Square planar geometry is typically seen with strong field ligands like cyanide, while tetrahedral geometry is common with weak field ligands like chloride.
Nickel(II) is a d\(^8\) ion, and whether a four-coordinate complex of it ends up square planar or tetrahedral comes down to the ligand's field strength. Strong-field ligands like cyanide favor pairing electrons into the lower-energy orbitals, leading to a square planar shape, seen in \( [Ni(CN)_4]^{2-} \). Weak-field ligands like chloride don't force that pairing, so the complex keeps a tetrahedral geometry instead, seen in \( [NiCl_4]^{2-} \).
