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guy
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| Quote: | Originally posted by not_important
Ok, thanks guy! I suspected the possibility of Mn(III) simply because none of the complexes of higher oxidation states had colours in the right range.
This isn't going to be easy, Mn forms polynuclear complexes. As an example, even though it's done at 100 K, here is one with two Mn(III) and four
Mn(II)
http://scripts.iucr.org/cgi-bin/paper?gk2005&buy=1
Note that the ligands ketones and carboxylic acids, previous to finding this and your experiment with Mn(OH)2, I wondered if oxyidised glycerol is at
least part of the complex, even though Mn does complex with polyols. This doesn't discourage me from thinking that.
edit -
I suspect Mn(III) or a mixed state complex. But it is possible that there are higher states, complexing may lower the cost of getting there enough
that even air oxidation can reach them; think of the Co(III) complexes.
[Edited on 6-8-2006 by not_important] |
Damn thats a huge molecule. Maybe I should try oxidizing all the Mn(OH)2 to MnOOH then add glycerol to see, then that could narrow it down.
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not_important
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I did pick one of the larger complexes I'd encountered; it was interesting for being purely oxygen links. Many of the complexes seem to be 2 to 4 Mn
per complex; all the Mn may be in the same oxidation state or it may be a mixed state complex.
The MnO(OH) might be able to oxidise glycerol, which would give you Mn(II) again. However the test of using as close to 100% MnO(OH) as possible does
sound worthwhile.
I'm thinking on some ways to figure what organics are in the complex, without resorting to equipment or supplies that aren't easy to be had.
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guy
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I tried it again first by oxidizing the Mn(OH)2 in base to MnOOH, some were converted to MnO2 since Mn(OH)2 + 2OH- -----> MnO2 + 2H2O + 2e E=0.05.
Then I added glycerol and stirred it and same red solution.
I think that it could be just as simple as a glycerolate complex. Do you think it is possibe to deprotonate glycerol when it complexes? Glycerol has
only weaker electron donating groups than regular alcohols. The link I have on the first page had Cu glycerol complex and a boric acid gylcerol
complex.
How can we test for a presence of glycerol? Or if it was oxidized to an aldehyde you could use Tollen's reagent (which I don't have).
[Edited on 8/6/2006 by guy]
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not_important
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Did the red colour form quickly - complex formation vs oxidation then complex?
How about making some MnO(OH) in as little base as possible. Try to determine how much base is needed for the complex to form.
It could be a simple glycerolate complex, I'll agree. However manganese appears to like to form polynuclear complxes, so while this may be a
glycerolate complex, it may not be simple although not s bad as the monster I posted the link to.
Add a liitle borax to a bit, see if borate displaces Mn; boric complexes of polyols are pretty stable.
Add a bit of bisulfite, glucose or invert sugar, or other mild reductant. What doeas it take to get back to Mn(II). I think you've shown that Mn(II)
alone isn't making any interesting complex.
Charge transfer complexes, with an element in two different oxidation states, tend to have strong, deep colours. Another reason to suspect mixed
valency in this, but hard to tell without fancy gear we don't have.
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guy
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Yes it formed quickly almost the same speed. It takes about 20-30 seconds to fully form. I will try it with as little base as possible.
-------------
Edit:
It takes quite a lot of base to form this. I couldn't measure the exact amount since I have no scale though. To get it back to Mn2+ you need acid
and a reducing agent like H2O2.
[Edited on 8/7/2006 by guy]
[Edited on 8/7/2006 by guy]
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not_important
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Even little vs alot is useful, as it suggests the hydroxide is being used in a reaction. Many of the glycolates don't require a base or acid to form.
If the managese is already Mn(III) the base must be serving another purpose, I think. The energetics of complex formation are often such that you
don't need to deprotonate the diol/glycl so much as to soak up the protons levered off the OHs during complex format. Even bicarb works in some cases.
Problem with H2O2 is that it can potentially also be oxidising the glycerol. That's why I suggested bisulfite or other reducing agents.
I am going to cook some dry cell guts and ammonium sulfate together this evening, to get some MnSO4. Hopefully I will be able to replicate you
experiment and join in the fun.
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woelen
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I'm back from vacation and I'm pleased to read that this research continued! Guy, could you please describe in detail how you dried the material and
obtained crystals. Although you don't have weight measuring gear, try to give estimates of amounts.
I have weight measuring gear and quite a lot of chemicals, such as diverse phosphate salts, phosphoric acid, concentrated H2SO4, so I could try many
of the suggestions. If I can obtain a gram or so of the orange/brown compound in pure state, then I can do a lot of experiments and help solve this
riddle  .
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guy
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I obtained the orange crystals by evaporating about 90% of the solution. Then I filtered it and washed with denatured alcohol. The solid is bright
orange and quite stable in air. I hope you have good results when you try it.
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