Ligand

In chemistry, a ligand is an atom, ion or functional group that is bonded to one or more central (usually metal) ion(s) forming a complex.

The central atom or group of atoms will have a positive charge, and the ligands will bond by compensating that charge with their own negative charge or characteristics. As the central atom has a specific charge, it has a maximum potential number of ligands (as each must donate at least one electron into the charge compensation equation) that it can bond to. These ligands will also arrange themselves into a certain arrangement around the central atom. If a single ligand bonds to more than one of these bonding sites on the central atom, then it is said to be bidentate (three=tridentate, etc)

Ligand arrangements

These are named and described as if the central atom is in the middle of a polyhedron, and the corners of that shape are the locations of the ligands. For example, a complex with four, regularly distributed ligands would be described as tetrahedral.

Aside from the regular polyhedra, there are special descriptions, such as pyramidal (four ligands equally distributed in a plane, and one ligand normal to this plane).

Common ligands

• F^-
• Cl^-
• Br^-
• I^-
• CO
• RC:CR - compounds with double carbon bonds
• Benzene
• Cryptates?
• [Crown ethers]?
• OH^-

/Talk?