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Author: Subject: General Discussion of Terbium Compounds
Brain&Force
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wink.gif posted on 13-11-2013 at 17:12
General Discussion of Terbium Compounds


Hello,
I have a question for you all. I'm making hexakis(antipyrine)terbium(III) iodide for my science fair project. The idea for this project came from this thread: Green Smash-Glow Crystals
I just got terbium and antipyrine, and I have access to iodine. Pok stated that he dissolved the terbium in HCl and added antipyrine and potassium iodide. However, I'm going to make both hexakis(antipyrine)terbium(III) iodide and hexakis(antipyrine)terbium(III) chloride for comparison (my project is quite complex).
I want to make the compound without going this route - rather, I want to make pure TbI3 from direct union of the elements by dissolving terbium in an aqueous iodine solution and slowly adding more iodine. I would expect the iodine to complex with the iodide created by the reaction to form triiodide ions, and the terbium would react with the triiodide to form more iodide. Is this mechanism feasible? Would it work for other metals?
Thanks for all of your replies; this is my first time here.

<!-- bfesser_edit_tag -->[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: changed subject from "Synthesis of terbium(III) iodide" per OP request]

[Edited on 10.1.14 by bfesser]




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blogfast25
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[*] posted on 14-11-2013 at 06:19


The lanthanides are very electropositive, react vigorously with dilute strong acids etc so direct union of Tb and I2 (in water) might be possible. But reactivity towards water may ruin that plan. Have you considered direct union in the absence of water? It's harder to do of course.

Do you have any solubility data on TbI3? Several RE chlorides are extremely hygroscopic and hard to crystallise. Not sure about the REI3s...


[Edited on 14-11-2013 by blogfast25]




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[*] posted on 14-11-2013 at 06:35


TbI3 is well soluble in water. According to this site TbI3 can be made by direct reaction of terbium and iodine. Iodine is not very soluble in water so it may take longer to react than pure Tb + pure I2.

Maybe heating Tb metal with iodine will make the whole reaction proceed much better. In this case I would recommend to use a massive piece of Tb an not powder. Because powder will probably react much too violent.

But I don't understand why you don't want to use the method with potassium iodide. Do you only have pure iodine and not KI ?



[Edited on 14-11-2013 by Pok]
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[*] posted on 14-11-2013 at 08:46


I would follow the pre-conceived procedure, and separate by crystallization.

Looks like you have enough terbium!
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[*] posted on 14-11-2013 at 09:19


I've never worked with terbium, but my students make zinc iodide by heating zinc metal with iodine in dry methanol. If you're worried about it being too reactive, I'd use a small amount of iodine, and just add more iodine as the colour disappears from solution.



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[*] posted on 14-11-2013 at 10:30


I like DA's idea a lot. For want of a better term, 'reactivities' of Tb and Zn are probably quite comparable. This has the potential of being highly exothermic, especially if the TbI<sub>3</sub> turns out to be insoluble in the solvent.

[Edited on 14-11-2013 by blogfast25]




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[*] posted on 14-11-2013 at 16:11


Thank you all for your replies.

blogfast25, direct union is quite favorable, but terbium is nearly as reactive as magnesium (-2.28V for Tb3+ + 3e- → Tb) and I don't want to have a fire or explosion risk. If the aqueous iodine solution is acidic enough, my idea should work.

Pok, I'm trying to make absolutely pure terbium chloride and terbium iodide as well as their antipyrine complexes. My goal is to figure out whether swapping the anion has an effect on the intensity of the triboluminescence. Also, I need to determine the hydration number of pure terbium iodide (I can't find a reference to this anywhere).

DraconicAcid: I might try two batches, one with methanol and one with water. I have access to a vacuum dessicator, so that'll help if terbium iodide is soluble in methanol. Also I won't have to worry about unknown hydration numbers this route.




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[*] posted on 15-11-2013 at 05:23


Quote: Originally posted by Brain&Force  
If the aqueous iodine solution is acidic enough, my idea should work.



