Monodentate and Bidentate Ligands

[Cassidy Kohlenberger 3D]

In homework problem 9C.5, (CO3)2- is revealed to be both monodentate and bidentate. Can someone explain how this is possible? Also, are there any other ligands that fall under this category we need to know?

[Jonathan Gong 2H]

When you draw the Lewis structure of CO3^2-, one resonance has C=O double bond and 2 C-O^1- single bonds, these two O^1- are capable of binding to a metal center at 2 places, therefore making it a bidentate ligand. A different resonance of CO3^2- has the double bond between the two C-O bonds, leaving only one O- to be able to bind to the metal center, therefore making CO3^2- a monodentate ligand. I'm sure that there are a few more ligands under this category, you would just have to draw their lewis structures to find out.

[105311039]

How I look at it when i am determining such things like monodentate or polydentate is the charges. On CO3^2- there are two oxygens with a negative charge and one without. Therefore, there can either be two places for a transition metal to attach since they are both negatively charged. Or the transition metal can ignore the two negatively charged anions and attach to the neutral oxygen.