Question

Which is more stable [Co(OX)3]3- or [CoF6]3- ? Why?

Answer 1

[Co(ox)3]3- is more stable than [CoF6]3-because as oxalate is a bidentate ligand it forms a chelated ring compound, by occupying all the coordination sites, which is more stable than the normal compound containing a monodentate ligand like F- .

Answer 2

Answer: $[Co(ox)_3]^{3-}$ is more stable because it has chelate effect.

Explanation:

$[CoF_6]^{3-}$ is known as cobalt (III) hexafluoride complex which has 6 monodentate ligands which is fluorine atom. Monodentate ligands are the ones which use only one donor atom for complexation.

But, $[Co(ox)_3]^{3-}$ is known as cobalt (III) oxalate complex which has 3 bidentate ligands that is oxalate ions. Bidentate ligands are the ligands which use 2 donor atoms for complexation.

For the stability of complexes, many factors work, one of which is chelation effect.

More the chelation, more will be the stability. Chelate effect states that complexes having chelate rings in their structure are more stable than complexes having no rings.

Chelate rings are formed only in those complexes which contain one or more polydentate ligands.

Hence, $[Co(ox)_3]^{3-}$ is more stable because it has chelate effect.