Tetrahedral complex

Worked tetrahedral example: [NiCl4]2-. Nickel's oxidation state in this complex is +2, giving Ni2+ a free-ion valence configuration of 3d8. Four Cl- ligands require four vacant metal orbitals for bonding. The four orbitals actually used for this are one 4s orbital and all three 4p orbitals, giving sp3 hybridisation -- geometrically, sp3 hybrid orbitals point toward the four corners of a tetrahedron, so [NiCl4]2- is tetrahedral. These four sp3 hybrid orbitals then each overlap with one Cl- ligand's donor orbital, forming the four Ni-Cl coordinate bonds. Since the hybridisation here draws only on the metal's s and p orbitals (Cl- being a weak-field ligand, no pairing is forced and no d orbital needs to be vacated), the original 3d8 electron arrangement is left completely undisturbed -- it still has two unpaired electrons (from filling five d orbitals with eight electrons: three orbitals doubly oc …