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Electronic Circular Dichroism of Transition Metal Complexes within TDDFT

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To understand, experimental CD spectra, quantum ... Trigonal Dihedral: ... Complexes with Conjugated Ligands (Trigonal Dihedral) M: Fe, Ru, Os. N-N: bpy, phen ... – PowerPoint PPT presentation

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Title: Electronic Circular Dichroism of Transition Metal Complexes within TDDFT


1
Electronic Circular Dichroism of Transition Metal
Complexes within TDDFT
Jing Fan University of Calgary
2
Objectives
  • To understand, experimental CD spectra, quantum
    mechanical calculations of electronic structure
    and CD based on TDDFT
  • To elucidate the origin of CD in typical
    transition metal complexes, relationship between
    CD and molecular geometry
  • To evaluate the reliability and accuracy of TDDFT
    for transition metal compounds

3
Complexes Studied
Trigonal Dihedral
- ?-bonded complexes M(en)33 (M Co, Cr)
(d-to-d, L?MCT)
- both ?- and p-bonded complexes M(L-L)3n (M
Co, Cr L ox, acac, thiox, etc.) (d-to-d,
LMCT, MLCT, LC)
- complexes with conjugated ligands M(L-L)32
( M Fe, Ru, Os L bpy, phen) (LC exciton CD )
4
Computational Details ADF package
  • Basis sets (STO)
  • ligand atoms frozen core triple-? polarized
    TZP -C, N, O (1S) S (2p)
  • metal atoms
  • -Co, Cr TZP (2p)
  • -Fe, Ru, Os TZ2P (2p, 3d, 4f)
  • Functionals VWN (LDA) BP86 (GGA)
  • Relativistic effect for Fe group metals (scalar
    ZORA)
  • Un-restricted calculations for Cr(III)
  • The COnductor-like continuum Solvent MOdel
    (COSMO) of solvation

5
?-bonded Complexes Co(en)33 and Cr(en)33
en
  • Calculated ?E are systematically overestimated
    for the d-d region (by 5,500 cm-1)
    underestimated for the LMCT region (by 6,000
    cm-1)

6
Assignment of Transitions
Lowest singlet excited states and their splitting
in D3 symmetry
?-Co(en)33
7
Why Optically Active?
1A1g 1T1g d-d transitions magnetically
allowed 1A1g 1T1u LMCT transitions
electrically allowed
8
Origin of Optical Activity
  • Metal-ligand orbital interactions

8
  • Metal-ligand Orbital Interaction
  • Metal-ligand Orbital Interaction

9
(No Transcript)
10
MO diagram
Energy (eV)
10
11
  • Prediction of the Sign of Rotatory Strengths

and in terms of one-electron excitations 4e(d?)??
5e(d?)
12
Both ?- and p-bonded Complexes
Metal and Ligand Frontier Orbitals
L?-orbitals
L?-orbitals
12
  • Metal-ligand Orbital Interaction
  • Metal-ligand Orbital Interaction

13
Symmetry Unique Metal-ligand Orbital Overlaps
Only p-orbitals on the N atoms are considered
13
14
Case I Oh Case II D3
15
CD spectra - acac
theor.
expt.
  • d-to-d, LMCT as well as ML?CT and LC, etc.
  • Global red-shift applied to the computed
    excitation energies
  • Cr(III) 5.0 ? 103 cm1
  • Co(III) 4.0 ? 103 cm1

15
16
  • - thiox

17
Relationship between CD of the d-d transitions
and geometry in ?-M(L-L)3n
a Sign of rotatory strength of the E symmetry. b
Azimuthal distortion ?? 0? for ideal
octahedrons. c Trigonal splitting of the T1g
state. d Polar distortion s/h 1.22 for ideal
octahedrons.
17
18
Rotatory strengths R ( ) and overlaps S(d?2,
) ( ) against ?
19
Relationship between CD of the d-d transitions
and geometry in ?-M(L-L)3n
a Sign of rotatory strength of the E symmetry. b
Azimuthal distortion ?? 0? for ideal
octahedrons. c Trigonal splitting of the T1g
state. d Polar distortion s/h 1.22 for ideal
octahedrons.
19
19
20
Complexes with Conjugated Ligands (Trigonal
Dihedral)
theor.
?? ? 5
expt.
?-Os(bpy)32
M Fe, Ru, Os N-N bpy, phen
For the ? configuration R(E) gt 0, R(A2) lt 0,
?(A2-E) gt 0
21
ßp
Energy (eV)
ap
22
(ap-gtßp)
23
Energy Splitting of CD Bands
  • d-to-d trigonal splitting of dp orbitals due to
    metal-ligand interactions

24
  • LC trigonal splitting of dp orbitals due to
    metal-ligand interactions and electron-electron
    repulsion energy involving different number of
    ligands

25
Determination of Absolute Configuration by CD
  • ?-bonded d-to-d, L?MCT ??
  • ?/?-bonded d-to-d (might be safe), CT (not safe)
  • ?/?-bonded (conjugated ligands) LC exciton
    excitations ?

25
26
Complexes with Tripodal Tetradentate Ligands
(Trigonal bipyramidal)
MeTPA
MeBQPA
MeTQA
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