Coordination Sphere
Definition and meaning of Coordination Sphere in chemistry.
Coordination sphere refers to the central metal ion or atom together with the ligands directly bonded to it in a coordination compound, forming the complex's inner sphere as distinct from any outer-sphere counter ions.
In more detail
The coordination sphere is written inside square brackets in a formula and includes the metal center plus all ligands attached to it through coordinate covalent (dative) bonds. The number of donor atoms bonded to the metal defines its coordination number, which in turn sets the complex's geometry, such as octahedral or tetrahedral. Species outside the brackets are outer-sphere counter ions; they balance charge but are not bonded to the metal and dissociate freely when the compound dissolves in water.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Also called | Inner coordination sphere |
| Common coordination numbers | 4 and 6 (also 2, 5, 7, 8) |
| Example ion | [Co(NH3)6]3+ |
In [Co(NH3)6]Cl3, the coordination sphere is [Co(NH3)6]3+, where cobalt(III) is bonded to six ammonia ligands. The three chloride ions lie outside the brackets as outer-sphere counter ions and dissociate completely in aqueous solution.
Frequently asked questions
How is the coordination sphere different from counter ions?
The coordination sphere consists of the metal and ligands joined by coordinate covalent bonds; counter ions merely balance overall charge and are not bonded to the metal, so they separate from the complex in solution.
What determines the coordination number?
The coordination number equals the number of donor atoms from ligands that are directly bonded to the central metal within the coordination sphere.