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Author: Subject: Mn2O7 to manganyl cation
Sulaiman
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[*] posted on 3-12-2020 at 01:33
Mn2O7 to manganyl cation


I have made and played with Mn2O7 a couple of times by pouring conc. sulphuric acid onto potassium permanganate crystals,
(as in too many YT videos)
then using the green oil to react with various substances.

This morning I read the wikipedia article on Mn2O7 and came across this statement
"Mn2O7 can react further with sulfuric acid to give the remarkable manganyl(VII) cation MnO+3, which is isoelectronic with CrO3

Mn2O7 + 2 H2SO4 → 2 [MnO3]+ [HSO4]- + H2O"

So to c30ml Az. H2SO4 I added about 100mg KMnO4 crystals.
Initially I saw a little of the familiar green oil but with occasional stirring the green vanished,
and the solution is now mostly BLUE

Q1) is the blue due to "the remarkable manganyl(VII) cation MnO+3" ?
so far no useful internet hits for manganyl cation.

Q2) what is remarkable about the manganyl cation ?

Q3) any suggestions for analysis, or use ?




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woelen
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[*] posted on 3-12-2020 at 01:49


This may be interesting: https://www.sciencedirect.com/science/article/abs/pii/002219...

I also thought that permanganyl ions are green, as mentioned in this paper.
You write that your solution is _mostly_ blue, what do you mean with that? Is it a greenish blue (cyan), or is it really blue, like copper sulfate?




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[*] posted on 3-12-2020 at 02:14


Mn in the +5 oxidation state is generally unstable. So, that is remarkable in itself.
The blue of Mn(V) I believe is quite pretty. I have only seen photos but it is domethinv I would like to do some time.

This reference may be complimentary to what you are doing. (The first photo shows a Mn(V) compound. Procedure is given: just click on experiments then on Mn on the periodic table.)
www.explorechem.com/home.html
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Sulaiman
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[*] posted on 3-12-2020 at 02:38


Blue like blue/black ink, dark royal blue or ultramarine,
not cyan or copper sulphate.. much darker.

I just put one drop of the blue liquid into 2ml conc. sulphuric acid,
the drop sank to the bottom of the acid and turned green... then stirring produced a pale pink solution which faded to colourless.

Other than risking an explosion I have no idea what I'm doing :(
................................................

"Mostly", because there seems to be some MnO2 in suspension and a hint of green.
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P.S. adding the blue liquid to water produces the familiar pink/purple permanganate colour.
I have now diluted and disposed of the liquids - of unknown stability.
I will (probably) do more research before I try again.
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j_sum1 ... nice link ... thanks.
I got a little excited when I read this;

Oxidation State, Stable in, Colour,

+7 Acid, Neutral and Base, Purple

+6 Base, Green

+5 Not Stable – Not observed, Blue

+4 Neutral, Base, Yellow/orange/brown

+3 Acid, Pink/red/flesh

+2 Acid, Neutral and Base*, colourless *

[Edited on 3-12-2020 by Sulaiman]




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DraconicAcid
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[*] posted on 3-12-2020 at 08:24


I'm pretty sure the cation in question is not MnO+3, but MnO3 (+). It would be remarkable due to it's high reactivitiy.



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clearly_not_atara
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[*] posted on 3-12-2020 at 08:31


https://www.sciencedirect.com/science/article/abs/pii/002219...



[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 3-12-2020 at 08:36


Sulaiman: When I made permanganyl solution, it was green. It may contain some MnO2 from decomposition, but not much. I also reduced it with manganese sulfate to violet Mn(III) aqua and sulfato complexes.

https://www.sciencemadness.org/whisper/viewthread.php?tid=15...

My permanganyl solution in link above looks more brown than normally because I used old permanganate solution, which contain some MnO2, for preparation. When I used fresh, it looks green.

Your observation is interesting and I really don't know, why your solution is blue. Try it again, maybe your solution was contaminated with something, which caused partial reduction of permanganate. And don't worry about explosion. 100 mg of KMnO4 in 30 ml of conc. sulfuric acid is very dilute solution of Mn2O7, there is no serious risk of explosion.

If you want to see (and make) some hypomanganate solution, look at my website: https://colourchem.wordpress.com/2019/07/13/manganese-redox-...




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[*] posted on 3-12-2020 at 08:49


"Deep blue sodium manganate (V) is obtained on reduction of KMnO4 in concentrated aqueous NaOH, with Na2SO3, KI, or HCOONa, or by oxidatron of manganese (II) or MnO2
in an alkaline melt. A simple method for obtaining the Na, K, Rb compounds has recently been described. Pure anhydrous alkali manganates (V) (including Li3MnO4) are
formed by heating the permanganate with MOH.
Lux obtained a deep blue hydrate which he formulated as Na3MnO4 * 10H2O ... and found that on recrystalisation ... a compound ... analogous to the corresponding vanadate,
phosphate, and arsenate has been obtained . Klemm showed that Na3MnO4 * 10H2O contams Mn(V) and not Mn(VI) and Mn(lV) by magnettc analys."

https://doi.org/10.1016/S0010-8545(00)80017-X

[Edited on 3-12-2020 by teodor]

Are you talking about Mn(V) or Mn(VII) ?

[Edited on 3-12-2020 by teodor]

OK, I see, MnO3+ supposed to be Mn(VII). From the same source:
"The green solution formed on dissolving KMnO4 in concentrated H2SO4 contains MnO3+ or O3MnOSO3H, or possrble both, depending upon concentration"

So, it is possible the colour can also vary.

[Edited on 3-12-2020 by teodor]
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woelen
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[*] posted on 3-12-2020 at 09:38


I absolutely do not believe that Sulaiman's solution contains any manganese(V). The blue manganese(V) only exists in strongly alkaline solution. I'm quite sure that this cannot exist in concentrated H2SO4.

I am inclined to think that the solution contains some contamination, but still, it is interesting. I have done the experiment myself several times and never saw the dark blu color, described by Sulaiman in this thread. I always obtained a green solution.




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Bedlasky
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[*] posted on 3-12-2020 at 10:54


Teodor: Hypomanganate certainly cannot be prepared by heating permanganate with hydroxide. This leads to formation of manganate.

Na3MnO4.10H2O is actually Na3MnO4.0,25NaOH.12H2O.

I agree with Woelen. Hypomanganates are stable only in cold concentrated hydroxide solutions.




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