Crystal field theory CFT is a model used to describe the electronic structure of transition metal complexes. It explains the color of these complexes and helps predict their absorption spectra by considering the interaction between the central metal ion and the surrounding ligands.In a transition metal complex, the central metal ion has a partially filled d-orbital, and the ligands are considered as point charges or dipoles that create an electric field around the metal ion. This electric field, known as the crystal field, affects the energy levels of the d-orbitals.In an isolated metal ion, the five d-orbitals have the same energy level degenerate . However, when the ligands approach the metal ion, the crystal field causes the degeneracy of the d-orbitals to be lifted, splitting them into two different energy levels. The extent of this splitting depends on the geometry of the complex and the nature of the ligands.The most common geometries are octahedral and tetrahedral. In an octahedral complex, the d-orbitals split into two sets: the lower energy level t2g consisting of three orbitals dxy, dyz, and dxz and the higher energy level eg consisting of two orbitals dx^2-y^2 and dz^2 . In a tetrahedral complex, the splitting is reversed, with the higher energy level being the t2 set and the lower energy level being the e set.The color of a transition metal complex arises from the absorption of light in the visible region, which promotes an electron from a lower energy d-orbital to a higher energy d-orbital. The energy difference between these orbitals corresponds to the energy of the absorbed photon, which is related to its wavelength and, consequently, its color.The absorption spectra of transition metal complexes can be predicted using CFT by calculating the energy difference between the split d-orbitals. This energy difference, known as the crystal field splitting parameter , depends on factors such as the type of metal ion, the oxidation state of the metal, the nature of the ligands, and the geometry of the complex. By determining the value, the wavelength of light absorbed by the complex can be estimated, and thus its color can be predicted.In summary, crystal field theory explains the color of transition metal complexes by describing the splitting of d-orbitals due to the interaction with surrounding ligands. This splitting results in electronic transitions that correspond to the absorption of specific wavelengths of light, which can be used to predict the absorption spectra of these complexes.