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Topic: explain why F- has a bigger field than I- (ligand field theory)  (Read 249 times)

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Offline xshadow

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explain why F- has a bigger field than I- (ligand field theory)
« on: January 25, 2021, 05:35:47 AM »
HI
How can I explain that F- has a bigger field than I- (Δ bigger) using the ligand field theory ( so using the MO diagram and not the electrostatic theory)???

Here is a MO diagram:

https://en.wikipedia.org/wiki/Ligand_field_theory#/media/File:LFTi(III).png



2 case:
M(I)6  n-
MF6  n-


Now looking at  the MO diagram when I pass from I- to F- the electronegativity increases...so the SALC for the 6 "s" F orbitals (the ones on the right in the diagram) are lower in energy than the Iodine one


WIth fluorine so there is a bigger difference between the 6 F salc s  and the metal transition orbitals...so a bigger energy gap means  a weaker interaction /overlap and so the stabilization energy of bonding MO is less and also the destabilization energy for the e*g  is less .(they are lower in energy)

SO for fluorine I should have  a small Δ because e*g is lower in energy (in comparision with iodine) and the t2g non bonding are also at the same energy...


BUt I know that in the spectrochemical series I have an opposite trend  ???

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