Strongest chloride complex as predicted by HSAB theory Why won't NiX2+NiX2+ form a complex with ClX?ClX? , while the ions CuX2+CuX2+ and CoX2+CoX2+ form the complexes [CuClX4]X2?[CuClX4]X2? and [CoClX4]X2?[CoClX4]X2? ? According to the HSAB theory, ClX?C..