. Definition of important terms pertaining to co-ordination compounds . . Coordination entity: Coordination entity is an ion or a neutral molecule, composed of a central atom, usually a metal and the array of other atoms or groups of atoms (ligands) that are attached to it.
In the formula, the coordination entity is enclosed in square brackets. For example, in potassium ferrocyanide, K [Fe(CN) ], the coordination entity is [Fe(CN) ] - . In nickel tetracarbonyl, the coordination entity is [Ni(CO) ]. .
. Central atom/ion: The central atom/ion is the one that occupies the central position in a coordination entity and binds other atoms or groups of atoms (ligands) to itself, through a coordinate XII U5 Coordination XII U5 Coordination - - - - covalent bond. For example, in K [Fe(CN) ], the central metal ion is Fe + . In the coordination entity [Fe(CN) ] - , the Fe + accepts an electron pair from each ligand, CN - and thereby forming six coordinate covalent bonds with them.
since, the central metal ion has an ability to accept electron pairs, it is referred to as a Lewis acid. . . Ligands: The ligands are the atoms or groups of atoms bound to the central atom/ion.
The atom in a ligand that is bound directly to the central metal atom is known as a donor atom. For example, in K [Fe(CN) ], the ligand is CN - ion, but the donor atom is carbon and in [Co(NH ) ]Cl the ligand is NH molecule and the donor atom is nitrogen. Coordination sphere: The complex ion of the coordination compound containing the central metal atom/ion and the ligands attached to it, is collectively called coordination sphere and are usually enclosed in square brackets with the net charge. The other ionisable ions, are written outside the bracket are called counter ions.
For example, the coordination compound K [Fe(CN) ] contains the complex ion [Fe(CN) ] - and is referred as