Spectroscopic in Inorganic Chemistryr.takjoo.profcms.um.ac.ir/imagesm/1006/stories/...Inorganic of...
Transcript of Spectroscopic in Inorganic Chemistryr.takjoo.profcms.um.ac.ir/imagesm/1006/stories/...Inorganic of...
Electronic Absorption Spectroscopy
Spectroscopy in Inorganic Chemistry
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Charge transfer
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SO42-
ClO4-
Electronic Absorption Spectroscopy
UV
O→S
O→Cl
MO4 Td d-d MnO4
2-
CrO42-
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Charge transfer
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MO4 Td
CrO42-
Electronic Absorption Spectroscopy
nb→π* (LMCT)
Oxygen Cr
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Charge transfer
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MO4 Td
MnO42-
CrO42-
Electronic Absorption Spectroscopy
Metal Oxygen Ferdo
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Electronic Absorption Spectroscopy
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Electronic Absorption Spectroscopy
MnO42-
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CT from I- to ring antibonding orbital
Electronic Absorption Spectroscopy
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Polarized absorption spectra
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Electronic Absorption Spectroscopy
x
z axis of crystal
Plane polarized oscillator
Nicole prism
Source
z
y axis of crystal
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Canadian Journal of Chemistry, 1974, 52(1): 174-181
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Electronic Absorption Spectroscopy
b1g
b2u
eg
a2u
Eu A2u B2u b2ub1g egb1g a2ub1g
Cl
π
A1g
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PtCl42-
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Electronic Absorption Spectroscopy
1A1g→ 1A2u
1A1g→ 1Eu
1A1g→ 1B2u
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Electronic Absorption Spectroscopy
Character table for D4h point group
E 2C4 (z) C2 2C'2 2C''2 i 2S4 σh 2σv 2σd linears,
rotations quadratic
A1g 1 1 1 1 1 1 1 1 1 1 x2+y2, z2
A2g 1 1 1 -1 -1 1 1 1 -1 -1 Rz
B1g 1 -1 1 1 -1 1 -1 1 1 -1 x2-y2
B2g 1 -1 1 -1 1 1 -1 1 -1 1 xy
Eg 2 0 -2 0 0 2 0 -2 0 0 (Rx, Ry) (xz, yz)
A1u 1 1 1 1 1 -1 -1 -1 -1 -1
A2u 1 1 1 -1 -1 -1 -1 -1 1 1 z
B1u 1 -1 1 1 -1 -1 1 -1 -1 1
B2u 1 -1 1 -1 1 -1 1 -1 1 -1
Eu 2 0 -2 0 0 -2 0 2 0 0 (x, y)
Mz
My
Mx
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Electronic Absorption Spectroscopy
∫ ΨeMzΨeex
=A1gA2uA2u=A1g
∫ ΨeMyΨe
ex =A1gEuEu=A1
∫ ΨeMxΨeex
=A1gEuB2u=0
forbidden
1A1g→ 1A2u
1A1g→ 1Eu
1A1g→ 1B2u
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application
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Electronic spectra 210 nm – 750 nm
Near IR spectra 800 nm – 2500 nm
Sample: solid liquid gas
Electronic Absorption Spectroscopy
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Fingerprint
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Electronic Absorption Spectroscopy
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Fingerprint
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Saturated molecules:
Saturated molecules without lone pair: σ→σ*
eg. Methane 122 nm ethane 135 nm
lone pair electron: n→σ*
eg. triethylamine 227nm n→σ* 199 nm σ→σ*
Electronic Absorption Spectroscopy
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Fingerprint
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Carbonyl compounds:
Electronic Absorption Spectroscopy
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Fingerprint
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Inorganic system
Nitroso visible light
NO2- 355 nm (ε=23) n→π* 1A1→
1B1 oxygen lone pair
287 nm (ε=9) n →π* 1A1→1A2 oxygen lone pair
210 nm (ε=5380) n→π* 1A1→1B2
SO2 360 nm (ε=0.05) triplet
290 nm (ε=340) singlet
Simple ions (OH-, Cl-, Br-,…) Ion→Solvent charge transfer
Electronic Absorption Spectroscopy
n→π*
n→π*
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Molecular addition compounds of
iodine
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I2 σ2π4n4π*4 λmax= 520 nm (CCl4) π*→σ*
wavelenght
Electronic Absorption Spectroscopy
adso
rpti
on
Wavelength nm
New band at 250 nm Blue shift
I2:OH
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vibrational-electronic spectrum of I2 in the region from 500-
650 nm displays a large number of well-defined bands
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φ0 = aφcov. + bφel
Usually in adduct b>a (ground state)
a>b (excited state)
Electronic Absorption Spectroscopy
σ*
σ*
nb
π* π*
σ
I2 adduct base
CT
π*→σ*
then charge transfer: nb(base)→σ*(I2)
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Effect of solvent polarity on charge-
transfer spectra
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N-methylpyridinium iodid
Electronic Absorption Spectroscopy gas phase solution
Lone pair
Excited state pair
ET
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methanol formaldehyde
Z (ET) 83.6 83.6
dielectric cons. 32.6 109.5
Electronic Absorption Spectroscopy
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Structures of excited state
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Electronic Absorption Spectroscopy
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Optical rotary dispersion, circular
dichroism and magnetocircular
dichroism
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Electronic Absorption Spectroscopy
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Electronic Absorption Spectroscopy
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Electronic Absorption Spectroscopy
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If for instance we take horizontally and vertically polarised
light waves of equal amplitude that are in phase with each
other, the resultant light wave (blue) is linearly polarised at
45 degrees.
