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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