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.