Sciencemadness Discussion Board

Tetraethylammonium metal complexes

ItalianChemist - 6-4-2024 at 04:56

Tetraethylammonium metal complexes can be prepared quite easily and have very beautiful colors and crystals.
There are many reported complexes, the first prepared is the Copper(II) complex, or Bis(Tetraethylammonium) Tetrachlorocuprate.
This complex consists in yellow-orange crystals, wich is a quite unusual color for copper(II) compounds.
Now let's see how to prepare it!

Needed Materials:

-Anhydrous Copper(II) chloride (also the dihydrate works well adjusting the quantities)
Ethanol 95%
-Tetraethylammonium chloride monohydrate
-Some beckers and filtering apparatus


0,62g of Anhydrous Copper(II) chloride are placed in a small Becker and dissolved in about 5ml of 95% Ethanol.
1.JPG - 592kB
After fully dissolution a dark green solution is formed. If dihydrate Copper(II) chloride is used, about 0,85g are needed.
2.JPG - 636kB
In another bigger Becker 1,84g of Tetraethylammonium chloride monohydrate are dissolved in about 5-10 ml of 95% Ethanol.
The solution of Copper(II) chloride is then added to the Tetraethylammonium chloride solution.
3.JPG - 870kB
The solution immediately turns cloudy and is heated on an hotplate for a couple of minutes until everything dissolves.
At this point a dark yellow solution is obtained.
4.JPG - 871kB This solution is left to stand at room temperature for about half an hour. 
The yellow crystals that precipitate are vacuum filtered and washed with few milliliters of cold 95% Ethanol. They are then left to dry for some hours and then put in a vacuum desiccator overnight.
0,62g of crystals are recovered. The complex seems to be quite stable in air, but if put in enough water, it seems to decompose giving a cloudy blue solution.
5.JPG - 2MB

This synthesis is take from Inorganic Synthesis vol.9 Pag 141
The original synthesis used absolute Ethanol, but the reaction also works using 95%.
Maybe using the absolute one the final held could be improved since this complex seems to be quite soluble in water.
Also other metal complex are reported to have very unusual color, like the green manganese complex.

woelen - 6-4-2024 at 11:39

Interesting find! Getting the tetraethylammonium salt is not easy though. I can obtain tetramethylammonium chloride, but tetraethylammonium salts are harder to find.

It's most remarkable that you get an orange complex, which dissolves with blue color and precipitates from a dark green solution. It reminds me somewhat of the experiment I did with CuCl2 in concentrated HCl with CsCl, giving a red complex.

ItalianChemist - 7-4-2024 at 02:41

I think it should also work with the tetramethylamonium or even triethylammoniun, but maybe the color of the complex could be different.
Even the complex wit tetraethylammonium bromide seems to be purple!
I didn't know about the cesium!I will also try to prepare it!

woelen - 7-4-2024 at 09:57

The reaction with cesium is described on this web page:

I do have triethylamine, I'll try formation of complexes of this with copper. IIRC, I once tried formation of a complex with trimethylamine and copper(II), but that did not work. I just obtained a pale blue precipitate of Cu(OH)2. I expected a deep blue complex, like the complex with ammonia, but the methyl groups apparently prevent formation of the deep blue complex at the nitrogen atom.

DraconicAcid - 7-4-2024 at 11:26

I've made a couple of the tetramethylammonium compounds- tetrachlorocuprate, tetrachloroferrate(III), tetrachlorocobaltate(II), and tetrachloroiodate(III).

I've tried making the red trichlorocuprates, but without much luck.

woelen - 7-4-2024 at 23:07

You tried the red chlorocomplex salt of tetramethylammonium instead of cesium? I also tried that, but it did not work. It did not even produce a precipitate and the liquid remained green.

chornedsnorkack - 8-4-2024 at 02:28

Stupid question: this is an example where K and Cs give completely different looking reactions. What does Rb do in the same conditions?

DraconicAcid - 8-4-2024 at 12:03

Quote: Originally posted by woelen  
You tried the red chlorocomplex salt of tetramethylammonium instead of cesium? I also tried that, but it did not work. It did not even produce a precipitate and the liquid remained green.

Apparently, you can make ammonium and potassium trichlorocuprates, but none of them have worked well for me.

woelen - 9-4-2024 at 02:28

Same to me. With potassium I just get a white precipitate of KCl, and with tetramethylammonium I got no precipitate at all. The liquid in both cases was olive-green, the color of a concentrated copper(II) solution in concentrated HCl.

chornedsnorkack - 9-4-2024 at 02:57

The solubilities in water are quoted:
NaCl - 360 g/l (solvent?)@25C, weakly dependent on temperature, mass 58,5 - about 6,15 mol/l solvent
KCl - 340 g/kg (solvent) @20C, mass 74,5 - about 4,55 mol/l solvent
RbCl - 910 g/kg (solvent) @ 20C, mass 120,9 - about 7,5 mol/l solvent
CsCl - 1865 g/l (solvent) @20C, mass 168,4 - about 11,05 mol/l solvent. Expressly readily dissolves in concentrated HCl, in contrast to both NaCl and KCl
So how does RbCl behave? Does RbCl dissolve in concentrated HCl? Does RbCl form chlorocuprates?

Texium - 9-4-2024 at 06:01

I have a lot of RbCl for sale if you’d like to find out :D