Definition of Coordination compound:
- Ligand : Any species(ion or molecule) that have at least one lone pair of electron and can donate its lone pair of electron to a metal cation or atom is called a ligand. Since a ligand is an electron rich species it is also called Lewis base or nucleophile.
- A metal cation is an electron deficient species and can accept a lone pair of electron, there fore it act as a Lewis acid or electrophile.
- When a group of ligand donate its lone pair of electron to the metal cation or atom coordinate bonds are formed and the product formed is called a coordination compound
- Thus the compound in which metal cation or atom is attached to a group of ligand by coordinate bond is called a coordination compound.
- Or a complex ion in which a metal cation is attached to the ligand by coordinate bonds.
Structural formula of Coordination compound:
- Here the central metal cation or atom and the ligand attached to it are written in a square bracket i.e.[ ] which is called coordination sphere.
- The cation or anion outside the coordination sphere is called the ionization sphere or counter ion.
- The atom in a ligand that is directly attached to a metal cation or atom is called the donor atom and the number of donor atom attached to a metal cation or atom is called the coordination number .
- For example ,coordination number of Ag+ in [Ag(NH3)2]2+ is 2
Cu+ in [Cu(NH3)4]2+ is 4
Co3+in [Co(NH3)6]3+ is 6
Properties of Coordination compound;
- The coordination compound may be either neutral molecule or ionic compounds. In ionic coordination compound either the cation or anion or both may be complex ion.
- The coordination compound retain their identity more or less even in solution though partial dissociation may occur.
- These compound do not give the tests of all their constituent ion in aqueous solution i.e. some constituent ion lost their identity in aqueous solution. For example [Co(NH3)6]Cl3 is a complex compound and it does not give the test of all the constituent ions, Co3+and Cl- instead it gives the Co3+ as [Co(NH3)6]3+ complex ion and Cl- ion.