single toothed. Ligands that donate two, three, four, five, or six lone pairs of electrons are collectively referred to as polydentate, and bidentate, tridentate, tetradentate, pentadentate, and sexadentate respectively. Polydentate ligands typically form five- and six-membered rings and are referred to as chelating agents and the complex is referred to as chelate. Chelate comes from the Greek chela meaning claw.
The number of coordinate covalent bonds formed typically ranges from two to eight depending on the charge, size, and electron configuration of the transition metal atom or ion. The coordination number may also be as low as 1 and as high as 12. The number of ligands attached to the central metal atom or ion, the number of coordinate covalent bonds, is the coordination number, (CN); with two, four and six the most common coordination numbers. The coordination sphere is the number of coordinate covalent bonds plus the number of central metal atoms or ions, often the coordination sphere is one more than the coordination number.
Simplified IUPAC Rules for Naming Coordination Compounds:
Cations are always named before the anions.
Ligands are named before the metal atom or ion.
Ligand names are modified with an -o added to the root name of an anion. For neutral ligands the name of the molecule is used, with the exception of OH2, NH3, CO and NO. Names of common neutral ligands are listed in Table 1, and common anionic ligands are listed in Table 2.
ethylenediamine or en
diethylenetriamine or dien
triethylenetetraamine or trien
1,10-phenanthroline or phen
pyrdidine or py
2,2′-bipyridine or bipy
2,2′,6′,2′′terpyridine or terpy
bis(diphenylphosphine) ethylene or dppe
bis(dimethylphosphino) ethylene or dmpe