Ligand

A ligand (Latin ligare = bind ) referred to in coordination chemistry ( organometallic chemistry, organometallic and Bioinorganic Chemistry ) an atom or molecule which is coordinated by a dative bond ( coordinate bond ) to a central metal ion. The coordinative bond comes about through the Lewis character of the binding partners involved: ligands are Lewis bases ( electron pair donors) and metal ions are Lewis acids ( electron pair acceptors ).

The specificity of the complex compound, and the difference for the covalent binding is that when the coordinate bond both the bonding electrons are provided by the ligand: a ligand must therefore have at least one lone pair of electrons include ( Lewis base ). Complex compounds are, for example, red prussiate of potash ( Kaliumhexacyanidoferrat (III) ), wherein the central iron ion of six ligands in this case is cyanide ions, surrounded.

Examples of Bioinorganic are the heme and chlorophyll: here act the four nitrogen atoms in the porphyrin skeleton as polydentate ligand for the central iron or magnesium ion.

The purely donative nature of ligand binding, however, is simplistic. Especially in heavy transition metal ions, the bonds are usually highly covalently ( see, e.g., hydrogen as a ligand). Also play back-bonding effects from the metal to ligand often a crucial role in binding strength ( binding energy ) ( see, eg, carbon monoxide as a ligand ).

Ligands are traditionally classified according to their charge: negatively charged ligands are used as X-type (abbreviated as halides ), while neutral bases are abbreviated as L- type ( eg phosphines ).

In the Organometallik and organometallic ligands have long been used to maintain active metal centers stable in solution and to prevent them from metallic colloids (or above: nanoparticles) to agglomerate. These soluble metal complexes can be optimized properties of the ligands to highly active catalysts ( = homogeneous catalysis ) by judicious choice of electronic and steric (steric hindrance).