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Topic: [Te4]2+ aromatic inorganic cation  (Read 2592 times)

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Offline Rutherford

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[Te4]2+ aromatic inorganic cation
« on: September 13, 2013, 11:07:58 AM »
[Te4]2+ is an aromatic inorganic cation. Draw its structure.

I think it should look like cyclobutane. Could this be it? *The less important electrons and free electron pairs I left out.

Offline magician4

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Re: [Te4]2+ aromatic inorganic cation
« Reply #1 on: September 13, 2013, 12:58:33 PM »
from what I see, "aromatic" ( in the Hueckel type definition) has some conditions, "conjugated" being amongst them, meaning that there should be parallel p-orbitals at each and every atom of the cycle (so they can form one single delocalized pi-system)

those p-orbitals on individual atoms might be*)  fully occupied (like the one bearing the negative charge in the cyclopentadienyl anion) , part of a bond (like all the C's in benzene) or empty (like the ones bearing the positive  charge in cyclopropenyl, cycloheptatrienyl cations)

therefore, in a 4-membered ring with a single double bond and two positive charges, from my analysis the atoms bearing the positive charges should be the ones not involved in the double bond.
so, in my opinion, you've got that aspect wrong: those charges should be shown at the other two Telluriums

regards

Ingo

*)
this , of course , is just a discussion of the hypothetical Lewis structure
in reality, these orbitals are part of the aromatic resonance system, and hence won't be empty (in aromatic cations) or "isolated, occupied" (in aromatic anions) as soon as you look into HOMO/LUMO schemes for the whole molecule
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Offline Rutherford

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Re: [Te4]2+ aromatic inorganic cation
« Reply #2 on: September 13, 2013, 01:43:34 PM »
Okay, then the two Te atoms bounded by single bonds only will have one lone pair and one electron, while the other two will have the same. How to represent the resonance structures then? I can't see how the lone pairs from the two sigma bonded Te atoms take part in the resonance stabilization.

Offline magician4

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Re: [Te4]2+ aromatic inorganic cation
« Reply #3 on: September 13, 2013, 06:21:35 PM »
in my opinion, the best way to show this resonance is to draw it: have 4 p-orbitals interacting, and "work" over the whole of the molecule, i.e. form 4 Te42+ - MO's from 4 Te - AO's of p-type
the result basically would be exactly the same as the situation in butadiene, except that you only had two (instead of four with butadien) electrons to occupy this system: you'll have 4 MO's with respective bonding and antibonding properties (were they occupied)

this is how it looks like with butadiene:


(Butadiene , frontier orbitals and electronic occupation, from: link )

and with Te42+ it would be exactly the same, except that the HOMO of butadien would be empty in this case, (hence would become the LUMO for Te42+) , whereas the lowest occupied MO ( the one where the 4 p  have the same +/- lobes orientation for all of them) of butadien in Te42+ would be occupied , too, and hence become the HOMO of Te42+

regards

Ingo
« Last Edit: September 13, 2013, 07:38:36 PM by magician4 »
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