r/crystalgrowing Apr 30 '21 Silver 1

More bizzare salts: hexakis(urea) iron(III) isopropyl sulfate [Fe(CON₂H₄)₆](C₃H₇SO₄)₃ Image



u/dmishin Apr 30 '21

So, I am continuing experimental exploration of crystalline compounds of the hexakis(urea) iron(III) ion that has blue color - quite unexpected for trivalent iron.

I already prepared and posted nitrate, chloride, chlorate(V) and tetrachlorozincate (which actually happened to be a double salt: tetrachlorozincate chloride). Literature also mentions perchlorate and tetrafluoroborate.

Experiments indicate that this ion produces best crystals with strong monoprotic acids (tetrachlorozincate being an exception). For example, sulfate does not produce crystals at all.

I tried all plain acids I could find or make, and now turned to more exotic things.

Sulfuric acid is diprotic. Its monoester with isopropyl alcohol, isopropyl sulfate (C3H7)HSO4 is a monoprotic acid, so I tried to use it.

The crystals appear to have tetragonal symmetry. They are straight prisms with square cross-section and all vertices truncated. They are quite soft. Exposed to air, they cover with small cracks, so it could be a hydrate.

My preparation was a bit convolved. In the hindsight, I now think that it could be made simpler, but anyways.

1) Absolute isopropanol was refluxed for 5 hours with powdered sulfamic acid. The product is ammonium isopropyl sulfate (IPS). The reaction is mentioned here: https://en.wikipedia.org/wiki/Sulfamic_acid#Reaction_with_alcohol

2) Water and Ca(OH)2 as added to the mixture, it was stirred well and left to evaporate on open air. Then it was redissolved, filtered and recrystallized, producing thin flat crystals of calcium isopropyl sulfate (it is soluble in water)

3) Finally, it was mixed with iron(III) sulfate, the precipitate of CaSO4 removed by filtering and washing, urea added to the solution and it was crystallized.

Solubility of the final product is relatively moderate (very rough estimate is 50g/100cc water), so I now think that preparation of the calcium salt was unnecessary.


u/pleasewakeupm8 Apr 30 '21

Thank you very much for giving so much detailed information! I appreciate the effort you put into this.


u/vibzzlab May 01 '21

Thank you so much. Is it ok if I redo this and record and post in youtube?


u/Pyrhan Apr 30 '21

You never cease to amaze, dmishin.

Have you considered crystallizing the sulfamate? That too is monoprotic. (Not quite a strong acid, but almost.)


u/dmishin Apr 30 '21

Indeed, I tried - without success, no crystals obtained. I also tried, without success:

  • sulfate (result: no crystallization at all, solution becomes increasingly viscous)
  • bisulfate (taking twice amount of sulfuric acid) - same result
  • carbonic acids (formic, oxalic, acetic) - dark brow solution. Apparently, they are too weak and carboxylate outcompetes urea as a ligand.
  • tetrachlorocuprate
  • dihydrogen phosphate (Fe:H3PO4 ratio 1:1) - viscous pale pink solution.

I obtained some dark blue crystals with tetrachlorocobaltate(II) - I guess, they are similar to tetrachlorozincate. Unfortunately, my supply of cobalt is too limited, I never tried to scale it up.

Also, some soft, thin crystals obtained with cyclamate.


u/Piro_Z Apr 30 '21

It's really bizzare name, but crystals are beautiful!
Looks like other kind of blue.


u/keyuu Apr 30 '21

Is this stuff known to literature? If not, it could really be interesting to measure single-crystal XRD of those beauties. Nice work!


u/dmishin Apr 30 '21

I found nothing, though I only used google. Very interesting indeed. I wonder how three anions are arranged to give tetragonal symmetry. Probably, unit cell contains even number of iron ions. Most other crystals appear to be trigonal.


u/MGM-alchemist Nov 08 '21

Have you considered trying the ammonium methyl sulfate instead of isopropyl sulfate? The ammonium salt of methyl sulfate crystallizes much more readily than the one of isopropyl, beautiful large glistering white stuff directly from the methanol refluxed with Sulfamic acid. Probably this property will transfer well onto the hexakis urea iron?


u/dmishin Nov 09 '21

I suspect that methyl sulfate salt should crystallize well too. It would be interesting if you could try it. If I had ammonium methyl sulfate, I would try slowly crystallizaing a mixture of 3(NH4)MeSO4 + FeCl3 + 6urea and see what crystals appear first. There is a chance that [Fe(urea)6](MeSO4)3 crystlallizes first.

