Question

Why low spin tetrahedral complexes are rarely observed?

Answer 1

In tetrahedral complex, the d-orbital is splitting to small as compared to octahedral. For same metal and same ligand . Hence, the orbital splitting energies are not enough to force pairing. As a result, low spin configurations are rarely observed intetrahedral complexe

Answer 2

A tetrahedral compound has sp3 hybridization,where four ligands form a tetrahedron structure around the metal ion. During crystal field splitting ,the d-orbitals split into two groups-one with a higher energy and the other with a lower energy with an energy difference of  Δt. In case of low spin complexes, the energy required to pair electrons in a lower energy d-orbital is less than the energy required to place the additional electron into a higher energy d-orbital. If the case is just the reverse then high spin splitting occurs.

As the ligands in a tetrahedral complex do not directly approach the d-orbitals,instead they approach in between the axes ,the splitting energy is much lower than that of the pairing energy, and therefore the electrons jump to the higher energy level d-orbitals rather than pairing,resulting in formation of high-spin complexes.

High Spin Complex: Splitting energy < Pairing energy

Low Spin Complex: Splitting energy > Pairing energy