Co-ordination compounds exhibit colour, attributed to the crystal field theory, corresponding to the d-d transition of elements.
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.
- Ligands are Lewis bases that are also called complexing agents – they contain at least one pair of electrons to donate to a metal atom/ion.
- Metal atoms/ions are Lewis acids – they can accept pairs of electrons from Lewis bases.
- The atom that is directly bonded to the metal atom/ion within the ligand is called the donor atom.
- A coordinate covalent bond is a covalent bond in which one atom (i.e., the donor atom) supplies both electrons. This type of bonding is different from a normal covalent bond in which each atom supplies one electron.
- If the coordination complex carries a net charge, the complex is called a complex ion.
- Compounds that contain a coordination complex are called coordination compounds.