Porous organic cages Flashcards
Describe porous organic cages
1) have an INTERNAL void
2) windows to allow guest access
3) rigid structure to prevent collapse
4) can be porous to gases and small molecules when packed in the solid state
5) pore channels
List other porous materials which aren’t cages
why aren’t they cages?
activated carbon, zeolites, MOFs, COFs (covalent w/o metals), CMPs (conjugated microporous), PIMs (polymers of intrinsic porosity)
lack the strong bonding to maintain porosity after solvents have been removed
which of the non-cage materials are not soluble?
MOFs, COFs, hyper-crosslinked polymers (styrene), CMPs - all are extended structures
which of the non-cage materials are soluble?
PIMs (polymers of intrinsic porosity) are soluble but don’t contain internal void space, only extrinsic property so ARE NOT cages
what are micro/meso/macro porous values?
micro = <2nm
meso = 2-5 nm
macro = >50nm
give an example of an extrinsic property
porous molecules with hydrogen bonded networks - rigid and pack together with space inbetween them = porosity
the spaces (pore channels) are outside the molecule not in it so they dont count as cages
what does a material need to be porous?
permanent interconnected voids that are permeable to gases or liquids
how are the polymers for porous organic cages formed?
condensation reaction between aldehyde and amine to form imine, another aldehyde added to the other end of the imine
forms a hyperbranched imine polymer with both amine and aldehyde end groups
forms a cage linked with imine bonds
What changes the properties of porous organic cages?
changing the imine bridge structure modifies the crystal packing and gas uptake
how are cages made instead of just polymer?
1) needs increased reversibility (from acid catalyst) gives good yield without by-products so the cages self-assemble
2) high temperature, long reaction, and high dilution time to encourage intramolecular reaction rather than inter (between molecules)
3) a rigid diamine directs to a cage shape rather than a flexible diamine
How does the angle of the linkers direct to the cage size and shape?
narrower angle = smaller cage, wider = larger cage
What can cause cage collapse?
a lack of steric hindrance and narrow angles - the cage collapses to fill the void space
What is the difference between topology and geometry?
topology = the shape determined from the number of edges and corners for example
geometry = the visual shape
How do you label the topologies/stoichiometries/linkers for cages?
X^m_p Y^n
X and Y are the connectivities of each linker (1&2) e.g. di, tri, tet
m and n are the number of each molecule in the cage
p is the number of double connections
ALWAYS START WITH THE HIGHEST NO. FOR X
What can form extra second pore channels outside the cages?
Meor other external groups can push the cages further apart enough to form a second pore channel
