Ligands

[Lilia Hacoupian 2E]

How is it possible for a ligand to be both monodentate and bidentate? How would one know which category to assign it to?

[Kaija Frassrand 2F]

A ligand can exhibit both monodentate and bidentate behavior if it has multiple sites capable of forming coordination bonds with a metal ion. The classification of a ligand as monodentate or bidentate depends on the number of donor atoms it contributes to the metal coordination complex.

[Rebecca Kam 3D]

To know whether a ligand is monodentate or bidentate you can draw out the Lewis structure to see how many and where the lone pairs are. If the atom has one lone pair, it would be monodentate, and if there are two lone pairs, this would be bidentate because there are two locations a metal can be attached to. A ligand can be monodentate and bidentate due to differences in resonance structures. For example, (CO3) ^-2 is both monodentate and bidentate because one resonance structure has a double bond between C and O and two single bonds, while another resonance structure has two double bonds between C and O with one single bonded C and O. As a result, the differences in the structures and number of lone pairs on each result in differences in categorization of whether a ligand is monodentate or bidentate.