you will get basic information about crown ethers and inclusion compounds

1. Crown Ethers and Inclusion
Compounds
SUPERVISED BY PRESENTED BY
Prof. Asmita Gajbhiye Deepa Parwani
Roll no Y18254013
DEPARTMENT OF PHARMACEUTICAL SCIENCES
Dr. Harisingh Gour Central University, Sagar (M.P.)

2. Crown Ether
Crown ethers are large-ring compounds that contain several
oxygen atoms, usually in a regular pattern.
These compounds have the property of forming complexes
with positive ions, generally metallic ions or ammonium
and substituted ammonium ions.
 Examples of crown ethers
• 12-crown-4
• Dicyclohexano-18-crown-6 etc.
18-crown-6

3. 12-crown-4
OO
O O
Where 12 is the size of the ring and 4 represents the
number of coordinating atoms, here oxygen

4. Dicyclohexano-18-crown-6
O
O
O
O
O
O
Where 18 is size of the ring and 6 represents the number
of coordinating atoms.

5.  The crown ether is called host and the ion is the guest.
 In most cases, the ion are held tightly in the center of the
cavity.
 Each crown ether binds different ions, depending on the
size of the cavity.
For example
18-crown-6 coordinating a potassium ion and 12-crown-4
binds lithium ion

6. Utility of Crown Ethers
 Utility of crown ethers in separating mixtures of cations.
(The high degree of selectivity enables the crown
compounds to identify the guest atom in a solution and
wrap around it)
 Crown ethers are widely used in organic synthesis.
 Crown ethers are useful in phase transfer catalysis.
 Crown ethers are most frequently used to complex
cations, amines, phenol etc.

7. Cryptates
Bicyclic molecules can surround the enclosed ion in 3D,
binding it even more tightly than the monocyclic crown
ethers.
Bicyclics and cycles of higher order are called cryptands
and the complexes formed are called cryptates.
Cryptands (from the greek ‘kryptos’ meaning “hidden”)
are compounds that can completely surround a cation
with lone pairs of electrons on oxygen and nitrogen
atoms.
The number of in the name of cryptand is the number of
oxygen atoms in each strand of the molecule.

8. Cont…
For example
The potassium complex of 2,2,2,-cryptand, showing how
the cation is almost hidden by the cryptand

9. Bonding in crown ether complexes is the result of ion-
dipole attractions between the heteroatom and the
positive ions.
The parameters of the host-guest interactions can
sometime be measured by NMR.
It has been implied that the ability of these host
molecule to bind guests is often very specific, often
linked to the hydrogen bonding ability of the host,
enabling the host to pull just one molecule or ion out of
a mixture.
This is called molecular recognition.

10. In this, the host forms a crystal lattice that has spaces
large enough for the guest to fit into.
Vander waals forces constitute the only bonding between
the host and guest.
 Types
(depending on the shape of the space)
 Long tunnels or channels
 Clathrate or cage compounds

11. Cont….
In both types, the guest molecule must fit into the space
and guests that are too large or too small will not go into
the lattice.
Example
• Hydrogen sulfide forms hexagonal clathrate cages, and a
guest molecule is pinacolone

12. Cyclodextrins
• There is one type of host that can form both channel and
cage complexes, this type is called cyclodextrins or
cycloamyloses.
• The host molecules are made up of six, seven or eight
glucose units connected in a large ring, called
respectively alpha, beta or gamma cyclodextrin.
• As expected for carbohydrate molecules, all of them are
soluble in water.

13. Since the cavities of the three cyclodextrins are
of different sizes, a large variety of guests can
be accommodated.

14. The cyclodextrins also form channel-type
complexes.

15. Applications of inclusion compounds
 Since cyclodextrins are non toxic (they are actually
small starch molecules), they are now used industrially
to encapsulate foods and drugs.
 Zeolites are three dimensional, microporous, crystalline
solids with well defined structures that contain
aluminium, silicon and oxygen in their regular
framework , which is used as ion exchangers to convert
hard water to soft water.