Q. What are the Ligands?
Ligands: The ions and/or molecules which are directly attached to the central atom/ion are called ligands. A ligand could be an iron, an atom or a neutral molecule but should contain at least one atom which can donate a pair of electrons to the metal ion for the bond formation.
Since the ligands are directly attached to the metal ion. They are said to be in the first coordination sphere of the central atom. In writing the formula of a complex, the metal ion and all the ligands are put in square brackets. The sum total of all the ligands so attached to the metal ion is called the coordination number of the metal. For example, in a compound like [Ag (NH3)21CI, there are two ammonia molecules acting as ligands and are said to be in the first coordination sphere of the Al+ ion. The coordination number of Al+ ion in the complex is 2.