Q. Among the following ions, which one has the highest paramagnetism?
NTA AbhyasNTA Abhyas 2020Coordination Compounds
Solution:
Water is a weak-field ligand, so the crystal field splitting paired in lower energy. Hence, electrons are not paired in lower energy d-orbitals (i.e., no pairing of electrons in d-orbitals occurs aganist the Hunds rule).
Species
Oxidation state of central metal ion
Configuration of central metal ion
Number of unpaired d-electrons
A
$[Cr(H_2O)_6]^{3+}$
+3
$Cr^{3+}(3d^3)$
3
B
$[Fe(H_2O)_6]^{2+}$
+2
$Fe^{2+}(3d^6)$
4
C
$[Cu(H_2O)_6]^{2+}$
+2
$Cu^{2+}(3d^9)$
1
D
$[Zn(H_2O)_6]^{2+}$
+2
$Zn^{2+}(3d^{10})$
0
The more the number of unpaired electrons, the higher is the paramagnetic character of the metal ion, As a result, $[Fe(H_2O)_6]^{2+}$ has the highest paramagnetism.
| Species | Oxidation state of central metal ion | Configuration of central metal ion | Number of unpaired d-electrons | |
|---|---|---|---|---|
| A | $[Cr(H_2O)_6]^{3+}$ | +3 | $Cr^{3+}(3d^3)$ | 3 |
| B | $[Fe(H_2O)_6]^{2+}$ | +2 | $Fe^{2+}(3d^6)$ | 4 |
| C | $[Cu(H_2O)_6]^{2+}$ | +2 | $Cu^{2+}(3d^9)$ | 1 |
| D | $[Zn(H_2O)_6]^{2+}$ | +2 | $Zn^{2+}(3d^{10})$ | 0 |