Ch 23 - error in EOCE 23.64(e)

[Zellmer, Robert]

There's an error in either the question for EOCE 23.64(e) or the solutions manual.
The problem is asking you to draw the CFT energy-level diagram for [PtBr6]^2-.
If the charge on the complex is correct, then the Pt would have an ox. state of +4
and an electron config. of [Xe]5d^6.  The solutions manual has it as [Xe]5d^8,
which means they're treating it as Pt^2+.  This probably makes more sense as
Pt usually has an ox. state of +2 in compounds.  That would mean the charge
on the complex in the question is wrong and it should be 4-, [PtBr6]^4-.  However,
it is possible for PT to be +4.

Since this is octahedral there's two possibilities here.  Br- is a weak-field ligand.
That means the CF splitting energy will be small (small energy gap between the
three lower t_2 orbitals and the two upper e orbitals.  This means electrons go
into all 5 orbitals one at a time until you have to pair them up (high spin case).

[PtBr6]^2-, with Pt^4+, [Xe]5d^6, then there would be 3 electrons in the lower
t_2 orbitals and 2 electrons in the upper e_g before you pair them up.  Then
the 6th electron would pair up with an electron in one of the lower t_2 orbitals.
This would give a configuration with 4 unpaired electrons.

[PtBr6]^4-, with Pt^4+, [Xe]5d^8, then there would be 3 electrons in the lower
t_2 orbitals and 2 electrons in the upper e_g before you pair them up.  Then
the next three electrons would pair up with electrons in the lower t_2 orbitals,
which would wind up filled.  This would give a configuration with 2 unpaired
electrons (in the upper e_g orbitals).

I can't really tell you which it should be but hopefully you understand both
possibilities.

Dr. Zellmer
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