Electronic%20(UV-visible)%20Spectroscopy

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Electronic (UV-visible) Spectroscopy
Electronic XPS UPS
UV-visible
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UV-visible spectroscopy ligand p (1)
metal-metal (d-d) transition s metal-ligand
metal d (2) charge transfer (MLCT) ligand-met
al n (LMCT) metal d n (3) ligand-centered
transition ligand p   s instrument  
sample
energy energy
energy output source selector
analyzer    
computer electric
connection light path absorbance
Io A log ?? ecl
I   e extinction coefficient
c concentration mol/L (M) l path
length (cm)
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• selection rules
• 1. only one electron is involved in any
  transition
• 2. there must be no net change of spin DS 0
• 3. it must involve an overall change in orbital
• angular momentum of one unit DL 1
• 4. Laporte (or parity) selection rule
• only g ?u and u ?g transitions are allowed
• vibronic coupling interaction between
  electronic
• and vibrational
  modes
• electronic transition e
• Laporte allowed (charge transfer) 10000
• (100050000)

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CoCl42-

• Co(H2O)62

Mn(H2O)62
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• d-d transition crystal field splitting
• Do size and charge of the metal ion and
  ligands
• 4d metal 50 larger than 3d metal
• 5d metal 25 larger than 4d metal
• 5d gt 4d gt 3d
• crystal field stabilization energy (CFSE)
• spin-pairing energy
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• high-spin/low spin configuration d4 d7
• d4

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• other shapes
• tetrahedral
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  Dt 4/9 Do
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tetrahedron octahedron elongated
square
octahedron planar
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• d1
  Ti(H2O)63
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•  hole formalism
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•   d2
  possible electron
• possible arrangements of electrons transitions
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hu Do
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• Russell-Saunders term symbols
• for free atoms and ions
• S total spin quantum number Sms
• L total orbital angular quantum number Sml
• L 0, 1, 2, 3, 4, ..
• S P D F G
• 1 3 5 7 9
• J total angular quantum number LS, ,L-S
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• d2 configuration 10!
• 45
  microstates
• 8! 2!
• S 1 0 -1
• L
• 4 (2 2-)
• 3 (2 1) (2 1-) (2- 1) (2- 1-)

2S1LJ
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• splitting of terms in various chemical
  environments
• d orbitals in Oh environment
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•   consider pure rotational O subgroup

states for dn systems in Russell-Saunders coupling
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• transformation matrix
•   e2ia 0 0 0 0
• 0 eia 0 0 0
• 0 0 e0 0 0
• 0 0 0 e-ia 0
• 0 0 0 0 e-2ia
• sum of the diagonal elements
• sin(l 1/2)a
• c (a)
• sin(a/2)
• for d orbitals
• 
  sin(5p/2)
• c (E) 5 c (C2)
  1
• 
  sin(p/2)
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• sin(5p/3)
  sin(5p/4)
• c (C3) -1 c (C4) -1
• sin(p/3)
  sin(p/4)

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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 term
• d2 configuration in Oh environment
• (i) t2g2 aA1g bEg cT1g dT2g
• total degeneracy 15
• a b c d
• I 1 1 1 3
• II 1 1 3 1
• III 3 3 1 1
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• (ii) t2g1eg1 aT1g bT2g
• total degeneracy 24
• only possibility 1T1g 1T2g 3T1g 3T2g
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• (iii) eg2 aA1g bA2g cEg
• total degeneracy 6
• a b c
• I 1 3 1
• II 3 1 1
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• method of descending symmetry
• consider d2 ion in Oh environment
• from correlation table for group Oh
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• (i) t2g2 A1g Eg T1g T2g
• lowering the symmetry to C2h t2g
  ag ag bg
• t2g t2g 1A1g 1Eg
  3T1g 1T2g
• possible spin 1 1 1
  3
• multiplicity 1 1 3
  1 ?
• 3 3 1 1
• corresponding 1Ag 1Ag 3Ag
  1Ag
• representations 1Bg 3Bg 1Ag
• in C2h 3Bg 1Bg

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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
• gt D4h Oh
• 1A1g 1A1g
• 3B2g 3A1g
• 1A1g 1B1g 1Eg
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• (iii) t2g1eg1 ????
• consider d2 ion in Td environment
• from splitting of energy level in Td symmetry
• 3F 3A2 3T1 3T2
• 1D 1E 1T2
• 3P 3T1
• 1G 1A1 1E 1T1 1T2
• 1S 1A1

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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 diagrams
• d1, d6/d4, d9
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•   u 10 Dq

d1, d6 tetrahedral d1, d6 octahedral d4, d9
octahedral d4, d9 tetrahedral
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• d2, d7/d3, d8
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• A2?T2 u1 10Dq T1?T2 u1 8Dq
  c
• A2?T1(F) u2 18Dq - c T1(F)?T1(P) u2 18Dq c

cm-1
d2, d7 tetrahedral Dq d2, d7
octahedral d3, d8 octahedral d3, d8 tetrahedral
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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 Do
• Mn(II) lt Ni(II) ltCo(II) lt Fe(II) lt V(II) lt
  Fe(III)
• lt Cr(III) lt V(III) lt Co(III) lt Mn(IV) lt Mo(III)
• lt Rh(III) lt Pd(IV) lt Ir(III) lt Re(IV) lt Pt(IV)
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• Do values for octahedral M(H2O)6n complexes
• Do (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 series
• I- lt Br- lt -SCN- lt Cl- lt F- lt urea lt OH- lt
  CH3COO-
• lt C2O4- lt H2O lt -NCS- lt glycine lt pyridine NH3
  
• lt en lt SO32- lt o-phenanthroline lt NO2- lt CN- lt
  PR3
• lt CO
• ex. Co(H2O)63 Do 19000
  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
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• Jahn-Teller distortions
• distortion will occur whenever the resulting
  splitting
• energy levels yields additional stabilization
• __ dx2-y2 __ dz2
• eg __ __

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• M(H2O)6n

Ti3 (d1)
Mn2 (d5)
V3 (d2)
Fe2 (d6)
Co2 (d7)
Cr3 (d3)
Ni2 (d8)
Cu2 (d9)
Cr2 (d4)
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• d1
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• 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
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• d9