When do when use prefixes "Bis-," "Tris-," & etc?

[Jaipal Virdi 2I]

Hey! I was wondering if anyone could help provide some examples or cases for when these prefixes would be used. We covered it in lecture when we first went over how to name coordination compounds, but I am still a bit confused on when it is relevant.

[205686400]

Hi! These are often used when the molecule is a polydentate. A polydentate basically means the same molecule bound to an atom at multiple points rather than just one. For example, if you were to look at a coordination complex with 2 Oxalato molecules you'll see how it binds differently to the central atom rather than a coordination complex with just normal atoms and other small molecules.

[Joshua Lee 3C]

You would use the prefixes "bis,tris,tetrakis etc." to describe the number of ligands present in a compound. However, you would only use these if the ligand you are describing already has one of the normal prefixes in its name "di,tri,tetra etc." or if the ligand is polydentate.

Ex.
[Co(H2NCH2CH2NH2)3]2(SO4)3
tris(ethylenediamine)cobalt(III) sulfate

In this case, we see tris used instead of tri because the ligand, ethylenediamine is a polydentate ligand. Tris is also used because we see the prefix "di" within the ligand's name "ethylenediamine".

[205677523]

Correct, the prefixes "bis, tris, etc" have the same function as the classic "mono, di, tri, tetra" prefixes, but are used to prevent confusion. As previously mentioned,

Ex.
[Co(H2NCH2CH2NH2)3]2(SO4)3
tris(ethylenediamine)cobalt(III) sulfate

In this case, we see tris used instead of tri because the ligand, ethylenediamine is a polydentate ligand

To further clarify, tris is used instead of tri to clarify that the ligand doesn't have three ethylenes, because given that there's already the di- prefix used to indicate two amine, one might think that the similar tri- prefix indicates three ethylenes in the ligand instead of three ethylenediamines. Using the prefix tris- clears this up.