Chemistry INTRODUCTION TO COORDINATION COMPOUNDS
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INTRODUCTION TO COORDINATION COMPOUNDS

Double Salts and Co-ordination Compound :

When solutions of two or more stable compounds are mixed in stoichiometric (simple molecular) proportions new crystalline compounds called molecular or addition compounds are formed. These are of two types :



(a) `text(Double Salts)` : Addition compounds stable in solid state. Dissociate into ions in aqueous solution as such give test for each constituent ion. Examples:


(b) `text(Co-ordination or Complex compounds)` : Addition compound, stable in solid state. Retain their identity even in solution. Central metal ion form dative or coordinate bond with the species surrounding it (ligands). Examples :

Terminology of co-ordination compounds :

(a) `text(Central metal atom or ion)` : A complex ion contains a metal atom or ion known as the central metal atom or ion. It is sometimes also called a nuclear atom.

(b) `text(Complex ion)` : It is an electrically charged radical which is formed by the combination of a simple cation with one or more neutral molecules or simple anions or in some cases positive groups also.

(c) `text(Ligands)` : Neutral molecules or ions that attach to central metal ion are called ligands. The donor atom associated with the ligands supplies lone pair of electrons to the central metal atom (forming dative bond) may be one or two more. Monodentate (one donor atom), bidentate (two donor atom), tridenatate (three donor atom) etc.

(d) `text(Co-ordination Sphere)` : Ligand with central metal ion is kept in square bracket `[` `]` retains its identity in the same form is called co-ordination sphere (non-ionisable).

(e) `text(Co-ordination Number)` : Number of monodentate ligands attached to central atom/ ion are called coordination number of the central metal atom/ion.

(f) `text(Ionisation Sphere)` : The part present out side of the square bracket is called ionization sphere (ionisable).

(g) `text(Oxidation state)` : It is number which represents the electric charge on the central metal atom of a complex ion.

(h) `text(Charge on the complex ion)` : It is the algebraic sum of the total charge of the ligands and central metal ion.

Anionic Ligands (Negative legands) :

 
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