Do compare the half potentials for:

H3O+ + e- === > H2O + 1/2 H2

And:

1/2 I2 + e- === > I-

... to ensure your precious terbium doesn't get chewed up by the acid.

Also, methanol should be bone dry: dry with lime (CaO) for instance.

I'll be having a go at ZnI2 (and maybe some other iodides in anhydrous denaturated ethanol).




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Brain&Force
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[*] posted on 15-11-2013 at 15:32


Quote:

Do compare the half potentials for:

H3O+ + e- === > H2O + 1/2 H2

And:

1/2 I2 + e- === > I-

... to ensure your precious terbium doesn't get chewed up by the acid.


Acidification of the solution shouldn't be necessary. I thought I2 would disassociate slightly into HI and HIO, and that the produced H3O+ and IO- would oxidize the terbium.

However, I'm pretty sure I'll be doing this in methanol or ethanol - it sounds a whole lot simpler, and I may be able to get data for the solubility of terbium iodide in these solvents - data which is very sparse. Nobody investigates lanthanide compounds. :(




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[*] posted on 15-11-2013 at 15:41


Quote:
However, I'm pretty sure I'll be doing this in methanol or ethanol - it sounds a whole lot simpler, and I may be able to get data for the solubility of terbium iodide in these solvents - data which is very sparse. Nobody investigates lanthanide compounds. :(

In the absence of data, I would think in this respect that RE halides behave a little like aluminium halides and would thus be highly soluble in polar solvents like alcohols.




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[*] posted on 15-11-2013 at 16:10


Both aluminum and lanthanide halides hydrolyze easily and act as Lewis acids, so you might be right on that. Antipyrine is extremely soluble in ethanol, so I might be able to make [Tb(C11H12N2O)6]I3 in it.

I wonder if terbium halides show fluorescence in alcohols - they don't show it in water solution.




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[*] posted on 16-11-2013 at 06:05


B&F:

There is actually quite a bit of research going on, on REs, now it appears they're not so rare anymore and with so many so useful. And there was a lot of it during the quest for the transuranium elements due to the expected similarities of lanthanides and actinides.

I think several of us here would appreciate a report on the TbI<sub>3</sub> synth (in MeOH or EtOH).




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[*] posted on 16-11-2013 at 10:47


Quote:

I think several of us here would appreciate a report on the TbI3 synth (in MeOH or EtOH).


I'll certainly keep you posted with pictures and hopefully videos.

What I'm particularly interested in is the formation of a terbium(II) species forming during the reaction - dysprosium(II) and samarium(II) iodides exist, but I can't find any references to terbium(II) iodide. WebElements lists a +2 oxidation state for terbium, but doesn't give a reduction potential for it.




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[*] posted on 17-11-2013 at 06:06


A Tb(II) species must transiently exist, as the ionisation must proceed in steps: I, II, III. If enough oxidant is present it will run all the way to III. Perhaps just using enough iodine for Tb + I<sub>2</sub> === > TbI<sub>2</sub> should do the trick?



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[*] posted on 17-11-2013 at 07:37


Quote: Originally posted by blogfast25  
A Tb(II) species must transiently exist, as the ionisation must proceed in steps: I, II, III. If enough oxidant is present it will run all the way to III.
Must it? This a claim that needs evidence. Particularly it should exclude the hypothesis that Tb+ + I2 --> Tb3+ + 2 I- is an elementary reaction. I'm not saying this is likely, but it's just not right to assert an ionization process as a necessity without supporting evidence for it.
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[*] posted on 17-11-2013 at 11:43


Quote: Originally posted by watson.fawkes  
[...] Tb+ + I2 --> Tb3+ + 2 I- is an elementary reaction


Two ionisations in one collision: I just don't think it's likely.

Tb<sup>+</sup> + I<sub>2</sub> === > Tb<sup>2+</sup> + I<sup>-</sup> + I*

or

Tb<sup>+</sup> + I* === > Tb<sup>2+</sup> + I<sup>-</sup>

... seem more likely to me. But I shouldn't have used to word 'must'.

