Nitrite Chemistry (3): K2A[B(NO2)6] (A=Ba/Pb, B=Ni/Cu)
Not sure whether I can really achieve this as NaNO2 is the only source material I can use.
Then this was added into a solution of 6.1g(>0.10mol) AcOH in ~80mL water. A very small excess is needed to prevent hydrolysis. After reaction we got a solution with different color than CuSO4 which indicates formation of complex(most probably molecular Cu2(OAc)4(H2O)2 as in solid), which I have seen since my very young age.
The Mn complexes should be unstable so I won't prepare them here. Cd and Hg complexes might be stable but due to their extremely high toxicity we won't prepare them either. Zn and Pb complexes may only exist as solid solution. So, the actual range is quite small.
Fe or Co complexes are extremely air-sensitive and would be separated into another page.
If B is trivalent, then this is a rather different family and won't be discussed here.
K2Ba[Cu(NO2)6]
Attempt 1
12.50g(0.05mol) CuSO4.5H2O was dissolved and solution of 6.90g(0.05mol) K2CO3 was added very carefully(gas evolved!), then this was filtered and washed to give basic copper carbonate.
Then in another beaker 6.90g(0.05mol) K2CO3, 9.85g(0.05mol) BaCO3 and 12g(0.20mol) AcOH was mixed in some water. After reaction we filtered to remove BaCO3 and added 24.15g(0.35mol) NaNO2. Then the Cu solution was added into it. Solution immediately became an extremely deep green color.
Nothing crystallized out even when 300mL EtOH was added. The only thing precipitated out was damn trace BaSO4. Holy... On the other hand I feel lucky that I did not waste the precious Ni.
Adding it into conc. KOAc reverts it back to blue.
Wait... is acetate forbidden here? But shouldn't be a big deal!
Freezing also gives nothing.
Adding more EtOH also precipitate nothing.
However we accidentally found that, if a solution is naturally evaporated to a minimal volume, then addition of EtOH can precipitate very much. Not possible now as it already decomposed to form much insoluble stuff, so we gave up.
Attempt 2
Very similar process was followed but Cu, Ba and K acetates were combined in a single solution, about 0.5g excess of AcOH was added, and 0.4mol NaNO2 was used, all to prevent decomposition. Also everything was used as slurry as possible to reduce volume and only the final solution was filtered. The volume was ~150mL, somewhat better. Filtration was very painful due to trace of BaSO4 but does not matter, just wait. This solution was added dropwise carefully into 300mL EtOH to precipitate with shaking, but no product appeared, instead a white solid appeared, which is soluble in water and might be Ba(OAc)2. That is to say the amount of EtOH cannot be too large.
Attempt 3
This time we reduced water further, to ~100mL, by using solid instead of solution as possible, and wait longer for reaction to happen. During filtration the funnel was almost completely stuck by BaSO4 so after a few hours we poured the solution out and removed BaSO4 then continued filtration, but this help little so I just waited many hours and went to play Project S...(lol I accidentally gained the ability to full combo some hard levels and almost so in an expert level). Then EtOH was added to it carefully, in batches of 100mL, since we are curious about the amount needed. It was found that 400mL might be enough, and more won't precipitate more.
Solution was still very deeply green(after settling upper layer was directly poured away to save time), and after filtration and washing solid was found to be a weird greyish-green color, but some white stuff was also observed on its top, which might be KNO3 or simply microcrystalline product and it is impossible to know, and such difference largely diminished after drying. Solid quickly dissolves in water to form the green solution.
Yield: 6.34g(22.8%). Already good enough. Due to different preparation method it's not sticky.
K2Pb[Cu(NO2)6]
I wanted to dissolve Pb into AcOH in the presence of air, but that's simply way too slow! So I used such method:
25.00g(0.10mol) CuSO4.5H2O was dissolved and solution of more than 13.80g(0.10mol) K2CO3 was added. Basic copper carbonate was produced as described before. Then it was thrown in 18.2g(slightly above 0.3mol) AcOH in ~60mL water. During reaction some acetate already separated out which affects the reaction much. We don't care, and after fixing the volume to ~150mL 10.4g(0.05mol) Pb powder was added into it and shaken. Nice, from the color we can know that it is quickly converted into Cu, and most acetate re-dissolved. This solution was filtered to remove Cu. Then 6.90g(0.05mol) K2CO3 was added to neutralize the remaining AcOH but some white stuff, obviously PbCO3 or something, separated. However the amount was not large so we can continue. Excess of NaNO2 (28g, 0.4mol) was added into minimal water(~20mL), and the Cu solution was added carefully with stirring to dissolve NaNO2. It immediately became the dark green color seen before, but something was different: if you look carefully some black stuff separated. Filter and wash with EtOH to get it.
