Complexation Flashcards
How does lewis theory relate to complexation?
An acid will accept electrons, forming a covalent bond and a base will provide a pair of electrons by which the base coordinates with the acid
What are complexes?
Coordination compounds resulting from donor acceptor mechanisms or lewis base reactions between two or more chemical constituents
What kind of structural relationships hold complexes together?
Hydrogen bonding
Ion pairing
Van der waals forces other than those of full covalent blnds
What is host guest chemistry also known as?
Inclusion complex which involves the entrapment of one compound in the molecular framework of another
How are complexes largely classified?
On the structure and the nature of the acceptor
1) inclusion complex
2) metal ion complex
3) organic molecular complex
What is an inclusion complex?
One constituent of the complex is trapped in the open lattice or cage like crystal structure of the other
Formation depends on the architecture of molecules as opposed to chemical affinity
This is also known as host guest inclusion
What are the different types of inclusion complexes?
channel lattice type
layer type
Clathrates
Monomolecular complex- cyclodextrins
What is a channel lattice type complex?
A type of inclusion complex
Compounds can crystallise in a channel like structure which permits enclosure of non branched compounds.
Urea can form this structure, can be used in the separation of interfering compounds in drug analysis.
What is layer type complex?
A form of inclusion complex where the constituent is trapped between the layers of their lattice
E.g. Clay minerals like betonite can trap a wide range of compounds like alcohols and glycols.
Probably responsible for many incompatibilities of betonite with
drugs
However betonite salicylate complex could be used for gradual release
What are clathrates?
A type of inclusion complex where the compound crystallises in the form of a cage like lattice to trap guest molecules.
Chemical bonds are not important, only the molecular size of the guest molecule is important
E.g. Hydroquinone has a suitable cage size to trap CO2 or HCl
What is a monomolecular complex?
Form of inclusion complex which involves the entrapment of a single guest molecule in the cavity of one host molecule
The classic example is cyclodextrins,
This type of complex is used in air freshners and cosmetics
What are cyclodextrins?
A form of monomolecular, inclusion complex.
These are a family of compounds made up of sugar molecules bound together in a ring (cyclic oligosaccharides)
They typically contain 6-8 sugar units
What does a CD look like?
The ring is cylindrical and like a truncated cone
Has a large interior cavity that can hold guest molecules
The outer surface is hydrophilic, the internal surface of the cavity is non polar.
Why are cyclodextrins modified?
Natural ones are toxic to the kidney and are poorly water soluble.
Modification generates a wide range of molecular hosts which can tailor a CD host to a particular guest and meet specific requirements
Sulfobutylether-β-CD and hydroxypropyl-β-CD are well tolerated in humans and have no adverse effects
Why do cyclodextrins make good inclusion complexes.
They are able to form host guest complexes with lipophilic molecules given the nature imparted by their structure
Lipophilic molecules with appropriate size can be accommodated wholly or partially in the complex
It exhibits Reversible non covalent interactions between molecules
