Bedlasky - 27-12-2019 at 06:56
Hi.
Cobaltous ions easily form blue [CoCl4]2- in aqueous solution just by adding NaCl in to the solution of cobalt salt. Formation of the complex is
supported by heating or adding an organic solvent e.g. ethanol, acetone...
Why this doesn't work with [CoBr4]2-? I dissolved as much as possible KBr in acidified CoCl2 solution (chloride complexes are formed in strongly
acidic solution, so I suppose that bromides behaves similary), but solution only turned darker, any sign of green colour. Addition of ethanol nothing
changed.
Why this complex isn't formed in aqueous solution? Have you experience with it? I'll try make it in ethanol or acetone, maybe it will work.
Fery - 28-12-2019 at 06:37
Why do you think [CoBr4]2- was not formed in your experiment? Why did you spoil your experiment with Cl? Which acid did you add and how much?
Btw. I found also something about [CoBr6]4- complex but I'm not sure whether it is only theoretical or whether it was prepared practically, e.g. here
at page 743
https://web.chem.ucsb.edu/~devries/chem1C/handouts/zumdahl_c...
Bedlasky - 28-12-2019 at 13:14
Because red colour is typicall for octahedral complexes of cobalt. Tetrahedral complexes have different colours - NCS and Cl complexes are blue, Br
complex should be green. I used sulfuric acid.
[Edited on 28-12-2019 by Bedlasky]
DraconicAcid - 28-12-2019 at 15:26
It should work.
https://www.degruyter.com/view/j/ncrs.1999.214.issue-3/ncrs-...
https://www.researchgate.net/publication/225249017_Bistetrae...
Fery - 29-12-2019 at 06:13
Bedlasky I think you obtained the complex. I'll try to dissolve CoO in various ratios of 48% HBr and variuos dilutions in about 1 week, currently I'm
out of my lab.
Fery - 5-1-2020 at 12:26
[0]
0,633 g 48% HBr + 0,020 g CoO very dark, thin layer on glass wall of test tube reveals green color, this should be [CoBr4]2- complex
[1]
1 ml of H2O + 3 drops of the dark green solution [0] (dilution by approx 10 times)
[2]
boiling the [1] for a short time, a little of Br2 vapor formed above the solution and I had to blow it away, I did not use freshly distilled HBr for
preparation of [0] so it was slightly contaminated with Br2... maybe boiling expelled also some HBr???
[3]
the dark green solution [0] after adding excess of CoO and boiling for a short time
Fery - 5-1-2020 at 12:34
and here CoBr2 complexes with various organic solvents (contains also info about the color change depending on concentration)
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