Solution was green but with CuSO4 we can know that no any Pb2+ exists in it. So 1) this salt is very insoluble 2) some Pb was definitely lost so next time we should change a little, see below.
This solid is almost black, but extremely shiny. It is also slightly soluble in or reacts with water, but the "solution" is green so reaction might be very limited. It is not sticky.
Yield: 10.22g(32.7%). Clearly much Pb was lost during the reaction, and since this is very beautiful I may do it again later.
K2Ba[Ni(NO2)6]
2.95g(0.05mol) Ni powder and 14g(0.053mol 37.4%)H2SO4 was mixed and diluted to 100mL, then boiled until metal all dissolved(beaker was covered with a wet tissue to stop the exceedingly toxic and corrosive acid fog), this took a few hours. Since the reaction was too slow at later stage I added a little more acid. But a little still didn't dissolve so I gave up. After filtration solution of 10.35g(0.075mol) K2CO3 was added very carefully, then this was filtered to give green NiCO3(composition unknown).
On the other side, 18g(0.3mol) AcOH, 6.90g(0.05mol) K2CO3 and 9.85g(0.05mol) BaCO3 was mixed in ~100mL water and boiled to clear, then NiCO3 thrown into it and shaken violently. Some still didn't dissolve and solution became opaque due to trace of sulfate, so I filtered it to give a green solution.
21g(0.3mol) NaNO2 was dissolved in ~50mL water, then the filtered solution was poured into it. Initially nothing happened and it just became deeper, but upon shaking it quickly became opaque and a brick-colored solid separated. Filter to get it and solution is slightly green.
Solid was washed with EtOH then dried. Yield: 12.83g(46.7%). Although somewhat low it is in fact much higher than Manual claimed(which is 25%), probably because we did not recrystallize.
This compound seems to be sparingly soluble in(or reacts with) H2O, but a little NaNO2 should be enough to stabilize it as Manual said.
Color of solution may be assumed to be due to insufficient amount of NaNO2 due to oxidation, but in fact, when EtOH was added into it, a little more solid appeared, so some complex is definitely there.
Being an extremely fine powder, it tends to stick on the wall even when completely dry. Not a big deal.
K2Pb[Ni(NO2)6]
We realized that Cu2+ can also oxidize Ni very quickly, so almost the same process as the Pb/Cu one was made, but K2CO3 was first added, then the basic Cu carbonate, then Ni, then Pb. However the solution was pure blue and seems that Ni does not react with Cu2+ here, probably because AcOH cannot remove the passivation. The prepared NaNO2 solution had to be discarded, but we added some FeSO4 into it and found that while color immediately became deeply brown, no gas was evolved, but upon dilution the color became weird. This is very useful in the future.
Seems that Ni does not react with Cu2+ even in the presence of some H2SO4, and treating it with CuSO4 even makes it inert to H2SO4...
Unlike Co which is hcp, Ni is fcc which is the same as Cu, and Ni and Cu has nearly the same atomic radius, so maybe Cu2+ immediately passivates Ni.
This time we still use H2SO4 to dissolve, but in an excess to ~20g, then neutralize to NiCO3. The K/Pb/Ni acetate solution was made as such(changed a little): K2CO3, then basic CuCO3, then Pb(as K2CO3 precipitates insoluble PbCO3 or something), then NiCO3, then filter. It was found that reaction requires more than calculated Pb, so next time when preparing the Pb/Cu salt we need to do as this. This was added carefully into 28g(0.4mol) NaNO2 in ~50mL water, and brown solid immediately separated. It is visually identical to the Ba salt, but with much lower solubility(almost insoluble) and much better crystallinity(not sticky). Filtered solution was almost colorless. Yield: 18.23g(58.8%). Loss is mainly during the preparation of NiCO3.
Conclusion
In general, these complexes can be prepared simply by adding the mixed acetate solution into solution of excess NaNO2, both in minimal water. Ni2+ and Cu2+ cannot be oxidized so excess of AcOH is allowed and even encouraged to avoid hydrolysis. K and Ba acetates are from the carbonates, Pb acetate is from excess of Pb powder and Cu acetate, and Ni and Cu acetates are from the freshly prepared (basic) carbonates. The correct order of addition is K-Ba/Pb-Ni/Cu, and a filtration is usually needed here due to presence of [SO4]2-. Pb salts are almost insoluble and are large grains, while Ba salts are markedly more soluble and in a much finer state. Ba-Cu salt has an abnormally high solubility and must be precipitated with ~4x EtOH from a very concentrated(>0.5M) solution(see above). For Ni2+(d8) Ba and Pb salts look the same except different size, but for Cu2+(d9) the divalent ion can strongly affect Jahn-Teller distortion and thus very different color. While Ca/Sr/Ba-Cu are tetragonal with a typical J-T distorted complex ion, all others including Pb-Cu and *-Co are cubic. We won't try to explain this...
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