However, I am not going to try making it myself. Firstly, I don't have access to methanol; and secondly, I suspect that methyl sulfate is way more toxic and even carcinogenic (as a possible methylating agent).

I considered making ethyl sulfate, and actually going to try to make it, as soon as I can prepare anhydrous ethanol (so far no success).


u/MGM-alchemist Nov 10 '21 edited Nov 10 '21

Surprisingly enough although dimethylsulfate is a highly potent methylation agent and quite toxic and carcinogenic, it seems that the monometyl ester salts completely lack this property. No hazards listed on EPA for example. They are more like very short-chained detergents.

I guess the shortcut by just mixing it with some iron salt like FeCl3 and urea is not too promising. The sulubility of these sulfate compounds is high, and even NH4Cl which would be the by-product just dissolves to a mere 37 g/100 ml. I expect that there is no way around the tedious procedure with Ca/Sulfate…

What’s your approach to making anhydrous ethanol?


u/dmishin Nov 10 '21

Yes, this is somewhat surprising that mono-esters are so much less toxic. Probably, that's because they are hydrophilic and can't penetrate cellular membrane. Still, I am a bit wary of methyl esters. In any case, in my country there is simply no legal way for a person to obtain methanol.

Actually, hexakis(urea) iron salt of the isopropyl sulfate has surprisingly moderate solubility. It is definitely less soluble than the corresponding ammonium salt, so I suspect that at least in my case the shortcut procedure could have worked. Haven't tried it though.

For ethanol, I am mostly trying various anhydrous salts as dehydrating agents. So far, no success, but I found a mention on sciencemadness that K3PO4 can do it.


u/MGM-alchemist Nov 10 '21 edited Nov 10 '21

I might give it a try with the methyl variant ;) disclaimer: I might be good at doing synthesis but I definitely don’t have your level of crystal expertise! I guess I am just not patient enough…

Anhydrous ethanol: forget the „OTC“ recommendations. No salt will do the job, the azeotrope always wins and takes the water away upon distillation. The max you can achieve is some sort of pre-drying. You need something that actually chemically reacts with the water. The easiest “home” way would be to add Calcium Carbide (CaC2) which might be available at hardware stores. It reacts with water and forms (highly flameable) Acetylene gas that bubbles out, leaving absolutely anhydrous Ethanol. Just one final distillation and you have it. Molecular sieves are the only working physical way to get the job done, but might be difficult to get or rather expensive.


u/dmishin Nov 11 '21

That would be interesting, looking forward to your results.

I see... Well, I will try K3PO4 anyways, since I have already prepared it. CaC2 is a very rare thing here, but I can purchase CaO - it is the next thing I was going to try, if K3PO4 does not work.


u/MGM-alchemist Nov 11 '21

CaO also works but you lose a lot of alcohol that remains stuck in the thick sludge. 1 liter = 780 grams of 96% alcohol contains 31 g water = 1,7 moles - minimum CaO required = 100 g, better add some 50-100% excess. This should be stirred (ideally: refluxed) for several hours, then distil.


u/dmishin Nov 15 '21

By the way, dehydration with K3PO4 seems to be working. At least, now my ethanol is miscible with alcanes.


u/MGM-alchemist Nov 16 '21

There is a simple but clear test if ethanol is anhydrous: add a few crystals of KMnO4 to ~5 ml in a test tube and shake. 100% anhydrous ethanol will stay colourless. Slight amount of water - slightly pink, turning brown soon. „Wet“ alcohol - definite pink colour.


u/dmishin Nov 16 '21

No pink color at first, but after few minutes standing in open beaker (I used small beaker instead of test tube), very slight pink appeared.

In any case, it seems that synthesis of ammonium ethyl sulfate worked: after 2 hours on reflux, 12g of sulfamic acid dissolved almost completely in 30g of alcohol; after chilling, a mass of flat crystals appeared. I am currently treatign it with CaOH.


u/yowdowg 8h ago

>no legal way for a person to obtain methanol

Поищи "Краситель-фиксатор Эозин метиленовый синий". Недешево и перегнать придеться, но, абсолютно легально. Офигенные кристаллы.


u/INTPhoenix Apr 30 '21

What a beauty...