A coordination entity is composed of a central atom, usually that of a
metal, to which is attached a surrounding array of other atoms or group
of atoms, each of which is called a ligand. A coordination entity may
be a neutral molecule, a cation or an anion. The ligands may be viewed
as neutral or ionic entities that are bonded to an appropriately
charged central atom. It is standard practice to think of the ligand
atoms that are directly attached to the central atom as defining a
coordination polyhedron (tetrahedron, square plane, octahedron, etc.)
about the central atom. The coordination number is defined as being
equal to the number of sigma-bonds between ligands and the central
atom; this definition is not necessarily appropriate in all areas of
(coordination) chemistry. In a coordination formula, the central atom
is listed first. The formally anionic ligands appear next and they are
listed in alphabetic order according to the first symbols of their
formula. The neutral ligands follow, also in alphabetical order,
according to the same principle. The formula for the entire
coordination entity, whether charged or not, is enclosed in square
brackets. In a coordination name, the ligands are listed in
alphabetical order, without regard to charge, before the name of the
central atom. Numerical prefixes indicating the number of ligands are
not considered in determining that order. All anionic coordination
entities take the ending -ate, whereas no distinguishing termination is
used for cationic or neutral coordination entities.
The term "coordination" was found in the following pages: