In isolation, the d orbitals of a metal atom/ion are degenerate due to spherical symmetry. However, the presence of ligands, forming an asymmetrical negative field, leads to the lifting of d orbital degeneracy through splitting.

CFT views the metal-ligand bond as ionic, emphasizing electrostatic interactions between the metal ion and ligands. Ligands are treated as point charges for anions or point dipoles for neutral molecules in this model.

[Co(C₂O₄)₃]³⁻ is an inner orbital complex with d²sp³ hybridization, resulting in diamagnetic behavior. In contrast, [CoF₆]³⁻ is an outer orbital complex with sp³d² hybridization, leading to paramagnetism due to the presence of four unpaired electrons.

Valence Bond Theory attributes the anomalies to the formation of inner orbital and outer orbital coordination entities. Inner orbital complexes like [Mn(CN)₆]³⁻ and [Fe(CN)₆]³⁻, with d²sp³ hybridization, are paramagnetic, while outer orbital complexes like [MnCl₆]³⁻ and [FeF₆]³⁻, with sp³d² hybridization, ...

The magnetic data show anomalies in compounds like [Mn(CN)₆]³⁻ and [Fe(CN)₆]³⁻, where [Mn(CN)₆]³⁻ has a magnetic moment of two unpaired electrons, while [Fe(CN)₆]³⁻ exhibits a paramagnetic moment with five unpaired electrons.

In d⁴ (Cr²⁺, Mn³⁺), d⁵ (Mn²⁺, Fe³⁺), and d⁶ (Fe²⁺, Co³⁺) cases, a vacant pair of d orbitals for octahedral hybridization is achieved by pairing 3d electrons, resulting in two, one, and zero unpaired electrons, respectively.

Metal ions like Ti³⁺ (d¹), V³⁺ (d²), Cr³⁺ (d³) exhibit similar magnetic behavior in both free ions and coordination entities as two vacant d orbitals are available for octahedral hybridization with 4s and 4p orbitals.

The magnetic moment of coordination compounds is determined through magnetic susceptibility experiments, providing insights into the number of unpaired electrons and the structures adopted by metal complexes.

In square planar complexes like [Ni(CN)₄]²⁻, the hybridization involved is dsp², whereas tetrahedral complexes involve the hybridization of one s and three p orbitals. Nickel in [Ni(CN)₄]²⁻ is in the +2 oxidation state with the electronic configuration 3d⁸.

[NiCl₄]²⁻ is paramagnetic due to the presence of two unpaired electrons in the nickel ion, which has the electronic configuration 3d⁸ in the +2 oxidation state.