Crystal Field Splitting Energy (${\Delta }_o$) vs Pairing Energy ($P$):

• Strong Field Ligands: Cause a large ${\Delta }_o$. If ${\Delta }_o>P$, electrons prefer to pair up in the lower $t_{2g}$ orbitals rather than jump to high-energy $e_g$ orbitals. This results in the minimum possible number of unpaired electrons (Low Spin Complex).
• Weak Field Ligands: Cause small splitting. If ${\Delta }_o<P$, electrons occupy $e_g$ before pairing. This leads to the maximum number of unpaired electrons (High Spin Complex).