I discovered a very interesting thing by experimenting with strong oxidizers. Quite a few years ago, I made a copper(III) periodato complex and while
cleaning up my lab, I found the little vial with this compound again. I have half a gram or so left of this copper(III) compound. This raised my
interest again in the combination of peroxodisulfate and periodate.
I now did an experiment with nickel(II). The following experiment is really interesting:
- Dissolve some nickel(II) sulfate or nickel(II) nitrate in water.
- Add a little sodium periodate to the solution. Assure that there is excess nickel(II).
- Add a little sodium peroxodisulfate to the solution
Heat the solution until it starts boiling. Both the periodate and peroxodisulfate dissolve.
When it is boiling, then the color of the solution changes from pale green to deep purple, almost black. The glass also is covered with a peculiar
semitransparent red/purple layer. The purple material is only marginally soluble in water.
If too much peroxodisulfate is added, then a black compound is formed as well.
So, nickel(II) also forms a special compound. It almost certainly must be a nickel(III) or even nickel(IV) compound.
The interesting thing is that it is the combination of periodate and peroxodisulfate which has such a strong oxidizing property. Does any one of you
know of this combination? It seems to be capable of forming very interesting high oxidation state metal complexes. These complexes may be interesting
in other applications as well, as very strong oxidizers, capable of doing unusual oxidations. More investigations are needed. I will try with cobalt
and other metal ions as well.Boffis - 15-2-2017 at 07:29
Interesting;
I notice you say "Add a little sodium periodate to the solution. Assure that there is excess nickel(II)."
Have you tried it with periodate in excess and it didn't work? I wonder if periodate is acting as a ligand that stabilizes the higher valency as in
the case of copper and periodate.
Is the purple black compound in solution or a precipitate and is the stuff on the glass a solid or immiscible liquid?
Ditto the black compound. I have certainly not heard of such a nickel compound before. kmno4 - 15-2-2017 at 11:30
It is reinventing the wheel, see informations about periodatonickelates in wikipedia (for exaple)
Similar Co(III) complexes are green.
ps.inabilty of finding some bacis informations by woelen is almost legendary. Bezaleel - 15-2-2017 at 16:40
It is reinventing the wheel, see informations about periodatonickelates in wikipedia (for exaple)
Similar Co(III) complexes are green.
ps.inabilty of finding some bacis informations by woelen is almost legendary.
If so, then not only
woelen....
And again, some basic questions seem to remain unanswered despite...Panache - 15-2-2017 at 18:50
It is reinventing the wheel, see informations about periodatonickelates in wikipedia (for exaple)
Similar Co(III) complexes are green.
ps.inabilty of finding some bacis informations by woelen is almost legendary.
If so, then not only
woelen....
And again, some basic questions seem to remain unanswered despite...
So by basic questions I assume your referring to any transforms that may occur at higher pH's?
I notice you say "Add a little sodium periodate to the solution. Assure that there is excess nickel(II)."
Have you tried it with periodate in excess and it didn't work? I wonder if periodate is acting as a ligand that stabilizes the higher valency as in
the case of copper and periodate.
Is the purple black compound in solution or a precipitate and is the stuff on the glass a solid or immiscible liquid?
Ditto the black compound. I have certainly not heard of such a nickel compound before.
If I use too much oxidizer (either periodate or peroxodisulfate), then I get a black precipitate and the remaining liquid becomes fairly dark green.
Next weekend I'll try more carefully with more accurately measured stoichiometry.
The wiki page, mentioned by kmno4 also mentions the existence of two types of complexes, with one ligand and with two (somewhat different) ligands.
Based on that stoichiometry I should be able to come up with the right ratios of NaIO4, NiSO4 and Na2S2O8.
In practice, such wiki-pages, however, are quite inaccurate. I can imagine that just adding the right ratios of chemicals is not sufficient. Maybe I
need fairly precise pH-control or an excess of one of the reagents.
