Question

Among the complex ions $\left[Ti\right(H_{2}O{)}_6{]}^{3+},\left[Cr\right(H_{2}O{)}_6{]}^{2+},\left[Fe\right(H_{2}O{)}_6{]}^{2+}$ and $\left[Co\right(H_{2}O{)}_6{]}^{2+}$, the one that shows strongest distortion from regular octahedral structure is:

• A. $\left[Ti\right(H_{2}O{)}_6{]}^{3+}$
• B. $\left[Cr\right(H_{2}O{)}_6{]}^{2+}$
• C. $\left[Fe\right(H_{2}O{)}_6{]}^{2+}$
• D. $\left[Co\right(H_{2}O{)}_6{]}^{2+}$

Answer 1

Answer: (B)

$\left[Cr\right(H_{2}O{)}_6{]}^{2+}$

$\left[Cr\right(H_{2}O{)}_6{]}^{2+}$ shows the strongest distortion from the regular octahedral structure.
The central $Cr$ atom in +2 oxidation state has $3d^4$ outer electronic configuration.
It has degenerate electronic states occupying the eg orbital set and tend to show stronger Jahn-Teller effects.