2012 quiz 3 prep #1

[Rene Phan 3D]

The question is: what is the name of the complex [Cr(en)2(H2O)Cl]Cl2?

Why is the answer aquachlorobis(ethylenediamine)chromium(II) chloride instead of with a dichloride at the end?

In an example in the course reader [Co(NH3)5Cl]Cl 2H2O was named pentaamminechlorocobalt(II) chloride dihydrate, so what makes these two different? Why does this have dihydrate instead of just hydrate?

Thanks!

[HelenMach 1J]

For the water, there was a coefficient two in front of the water molecule, meaning there were two water molecules... and it's written separately, so you know there are for sure two different water molecules.

As for the chloride, I am going to assume that it is the same reason?

"Since the Cl2 (total 2- charge) balances the positively charged coordination complex ion, it can be referred to as "chloride," similarly to CaCl2 being called "calcium chloride." If the overall charge of the coordination complex ion is known, the number of chloride ions needed to balance the charge can be determined." -Chem Mod

Judging from above, it is only Cl2 because it is the number of chloride ions needed to balance the charge.

Someone please add on to this?

[Megan White 2C]

Unfortunately, I can't help with clearing up some of this confusion (I am having trouble with this problem as well), but I do have an additional question to add to this stream:

I'm having trouble figuring out the order of the naming process for the compound. Why is chromium(II) listed after bis(ethylenediamine)? If we are to list the names of the molecules comprising the coordination compound in alphabetical order excluding prefixes, how does this example follow suit?

I have run across this problem with almost all of the exercises I have been going over. What am I missing?

Any and all help is greatly appreciated! (I am also interested in the answers to the above questions!) Thanks!

[Eduardo Torres 3G]

As for the original question, when it comes to ions, the nonmetal at the end is not given a prefix because the number of atoms is assumed according to charge. For example, for MgCl2 you write magnesium chloride and it is assumed that there are 2 Cl because of the charges. Since H2O has a charge of 0, it is necessary to add the prefix to know how many water molecules are in the compound. As for Megan's question, the names of the ligands (in alphabetical order) are always written before the name of the metal regardless of alphabetical order. This is why chromium(III) is after bis(ethylenediamine). I hope this clarifies things.

[Megan White 2C]

Thank you so much, Eduardo! That clears it all up!

[HelenMach 1J]

Yes! Thank you so much Eduardo!