Zool
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Reaction of pyridine with [Cu(Cl)2(H2O)2] product is pyridine complex or the hydroxide ?
I made a solution of 10 mmol [Cu (Cl)2 (H2O)2] witch is a square planar complex of Copper (due to Jang Teller effect) in 20 ml of ethanol and it had a
deep emerald green colour . After I putted a second solution of 2 ml of pyridine (25 mmol) in 3 ml of ethanol to make a total of 5 ml solution in the
first copper II chloride solution and imediatly I get a light blue precipitate that looks very similar to the hydroxide complex . So my problem is .
Is this the hydroxide or the pyridine complex because maybe pyridine acted as a base to the aqua acid copper chloride picked one hydrogen from every
water that is coordinated to the copper and give as final result Copper II hydroxide and pyridine hydrochloride. I know some complexes that have the
same colour as the hydroxide of copper for example copper oxaxate has this colour and for sure If I could easily run an IR spectrum I would know the
answer . Also I can try to dehydrate copper II chloride to make anhydrous copper II chloride (brown solid happens at aroun 100 degrees celsius) and
run the same reaction again and this time since there is no water should be no hydroxide . But before all this I ask If somebody had the same problem
with me before me and can give an answer without the need of waste of more chemicals for a reaction I have already done some hours ago (also I am a
little tired to do the same synthesis after I have done it some hours ago ). Anyway if somebody can help me I would be grateful here is a photo of the
complex . And of course I searched already in internet and I cannot find any picture of this complex just in some references that they have made it
before and some research on crystal structure (space group) and magnetic properties . not the colour .
Bis pyridine Dichloro copper II [Cu (py)2 (Cl)2]
or
Copper II hydroxide
??
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DraconicAcid
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I suspect that's the hydroxide. I would think the pyridine complex would be much deeper blue, simply because the ammonia complex should be similar.
Rather than heating the chloride to dehydrate it, it may be better to add something like triethyl orthoformate to dry your ethanol solution with the
copper chloride dissolved in it. Or, add a large excess of pyridine to the solution so that you get [Cu(py)4]Cl2, and then heating after isolation to
drive off half the pyridine?
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Zool
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But not all amines give the same colour for example the phenyl amine complex with copper II is a green one not blue at all!!!. So I will do the same
reaction with dry copper II chloride and see if it makes the same colour then probably is the same complex
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Praxichys
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If you can isolate and dry a small amount of the suspected complex, heat it in a test tube over a flame and see what happens. Obviously copper
hydroxide will just dehydrate into CuO, but a pyridine complex should lose its pyridine and stink like hell before doing so.
If you have a 1mg balance, you can get the mass before and after pyrolysis, calculate % weight loss and figure it out empirically with <100mg.
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Texium
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Thread Moved
23-1-2017 at 07:42 |
Zool
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I did it with anhydrous copper II chloride get exactly the same colour since there was not any water in the second reaction I must assume that this is
not the hydroxide but the [Cu (py)2 (Cl)2] now I wait for it to get dry to measure both products weights to see if there is any difference since I
used exactly the same molar quantities .
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Zool
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Praxichys I take the dried complex from yesterday (the suspected hydroxide ) and I putted it in a test tube with some water two things happened first
it dissolved and second it stink pyridine like crazy and since it was dry and not smell pyridine before the adittion of water I must assume this is
the pyridine complex that the water substitued the pyridines and let them free in water and so It stink after. Never the less I will do the test you
say also ... thanks for the help guys !!!
[Edited on 23-1-2017 by Zool]
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Zool
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So I putted in a test tube a small sample and two things happened first I shrink in size and turno from blue to black . Second a lot of pyridine come
out witch means it is not the hydroxide but the pyridine complex . And because the starting material is supposed to be tha trans dichloride (square
planar geometry) we should get according to theory the trans bis pyridine dichloro copper II .
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DraconicAcid
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I stand corrected.
However, just because you start with the trans dichloride (cite?) doesn't mean that you'll end up with a trans dichloro complex.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Eddygp
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Quote: Originally posted by DraconicAcid  | I stand corrected.
However, just because you start with the trans dichloride (cite?) doesn't mean that you'll end up with a trans dichloro complex.
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I'd assume that it would (both trans-directing effect and sterics)
there may be bugs in gfind
[ˌɛdidʒiˈpiː] IPA pronunciation for my Username |
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DraconicAcid
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Sterics, sure, but I'm not sure the trans-directing effect applies in something as labile as copper(II).
ETA: The complex is reported as blue and trans:
https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&a...
ETAA: I should try and get some bipyridine, since that would be analogous, but cis. It might have a different colour.....
[Edited on 23-1-2017 by DraconicAcid]
[Edited on 23-1-2017 by DraconicAcid]
Please remember: "Filtrate" is not a verb.
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harderm
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| Quote: Originally posted by Zool | | So I putted in a test tube a small sample and two things happened first I shrink in size and turno from blue to black . Second a lot of pyridine come
out witch means it is not the hydroxide but the pyridine complex . And because the starting material is supposed to be tha trans dichloride (square
planar geometry) we should get according to theory the trans bis pyridine dichloro copper II . |
That sounds like your product is indeed the complex, or at least a mixture of products that are insoluble in etOH. I'm guessing that the reaction
upon dissolution in water shows that the aquo complex(es) are more stable than the di-pyridyl complexes. The water displaces the pyridine ligands,
producing the smell, and the aquo/aquo-chloro complexes remain in aqueous solution. As somebody else said, the black residue after heating the dry
blue stuff is probably copper oxide - one of the oxides is red, the other blue, I forget which is which.
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harderm
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Just looked it up. Cupric oxide is black, cuprous oxide is red.
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mnick12
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Its for sure the dichloride.
the pka of the pyrdidinium ion is less than 0 IIRC, there is practically no chance of pyridine acting as a strong enough base to deprotonate enough
water to form the bis hydroxy complex. Also, I would guess that the bishydroxy complex, if it even exists, is not stable.
Another thing to keep in mind. Color is not really a reliable indicator for determining metal complexes. We all know aqueous transition metal
solutions have common colors associated with each metal, but all that goes out the window when you start slapping on organic ligands like pyridine.
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DraconicAcid
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| Quote: Originally posted by mnick12 | | the pka of the pyrdidinium ion is less than 0 IIRC, there is practically no chance of pyridine acting as a strong enough base to deprotonate enough
water to form the bis hydroxy complex. |
Incorrect. Kb for pyridine is given in my textbook as 1.5e-9, which, when combined with a Ksp of 2.2e-20 for Cu(OH)2, give a K = 100 for
Cu(2+) + 2 py + 2 H2O = 2 Hpy(+) + Cu(OH)2
(In aqueous solution, of course. In ethanol, all bets are off.)
[Edited on 25-1-2017 by DraconicAcid]
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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mnick12
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| Quote: Originally posted by DraconicAcid | | Quote: Originally posted by mnick12 | | the pka of the pyrdidinium ion is less than 0 IIRC, there is practically no chance of pyridine acting as a strong enough base to deprotonate enough
water to form the bis hydroxy complex. |
Incorrect. Kb for pyridine is given in my textbook as 1.5e-9, which, when combined with a Ksp of 2.2e-20 for Cu(OH)2, give a K = 100 for
Cu(2+) + 2 py + 2 H2O = 2 Hpy(+) + Cu(OH)2
(In aqueous solution, of course. In ethanol, all bets are off.)
[Edited on 25-1-2017 by DraconicAcid] |
Yup, you are correct on the pka issue. According to wiki the pka of the pyridinium ion is 5.25. Still the point remains.
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