Why tetrahedral complexes are high spin ?
Tetrahedral complexes are high spin because
(i) Δt = 4/9 Δo, i.e., tetrahedral crystal field splitting is half the crystal field splitting in octahedral complexes.
(ii) Δt is always less than the pairing energy.
Due to these two reasons, no pairing of electrons occurs in d3, d4, d5, d6 and d7 tetrahedral complexes. Therefore, the tetrahedral complexes of these configurations are always high spin whether the ligands are strong or weak.