Coordination Compound
Definition and meaning of Coordination Compound in chemistry.
A coordination compound is a chemical species containing a central metal atom or ion bonded to a surrounding set of molecules or ions, called ligands, through coordinate covalent bonds.
In more detail
Each ligand donates a lone electron pair to an empty orbital on the metal, forming a complex ion or neutral molecule with a specific coordination number (commonly 4 or 6) and geometry, such as tetrahedral, square planar, or octahedral. The number and arrangement of ligands, governed by crystal field and ligand field theory, determine the compound's color, magnetism, and reactivity, which often differ sharply from those of the free metal ion. Coordination compounds are essential in biology (hemoglobin, chlorophyll, vitamin B12), industrial catalysis, and analytical chemistry, where chelating ligands are used in titrations like EDTA complexometry.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Example formula | [Co(NH3)6]Cl3 |
| Typical coordination numbers | 4 and 6 |
| Bond type | Coordinate (dative) covalent bonds |
In [Co(NH3)6]Cl3, hexaamminecobalt(III) chloride, six ammonia molecules act as ligands coordinated octahedrally to the central Co3+ ion, while the three chloride ions remain as separate counter-ions in the crystal lattice and dissociate freely in water.
Frequently asked questions
How is a coordination compound different from a double salt?
In a coordination compound, the ligands stay bonded to the metal even when dissolved in water, so the complex ion retains its identity; a double salt like potassium alum fully dissociates into its simple constituent ions in solution.
What is a ligand?
A ligand is a molecule or ion, such as NH3, H2O, Cl-, or CN-, that has at least one lone electron pair it can donate to a central metal atom or ion to form a coordinate bond.