Reaction between Sodium Thiosulfate and Iron Chloride

I'm doing a paper on catalytic effectiveness in this reaction, and am trying to identify how the catalysts are speeding up the reaction. Based on what I can find, 
$\ce{Fe}$ starts as $\ce{Fe^3+}$, and it will react to form a transitional violet compound, which I think is $\ce{Fe2(S2O3)2}$. This will then break down into $\ce{Fe^2+}$. 


I am using various catalysts including iron sulphate, cobalt chloride, etc. However, as far as I can tell, the catalysts are not speeding up the first step ($\ce{Fe^3+}$ to violet compound), but the second (violet compound breaking down to $\ce{Fe^2+}$ and other ions). The catalysts I've used have varying levels of effectiveness. The main 3 factors that would change how catalysts could affect this, as far as I can tell, are electron transfer,complex shape, and ligands. I don't think they are acting to transfer electrons here, and I think all the catalysts would have the same complex shape (octahedral). Therefore, I want to know how the ligands formed from each catalyst (causing it to go from linear monodendate violet compound to octahedral ions) would affect this differently. The catalysts I'm using are copper sulphate, iron sulphate, cobalt chloride, and nickel sulphate. I can't find much information about what is happening in this reaction. If anyone knows what ligands are formed, and how the shape/electrons/ligands of the catalysts are affecting this reaction speed, I would really appreciate it.


