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Magnetic moments of tetrahedral Cobalt (II) and (III) complexes
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Ken Stewart
Magnetic moments of tetrahedral Cobalt (II) and (III) complexes
The question isn't really clear exactly what complexes you are referring to. However, cyanide is quite a high field ligand, so perhaps the Co(II) cyanide compound is low spin while the 3.87 value is for high spin (3/2). I don't see how it could be low spin if it is really tetrahedral, but isn't $\ce {Co(CN)_4^2-}$ square planar?
For Co(III) alkyl, alkyl ligands can also be relatively high field, and it is at least theoretically possible to have low spin (s=1) Co(III) tetrahedral complex. However, it is rare for tetrahedral complexes to be low spin because the ligand field splitting energy is lower than for octahedral.
The question isn't really clear exactly what complexes you are referring to. However, cyanide is quite a high field ligand, so perhaps the Co(II) cyanide compound is low spin while the 3.87 value is for high spin (3/2). I don't see how it could be low spin if it is really tetrahedral, but isn't $\ce {Co(CN)_4^2-}$ square planar?
For Co(III) alkyl, alkyl ligands can also be relatively high field, and it is at least theoretically possible to have low spin (s=1) Co(III) tetrahedral complex. However, it is rare for tetrahedral complexes to be low spin because the ligand field splitting energy is lower than for octahedral.
@J.LS magnetic moment of 3.15 would mean cobalt (III) norbornyl complex is low spin (s=1) tetrahedral, so it looks like both Co(III) and Co(IV) norbornyl complex are both extremely rare low spin tetrahedral complexesMore
The cyanide complex is indeed square planar, which explains the magnetic data - my textbook didnt make that clear. As for Co(III) alkyl, assuming an e(3) t2(3) configuration in a tetrahedral ligand field you would have a magnetic moment of 4.89 - but the observed values are much lower. I assume square planar geometry would be out of the question with a ligand such as norbornyl (tetra Co(III) complex magnetic moment 3.15).More
The question isn't really clear exactly what complexes you are referring to. However, cyanide is quite a high field ligand, so perhaps the Co(II) cyanide compound is low spin while the 3.87 value is for high spin (3/2). I don't see how it could be low spin if it is really tetrahedral, but isn't $\ce {Co(CN)_4^2-}$ square planar?
For Co(III) alkyl, alkyl ligands can also be relatively high field, and it is at least theoretically possible to have low spin (s=1) Co(III) tetrahedral complex. However, it is rare for tetrahedral complexes to be low spin because the ligand field splitting energy is lower than for octahedral.
If those are not the reasons, see Iron, Cobalt, and Nickel Complexes having Anomalous Magnetic Moments Quarterly Review Chemical Society volume 22, pp 457-498.
The question isn't really clear exactly what complexes you are referring to. However, cyanide is quite a high field ligand, so perhaps the Co(II) cyanide compound is low spin while the 3.87 value is for high spin (3/2). I don't see how it could be low spin if it is really tetrahedral, but isn't $\ce {Co(CN)_4^2-}$ square planar?
For Co(III) alkyl, alkyl ligands can also be relatively high field, and it is at least theoretically possible to have low spin (s=1) Co(III) tetrahedral complex. However, it is rare for tetrahedral complexes to be low spin because the ligand field splitting energy is lower than for octahedral.
If those are not the reasons, see Iron, Cobalt, and Nickel Complexes having Anomalous Magnetic Moments Quarterly Review Chemical Society volume 22, pp 457-498.
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