Ligand substitution can significantly affect the photochemical properties of transition metal complexes. This is because the nature of the ligands surrounding the metal center can influence the electronic structure, stability, and reactivity of the complex. In the case of the [Fe CN 6] complex, we can explore how ligand substitution impacts its photochemical properties.The [Fe CN 6] complex consists of an iron II center coordinated to six cyanide CN ligands. The cyanide ligands are strong-field ligands, meaning they cause a large splitting of the d-orbitals of the metal center. This results in a low-spin configuration for the iron II center, with the majority of the d-electrons occupying the lower-energy orbitals.When a ligand substitution occurs, one or more of the cyanide ligands are replaced by another ligand. This can lead to changes in the electronic structure of the complex, affecting its photochemical properties in several ways:1. Ligand Field Strength: Replacing a strong-field ligand like cyanide with a weaker-field ligand will decrease the splitting of the d-orbitals. This can lead to a change in the spin state of the metal center, which in turn affects the energy levels and absorption spectra of the complex. As a result, the complex may absorb light at different wavelengths, altering its photochemical reactivity.2. Charge Transfer Transitions: Ligand substitution can also affect the charge transfer transitions within the complex. For example, replacing a cyanide ligand with a ligand that has a different electron-donating ability can change the energy levels of the metal-to-ligand charge transfer MLCT or ligand-to-metal charge transfer LMCT transitions. This can lead to changes in the absorption spectra and the overall photochemical reactivity of the complex.3. Stability and Reactivity: Ligand substitution can impact the stability of the complex, which in turn affects its photochemical properties. For instance, replacing a cyanide ligand with a more labile ligand can make the complex more susceptible to photodissociation or other photochemical reactions.4. Solvent Effects: The nature of the ligands can also influence the solubility and interactions of the complex with the surrounding solvent molecules. This can affect the photochemical properties of the complex by altering the energy levels and transition probabilities of the electronic states.In summary, ligand substitution in transition metal complexes like [Fe CN 6] can significantly impact their photochemical properties by altering the electronic structure, stability, and reactivity of the complex. The specific effects will depend on the nature of the substituting ligands and their interactions with the metal center and the surrounding environment.