Hi Dr.Bob,

Which is the correct formula for
dinitrobis(ethylenediamine)cobalt(III) nitrate?
I'm not sure which is the correct one out of these two:
a)[Co(en)2(NO2)2]NO3 or
b)[Co(NO2)2(en)2]3(NO3)3 ?

At the instance, I've choosen option a). Is my naming correct?

I would go with a also. b appears to be just the trimer of a and unless we know the compound is a trimer (and thus the molecular formula instead of the empirical formula) I think the empirical formula is the way to go. You know we write NaCl even though it really is NaxClx.

Hi! I can help you determine whether your naming is correct or not. To name coordination compounds, we generally follow a set of rules.

In this case, let's break down the given name, "dinitrobis(ethylenediamine)cobalt(III) nitrate."

The central metal ion is cobalt(III), indicating that the cobalt ion has a +3 charge.

The ligand involved here is ethylenediamine, denoted as "en." It is a bidentate ligand, meaning it can bind to the metal ion through two of its donor atoms, which in this case are the Nitrogen atoms.

The compound also contains two nitrate ions, NO3-.

Now, let's examine the two options you provided:

a) [Co(en)2(NO2)2]NO3
b) [Co(NO2)2(en)2]3(NO3)3

In both options, we have the ethylenediamine ligand, the nitrate ion, and the dinitro ligand (NO2)2. However, the arrangement of these ligands around the cobalt ion differs.

To determine the correct formula, we need to consider the coordination number of the cobalt ion, which indicates the total number of ligands bound to it.

In option a, [Co(en)2(NO2)2]NO3, we have two ethylenediamine ligands and two dinitro ligands coordinated around the cobalt ion. The nitrate ion is outside the coordination sphere.

In option b, [Co(NO2)2(en)2]3(NO3)3, we have two ethylenediamine ligands and two dinitro ligands coordinated around the cobalt ion. Additionally, we have three nitrate ions coordinated to the cobalt ion.

Based on the given name "dinitrobis(ethylenediamine)cobalt(III) nitrate," it implies that there are two dinitro groups coordinated to the cobalt ion. Therefore, option a, [Co(en)2(NO2)2]NO3, is the correct formula.

So, your choice is correct!

Let me know if there is anything else I can help you with.