What is the oxidation state of iron in #"Fe"_3["Fe"("CN")_6]_2#?

1 Answer
Truong-Son N.
Jan 12, 2018

Well, hopefully you can see that there are two different iron atoms here. Otherwise, it wouldn't make sense to write the two #"Fe"# atoms separately like this.

If you really meant #"Fe"_4["Fe"("CN")_6]_3#, Prussian blue, then going through the same process, you would instead get #"Fe"^(3+)# on the outer sphere and #"Fe"^(2+)# on the inner sphere.

This is similar to #"Al"_2"O"_3# in the sense that we have two prime numbers for the subscripts. So the charge of the ions interacting via the outer sphere are apparently:

#overbrace(color(blue)bb("Fe"^(2+)))^"Outer Sphere"#, #[overbrace("Fe")^"Inner Sphere"("CN")_6]^(3-)#

As a result, knowing that #"CN"^(-)# is cyanide, the inner sphere iron is #color(blue)bb("Fe"^(3+))#, since #6 xx -1 + 3 = -3# for the total anionic charge.

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