Properties of ligands?

Question

What are the properties of ligands and what properties of ligands make it a strong ligand?

Answer 1

The ligand must be a good electron pair donor. Examples are NH3, H20, CN-, etc

Note that the transition metal form complexes by using the d or d hybrid orbitals that are not fully filled. By, complexation, the transition metal is able to attain a stable configuration by having a full d^10, much like a fully filled octet of s^2p