The nature of the ligand in a coordination complex containing a transition metal can significantly affect the color of the complex. This is due to the interaction between the ligand and the d-orbitals of the transition metal, which influences the energy gap between the d-orbitals. The color of the complex is determined by the absorption of light in the visible region of the electromagnetic spectrum, which corresponds to the energy difference between the d-orbitals.When a ligand binds to a transition metal, it causes the degeneracy of the d-orbitals to be lifted, resulting in a splitting of the energy levels. The magnitude of this splitting depends on the nature of the ligand, with some ligands causing a larger splitting than others. This is known as the spectrochemical series, which ranks ligands based on their ability to cause splitting of the d-orbitals.The color of the coordination complex is determined by the energy difference between the split d-orbitals, as this corresponds to the energy of the light absorbed. When the energy gap is larger, the complex absorbs light of shorter wavelengths towards the blue/violet end of the spectrum , and the color observed is complementary to the absorbed light towards the yellow/red end of the spectrum . Conversely, when the energy gap is smaller, the complex absorbs light of longer wavelengths towards the red end of the spectrum , and the color observed is complementary to the absorbed light towards the blue/violet end of the spectrum .Here are some specific examples:1. Hexaaquacopper II complex [Cu H2O 6]2+: In this complex, the copper II ion is surrounded by six water molecules as ligands. The energy gap between the split d-orbitals is relatively small, resulting in the absorption of red light and the complex appearing blue-green in color.2. Tetraamminecopper II complex [Cu NH3 4]2+: In this complex, the copper II ion is surrounded by four ammonia molecules as ligands. Ammonia is a stronger field ligand than water, causing a larger splitting of the d-orbitals. As a result, the complex absorbs light of shorter wavelengths towards the blue end of the spectrum and appears deep blue in color.3. Hexacyanoferrate III complex [Fe CN 6]3-: In this complex, the iron III ion is surrounded by six cyanide ions as ligands. Cyanide is a strong field ligand, causing a large splitting of the d-orbitals. The complex absorbs light of shorter wavelengths towards the violet end of the spectrum and appears yellow-orange in color.In summary, the nature of the ligand in a coordination complex containing a transition metal can significantly affect the color of the complex by influencing the energy gap between the d-orbitals. Different ligands cause different degrees of splitting, which in turn determines the color of the complex based on the absorbed light and its complementary color.