A coordination complex or metal complex is a structure consisting of a central atom or ion, bonded to a surrounding array of molecules or anions (ligands, complexing agents). The atom within a ligand that is directly bonded to the central atom or ion is called the donor atom. Polydentate (multiple bonded) ligands can form a chelate complex. A ligand donates at least one pair of electrons to the central atom/ion. Compounds that contain a coordination complex are called coordination compounds. The central atom or ion, together with all ligands forms the coordination sphere.Coordination refers...

In order to explain the formulae and structures of the complex compounds or complexes, formed by transition metal salts with molecular species such as ammonia, Werner coined the terms primary valence and secondary valence.. These concepts remain valid today except that the term oxidation state has replaced 'primary valence' and the term coordination number has replaced 'secondary valence' Werner had recognized that a transition metal salt could form a complex compound in which the metal ion became bonded to a number of groups which need not necessarily be the counter anions originally present...

A coordination complex or metal complex is a structure consisting of a central atom or ion, bonded to a surrounding array of molecules or anions (ligands, complexing agents). The atom within a ligand that is directly bonded to the central atom or ion is called the donor atom. Polydentate (multiple bonded) ligands can form a chelate complex. A ligand donates at least one pair of electrons to the central atom/ion. Compounds that contain a coordination complex are called coordination compounds. The central atom or ion, together with all ligands forms the coordination sphere. Coordination refers...