Why is CO (carbon monoxide) monodentate?

[vuongnaomi1L]

So the lewis structure of CO is C and O having triple bonds and there are 1 lone pair on each C and O. Since there are two lone pairs on the CO molecule, why isnt it a bidentate ligand?

[Gabby Magat 3F]

Hi! I'm not too sure since I'm just starting to understand chelating complexes/polydentate ligands, but even though both atoms in carbon monoxide have a lone pair, you can't physically get both to bond to the central metal atom in a complex. You'd essentially be trying to "bend" the triple bond in between them, which wouldn't work.

So for polydentate ligands, you'd be looking for geometry where the lone pairs in the molecule are separated by a "spacer" (some atom without a lone pair itself. Because you can't bend/curve bonds between atoms, you need these spacers to form a ring-like shape so that the lone pairs are separated and both can bond to the same metal atom. I hope this made sense!

[FrancescaHawkins2H]

In my understanding, CO is a monodentate ligand because when one of the lone pairs becomes a bonding pair, it repels the other lone pair, which becomes too far away to create a second bond.

[vuongnaomi1L]

In my understanding, CO is a monodentate ligand because when one of the lone pairs becomes a bonding pair, it repels the other lone pair, which becomes too far away to create a second bond.

This makes perfect sense! Thank you!

[rhettfarmer-3H]

CO is monodentate for many reasons to begin with the structure of CO-. Its one lone pair on C with a triple bond and a lone pair on O. Therefore, the O is negatively charged. Hence, since the structure is only 2 molecules long there are not enough spacers. Usually, you need 2 spacers because it wouldn't make sense for it to hit both ends if one side is bonded. Another reason is the minus charge is very EN so its going to hit the end mostly. to to note.

[Astha Patel 2J]

The structure doesn't have spacers making it impossible for two lone pairs to become bonding pairs simultaneously. It would try and bend the bond.

[Nancy Yao]

H2O also has two lone pairs but it is a monodentate as well. I read some explanations online and they say that it is because water only has one donor atom and in polydentates there are more than one donor atoms. The other lone pair on the same atom cannot bond to the metal due to geometrical reasons.