Module 6

Question 1

how can elements with the same electronic configuration still vary

Answer 1

different ml values

different spins

Question 2

what are microstates

Answer 2

different arrangements of electrons with a electronic configuration

Question 3

how is the energy of a microstate determined

Answer 3

how angular momentum of electrons couple

Question 4

what coupling scheme is used for Ln elements

Answer 4

Russell-Saunders coupling scheme

Question 5

what assumptions are made in the Russell-Saunders coupling scheme

Answer 5

interactions are sized in this order

spin spin>orbital orbital> spin orbital

Question 6

what rules are used to determine term symbolys

Answer 6

hunds rules

Question 7

how can the ground state term symbol be determines

Answer 7

has Max S
If more than 1 L term has max S then max L
if shell less than 1/2 full J=L-S
If shell is more than half full J = L+S

Question 8

what is the template of a term symbol

Answer 8

(2S+1) X J

Question 9

why are crystal field splittings much smaller for Ln than TM

Answer 9

4f is not involved in bonding

Question 10

why do Ln have weak absorbtions

Answer 10

f-f transitions are lapoorte forbidden

Question 11

why are Ln absorbtions sharp

Answer 11

no spectral broadening

Question 12

when elements is charge transfer particularly common for

Answer 12

Eu3+ and Yb3+ as they are easily reduced

Question 13

what is luminescene

Answer 13

when an excited state can decay by emission of a photon

Question 14

in what state does most Ln luminescence occur

Answer 14

solid state

Question 15

what are the 3 Ln that luminesce in solution

Answer 15

Eu3+, Tb3+, Yb3+

Question 16

what must be true about the emission energy level

Answer 16

must be greater an absorbtion energy level

Question 17

what Ln emit IR

Answer 17

Pr3+, Nd3+, Er3+ Yb3+

Question 18

what Ln emit visible light and what colour

Answer 18

Eu3+ (red)

Tb3+ (green)

Question 19

what Ln emit UV

Answer 19

Gd3+

Question 20

how can efficacy of excitation be increased

Answer 20

sensitisation - antenna effect

Question 21

how does the antenna effect work

Answer 21

singlet state of ligand is excited
intersystem crossing to triplet state
energy tranfer to Ln ion
emmission

Question 22

what must be true about the ligand triplet state in the antenna effect

Answer 22

must have higher energy than Ln

Question 23

what are the 4 un productive pathways in the antenna effect

Answer 23

fluorescence of ligand singlet state
phosphorescence of ligand triplet state
back transfer from Ln to ligand
non radiative deexcitation

Question 24

give examples of good ligands for the antenna effect

Answer 24

beta-diketonates
polypyridines
delocalised pi systems

Question 25

give an example of betaketonate antenna ligand

Answer 25

dbm diphenyl-betaketonate

Question 26

what is dbm not a good antenna ligand doe Tb3+

Answer 26

triplet state too low in energy

Question 27

what effect does coordinated water have on luminescence

Answer 27

non-radiative deexcitation

Question 28

how does the amount of quenching of luminescene change if D2O is used instead of water

Answer 28

decreases

Question 29

how can the number of complexed waters to Eu be calculated

Answer 29

more h2o = less luminescence can plot difference between h2o and d2o effect increases with more waters

Question 30

give 2 examples of applications of Ln luminescence

Answer 30

euro note - Eu(Bketonate) | Neodinium laser

Question 31

what property does a neodinium laser need to work

Answer 31

needs higher population in emissive state than ground sate

Question 32

how does a neodinium laser work

Answer 32

excited with red light to excited state non radiative decay to metastable state intense decay to terminal state non radiative decay to ground state

Question 33

how can Eu2+ luminescence be tuned

Answer 33

depending on ligands bound 4f6d1 config CF split changes energy of d1

Question 34

why is orbital angular momentum not quenched

Answer 34

f electrons are degenerate - no CF split electrons can move between orbitals creates current and electric field

Question 35

what formula is used to calculated the magentic moment

Answer 35

free ion formula

Question 36

what is the free ion formula

Answer 36

ueff=gJ = root(J(J+1)

Question 37

how well go observed moments match calculated moments

Answer 37

well apart from for Sm3+ and Eu3+

Question 38

why do calculated moments not match well of Sm3+ and Eu3+

Answer 38

have low lying excited states which are easily populated at RT

Question 39

how does magnetic refrigeration work

Answer 39

without a magentic field moments are unaligned | when a field is applied the align - decrease in entropy and increase in T. when field is removed it will cool

Question 40

what is the effect of paramagnetism on NMR spectra

Answer 40

nuclei experience magnetic field from paramagnet and NMR magnet gives very different spectrum

Question 41

when does paramagnetic shifting occur

Answer 41

when complex has low symmetry (anisotropic magnetic susceptability) pseudo contact shifting

Question 42

what are NMR peaks for Gd3+ and Eu2+ like and why

Answer 42

broad but unshifted | very spherical

Question 43

what are chiral lanthanoid reagents used for

Answer 43

to determine the enantiomeric excess of mixtures of chiral compounds

Question 44

how do chiral lanthanoid reagents work

Answer 44

chiral Bketonate ligands form adducts with lewis bases - forms diastereoisomers with different NMR spectra and potentially different pseudocontact shifting

Question 45

how does MRI work

Answer 45

body is 60 water image is built up of NMR of H2O resonances short relaxation time shows brightly contrast can be enhanced by a contrast agent

Question 46

what are the requirements for a contrast agent

Answer 46

must effect relaxation time but not chemical shift must be soluble and kinetically inert at body pH low osmotic effect (ion pair = 2) must under go rapid exchange of coordinated H2O with bulk

Question 47

what Ln makes a good contast agent

Answer 47

Gd3+

Question 48

what is the formula for relaxivity

Answer 48

^(1/T)/[contrast agent]

Question 49

how is relaxation cause

Answer 49

local field oscillating at Wo (larmor freq)

Question 50

what are the factors effecting relaxivity

Answer 50

``` rate of exchange of coordinated H2O No. coordinated h2o distance between H2o and Gd3+ dependence on external field rate of molecular tumbling ```

Question 51

which Gd3+ ligands have low osmotic value and why

Answer 51

ligands with 3- charge - no counterions needed