Chemistry - Spin only magnetic moments question? Watch

thenextchemist
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Account for the fact that trans-[NiCl2(en)2] has a spin-only magnetic moment of 2.83 μB whereas trans-[NiBr2(en)2] has a magnetic moment of 0.

I don't seem to understand this question as both are high spin because they are tetrahedral complexes and both have the same number of unpaired electrons.

Is it something to do with the spectrochemical series?

thank you
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MexicanKeith
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(Original post by Bloom77)
Account for the fact that trans-[NiCl2(en)2] has a spin-only magnetic moment of 2.83 μB whereas trans-[NiBr2(en)2] has a magnetic moment of 0.

I don't seem to understand this question as both are high spin because they are tetrahedral complexes and both have the same number of unpaired electrons.

Is it something to do with the spectrochemical series?

thank you
How can they be described as trans if they are tetrahedral...
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charco
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(Original post by MexicanKeith)
How can they be described as trans if they are tetrahedral...
They are not tetrahedral, they are octahedral.
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MexicanKeith
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(Original post by charco)
They are not tetrahedral, they are octahedral.
I was attempting to prompt the original poster to reach that conclusion
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thenextchemist
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(Original post by MexicanKeith)
How can they be described as trans if they are tetrahedral...
omg they are octahedral!
sorry!! It was the middle of the night, guessing I was tired!
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MexicanKeith
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(Original post by Bloom77)
omg they are octahedral!
sorry!! It was the middle of the night, guessing I was tired!
Yep octahedral, but the key to answering this question is to do with the fact that Ni 2+ d8 compounds like to have a square planar geometry, This means that the equatorial en ligands are tightly bound, whilst the axial halides are labile. So the molecules have a tetragonal distortion! (ie 2 long bonds and 4 shorter bonds to ligand which result in the T2g and Eg sets of orbitals splitting further)

The extent of the distortion effects the d orbital splitting, leading to the different electron configurations and hence differing magnetic moments!
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thenextchemist
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(Original post by MexicanKeith)
Yep octahedral, but the key to answering this question is to do with the fact that Ni 2+ d8 compounds like to have a square planar geometry, This means that the equatorial en ligands are tightly bound, whilst the axial halides are labile. So the molecules have a tetragonal distortion! (ie 2 long bonds and 4 shorter bonds to ligand which result in the T2g and Eg sets of orbitals splitting further)

The extent of the distortion effects the d orbital splitting, leading to the different electron configurations and hence differing magnetic moments!
Ooh, thank you so much!
I didn't know that d8 compounds like to have a square planar geometry.
So, both molecules are effected by the Jahn-Teller theorem

Thank you once again, makes sense
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