Classification on the basis of charge on the complex

A cationic complex has a positively charged coordination sphere -- either the whole compound is simply that cation (e.g. [Zn(NH3)4]2+), or the compound pairs a cationic coordination sphere with an anionic counter ion outside the brackets (e.g. [Co(NH3)5Cl]SO4, whose coordination sphere [Co(NH3)5Cl]2+ is balanced by the SO4(2-) counter ion). An anionic complex has a negatively charged coordination sphere -- either standing alone as the anion (e.g. [Ni(CN)4]2-) or paired with cationic counter ions (e.g. K3[Fe(CN)6], whose coordination sphere [Fe(CN)6]3- is balanced by three K+ counter ions, making the overall compound electrically neutral even though its coordination SPHERE is genuinely anionic). A neutral complex has NEITHER a cationic nor an anionic coordination sphere -- its net charge is already zero, so it needs no counter ion of any kind, as in [Pt(NH3)2Cl2] or [Ni(CO)4]. It is worth stressing the distinction this section draws between a compound's overall electrical neutrality (which is always true once counter ions are included) and whet …