[Cu(NH₃)₄]SO₄ is a coordinated complex with a coordination number of

Concept-

​Crystal field theory:

• A metal ion in a complex is surrounded by coordinating ligands anions or negative ends.
• An electric field is produced at the metal ion by the surrounding ligands.
• This electrostatic approach towards the interaction between metals and ligands is known as crystal field theory.
• CFT theory considers the ligands as point charges.
• There is no overlap between the ligand orbitals and metal ion orbitals.
• Ligands donate lone pair of electrons to the metal atoms and form coordinate complexes.

Explanation:

• The metal ion has two valencies:
  • The oxidation state or the primary valency.
  • The co-ordination number or the secondary valency.
• The secondary valencies are satisfied by co-ordinating with primary ligands.
• The number of ligands satisfying the secondary valency is called the coordination number of the metal.
• The bond formed by the ligands and the metal ion forms a coordination sphere.
• The coordination sphere is non-ionizable in solution because of the co-ordinate bond between them.
• The oxidation number or primary valency of the metal ion is satisfied by the side ions which form the ionizable sphere.
• In the complex [Cu(NH3)4]SO4, [Cu(NH3)4]²⁺ is the coordination sphere. The number of ligands attached to the metal Cu is four.

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Hence, the coordination number of the complex [Cu(NH3)4]SO4 is four.

​Additional Information

The geometry of the complex formed.

• Placement of the donor atoms at different stereochemical positions will perturb the metal ions to a different extent.
• This will result in the formation of different stereochemistry or structure.
• The stereochemistry depends on the co-ordination number.