The substitution of ligands in a coordination complex can significantly affect its coordination geometry and electronic properties. In the case of the reaction between [Fe H2O 6]2+ and SCN- to form [Fe SCN H2O 5]+, we can observe these changes through experimental data.Coordination Geometry:The coordination geometry of a complex refers to the arrangement of the ligands around the central metal ion. In the case of [Fe H2O 6]2+, the coordination geometry is octahedral, with six water molecules surrounding the Fe2+ ion. When one of the water molecules is replaced by a SCN- ligand to form [Fe SCN H2O 5]+, the coordination geometry remains octahedral. However, the bond lengths and angles may change due to the different properties of the SCN- ligand compared to the H2O ligand.Electronic Properties:The electronic properties of a coordination complex are influenced by the nature of the ligands and their interactions with the central metal ion. In the case of [Fe H2O 6]2+, the complex is colorless because the energy gap between the d-orbitals is too large for visible light absorption. However, when the SCN- ligand replaces one of the water molecules, the energy gap between the d-orbitals decreases, allowing the complex to absorb light in the visible region. This results in the formation of the red-colored [Fe SCN H2O 5]+ complex.Experimental Evidence:The change in electronic properties can be observed experimentally through UV-Vis spectroscopy. When [Fe H2O 6]2+ is mixed with SCN-, the absorption spectrum of the solution changes, showing a new absorption band in the visible region corresponding to the formation of the [Fe SCN H2O 5]+ complex. This new absorption band is responsible for the red color of the complex.Additionally, infrared IR spectroscopy can be used to study the changes in coordination geometry and bonding. The IR spectrum of [Fe H2O 6]2+ will show characteristic bands corresponding to the O-H stretching vibrations of the water molecules. Upon the formation of [Fe SCN H2O 5]+, new bands corresponding to the stretching vibrations of the SCN- ligand will appear, indicating the substitution of one water molecule by the SCN- ligand.In conclusion, the substitution of ligands in a coordination complex can significantly affect its coordination geometry and electronic properties. In the example of the reaction between [Fe H2O 6]2+ and SCN- to form [Fe SCN H2O 5]+, the changes in coordination geometry and electronic properties can be observed through experimental techniques such as UV-Vis and IR spectroscopy.