Oxidation number

[Jane Burgan 1C]

How do you figure out the oxidation number of coordination compounds?

[David S]

The oxidation state of the TM is often given in the name of the compound. If you only have the formula and not the name, then here are the steps.

1) If you aren't given the net charge of the coordination compound (everything inside the brackets), figure out the net charge of the coordination compound. If you are given a coordination compund with other ions that are outside the coordination sphere (outside the brackets) but are still part of the chemical formula, then the net charge of the coordination compound (stuff inside the bracket) will be = to -1*(sum of charges outside the coordination sphere).

2) subtract the sum of the charges of all ligands attached to TM from the net charge of the coordination compound. This will give you the oxidation # of the TM. (You either have to know the net charge of the ligands, or look them up)

Example case: [Co(NH3)_5(NO2)]Br2

In this case, since the coordination compound is associated with 2 Br anions, we know that it is a cation with net charge = -1*-2= +2.

Now since we know that Net charge - (sum of all ligand charges) = oxidation #, and we know that NH3 charge =0, NO2 charge= -1, we get:
+2- (0*5+ -1) = oxidation # = +3 for the Cobalt TM.