Crowns Flashcards
What is a crown ether?
Any class of organic compound whose molecules are large rings containing a number of ether linkages
They are cyclic polyethers (ligands) which form stable complexes with G1 metals in solvent
What is a multidentate ligand?
A ligand which has two or more donor atoms which can bond to a central metal atom
What is a ligand?
A molecule or ion that can interact with a metal centre
Forms coordinate bonds
What do the numbers mean in crown names e.g 15- crown- 5
X is the number of atoms in the ring
Y is the number of oxygen atoms
Describe the basic structure of crown complexes
The metal ion sits in the ring centre
It interacts with lone pairs on the oxygen atoms
Why are crowns size selective?
They form the most stable complexes with metal ions that fit best in the ring
What happens to cavity size as ring increases?
As ring size increase, the cavity size increases so large metals are needed to form a stable complex
What is a cryptand?
This is another class of ligands and form more stable complexes than crown ethers
- less arrangement of ligand is needed to coordinate to the cation
- size selective
- stable in water
What do square brackets mean in cryptand names?
Number of oxygen atoms in bridges between N
Describe the trend between bridge length and cavity size in cryptands
Increasing bridge length increases cavity size
What is k and what do the values mean?
K is the binding constant
Large values of k mean strong binding- this means the metal matches the size of the cavity
Small values of k mean weak binding
What happens if the metal is larger than the cavity?
It doesn’t fit effectively and k is smaller
What happens if the metal is smaller than the cavity
It cannot effectively interact with oxygen lone pairs and so k is small
