woelen
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Remarkable reaction with MoO3, producing vapor of molybdenum compound
If you have PCl5 and MoO3, then you can do a really interesting experiment. These chemicals allow formation of a very volatile compound of molybdenum
with a dark red/brown color in the gas phase.
https://woelen.homescience.net/science/chem/exps/MoO3+PCl5/i...
I also have some WO3 and I soon will try that as well. Maybe a similar compound can be formed with tungsten.
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Justin Blaise
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Really nice experiment and documentation, as always. WCl6 should be more stable if it forms under those conditions. Do you have any oxides of Re?
Could be interesting to see if you can make those chlorides too.
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Bedlasky
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Good job, Woelen! This is realy nice experiment. I read about this reaction some time ago, here is document abou this:
Attachment: smith1894.pdf (164kB)
This file has been downloaded 204 times
Your compount isn't MoCl5 but actually double chloride MoCl5. PCl5.
I don't think that this compound lose chlorine (at least molybdenum) during heating. Mo(IV) and Mo(III) are very easily oxidized by oxygen to Mo(V).
But phosphorus probably loose chlorine. MoCl4 and MoCl3 are soluble in water (and especially in HCl), they form various oxychloride complexes. I don't
know what the insoluble compound is, but its unlikely that one of these chlorides.
Green complex in HCl is [MoOCl5]2-. I often use it as test for Mo(V). I even manage to synthesise solid K2[MoOCl5]. When you dilute it with water, you
obtain other oxo-chloro complexes of molybdenum. Reaction is reversible, if you add some conc. HCl, you obtain [MoOCl5]2- again. I wrote something
about it here.
You can try to make some WCl6 in similar way as Justin suggested. And I am really interested in reaction of sodium or ammonium vanadate with PCl5. I
have some interesting results from reaction between Na3VO4 and conc. HCl, I will post them soon. I don't have PCl5 and I wonder how reaction would
differ.
[Edited on 7-11-2021 by Bedlasky]
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woelen
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Interesting read. I'll also have a look at your page in more detail.
I read that MoCl3 does not dissolve in water (Wikipedia also tells that). WCl4 indeed most likely will dissolve, but it will do so while hydrolysing.
It is interesting to see that the MoOCl5(2-) complex can be formed again, when the brown compound is added to conc. HCl. I'll have to do more research
on this and then I'll have to modify the text of the web page.
In the past I already did an experiment with vanadium. I might repeat it again, making a new video of better quality.
https://woelen.homescience.net/science/chem/exps/v2o5_pcl5/i...
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Bedlasky
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Thanks, this is awsome experiment! I maybe found answer how to explain your observations. Look at this paper:
https://sci-hub.se/https://pubs.rsc.org/en/content/articlela...
There is description of reaction of VOCl3 with PCl5. At room temperature compound [PCl4][VOCl4] is formed. When this is heated, vanadium is reduced to
IV oxidation state and some chlorine is released. At this higher temperature compound [PCl4][VCl5] is formed. This perfectly matches with my
observations from experiments with Na3VO4 in 36% HCl. V(V) in conc. HCl form complex [VOCl4]-. When this is heated, it react with excess HCl to form
[VOCl4]2-.
Both compound [PCl4][VCl5] and [PCl4][VOCl4] are described as black solids. So I think that when you mixed V2O5 with PCl5 and heat it, you obtained
mixture of VOCl3 and these two compounds. Firstly VOCl3 is formed which then react with excess PCl5.
V2O5 + 3PCl5 --> 2VOCl3 + 3POCl3
VOCl3 + PCl5 --> [PCl4][VOCl4]
2[PCl4][VOCl4] + 2PCl5 --> 2[PCl4][VCl5] + 2POCl3 + Cl2
In the paper there is also description of reaction between VOBr3 and PBr5, which leads to formation of VBr3.POBr3. This compound decompose on heating
to VBr3 and POBr3.
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teodor
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I am curious, could also SbCl5 be used in those reactions?
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Bedlasky
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SbCl5 act little bit different. Instead of forming [SbCl4]+ cation it form [SbCl6]- anion.
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