Crystal field theory CFT is a model that describes the electronic structure of transition metal complexes, particularly coordination compounds. It helps explain the magnetic properties exhibited by these compounds by considering the effect of the ligands surrounding ions or molecules on the energy levels of the central metal ion's d-orbitals. The ligands create an electric field that splits the degenerate d-orbitals into two sets with different energy levels.The magnetic properties of coordination compounds are determined by the number of unpaired electrons in the d-orbitals of the central metal ion. When the d-orbitals are split by the crystal field, electrons will occupy the lower energy orbitals first according to Hund's rule before pairing up in the higher energy orbitals. If there are unpaired electrons, the compound will exhibit paramagnetic behavior, meaning it will be attracted to an external magnetic field. If all electrons are paired, the compound will be diamagnetic, meaning it will not be attracted to an external magnetic field.Let's consider the example of the hexaaqua complex [Fe H2O 6]2+. In this compound, the central metal ion is Fe2+ with a 3d6 electron configuration. The ligands are six water molecules surrounding the Fe2+ ion in an octahedral arrangement. In an octahedral crystal field, the d-orbitals are split into two sets: the lower energy t2g orbitals dxy, dyz, and dxz and the higher energy eg orbitals dx2-y2 and dz2 .For the [Fe H2O 6]2+ complex, the 3d6 electron configuration will result in the following orbital filling:- t2g orbitals: 3 electrons, each in a separate orbital dxy, dyz, and dxz - eg orbitals: 3 electrons, each in a separate orbital dx2-y2 and dz2 Since there are four unpaired electrons in the d-orbitals of the Fe2+ ion, the [Fe H2O 6]2+ complex will exhibit paramagnetic behavior due to the presence of these unpaired electrons.