The structure of sodium cuprous thiosulphate 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:

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


  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:
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: