{\Delta }_o\left(iv\right)$