Question

How can one decide whether the high spin or the low spin configuration of a metal complex will be more stable ?Elaborate.

Answer 1

Answer on Question #86249 – Chemistry – Inorganic Chemistry

How can one decide whether the high spin or the low spin configuration of a metal complex will be more stable? Elaborate.

Solution:

Whether a complex is high spin or low spin depends on such factors as:

1) the crystal field splitting energy $\Delta$

2) the pairing energy P.

The electrons will take the path of least resistance - the path that requires the least amount of energy. If the pairing energy P is greater than $\Delta$, then electrons will move to a higher energy orbital because it takes less energy. If the pairing energy P is less than $\Delta$, then the electrons will pair up rather than moving singly to a higher energy orbital.

To predict the value of $\Delta$ we should determine from the spectrochemical series is the ligand observed is strong field or weak field.

Spectrochemical series

(weak) $I^{-} < Br^{-} < S^{2-} < SCN^{-} < Cl^{-} < NO^{3-} < N^{3-} < F^{-} < OH^{-} < C_{2}O_{4}^{2-} \approx H_{2}O < NCS^{-} < CH_{3}CN < py < NH_{3} < en < bipy < phen < NO^{2-} < PPh_{3} < CN^{-} \approx CO$ (strong)

If ligand is strong field, then $P < \Delta o$ and we should expect a low spin complex to be formed.

If ligand is weak field, then $P > \Delta o$ and we should expect a high spin complex to be formed.

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