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Re: Oxidation state of chelated iron
On Sun, 7 May 2000, Dave Gomberg wrote:
> Please see
>
> http://gill.tamug.tamu.edu/Chem316/Handouts/Chapter%205/EDTA%20(16%20colors)
> .pdf
>
> for more details on the chelation of metals by EDTA. It is the ferrous
> form that is chelated.
The article as near as I can say didn't say anything specific about iron
EDTA. The table at the bottom of the page lists formation constants for
both ferrous and ferric complexes. The constant for the ferric complex is
quite a bit higher than the contant for the ferrous complex.
I recall a thread a while back (OK, maybe years back?) where people
apparently in the know -- maybe Greg Morin -- said that that commercial
iron EDTA used ferric iron.
Of course, keep in mind Paul's point about not being able to really pin
down the oxidation state of the iron in a chelate. It might not make that
much difference what oxidation state the iron is in when the complex is
made. The oxidation state when the iron comes *out* of the complex would
make a difference, and that would depend on what mechanism breaks it out.
Roger Miller