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Author: Subject: A nice peroxo complex of vanadium
woelen
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[*] posted on 18-1-2009 at 11:05
A nice peroxo complex of vanadium


As some of you may know already, I have something with peroxo complexes of transition metals :P.

I already did some experiments with chromium and now I did an experiment with vanadium (inspired by Jor, so the real honor should go to him).

The following webpage shows the experiment with nice colors and some "fireworks":

http://woelen.homescience.net/science/chem/exps/KVO4/index.h...

The compound is very energetic, coarsely mixed with red phosphorus and without precise measurements, I already obtained a nice deflagration. I can imagine that with careful experiment and very good mixing, a really powerful explosion can be obtained, but I did not bother to find out about that.




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Jor
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[*] posted on 18-1-2009 at 11:39


Yes, I also have that beige/yellow powder. When some is added to dilute sulfuric acid, a red solution is obtained. But I do not know the percentage of KVO4.H2O to KVO3. Probably it contains quite some KVO3. However this is white, so maybe I do have quite a pure compound.

Now I know why I obtained no blue-ish solution, because I didn't use a large excess H2O2. Besides, my H2O2 is also low in concentration probably, due to decomposition. I tested that today. I once pipetted out of this 100mL bottle, and possible some compound was still on the pipette decomposing the hydrogen peroxide.

You state in your webpage a complex VO2(O2)2(3-) is formed. It should be VO2(O2)(3-). The blue complex is K(O2)3(3-), if not your charges are not balanced, unless it would contain superoxo-ligands :D
What's the color of the intermediate VO(O2)2(3-) or does this not exist?

It was a good thing to ask you if you could retry my experiment. :P Beautiful pictures! I wonder how you do that. I cannot never zoom in like that. What camera do you use?
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woelen
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[*] posted on 18-1-2009 at 13:26


Jor, the formulas I give really are the ones I meant:

VO2(O2)2(3-)

The central atom has oxidation state +5
There are two oxo-ligands, each contributing -2
There are two peroxo-ligands, also each contributing -2

The total is +5 + 2*(-2) + 2*(-2) = -3

The same is true for that dark blue complex V(O2)4(3-). You have +3 in mind for vanadium, but it is +5.


The camera I use is a Pentax Optio S for the pictures and a Canon Powershot A620 for the videos. The Optio is only a very simple 3 MPixel camera and for many things it is not suitable at all, but for macro photography I have never seen a better one than this. Even my $$$$-SLR-alike cannot match this Optio S. The reason for this is that the Optio S allows macro photography at a large distance from the object, allowing low perspective distortion in the pictures. Other camera's suffer from extreme fish-eye effect on 3D objects, they only are good for macro pictures at flat objects.




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Jor
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[*] posted on 18-1-2009 at 13:49


Sorry, stupid mistake. I was calculating from the KVO4, and made a thinking mistake by thinking that it is the following: VO4(3-).

Very stupid.
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[*] posted on 20-1-2009 at 23:15


How stable is the complex?
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woelen
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[*] posted on 20-1-2009 at 23:43


I have this complex around for almost 1 week now, and it did not change yet. I think it is fairly stable, and maybe it can be kept indefinitely, just like K3CrO8 (which I now have around for almost 20 years, total amount appr. 10 grams).

According to my book on inorganic chemistry, the blue peroxo complex based on V(O2)4(3-) can also be prepared, but that appears to be more dangerous/less stable. I'll try if I can succeed with that next weekend, and then I'll try 100 mg or so.

There is one advantage of working with these vanadium-compounds. Although they are toxic (like many transition metal salts), they seem not to be strong carcinogens, like the chromioum-based hexavalent and pentavalent complexes.

[Edited on 21-1-09 by woelen]




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[*] posted on 21-1-2009 at 00:39


Toxic is not a good description. I would rather call it very toxic.

http://msds.chem.ox.ac.uk/VA/vanadium_pentoxide.html

It would be very interesting to see the blue complex in isolated state. Can you email me how it is synthesised?
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[*] posted on 21-1-2009 at 02:42


Heres the abstract from:

Synthesis and study of some properties of potassium peroxooxyvanadates. Vorob'eva, N. A.; Bogdanov, G. A.; Yurchenko, G. K. Mosk. Tekst. Inst., Moscow, USSR. Izvestiya Vysshikh Uchebnykh Zavedenii, Khimiya i Khimicheskaya Tekhnologiya (1970), 13(9), 1242-6.

"By the addn. of KVO3 as a solid or soln. to 30-55% H2O2 at O2/V ratios of 0.5-1.5 at room temp. to -20, 4 insol. peroxyvanadates are produced: KVO4.0.5H2O, orange; K2H2V2O10.0.5H2O, lemon; KVO5.0.5H2O, bright yellow; and KVO5.H2O2.nH2O, olive. The stability of the compds. and their decompn. characteristics are indicated by DTA over the range 0-250. The order of stability is: KVO5.H2O2.nH2O < KVO5.0.5H2O < KVO4.0.5H2O < K2H2V2O10.0.5H2O. The decompn. of K2H2V2O10.0.5H2O yields a modification of KVO4.-0.5H2O which differs in stability from that obtained synthetically. The heat effects assocd. with the decompn. of these compds. are given."

It notes that they are all insoluble so I perhaps the product is more complex then as written. But gives some stabilities and colours.
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woelen
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[*] posted on 21-1-2009 at 03:14


Funny to see that the fomulas you give again are very different from what i have found. The same trouble as with the chromium peroxo compounds. Apparently the precise characterisation of these peroxo complexes is very difficult.

Your working conditions, however, differ quite a lot from mine. I added 15% H2O2 to an equal volume of solution, so in my experiments the concentration of H2O2 only is around 7%. The book I have mentions the existence of a dark blue solid compound and a light yellow compound (which is the one I have, albeit somewhat beige, but sometimes books can be quite inaccurate with descriptions of colors).

I do have 45% H2O2 and could add a spatula full of finely powdered KVO3 to this, but I have serious doubt on the purity of the products, obtained in this way. KVO3 hardly is soluble in water, and if the resulting compounds also are insoluble, then i am afraid that I'll end up with KVO3, covered by a thin layer of the peroxo complex. The stuff I made is really made from solution.




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