Nickel (Z = 28) combines with a uninegative monodentate ligand X- to form a paramagnetic complex [NiX4]2-. The number of unpaired electron(s) in the nickel and geometry of this complex ion are, respectively:

If X- is weak field ligand (say Cl-) then NiCl42− is tetrahedral (sp3) with two unpaired electrons. If X- is strong field ligand (say CN-), then NiCN42− is square planar (dsp2) with no unpaired electron. Also given NiX42− is paramagnetic.