(b) Central atom/ion
In a coordination entity, the atom/ion to which a fixed number
of ions/groups are bound in a definite geometrical arrangement
around it, is called the central atom or ion For example, the
central atom/ion in the coordination entities: [NiCl2(H2O)4],
[CoCl(NH3)5]
2+ and [Fe(CN)6]
3– are Ni
2+, Co
3+ and Fe
3+, respectively These central atoms/ions are also referred to as Lewis acids ( c ) Ligands
The ions or molecules bound to the central atom/ion in the
coordination entity are called ligands