Complexes are formed when ligands bond to a central metal atom through coordinate covalent bonds. Coordination complexes result from a Lewis acid-base reaction between ligands, which donate electron pairs, and metal ions, which accept them. There are several types of complexes including inorganic complexes based on primary and secondary valency and coordination number, and organic complexes such as chelates, charge transfer complexes, and inclusion complexes where one molecule is trapped within the crystal structure of another. Coordination complexes feature a central metal ion surrounded by ligands in a fixed coordination number.

2. Complexes:-
A species of definite substrate to ligand stoichiometry
formed in an equilibrium process in solution, but can
also exist in solid state is termed as COMPLEX.
=
A A A A

3. Coordinate complexes:-
A coordination complex is the product of a Lewis
acid-base reaction in which neutral molecules or
anions (called ligands) bond to a central metal
atom (or ion) by coordinate covalent bonds.
•LIGANDS are Lewis bases - they contain at least
one pair of electrons to donate to a metal
atom/ion. Ligands are also called complexing
agents.
•METAL IONS are Lewis acids - they can accept
pairs of electrons from Lewis bases.

5. Fig. 1: Metal complex

7. Classification :-

8. 1.Metal ion complex:
A metal ion surrounded by few other molecules or
ions is centrally located in the complex ion. These
surrounding molecules are called as ligands which
are linked to central atom by CO-ORDINATE
BONDS.

9. A. INORGANIC TYPE:

10. ✓ 1° (primary) valency
✓ 2° (secondary) valency
✓ Co-ordination number

11. Werner’s postulates:-
1. There are two types of valencies:
a. Primary valency
b. Secondary valency
1. Some anions ,radicals, or molecules are held
by one or both types of valencies .
2. Each central atom or ion has a fixed number
of non - ionic valencies ; this is Co-ordination
number.

12. B. CHELATES TYPE :-
•Ethylene di amine
•EDTA
Chelate is a compound which results
when cations reacts with organic
compounds to form a complex ring like
structure.

13. ..
..

14. C. OLEFIN TYPE:-

15. D. AROMATIC TYPE:-
✓ π - bond complexes:

16. ✓ Sigma bond complexes:-

17. ✓ Sandwich complexes:-

18. 2. ORGANIC MOLECULAR COMPLEX:-
Organic molecular complexes are formed by two organic
molecules linked via either electrostatic forces or hydrogen
bonds.

19. A. CHARGE TRANSFER COMPLEX:-
These complexes are formed by the sharing of π- electrons
. One of the constituent molecule of the complex polarises
the other resulting in a type of ionic interaction or charge
transfer.

20. B. QUINHYDRONE COMPLEX:-
These molecular complexes are formed between the
equimolar quantities of alcoholic solutions of
hydroquinone or benzoquinone where quinhydrone
complexes settle down.

21. C. PICRIC ACID COMPLEX:-
The molecular complexes are formed between
picric acid (2,4,6- trinitrophenol) and the
polynuclear aromatic compounds.

22. D. HYDROGEN BOND COMPLEX:-

23. E. CAFFINE DRUG COMPLEX:-
These are the complexes formed between acidic drugs and
CAFFINE .

24. F. POLYMER COMPLEX :-
Polythene glycol , polystyrene
,PVC like structures are polymeric
materials which complexes with
large number of drug materials to
form polymer complexes.

25. 3.INCLUSION OR OCCLUSION COMPLEXES:
Also known as occlusion complexes which have one of the
components trapped in open lattice or cage like crystal
structure of other .
A.CHANNEL -LATTICE COMPLEX:-
Guest
Host

26. B. LAYER TYPE:-

27. C. CLATHRATES:-

28. D. MONOMOLECULAR INCLUSION COMPLEX:-

29. E. MACROMOLECULAR COMPLEX:-