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Author: Subject: Trinitrotriamminecobalt - Co(NH3)3(NO2)3
teodor
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[*] posted on 25-5-2022 at 01:27
Trinitrotriamminecobalt - Co(NH3)3(NO2)3


This is "by far the most important starting material in the triamminecobalt series" as Inorganic Syntheses, Vol. VI says.
As far as I understand NO2- group could be exchanged for virtually any other group, so by reacting this material with acids it is possible to get different complexes.

I followed the preparation from Inorganic Syntheses (1/2 scale), for your convenience I put it here.

Co2.jpg - 155kB Co1.jpg - 283kB

It is better to use freshly prepared Co(II) carbonate. Mine was prepared 3 months ago (by the reaction of Co(NO3)2*6H2O and K2CO3) and after this period dissolution in hot acetic acid is quite slow and far from completion. But it is not a problem for the preparation - the suspension could be used for the preparation, CoCO3 doesn't interfere with the reaction (except for forming some green compound on flask walls which will be filtered off during the phase of hot filtration when the charcoal catalyst should be filtered-off).

I used a chemical pure Co source (bought from chemship1978):

Co3.jpg - 48kB

I have a pottery-grade carbonate too which could be converted to CoCl2 and back to carbonate (to make it fresh) for the preparation but the presence of other transitional metals could puzzle me when I will want to study crystals under a microscope - I had already this experience with another Co complex and now it is hard to say are the different forms of crystals the result of Ni impurities or they are isomeric forms of the compound.

And this experiment would not have been possible if woelen had not presented me this nice bottle:

Co5.jpg - 56kB

(OK, it is possible to make a nitrite by reducing a nitrate with lead, but I was lazy and woelen was generous. Woelen, now I can give Co(NH3)3(NO2)3 to you in exchange if you would like to make experiments with it).

I expected a change of the color during boiling with charcoal but actually mixing cold NaNO2 in NH3(aq) with hot Co(OAc)2 gives a solution with a color of the tee. The addition of H2O2 makes this color only darker. And boiling with charcoal doesn't change the color at all.

At the end of the boiling all unreacted CoCO3 forms some green Co(III) compound which deposits on the flask walls (what it could be?).

Co4.jpg - 141kB

This is the first crop of crystals and the filtrate for the next boiling with charcoal (to get the second crop):

Co6.jpg - 188kB



[Edited on 25-5-2022 by teodor]
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clearly_not_atara
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[*] posted on 26-5-2022 at 04:04


Quote:
I expected a change of the color during boiling with charcoal but actually mixing cold NaNO2 in NH3(aq) with hot Co(OAc)2 gives a solution with a color of the tee. The addition of H2O2 makes this color only darker.

Well I'm awake now :o

So this is a neutral, covalent complex? Does it dissolve in organic solvents?

...is it a primary? :P




[Edited on 04-20-1969 by clearly_not_atara]
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teodor
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[*] posted on 26-5-2022 at 06:44


Actually, I don't know whether the absence of conductivity of the aqueous solution is equivalent to being completely non-ionic. Still, logically, I don't see how an ionic compound can be nonelectrolyte.
I will return after some time with more information about the compound properties.
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