So, I made some Sodium Nitrite by the Lead oxidation process (the product reacts vigorously with HCl, liberating clouds of NO2, meaning it has a High
Nitrite content).
Anyway, I wanted to see if I could form some Copper (II) Nitrite (to view it's colour). I added a solution of Copper (II) Acetate (with a large
quantity of 5% acetic acid) to a solution of Sodium Nitrite, obtaining a beautiful light green solution.
I can't find any information regarding Copper (II) Nitrite colour so I'm not sure what happened. I thought about Nitrous Acid productuion (because of
the acetic acid content of the reagent) but all the Nitrous Acid I've seen is pale blue and usually evolves NO2.
Anyone knows what reaction happened?kmno4 - 30-3-2014 at 07:03
The reason of appearance of this green colour is the same as in case of mixing solution of CuSO4 and NaCl (it gives also green colour): complex
formation.
In both cases molecules of coordinated water around Cu(2+) are replaced by another ligands, in you case it is NO2(-) ion.
Such complex salts are green e.g Cu(NH3)2(NO2)2.
Try to mix some Pb salt with NO2(-) ions: this reaction gives orange colour .
Reason is the same.HgDinis25 - 30-3-2014 at 14:14
Interesting, I tryed the Pb complex, it indeed forms a yellow-orange complex. Do you know the NO2 anion distriution through the central copper ion? Is
it the same as the Nitrate complex?kmno4 - 31-3-2014 at 03:02
In the case of Cu(NO2)2(NH3)2, the most up-to-date structure determination is included in unavailable on-line paper. Fortunately, it is abstracted
here:
However, this compound also exists in a dark-purple form, with reversible transition about room temp. Some article explains this as change from
Cu-O-N-O coordiation to Cu-NO2.
But the best known Cu-nitrite complex is (also green) ion [Cu(NO2)6](3-). Its structure -> in attachment.
.