Maybe I can make some perbromate in this way. The wiki-page mentions that. I wonder whether it is just trace amounts of perbromate or indeed a
practical synthetic route.DJF90 - 16-2-2017 at 00:35
Could the dark solid be nickel peroxide, NiO2?PHILOU Zrealone - 16-2-2017 at 03:53
Perbromate would make my day...to be able to study vs perchlorate and periodate into energetic amine salts and mixes...Tdep - 28-9-2017 at 19:21
Hey Woelen, real interesting oxidiser you've made. But, the interest of the nickel species pales in comparison to the perbromate ion I feel. Did you
ever make any inroads with this, either practical or theoretical? woelen - 2-10-2017 at 00:48
I did not pursue this any further, due to having very limited time for experimenting. There are sooo many things which require my attention at the
moment, and then I am not only talking about my daily job Tdep - 2-10-2017 at 01:28
That's a feeling I, and I think everyone here can relate to too well.
You have synths for both the meta and orthoperiodate up on your website, which should be used for making periodatonickelates (which did you use, does
it matter?) Also, I only have ammonium persulfate. You think that will work, or will the ammonium ion try and get in the way, complexing with the
nickel and whatnot? woelen - 2-10-2017 at 09:21
I used the metaperiodate. If you have the orthoperiodate, then you can use H2SO4 (not HCl) to compensate for the additional basic properties of the
orthoperiodate. I do not know how critical pH is, but I know from experience with this kind of experiments that pH can affect the outcome quite
strongly.
I do not expect the ammonium ions to have much effect on the experiment. The liquid is not alkaline and no free ammonia will be present. Ammonium ions
are quite resistant to oxidation, you need rather harsh conditions for them to be oxidized.Tdep - 30-12-2017 at 19:17
I finally got around to trying this, using 6g of nickel(II) nitrate, sodium orthoperiodate and ammonium persulfate. Upon addition of the persulfate,
the mix went very dark purple. The very fine precipitate was filtered and upon drying, turned a greeny-black, metallic looking (picture).
It is insoluble in water, but the suspension goes back to the original purple, so the colour may just be deceiving, like how permanganate crystals
look black.
It is insoluble in dilute sulfuric acid, but soluble in concentrated KOH solution, to give a light brown solution.
All these solutions give off a very small amount of bubbles, presumably oxygen.
When added to concentrated HCl, a strong reaction occurs that gives off chlorine, and leaves behind the classic Ni(II) green colour. This is a big
tick for it being an oxidiser.
It does not oxidise acidic Mn(II) ions to permanganate, a test I tried to see it's oxidising power. Probably due to its insolubility in acidic
conditions, but you can't do that oxidation in basic conditions.
I still want to do more testing, to see it is infact this complex, not some sort of nickel oxide. So I'm open to suggestions of tests I can do that
will: 1) show me that it's an oxidiser and 2) that it contains periodate/iodine
Σldritch - 31-12-2017 at 11:04
If you heat it with some weak reducing agent you should be able to see iodine gas. Maybe try sulfur?
Starch will form a strongly colored complex with iodine in solution but i am not sure there is an easy way to reduce periodate in solution without
also reducing iodine to iodide.
[Edited on 31-12-2017 by Σldritch]DraconicAcid - 31-12-2017 at 11:44
If you heat it with some weak reducing agent you should be able to see iodine gas. Maybe try sulfur?
Starch will form a strongly colored complex with iodine in solution but i am not sure there is an easy way to reduce periodate in solution without
also reducing iodine to iodide.
[Edited on 31-12-2017 by Σldritch]
Or, add an organic solvent and some water, then a mild reducing agent.Σldritch - 31-12-2017 at 16:45
I underestimated the reactivity of periodate, i assumed it was similar to that of perchlorate but reading on wikipedia it seems much more reactive. It
will probably be reduced to iodate in solution with an alcohol or something (especially if it is a diol) but will it go all the way to iodine? Iodate
is not as reactive as periodate, yes?Tdep - 31-12-2017 at 23:00
The iodine is confirmed! Thanks for your help guys.
I added the Ni complex to some dilute nitric acid. No reaction. Then some spray starch for ironing was sprayed in. Some very slight colouration, could
be contamination from previous tests. Then, on the addition of some sodium thiosulfate, an intense colouration appears (picture).
This confirms periodate/iodate.
Also, on heating to several hundred degrees, the complex decomposes into a light green solid that is insoluble in water, and does not change the pH of
that water. This is in agreement with the literature reports, and the green solid is not NiO but a Ni-iodine complex.
woelen - 1-1-2018 at 09:57
Simply heating it strongly in a dry test tube most likely shows that it contains iodine, due to formation of purple vapor. Adding a sinlge drop of
concentrated H2SO4 before heating may make the experiment somewhat easier, less heating required.
