1 Electronic (UV-visible) Spectroscopy | Electronic | XPS UPS UV-visible.
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Transcript of 1 Electronic (UV-visible) Spectroscopy | Electronic | XPS UPS UV-visible.
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Electronic (UV-visible) Electronic (UV-visible) SpectroscopySpectroscopy
| Electronic |
XPS UPS UV-visible
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UV-visible spectroscopyligand *
(1) metal-metal (d-d) transition*
metal-ligand metal d(2) charge transfer (MLCT)
ligand-metal n (LMCT) metal d
n(3) ligand-centered transition ligand
instrument sample
energy energy energy outputsource selector analyzer
computer electric connection light path
absorbance Io A = log ―― = cl
I
: extinction coefficient c: concentration mol/L (M) l: path length (cm)
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selection rules1. only one electron is involved in any transition
2. there must be no net change of spin S = 0
3. it must involve an overall change in orbitalangular momentum of one unit L = ±1
4. Laporte (or parity) selection ruleonly g →u and u →g transitions are allowed
vibronic coupling – interaction between electronic and vibrational modes
electronic transition Laporte allowed (charge transfer) 10000
(1000—50000) Laporte forbidden (d-d transition) spin allowed; noncentrosymmetiric 100—200
(200—250) spin allowed; centrosymmetric 5—100
(20—100) spin forbidden 0.01—1
(< 1)
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[Co(H2O)6]2+
[CoCl4]2-
[Mn(H2O)6]2+
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d-d transition crystal field splitting
o size and charge of the metal ion and ligands
4d metal ~50% larger than 3d metal 5d metal ~25% larger than 4d metal
5d > 4d > 3d
crystal field stabilization energy (CFSE)spin-pairing energy
high-spin/low spin configuration d4 ~ d7
d4
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other shapestetrahedral
t = 4/9 o
tetrahedron octahedron elongated square octahedron planar
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d1 [Ti(H2O)6]3+
hole formalism
d2 possible electron possible arrangements of electrons transitions
ho
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Russell-Saunders term symbols for free atoms and ions
S: total spin quantum number ms
L: total orbital angular quantum number ml
L = 0, 1, 2, 3, 4, ………….. S P D F G 1 3 5 7 9
J: total angular quantum number L+S, ……,│L-S│
d2 configuration 10! ———— = 45 microstates
8! 2!
S +1 0 -1 L
4 (2+ 2-)
3 (2+ 1+) (2+ 1-) (2- 1+) (2- 1-)
(1+ 1-) 2 (2+ 0+) (2+ 0-) (2- 0+) (2- 0-)
(1+ 0+) (1+ 0-) (1- 0+) (1- 0-) 1 (2+ -1+) (2+ -1-) (2- -1+) (2- -1-)
(0+ 0-) 0 (1+ -1+) (1+ -1-) (1- -1+) (1- -1-) (2+ -2+) (2+ -2-) (2- -2+) (2- -2-)
1G 3F 1D 3P 1S9 + 21 + 5 + 9 + 1 = 45 ground term
2S+1LJ
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splitting of terms in various chemical environments
d orbitals in Oh environment
consider pure rotational O subgrouprotation by angle ==> R(r), (), ψs invariant
only () will be altered() = eim ==> () = eim(+ )
m = 2, 1, 0, -1, -2
e2ie2i+ )
eiei+ )
e0 ======>e0
e-ie-i+ )
e-2ie-2i+ )
states for dn systems in Russell-Saunders coupling
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transformation matrix
e2i0 0 0 0
0 ei0 0 0
0 0 e00 0
0 0 0 e-i0
0 0 0 0 e-2i
sum of the diagonal elements
sin(l + 1/2)() = ——————— sin(/2)
for d orbitals sin(5/2)
() = 5 (C2) = ————— = 1 sin(/2)
sin(5/3) sin(5/4)(C3) = ————— = -1 (C4) = ————— = -1
sin(/3) sin(/4)
==> = eg + t2g
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splitting of one-electron levels in an Oh environment
splitting of one-electron levels in various symmetries
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determine the spin multiplicity of each termd2 configuration in Oh environment
(i) t2g2 aA1g + bEg + cT1g + dT2g
total degeneracy 15
a b c dI 1 1 1 3II 1 1 3 1III 3 3 1 1
(ii) t2g
1eg1 aT1g + bT2g
total degeneracy 24
only possibility 1T1g 1T2g
3T1g 3T2g
(iii) eg
2 aA1g + bA2g + cEg
total degeneracy 6
a b cI 1 3 1II 3 1 1
1S 1A1g
1G 1A1g 1Eg
1T1g 1T2g
3P 3T1g 1D 1Eg
1T2g
3F 3A1g 3T1g
3T2g
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method of descending symmetryconsider d2 ion in Oh environment
from correlation table for group Oh
(i) t2g
2 A1g Eg T1g T2g
lowering the symmetry to C2h t2g ag + ag + bg
t2g × t2g = 1A1g 1Eg
3T1g 1T2g
possible spin 1 1 1 3multiplicity 1 1 3 1 ˇ
3 3 1 1
corresponding 1Ag 1Ag
3Ag 1Ag
representations 1Bg 3Bg
1Ag
in C2h 3Bg 1Bg
ag × ag Ag ====> 1Ag
ag × ag’ Ag ====> 1Ag 3Ag
ag × bg Bg ====> 1Bg 3Bg
ag’ × ag’ Ag ====> 1Ag
ag’ × bg Bg ====> 1Bg 3Bg
bg × bg Ag ====> 1Ag
===> total 41Ag + 3Ag + 21Bg + 23Bg
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(ii) eg2 A1g A2g Eg
lowering the symmetry to D4h eg a1g + b1g
a1g2 A1g possible spin multiplicity 1A1g
a1gb1g B1g possible spin multiplicity 1B1g 3B1g
b1g2 A1g possible spin multiplicity 1A1g
==> D4h Oh
1A1g 1A1g
3B2g 3A1g
1A1g 1B1g
1Eg
(iii) t2g
1eg1 ????
