The photochemical behavior of coordination compounds is highly dependent on the metal ion and ligands used in their synthesis. The metal ion and ligands can influence the electronic structure, stability, and reactivity of the coordination compound, which in turn affects its photochemical properties. Here are some specific examples to support this statement:1. Metal ion: The choice of metal ion can greatly affect the photochemical behavior of a coordination compound. For example, transition metal ions with d-electrons can exhibit various oxidation states and can form complexes with different geometries. The electronic transitions in these complexes can be influenced by the metal ion's oxidation state, coordination number, and the nature of the ligands.Example: Ruthenium II polypyridyl complexes, such as [Ru bpy 3]2+ where bpy = 2,2'-bipyridine , exhibit strong and long-lived luminescence due to the metal-to-ligand charge transfer MLCT transition. In contrast, the luminescence of the analogous iron II complex, [Fe bpy 3]2+, is weak and short-lived due to the rapid non-radiative decay pathways.2. Ligands: The choice of ligands can also significantly affect the photochemical behavior of coordination compounds. Ligands can influence the energy levels of the metal ion, the geometry of the complex, and the stability of the excited states.Example 1: In the case of the previously mentioned [Ru bpy 3]2+ complex, the strong-field ligand bpy leads to a low-energy MLCT transition, which results in strong luminescence. If the bpy ligand is replaced with a weaker-field ligand, such as pyridine, the energy of the MLCT transition increases, and the luminescence becomes weaker.Example 2: The photochemical behavior of platinum II complexes can be tuned by changing the ligands. For instance, cisplatin cis-[Pt NH3 2Cl2] is a well-known anticancer drug that forms DNA adducts upon photoactivation. However, when the chloride ligands are replaced with other ligands, such as cyclobutane-1,1-dicarboxylate CBDC , the resulting complex e.g., carboplatin, cis-[Pt NH3 2 CBDC ] exhibits a different photochemical behavior and does not form DNA adducts upon photoactivation.In summary, the photochemical behavior of coordination compounds is highly dependent on the metal ion and ligands used in their synthesis. By carefully selecting the metal ion and ligands, it is possible to tune the photochemical properties of coordination compounds for various applications, such as luminescent materials, photocatalysts, and photoactivated drugs.