Types of Ligands and Complexes

When a metal ion is present in aqueous solutions, there is frequently a rather definite number of water molecules that are attached to the ion in a specific geometrical 

Ethylenediamine has two electron donor atoms, so it attaches at two points in the coordination sphere of the metal, and it is referred to as a bidentate ligand. The molecule known as triethylenediamine, H2NCH2CH2NHCH2CH2NH2, contains three electron pair donor atoms (the nitrogen atoms), so it normally attaches at three points in the coordination sphere of the metal, and it functions as a tridentate ligand. The anion of ethylenediaminetetraacetic acid (written as EDTA4-) has the structure 

By utilizing four O atoms and two N atoms, the ethylenediaminetetraacetate ion can bind to six sites around a metal ion and is therefore a hexadentate ligand. 

As has been mentioned, a very large number of molecules and ions are potential ligands. Table 19.1 lists a few of the molecules and ions that form some of the most frequently encountered complexes. Because some ligands take on names in complexes that are 

Ammine Aqua Chloro Cyano Hydroxo Carbonato Thiocyanato Nitrito or Nitro Oxalato Carbonyl Ethylenediamine 

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