consider d2 ion in Td environment
from splitting of energy level in Td symmetry3F 3A2
3T1 3T2
1D 1E 1T2
3P 3T1 1G 1A1
1E 1T1 1T2
1S 1A1
electron configurationse2 A1 A2 E total degeneracy 6
et2 T1 T2 total degeneracy 24
t22 A1 E T1 T2 total degeneracy 15
assign the correct spin multiplicity ???
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splitting of the terms for d2 ion in several point groups
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correlation diagram for a d2 ion in Oh
environment
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correlation diagram for a d2 ion in Td
environment
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Orgel diagramsd1, d6/d4, d9
= 10 Dq
E T2 T2g Eg
E g T2 g T2 E
d1, d6 tetrahedral d1, d6 octahedrald4, d9 octahedral d4, d9 tetrahedral
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d2, d7/d3, d8
A2→T2 1 = 10Dq T1→T2 1 = 8Dq + c
A2→T1(F) 2 = 18Dq - c T1(F)→T1(P) 2 = 18Dq + c
A2→T1(P) 1 = 15B + 12Dq + c T1→A2 3 = 15B + 6Dq + 2c
d2, d7 tetrahedral Dq d2, d7 octahedrald3, d8 octahedral d3, d8 tetrahedral
cm-1
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Tanabe-Sugano diagrams
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simplified Tanabe-Sugano diagrams
d2 d3 d4
d5 d6 d7
d8
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magnitude of o
Mn(II) < Ni(II) <Co(II) < Fe(II) < V(II) < Fe(III) < Cr(III) < V(III) < Co(III) < Mn(IV) < Mo(III) < Rh(III) < Pd(IV) < Ir(III) < Re(IV) < Pt(IV)
o values for octahedral [M(H2O)6]n+ complexes
o (cm-1)
Ti3+ 20400 Mn3+ 21000 Co3+ 19000 V3+ 19000 Mn2+ 7500 Co2+ 9750 Cr3+ 17700 Fe3+ 21000 Ni2+ 8500 Cr2+ 12500 Fe2+ 10500 Cu2+ 12600
spectrochemical seriesI- < Br- < -SCN- < Cl- < F- < urea < OH- < CH3COO-
< C2O4- < H2O < -NCS- < glycine < pyridine ~ NH3
< en < SO32- < o-phenanthroline < NO2
- < CN- < PR3
< CO
ex. [Co(H2O)6]3+ o = 19000 cm-1
[Co(NH3)6]3+ o = 22900 cm-1
[Co(H2O)3(NH3)3]3+ o = ?
3/6 × 19000 + 3/6 × 22900 = 20950 cm-1
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Jørgensen prediction of 10Dq and B
10Dq = f · g (cm-1 × 10-3)
B = Bo (1 - h · k)
Bo : free ion interelectronic repulsion parameter
Jahn-Teller distortionsdistortion will occur whenever the resulting splitting energy levels yields additional stabilization
__ dx2-y2 __ dz2
eg __ __
__ dz2 __ dx2-y2
or __ dxy
__ __dxz, dyz
t2g __ __ __
__ __ dxz, dyz
__ dxy
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[M(H2O)6]n+
Ti3+ (d1)
V3+ (d2)
Cr3+ (d3)
Mn2+ (d5)
Fe2+ (d6)
Co2+ (d7)
Ni2+ (d8)
Cu2+ (d9)
Cr2+ (d4)
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d1
d2
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d3
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d3
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d4
d5
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d6
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d6
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d6
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d7
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d8
d9