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How are monodentate ligands different from didentate ligands?

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Structural diagram of the vitamin B12 coenzyme molecule, highlighting its organometallic core with five nitrogen-cobalt bonds and one cobalt-carbon bond at the center, surrounded by complex organic groups. — coordination compound Coordination compounds contain a central metal atom surrounded by nonmetal atoms or groups of atoms, called ligands. For example, vitamin B₁₂ is made up of a central metallic cobalt ion bound to multiple nitrogen-containing ligands.

In the study of coordination compounds, the primary difference between monodentate and didentate ligands lies in the number of atoms through which they attach to a central metal atom.12

Monodentate ligands: These ligands attach to the central metal atom through only one atom, forming a single coordinate covalent bond.123
Didentate ligands: These ligands attach to the central metal atom through two atoms, utilizing two bonds.124

Ligands that utilize more than one bond are generally classified as polydentate. Because didentate and other polydentate ligands bind to the metal at multiple points, they form cyclic structures known as chelates. These chelate complexes are typically more stable than those formed by monodentate ligands because the multiple points of attachment create a more secure bond with the metal ion.15

It is important to note that some ligands can act as either monodentate or polydentate depending on the specific chemical environment of the compound.5