[Edited on 17-11-2013 by blogfast25]




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[*] posted on 17-11-2013 at 14:41


Wikipedia has a reference to terbium(I) chloride and terbium(I,II) chloride. Perhaps in MeOH/EtOH Tb+, Tb2+ and Tb3+ can at least coexist (if a stepwise oxidation doesn't occur).

My plan is to put the whole piece of terbium in the alcohol and add only the amount of I2 needed, then extract the leftover terbium once the reaction is finished. That way no iodine remains in solution. But if I have leftover iodine dissolved in MeOH/EtOH after making TbI3, will vacuum desiccation cause the iodine to evaporate as well? Or do I have to remove the iodine through some other method?




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[*] posted on 18-11-2013 at 05:30


There's no reason why you shouldn't use an excess of Tb powder to react away the I<sub>2</sub>: with lump metal things will be much, much slower. I<sub>2</sub> is quite volatile, so leftovers should evaporate on removal of the solvent.

Coexistence of multiple metal oxidation states in water is quite rare: the equilibria tend to settle on the ion with the highest (well, most negative!) Free Energy of Formation. Tb(I) and Tb(II) would probably result in Tb(0) and Tb(III).


[Edited on 18-11-2013 by blogfast25]




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[*] posted on 18-11-2013 at 11:55


This certainly is a great synthesis. I would love to have those lanthanides now, but they are too expensive. Anyway, careful because it might start to oxidise if exposed to air, even if it's not among the most reactive.

Trivia: Yttrium, ytterbium, terbium and erbium are ALL named after the same city in Sweden: Ytterby.

[Edited on 18-11-2013 by Eddygp]




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[*] posted on 18-11-2013 at 12:54


Ytterby isn't even a city- it's a village.



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[*] posted on 18-11-2013 at 13:29


Quote: Originally posted by DraconicAcid  
Ytterby isn't even a city- it's a village.

Yes... well, I meant town or something hahaha.




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[*] posted on 19-11-2013 at 21:01


Eddygp, lanthanides aren't that expensive - that is, if you know where to look. Sigma and Alfa Aesar charge ridiculous prices for gram amounts.

Terbium doesn't oxidize quickly in air. It takes at least several years; check here. But the piece is dark from Tb4O7 contamination.

Blogfast: I don't have equipment to powder the terbium. Hopefully the metal is reactive enough for the reaction to proceed quickly.

I'm going to try the synthesis this Thursday. Hopefully, I'll have nice fluorescent crystals of TbI3 soon.




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[*] posted on 20-11-2013 at 04:34


Quote: Originally posted by Brain&Force  
Blogfast: I don't have equipment to powder the terbium. Hopefully the metal is reactive enough for the reaction to proceed quickly.



Then I must have misread, I thought you had powder. Lump could be very slow.




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shocked.gif posted on 20-11-2013 at 16:36
Lab report, day 1 - Funny story


Even though I can't get powder, I did discuss the idea with my mentor for the fair and we decided to to the next best thing - break it into small pieces. So he got a hammer. Our plan was to wrap it in paper, to tap it lightly and hope we'd get small pieces.
Tapping the terbium didn't work too well. The rough edges fractured, but not the whole thing. So he decided to give it a bit more force. That also didn't work, but the terbium did emit sparks.
And then came the second hit.
The terbium didn't fracture. It flew all the way from one end of the classroom to the other, and landed in the hallway (it took us a few minutes to figure that out) On retrieval, it was still in one piece.
We tried pretty much everything possible. A biotech student even suggested wrapping the terbium in parafilm. At the end of the whole ordeal, the bulk of the terbium had survived, only slightly flattened by the multiple, highly damaging impacts. The metal is so soft that pieces of paper had actually embedded themselves in the surface.
Terbium is VERY impact resistant, just not scratch resistant - the coating on a neodymium magnet can scratch the metal. We're hoping we can make some turnings with a drill.
(By the way, neodymium magnet really comes in handy for picking up small pieces.)
More updates coming up tomorrow.




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[*] posted on 21-11-2013 at 06:28


Hacksaw? Won't be easy either...



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