Question

Which one of the following aqua complexes will exhibit the minimum paramagnetic behaviour?
(Atomic number Cr = 24, Mn = 25, Fe = 26, Ni = 28)

• A. $\left[Cr\right(H_2{O}_6){]}^{2+}$
• B. $\left[Mn\right(H_2{O}_6){]}^{2+}$
• C. $\left[Fe\right(H_2{O}_6){]}^{2+}$
• D. $\left[Ni\right(H_2{O}_6){]}^{2+}$

Answer 1

The correct option is D

$\left[Ni\right(H_2{O}_6){]}^{2+}$

$H_{2}O$ is a weak field ligand, and the The d electron configuration of $C{r}^{2+},M{n}^{2+},F{e}^{2+}andN{i}^{2+}$ are $3d^4,3d^5,3d^{6}and3d^8$ respectively. $\left[Ni\right(H_2{O}_6){]}^{2+}$ will have just the two unpaired electrons and will show the least paramagnetic character. $\left[Mn\right(H_2{O}_6){]}^{2+}$ has 5 unpaired electrons whereas the other two have 4 unpaired electrons each.