Synthesize double tungstates using the polymeric complexing method is a challenge. Chelate the groups (WO4)2- , (MoO4)2- , (W2O7)62- & (Mo2O7)62- can be a hard work if you do not understand their interaction with the chelant agents. I used EDTA, citric acid, EDTA + citric acid in different proportions for trying to chelate these anionic groups. None of these options could give a good answer that my solution would no precipitate during the polymerization process. The pH control during the whole process is difficult to understand since I could not reproduce this in any experiment. For that reason I have the following questions:
Which are the best chelants for these anions (WO4)2- , (MoO4)2- , (W2O7)62- & (Mo2O7)62- ? What should additionally be considered for their choice?
EDTA, citric acid, EDTA+citric - it is chelating agents for cations, but (WO4)2- , (MoO4)2- , (W2O7)6 2- & (Mo2O7)62- are anions. Are you feel difference?
Polycations should be suitable, maybe protonated (or peralkylated) linear or branched polyethyleneimine (brPEI or l-PEI) , polyazamacrocycles like cyclam, cyclen ...
http://homepage.univie.ac.at/jeanluc.mieusset/Supramolecular%20Chemistry%203%20-%20Binding%20of%20anions.pdf
http://pubs.acs.org/doi/abs/10.1021/cr960393d
EDTA, citric acid, EDTA+citric - it is chelating agents for cations, but (WO4)2- , (MoO4)2- , (W2O7)6 2- & (Mo2O7)62- are anions. Are you feel difference?
Polycations should be suitable, maybe protonated (or peralkylated) linear or branched polyethyleneimine (brPEI or l-PEI) , polyazamacrocycles like cyclam, cyclen ...
http://homepage.univie.ac.at/jeanluc.mieusset/Supramolecular%20Chemistry%203%20-%20Binding%20of%20anions.pdf
http://pubs.acs.org/doi/abs/10.1021/cr960393d
in my opinion, the best book dedicated to these compounds:
Michael Thor Pope "Heteropoly and isopoly oxometalates", Springer-Verlag, 1983
no chelate agents for POMs. I would use bulky cations to precipitate it (if you want to get rid of these anions in solution). Separation is less common (sephadex-50?)
The difference between anions and cations is clear. However, most articles report only the use of chelants even for the anions, controlling the pH of the solution to stabilize it. It is clear to me now, that using chelants for anions will just saturate the solution with them. This fact must be more discussed in the literature. Unfortunately, the complexing polymeric synthesis methods are being described for the synthesis of double tungstates is somehow a Pandora´s box. It is more difficult in this way to judge about the validity of these methods if you do not have a strong chemistry background.
Once we have a misture of cations and anions in the solution, may we use chelants and one or a misture of the above (answers) cited reagents in the same solution? I mean, chelants for alkali metals / rare earths and the above ones for the tungstates anion? Are there already reports about the interaction between chelants and them?
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