Question

The number of unpaired d-electrons in $[ \text{Co}(\text{H}_2\text{O})_6 ]^{3+}$ is ______

• A. 4
• B. 2
• C. 0
• D. 1

Answer 1

Answer: (C)

0

Answer 2

The complex $[ \text{Co(H}_2\text{O)}_6 ]^{3+}$ consists of a $\text{Co}^{3+}$ ion, which has a $d^6$ electronic configuration. In an octahedral field created by the water ligands, the splitting of the $d$-orbitals leads to the $t_{2g}$ and $e_g$ orbitals. As cobalt in this state is in a low-spin configuration (due to the relatively strong ligand field of water), all six electrons pair up in the $t_{2g}$ set, resulting in no unpaired electrons.

$\text{at } (0,0) \, t_{2g}: \quad (0,-0.3); \, (1.2,-0.3); \, (0.2,-0.3) \text{ circle (0.05); } \, (0.6,-0.3) \text{ circle (0.05); } \, (1.0,-0.3) \text{ circle (0.05);}$ $\text{at } (2,0) \, e_g: \quad (2.2,-0.3); \, (3.2,-0.3); \, (2.2,-0.3) \text{ circle (0.05); } \, (2.6,-0.3) \text{ circle (0.05);}$
Thus, there are no unpaired electrons in $[ \text{Co(H}_2\text{O)}_6 ]^{3+}$.