Example 9C.1

[Kelly McFarlane]

In Example 9C.1 in the textbook, it asks to name the coordination compound [Co(NH3)3(OH2)3]2 (SO4)3. The answer is triamminetriaquacobalt(III) sulfate. Why do you not specify that there are 3 sulfate molecules? Would saying trisulfate be incorrect?

[Wesley Zhou 1F]

Treat coordination compounds like ionic compounds.

[Co(NH3)3(OH2)3]2 is like a cation.

(SO4)3 is like an anion.

Remember that if you have charges, they switch when determining its formula (i.e. in Mg(OH)2. Mg2+ and OH-)

SO4 has a -2 charge, which explains why the coordination complex (aka complex ion) has a subscript of 2 at the end.

From this logic, we conclude that the charge of the complex ion is +3. Therefore, when applying ionic rules, SO4 becomes (SO4)3.

[Gabriel McDonald 1J]

You don't say trisulfate because the number of sulfate molecules are assumed by looking at the charge of the compound. The naming rules just work out so that we only say "sulfate" instead of trisulfate.