advanced coordination chemistry Flashcards
how to name crown ethers and explain the arrangement of [12]crown-4
first number = number of atoms in the ring
second number = number of oxygen donors
[12]crown-4
8 carbon atoms + 4 oxygen donors
explain the solubility of crowns
they are soluble in all common solvents
if there was a mixture of water and ethanol the crown will dissolve into each equally due to change in conformation thus being hydrophilic and lipophilic to the solvent
what are coronand complexes
coronand complex is a crown ether coordinated with an alkali metal
why do the first five crowns have a binding preference to K+
because the number of donor groups increases with ring size, therefore there is an increase in enthalpy due to more coordination interactions
the larger cavity can accommodate K+ better as its a bigger ion and has more coordination sites
what’s the difference between crowns and podands
podands are acyclic polyether analogues of a crown (the cycle is open)
podands have much lower binding affinity to metal ions due to Macrocylic effects
what are cryptands
Cryptands are crowns with a bridge across the middle. naming is just the number of donor groups
whats preorganisation
it enhances binding by minimizing the organisation cost for optimal conformation needed to bind to the guest.
difference between cryptands and crowns
cryptands have higher binding affinity due to their increased affinities and they have a large preorganisation component
why do cryptands selectively bind to specific metal ions?
cryptands cannot flex around ions that are too small for their cavity and they cannot expand for larger ions
what are spherands
the most rigid macrocycle where there is a binding pocket where donor groups were held closely in the correct geometry for metal binding
the most preorganised hosts
what is magnetic susceptibility and the equation for it
is a quantitative measure of the intensity of the magnetic dipole
fancy X = M/H
where M=magnetization and H=magnetic field
what is the equation for molar susceptibility
fancy Xmol = k x Mr/10^3
where k is mass susceptibility (fancy X/density)
what is the equation for the effective magnetic moment
µeff = sqr(n(n +1))
n= number of unpaired electrons
what is diamagnetism and paramagnetism
Diamagnetism - material that generates a weak magnetic field in the opposite direction when exposed to an external magnetic field. M is less than H. fancy X is negative and the material is repelled by a magnet.
material with paired electrons are diamagnetic
paramagnetism - materials that are weakly attracted to an external magnetic field. M is more than H, then fancy X is positive.
only materials with unpaired electrons are para
how are susceptibilities measured
the Gouy balance
consists of an accurate balance and a powerful magnet.
1. sample is measured in the magnetic field and outside it
2. difference in weight is the force the field exerts on the sample
3. the F is compared to known Xmol
4. so Xmol can be obtained for unknown sample
how does temperature affect paramagnetic dipoles
magnetic dipoles tend to align and order themselves in a preferred direction, leading to a stronger overall magnetic effect. As the temperature increases, thermal energy disrupts this alignment, causing the magnetic dipoles to become more randomized and less ordered
what is Curie law
magnetic susceptibility (χ) of a paramagnetic material is directly proportional to the reciprocal of the absolute temperature (T).
what is Antiferromagnetism
In an antiferromagnetic material, neighboring magnetic moments align in opposite directions, resulting in a net magnetization of zero. This occurs due to strong exchange interactions between adjacent magnetic atoms or ions.
how does temperature affect antiferromagnetism
When the temperature rises to the Neel temp the magnetic ordering becomes randomized
explain what ferromagnetism is
exhibit a permanent magnetic moment, magnetic moments align spontaneously in the same direction, creating a strong net magnetization
what is coercivity and hysteresis
coercivity - the ability to resist changes induced by the magnetic field
hysteresis - exhibiting a delay in magnetization changes and a memory of its previous magnetic state.
how do charge transfer salt magnets work
anions and cations are small so they can stack close together in the solid state. close enough for spin interactions.
what are lanthanides
are rare earth metals and in the bottom of the periodic table
why are some lanthanide alloys have very strong magnetic properties
- large number of unpaired f-electrons
- very high coercivity
what is the most stable oxidation state for lanthanides
3+ oxidation state
explain the relationship between lanthanides and ligand orbitals
- there is no overlap between 4f orbital and ligand orbital
this means ligands pack around metal cations to minimise steric interactions.
what does the decreasing radius across the group cause for Ln3+
- increases bond strength due to higher charge density
- reduce coordination number with smaller/heavier ion
what are J values
a combination of L (angular momentum) and S (spin angular momentum)
explain the energy term symbol 3^H6
S = 1 due to 2S+1
L = 5
J = 6
explain the difference between f-f and d-d absorption spectra
f-f transition is narrow due to having no interaction with the ligand so its fixed.
d-d transition are broad because of ligand vibration.
how does luminescence occur in lanthanides
emission of photons is the only way.
big energy gap = strong luminescence
how to photoexcite Ln3+
- absorption to give singlet excited state of ligand
- intersystem to give ligand-ligand triplet excited state
- energy transfer from ligand to f-f excited state
- emission from lanthanide excited state to various components of the ground state
what is the Nernst equation
E(bound) - E(free) = RT/nF x ln(K(red)/K(Ox))
E = cell potentials
R = Gas constant
T = Temperature
n = number of moles of electrons transferred
F = faradays constant (96485 C/mol)
K =
what are the best metals to bind to the corresponding macrocycles in general
spherand
cryptand
corand
podand
- spherand binds best with Li+
- cryptand binds best with Na+ (selectively binds)
- corand binds best with K+
- podand is shite
