1. Medicinal applications: Cisplatin is used as an anti-cancer drug.
2. Biological importance: Hemoglobin (iron complex) and chlorophyll (magnesium complex) are vital for life processes.
3. Industrial applications: Coordination compounds like \( [Ag(NH_3)_2]^+ \) are used in photography.
4. Analytical chemistry: Complexometric titrations use EDTA as a ligand.