The photochemical properties of transition metal complexes are highly dependent on the ligands attached to the central metal ion. The variation of ligands can lead to significant changes in the electronic structure, absorption spectra, and photochemical reactivity of the complexes. Here are some ways in which the photochemical properties of transition metal complexes change with the variation of ligands:1. Ligand Field Strength: The strength of the ligand field depends on the nature of the ligand and its ability to donate electron density to the central metal ion. Strong field ligands, such as cyanide CN- and carbon monoxide CO , lead to a larger splitting of the d-orbitals, resulting in low-spin complexes with a smaller number of unpaired electrons. This can affect the energy and intensity of the electronic transitions, leading to changes in the absorption spectra and photochemical reactivity.2. Spectrochemical Series: The position of a ligand in the spectrochemical series determines its effect on the energy of the electronic transitions. Ligands that are high in the spectrochemical series, such as CO and CN-, cause a greater splitting of the d-orbitals, leading to low-energy red-shifted absorption bands. On the other hand, ligands that are low in the spectrochemical series, such as iodide I- and bromide Br- , cause a smaller splitting of the d-orbitals, leading to high-energy blue-shifted absorption bands.3. Charge Transfer Transitions: The nature of the ligand can also influence the charge transfer transitions in transition metal complexes. Ligands with high electron-donating ability can facilitate metal-to-ligand charge transfer MLCT transitions, whereas ligands with high electron-accepting ability can facilitate ligand-to-metal charge transfer LMCT transitions. These charge transfer transitions can significantly affect the photochemical properties of the complexes, such as their ability to undergo photoinduced electron transfer reactions.4. Steric Effects: The size and shape of the ligands can influence the photochemical properties of transition metal complexes by affecting the geometry and stability of the complexes. Bulky ligands can lead to distorted geometries, which can affect the energy and intensity of the electronic transitions. Additionally, steric effects can also influence the accessibility of the central metal ion to other reactants, thereby affecting the photochemical reactivity of the complexes.5. Chelating Ligands: Chelating ligands, which can bind to the central metal ion through multiple donor atoms, can significantly affect the photochemical properties of transition metal complexes. Chelating ligands can lead to more stable complexes, which can affect the energy and intensity of the electronic transitions. Moreover, chelating ligands can also influence the photochemical reactivity of the complexes by affecting the accessibility of the central metal ion to other reactants.In summary, the photochemical properties of transition metal complexes are highly sensitive to the nature of the ligands attached to the central metal ion. Variations in ligand field strength, position in the spectrochemical series, charge transfer transitions, steric effects, and chelating ability can all lead to significant changes in the electronic structure, absorption spectra, and photochemical reactivity of the complexes.