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CHEM411 > Module 6 > Flashcards

Module 6 Flashcards

1
Q

how can elements with the same electronic configuration still vary

A

different ml values

different spins

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2
Q

what are microstates

A

different arrangements of electrons with a electronic configuration

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3
Q

how is the energy of a microstate determined

A

how angular momentum of electrons couple

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4
Q

what coupling scheme is used for Ln elements

A

Russell-Saunders coupling scheme

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5
Q

what assumptions are made in the Russell-Saunders coupling scheme

A

interactions are sized in this order

spin spin>orbital orbital> spin orbital

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6
Q

what rules are used to determine term symbolys

A

hunds rules

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7
Q

how can the ground state term symbol be determines

A

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

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8
Q

what is the template of a term symbol

A

(2S+1) X J

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9
Q

why are crystal field splittings much smaller for Ln than TM

A

4f is not involved in bonding

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10
Q

why do Ln have weak absorbtions

A

f-f transitions are lapoorte forbidden

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11
Q

why are Ln absorbtions sharp

A

no spectral broadening

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12
Q

when elements is charge transfer particularly common for

A

Eu3+ and Yb3+ as they are easily reduced

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13
Q

what is luminescene

A

when an excited state can decay by emission of a photon

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14
Q

in what state does most Ln luminescence occur

A

solid state

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15
Q

what are the 3 Ln that luminesce in solution

A

Eu3+, Tb3+, Yb3+

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16
Q

what must be true about the emission energy level

A

must be greater an absorbtion energy level

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17
Q

what Ln emit IR

A

Pr3+, Nd3+, Er3+ Yb3+

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18
Q

what Ln emit visible light and what colour

A

Eu3+ (red)

Tb3+ (green)

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19
Q

what Ln emit UV

A

Gd3+

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20
Q

how can efficacy of excitation be increased

A

sensitisation - antenna effect

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21
Q

how does the antenna effect work

A

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

22
Q

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

A

must have higher energy than Ln

23
Q

what are the 4 un productive pathways in the antenna effect

A

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

24
Q

give examples of good ligands for the antenna effect

A

beta-diketonates
polypyridines
delocalised pi systems

25
Q

give an example of betaketonate antenna ligand

A

dbm diphenyl-betaketonate

26
Q

what is dbm not a good antenna ligand doe Tb3+

A

triplet state too low in energy

27
Q

what effect does coordinated water have on luminescence

A

non-radiative deexcitation

28
Q

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

A

decreases

29
Q

how can the number of complexed waters to Eu be calculated

A

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

30
Q

give 2 examples of applications of Ln luminescence

A

euro note - Eu(Bketonate)

Neodinium laser

31
Q

what property does a neodinium laser need to work

A

needs higher population in emissive state than ground sate

32
Q

how does a neodinium laser work

A

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

33
Q

how can Eu2+ luminescence be tuned

A

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

34
Q

why is orbital angular momentum not quenched

A

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

35
Q

what formula is used to calculated the magentic moment

A

free ion formula

36
Q

what is the free ion formula

A

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

37
Q

how well go observed moments match calculated moments

A

well apart from for Sm3+ and Eu3+

38
Q

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

A

have low lying excited states which are easily populated at RT

39
Q

how does magnetic refrigeration work

A

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

40
Q

what is the effect of paramagnetism on NMR spectra

A

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

41
Q

when does paramagnetic shifting occur

A

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

42
Q

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

A

broad but unshifted

very spherical

43
Q

what are chiral lanthanoid reagents used for

A

to determine the enantiomeric excess of mixtures of chiral compounds

44
Q

how do chiral lanthanoid reagents work

A

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

45
Q

how does MRI work

A

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

46
Q

what are the requirements for a contrast agent

A

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

47
Q

what Ln makes a good contast agent

A

Gd3+

48
Q

what is the formula for relaxivity

A

^(1/T)/[contrast agent]

49
Q

how is relaxation cause

A

local field oscillating at Wo (larmor freq)

50
Q

what are the factors effecting relaxivity

A 
rate of exchange of coordinated H2O
No. coordinated h2o
distance between H2o and Gd3+
dependence on external field
rate of molecular tumbling
51
Q

which Gd3+ ligands have low osmotic value and why

A

ligands with 3- charge - no counterions needed

CHEM411 (5 decks)

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