4
$\begingroup$

While studying about copper sulphate, I came across a reaction involving sodium thiosulphate (Hypo) and copper sulphate.

Although I don't know the utility of this reaction, I felt that it was important to understand the structure of $\ce{Na4[Cu6(S2O3)5]}$, which is formed as a the major product of the overall reaction.

The full set of reactions is given as follows:

$$ \begin{align} \ce{CuSO4 + Na2S2O3 &-> CuS2O3 + Na2SO4}\\ \ce{2CuS2O3 + Na2S2O3 &-> Cu2S2O3 + Na2S4O6}\\ \ce{3CuS2O3 + 2Na2S2O3 &-> Na4[Cu6(S2O3)5]} \end{align} $$

What is the structure (3D, not Lewis structure) of $\ce{Na4[Cu6(S2O3)5]}$ (or the ion $\ce{[Cu6(S2O3)5]^{-4}}$)?

Reference: Allen JEE-Mains+Advanced Chemistry, Unit 10, Chapter: Transition Elements:

reference

$\endgroup$
2
2
$\begingroup$

For knowing these three dimensional complex structures, which are hard to predict theoretically, we have to use X-Ray diffraction or spectroscopic techniques (IR, NMR, or, mass). I don't have any such facilities to verify the complex structure, but I may logically predict a logical (possibly incorrect) structure.

In the complex ion $\ce{[Cu_6(S_2O_3)_5]^4-}$, all the $\ce{Cu}$ is in +1 oxidation state, and thus can form a tetrahedral geometry around it with the help of other $\ce{Cu^+}$ ions and $\ce{S_2O_3^2-}$ ions. On the other hand, thiosulfate can act as both a bidentate and a monodentate ligand.

So, in the predicted structure, all the $\ce{Cu^+}$ are in tetrahedral geometry. Three $\ce{S_2O_3^2-}$ act as bidentate ligands, whereas the other two $\ce{S_2O_3^2-}$ ions act as monodentate ligands.

Note that the donor atom of the thiosulfate anion can be either all $\ce{S}$, all $\ce{O}$, or a combination of $\ce{S}$ and $\ce{O}$. It is indeed hard to predict (because in some complexes, $\ce{Cu}$ binds with $\ce{O}$ regardless of being soft acid to preferably bind with $\ce{S}$ - as in $\ce{CuCl_2.4dmso}$) and thus is best to determine through IR spectroscopy by looking at $\ce{S-S}$ stretching frequency. Thus, the donor atoms may be different from what is shown in the possible structure.

The possible structure is:

enter image description here

$\endgroup$
3
  • $\begingroup$ In that case, two $Cu^+$ will be tri-coordinated, which is very unlikely to happen. and , more Importantly, This is a possible Structure. $\endgroup$ – Soumik Das Apr 11 '18 at 13:16
  • 1
    $\begingroup$ Has no spectroscopy or X-RAY diffraction ever been done for this compound? Is it really that uncommon? $\endgroup$ – Abhigyan Chattopadhyay Apr 11 '18 at 16:21
  • $\begingroup$ Spent quite a number of hours spread over days, to end up with no reference of the complex Could someone please refer to any related primary or secondary reference of the complex... $\endgroup$ – Che Mistry Apr 18 at 16:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.