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Coordination Compounds
Crystal Field Theory: High Spin Complexes
1 question from 1 paper, each with its answer.
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Concepts tested
- High spin d6 complex
All Questions
2003 AIPMT 1 question
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The number of unpaired electrons in the complex ion $[CoF_6]^{3-}$ is : (At. No. of Co = 27)Co (Z = 27): $[Ar]\,3d^7\,4s^2$
In $[CoF_6]^{3-}$: $x + 6(-1) = -3 \Rightarrow x = +3$. $Co^{3+} = [Ar]\,3d^6$.
$F^-$ is a weak field ligand, so $\Delta_o$ is less than the pairing energy. The electrons occupy the orbitals singly first (high spin): $t_{2g}^4\,e_g^2$.
In $t_{2g}^4$ one orbital is doubly filled and two are singly filled; both $e_g$ orbitals are singly filled. Unpaired electrons $= 2 + 2 = 4$.
($[CoF_6]^{3-}$ is an outer orbital $sp^3d^2$ complex and is paramagnetic.)
So the number of unpaired electrons is 4.