What Is A Coordination Compound?

A coordination complex is the product of a Lewis acid-base reaction in which neutral molecules or anions (called ligands) bond to a central metal atom (or ion) by coordinate covalent bonds.

Coordination compounds and complexes are distinct chemical species - their properties and behavior are different from the metal atom/ion and ligands from which they are composed.

The coordination sphere of a coordination compound or complex consists of the central metal atom/ion plus its attached ligands. The coordination sphere is usually enclosed in brackets when written in a formula.

The coordination number is the number of donor atoms bonded to the central metal atom/ion.

Some Coordination Complexes
example molecular formula Lewis base/ligand Lewis acid donor atom coordination number
[Ag(NH3)2]+ NH3 Ag+ N 2
[Zn(CN)4]2- CN- Zn2+ C 4
[Ni(CN)4]2- CN- Ni2+ C 4
[PtCl6]2- Cl- Pt4+ Cl 6
[Ni(NH3)6]2+ NH3 Ni2+ N 6