Coordination Chemistry

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Coordination Chemistry Electronic Spectra of
Metal Complexes
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Electronic spectra (UV-vis spectroscopy)
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Electronic spectra (UV-vis spectroscopy)
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DE
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The colors of metal complexes
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Electronic configurations of multi-electron atoms
What is a 2p2 configuration?
n 2 l 1 ml -1, 0, 1 ms 1/2
These configurations are called microstates and
they have different energies because of
inter-electronic repulsions
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Electronic configurations of multi-electron
atoms Russell-Saunders (or LS) coupling
For the multi-electron atom L total orbital
angular momentum quantum number S total spin
angular momentum quantum number Spin multiplicity
2S1 ML ?ml (-L,0,L) MS ?ms (S, S-1,
,0,-S)
For each 2p electron n 1 l 1 ml -1, 0,
1 ms 1/2
ML/MS define microstates and L/S define states
(collections of microstates) Groups of
microstates with the same energy are called terms
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Determining the microstates for p2
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Spin multiplicity 2S 1
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Determining the values of L, ML, S, Ms for
different terms
1S
2P
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Classifying the microstates for p2
Spin multiplicity columns of microstates
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Energy of terms (Hunds rules)
Lowest energy (ground term) Highest spin
multiplicity 3P term for p2 case
3P has S 1, L 1
If two states have the same maximum spin
multiplicity Ground term is that of highest L
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Determining the microstates for s1p1
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Determining the terms for s1p1
Ground-state term
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Coordination Chemistry Electronic Spectra of
Metal Complexes cont.
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Electronic configurations of multi-electron
atoms Russell-Saunders (or LS) coupling
For the multi-electron atom L total orbital
angular momentum quantum number S total spin
angular momentum quantum number Spin multiplicity
2S1 ML ?ml (-L,0,L) MS ?ms (S, S-1,
,0,-S)
For each 2p electron n 1 l 1 ml -1, 0,
1 ms 1/2
ML/MS define microstates and L/S define states
(collections of microstates) Groups of
microstates with the same energy are called terms
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before we did
p2
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For metal complexes we need to consider d1-d10
For 3 or more electrons, this is a long tedious
process
But luckily this has been tabulated before
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Transitions between electronic terms will give
rise to spectra
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Selection rules (determine intensities)
Laporte rule g ? g forbidden (that is, d-d
forbidden) but g ? u allowed (that is, d-p
allowed)
Spin rule Transitions between states of different
multiplicities forbidden Transitions between
states of same multiplicities allowed
These rules are relaxed by molecular vibrations,
and spin-orbit coupling
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Group theory analysis of term splitting
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High Spin Ground States
An e electron superimposed on a spherical
distribution energies reversed because tetrahedral
dn Free ion GS Oct. complex Tet complex
d0 1S t2g0eg0 e0t20
d1 2D t2g1eg0 e1t20
d2 3F t2g2eg0 e2t20
d3 4F t2g3eg0 e2t21
d4 5D t2g3eg1 e2t22
d5 6S t2g3eg2 e2t23
d6 5D t2g4eg2 e3t23
d7 4F t2g5eg2 e4t23
d8 3F t2g6eg2 e4t24
d9 2D t2g6eg3 e4t25
d10 1S t2g6eg4 e4t26
Holes in d5 and d10, reversing energies relative
to d1
A t2 hole in d5, reversed energies, reversed
again relative to octahedral since tet.
Holes dn d10-n and neglecting spin dn d5n
same splitting but reversed energies because
positive.
Expect oct d1 and d6 to behave same as tet d4 and
d9
Expect oct d4 and d9 (holes), tet d1 and d6 to be
reverse of oct d1
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d1 ? d6 d4 ? d9
Orgel diagram for d1, d4, d6, d9
Energy
D
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D
ligand field strength
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Orgel diagram for d2, d3, d7, d8 ions
Energy
A2 or A2g
T1 or T1g
T1 or T1g
P
T2 or T2g
T1 or T1g
F
T2 or T2g
T1 or T1g
A2 or A2g
d2, d7 tetrahedral d2, d7 octahedral d3, d8
octahedral d3, d8 tetrahedral
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Ligand field strength (Dq)
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d2
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Tanabe-Sugano diagrams
d2
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Electronic transitions and spectra
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Other configurations
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Other configurations
The limit between high spin and low spin
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Determining Do from spectra
d1
d9
One transition allowed of energy Do
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Determining Do from spectra
Lowest energy transition Do
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Ground state mixing
E (T1g?A2g) - E (T1g?T2g) Do
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The d5 case
All possible transitions forbidden Very weak
signals, faint color
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Some examples of spectra
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Charge transfer spectra
Metal character
LMCT
Ligand character
Ligand character
MLCT
Metal character
Much more intense bands