Question

ïf each cation in fe3o4 has a coordination number of 4, What is the expected coordination number of each anion?

Answer 1

The overall coordination number should equal the charge of the molecule right?
Since Fe3O4 has no charge it's overall coordination number will be zero.
Iron will form the cation with coordination number +4, since there are 3 iron atoms present it's coordination will be +12, since there are 4 oxygen atoms present (oxygen forms the anion so negative number) -12/4=-3

Answer 2

That seems to be the right answer.

But does that mean that the coordination number is the same as the oxidation number?

Answer 3

Sorry I got my ideas a bit muddled there.
Fe3O4 is magnetite which is made up of both ferric oxide (Fe2O3, hematite) and ferrous oxide (FeO)
I can't actually see how to find the anions coordination number for this molecule, the coordination number for transition metal compounds (for the cation) is just the number of ligands surrounding the central atom so I'm not too sure sorry