Sciencemadness Discussion Board - Reaction of pyridine with [Cu(Cl)2(H2O)2] product is pyridine complex or the hydroxide ?

Reaction of pyridine with [Cu(Cl)2(H2O)2] product is pyridine complex or the hydroxide ?

Zool - 22-1-2017 at 19:40

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

??

DraconicAcid - 22-1-2017 at 21:47

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?

Zool - 23-1-2017 at 05:51

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

Praxichys - 23-1-2017 at 07:37

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.

Zool - 23-1-2017 at 07:53

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 .

Zool - 23-1-2017 at 07:56

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]

Zool - 23-1-2017 at 08:34

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 .

DraconicAcid - 23-1-2017 at 08:43

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.

Eddygp - 23-1-2017 at 10:01

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.

I'd assume that it would (both trans-directing effect and sterics)

DraconicAcid - 23-1-2017 at 11:28

Quote: Originally posted by Eddygp

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.

I'd assume that it would (both trans-directing effect and sterics)

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]

harderm - 23-1-2017 at 23:06

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.

harderm - 23-1-2017 at 23:10

Just looked it up. Cupric oxide is black, cuprous oxide is red.

mnick12 - 24-1-2017 at 19:34

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.

DraconicAcid - 24-1-2017 at 19:55

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]

mnick12 - 24-1-2017 at 20:30

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.

Yup, you are correct on the pka issue. According to wiki the pka of the pyridinium ion is 5.25. Still the point remains.