The correct order of the number of unpaired electrons in the given complexes is
A. $\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}$
B. $\left[\mathrm{Fe} \mathrm{F}_{6}\right]^{3-}$
C. $\left[\mathrm{CoF}_{6}\right]^{3-}$
D. $\left.[\mathrm{Cr} \text { (oxalate})_{3}\right]^{3-}$
E. $\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]$
Choose the correct answer from the options given below:
Solution
<p>The number of unpaired electrons in a complex can be determined by the oxidation state of the central metal atom and the ligand field splitting energy. In general, a complex with a high-spin configuration will have more unpaired electrons than a complex with a low-spin configuration.</p>
<p>In the given complexes, the oxidation states of the central metal atoms are:</p>
<ul>
<li>Fe(II) in [Fe(CN)<sub>6</sub>]<sup>3-</sup></li><br/>
<li>Fe(III) in [FeF<sub>6</sub>]<sup>3-</sup></li><br/>
<li>Co(III) in [CoF<sub>6</sub>]<sup>3-</sup></li><br/>
<li>Cr(III) in [Cr(ox)<sub>3</sub>]3-</li><br/>
<li>Ni(0) in [Ni(CO)<sub>4</sub>]</li>
</ul>
<p>The ligand field splitting energy of a complex depends on the type of ligand. In general, ligands that are strong field ligands will split the d orbitals more than ligands that are weak field ligands.</p>
<p>The following table shows the number of unpaired electrons in each complex :</p>
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<table class="tg">
<thead>
<tr>
<th class="tg-1wig">Complex</th>
<th class="tg-1wig">Oxidation state</th>
<th class="tg-1wig">Ligand field splitting energy</th>
<th class="tg-1wig">Number of unpaired electrons</th>
</tr>
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<tbody>
<tr>
<td class="tg-0lax">[Fe(CN)<sub>6</sub>]<sup>3-</sup></td>
<td class="tg-0lax">Fe(II)</td>
<td class="tg-0lax">Low-spin</td>
<td class="tg-0lax">1</td>
</tr>
<tr>
<td class="tg-0lax">[FeF<sub>6</sub>]<sup>3-</sup></td>
<td class="tg-0lax">Fe(III)</td>
<td class="tg-0lax">High-spin</td>
<td class="tg-0lax">5</td>
</tr>
<tr>
<td class="tg-0lax">[CoF<sub>6</sub>]<sup>3-</sup></td>
<td class="tg-0lax">Co(III)</td>
<td class="tg-0lax">High-spin</td>
<td class="tg-0lax">4</td>
</tr>
<tr>
<td class="tg-0lax">[Cr(ox)<sub>3</sub>]<sup>3-</sup></td>
<td class="tg-0lax">Cr(III)</td>
<td class="tg-0lax">High-spin</td>
<td class="tg-0lax">3</td>
</tr>
<tr>
<td class="tg-0lax">[Ni(CO)<sub>4</sub>]</td>
<td class="tg-0lax">Ni(0)</td>
<td class="tg-0lax">None</td>
<td class="tg-0lax">0</td>
</tr>
</tbody>
</table>
<p>Therefore, the correct order of the number of unpaired electrons in the given complexes is :</p>
<pre>E < A < D < C < B</pre>
About this question
Subject: Chemistry · Chapter: Coordination Compounds · Topic: Ligands and Coordination Number
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