Definitions of some important terms pertaining to Coordination Compounds Preparation and Properties

Definitions of some important terms Pertaining to Coordination Compounds :

→ Central lon: (Centre of Coordination)

The cation to which one or more neutral molecules or anions are attached is called as centre of coordination.
Since the central ion acts as an acceptor and thus has to accommodate electron pairs donated by the donor atom of the ligands, it must have empty orbitals.
This explains why the transition metals having empty d-orbitals form coordination compounds very readily.
In the complexes [Ni(NH₃)₆]²⁺ and [Fe(CN)₆]^3-Ni²⁺ and Fe³⁺ respectively are the central ions.

→ Ligand :

The neutral molecules, anions or cations which are directly linked with the central metal atom or ion in a complex ion are called ligands. For example, in [COCI(NH₃)₅]²⁺ ligand is NH₃, central ion is Co³⁺.
Ligand donates a pair of electrons to the central atom.
Ligands are attached to the central metal ion or atom through coordinate bonds or dative linkage.
Ligands are normally polar molecules like NH₃; H₂O: or anions much as Cl^–, OH^–, CN^– etc.
which contain atleast one unshared pair of electrons.
With few exceptions, free ligands have lone pair of electrons that is not engaged in bonding. For example : C ≡ N:^–, :CE:^–
Ligands may be called as Lewis base and central ion as Lewis acid.