Question

The d-electron configuration of $C{r}^{2+},M{n}^{2+},F{e}^{2+}\text{and}C{o}^{2+}\text{are}{d}^4,d^5,d^6\text{and}{d}^7$ respectively. Which one of the following will exhibit minimum paramagnetic behaviour ?

(At, nos. $Cr=24,Mn=25,Fe=26,Co-27$)

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

Answer 1

The correct option is A $\left[Co\right(H_{2}O{)}_6{]}^{2+}$

All the given complexes are aqua complex. $H_{2}O$ is weak field ligand.

$C{o}^{3+}$ complex has only 3 unpaired electron so it will have less magnetci moment.

Minimum Paramagnetic behaviour = $\left[Co\right(H_{2}O{)}_6{]}^{2+}$