Lion850 - 25-11-2020 at 23:55
I came across the attached thesis on the web that details the preparation of complexes between transition metals and thiourea.
Attachment: 31295015502312.pdf (2.6MB)
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The first metal I tried was cobalt:
- 5.6g CoSO4.7H2O in 100ml warm methanol. It took some time to dissolve; the methanol got close to boiling but eventually it all dissolved.
- 6.1g thiourea in 100ml methanol. It dissolved much quicker than the cobalt sulphate.
- Add the CoSO4 solution to the thiourea solution, this gave a deep blue solution that after some 10 minutes stirring also had a green color in it.
- After another 15 minutes stirring was stopped. I green ppt settled out with a blue supernatant solution. Going by the referenced document, the fact
that I got a green ppt means my methanol was not completely anhydrous. It had some water. Photo below.
- Leave beaker overnight to cool slowly with the hot plate.
Next day:
- Gravity filter. The filtrate was deep blue and the remainder dark green. Beautiful colors! See below photo of the remainder and filtrate.
- The filtrate was boiled down on a steam bath and the resulting crystals were completely dry. The result was 3.5g of a sea green powder.
- The remainder was dried in the sun for an hour (under a steel dish). That left 5g of hard deep green crystals. My favourite color 
- Below photo of the 2 products side by side. I wonder if it is the same compound but just different colors due to the different ways that they
crystallized?
According to the attached thesis the compound could be Tetrakis(thiourea)cobalt(II) sulfate dihydrate, [Co(tu)4]S04.2H2O.
One other observation: it does not seem to be hygroscopic, but it is very easily soluble in water, and then gives a pale pink solution. I have the
pink solution that resulted from washing out everything in a shallow dish evaporating, await with interest to see what I get after a few days.
Bedlasky - 26-11-2020 at 00:33
Different colours are probably caused by different particle size.
valeg96 - 20-12-2020 at 06:38
Tried this two days ago on a half-gram scale.
My methanol was dried over fine CaO filtered thrice over celite and gave the green precipitate immediately (after what, 2 seconds of stirring?) in
nearly quantitative amounts, and the blue solution left aside gave only a trace of green compound after a day, but some nice single green crystals on
the walls. I bet this compound could yield big beautiful crystals if the two solutions were layered on top of each other, and/or more diluted.
Complex is also insoluble in diethyl ether (not mentioned in the original work) so it's very easy to wash and dry on the pump, though it shouldn't
stay longer than a few seconds while air is drawn through it, as moisture degrades it to a white powder.
The complex turns light blue when dried in the oven at 110-130°C, but goes back to aqua green when it cools down. I don't even need to calculate the
yield of dried complex to say it's at least around 90%.
I suggest working with an excess of Co, as excess thiourea gives off nasty acrid fumes when the compound is dried in the oven.
[Edited on 20-12-2020 by valeg96]
valeg96 - 23-12-2020 at 06:01
Update: after about a week the compound turned blue.
[Edited on 23-12-2020 by valeg96]
[Edited on 23-12-2020 by valeg96]
