The conditions and consequence that favours the t_ 2 g ^3 e_g^1...

The conditions and consequence that favour $t_{2 g}^3 e_g^1$ configuration in a metal complex are (i) weak field ligand, and (ii) high spin complex For weak field ligands, splitting energy ( $\Delta_0$ ) is lower than pairing energy $(P)$. As a result distribution of electrons for $3 \mathrm{~d}^4$ will be $t_{2 \mathrm{~g}}^3 \mathrm{e}_{\mathrm{g}}^1$. It results in high spin complex due to maximum number of unpaired electrons.