Page "Coordination complex" Paragraph 8

The ions or molecules surrounding the central atom are called ligands.

Ligands are generally bound to the central atom by a coordinate covalent bond ( donating electrons from a lone electron pair into an empty metal orbital ), and are said to be coordinated to the atom.

There are also organic ligands such as alkenes whose pi bonds can coordinate to empty metal orbitals.

An example is ethene in the complex known as Zeise's salt, K < sup >+</ sup >< sup >-</ sup >.