Electronic Absorption Spectroscopy
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If the two polarisation states are out of phase, the resultant wave ceases to be linearly
polarised. For example, if one of the polarised states is out of phase with the other by
aquarter‐wave, the resultant will be a helix and is known as circularly polarised light
(CPL). The helices can be either right‐handed (R‐CPL) or left‐handed (L‐CPL) and are
non‐superimposable mirror images.
Electronic Absorption Spectroscopy
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Electronic Absorption Spectroscopy
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Electronic Absorption Spectroscopy
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optical rotation
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Electronic Absorption Spectroscopy
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Electronic Absorption Spectroscopy
nl - nr
λ α =
α c'd'
[α] =
g/cm3 Sample thickness
[M] = M[α] 10-2 = Mα 10-2 /c'd'
Molar rotation
Rotation angle
Refractive index
Specific rotation angle
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circular dichroism
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Plane polarized light is made up of a left-handed
(L) and a right-handed component (R) which are
equal in magnitude. Circular Dichroism (CD)
refers to the difference in absorption of these two
components by a sample.
Electronic Absorption Spectroscopy
kl - kr
c εl - εr =
K: absorption coefficient
I=I010-kd d:Sample thickness
I: intensity
εl - εr
or θ
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CD
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visible and ultra‐violet region
A circular dichroism signal can be positive or negative, depending
on whether L‐CPL is absorbed to a greater extent than R-CPL
(CD signal positive) or to a lesser extent (CD signal negative).
Only chiral chromophores will produce a CD signal which can
occur for the following reasons:
-An intrinsically chiral chromophore such as a carbon atom bonded
to four different ligands or a disulphide bond with chirality
because of dihedral angles in its C-S-S-C chain of atoms.
-Chromophores covalently bonded to a chiral center.
-Chromophores placed in an asymmetric environment due to the
3D structure of the molecule
Electronic Absorption Spectroscopy
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CD
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Elliptically polarized not plane polarized
Electronic Absorption Spectroscopy
φ' c'd' [φ] =
g/cm3 Sample thickness
Specific ellipticity Tan (a\b)
a b
[θ] = M[φ]10-2 molar ellipticity
εl - εr = 0.3032 10-3[θ]
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CD varies as a function of wavelength, and that a CD
spectrum may exhibit both positive and negative peaks
Electronic Absorption Spectroscopy
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Electronic Absorption Spectroscopy
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Electronic Absorption Spectroscopy
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If for instance we take horizontally and vertically polarised
light waves of equal amplitude that are in phase with each
other, the resultant light wave (blue) is linearly polarised at
45 degrees.
Electronic Absorption Spectroscopy
Ferdo
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ersity
of Mash
had
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If the two polarisation states are out of phase, the resultant wave ceases to be linearly
polarised. For example, if one of the polarised states is out of phase with the other by
aquarter‐wave, the resultant will be a helix and is known as circularly polarised light
(CPL). The helices can be either right‐handed (R‐CPL) or left‐handed (L‐CPL) and are
non‐superimposable mirror images.
Electronic Absorption Spectroscopy
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Electronic Absorption Spectroscopy
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Electronic Absorption Spectroscopy
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Optical rotary dispersion
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Measuring optical rotation (or [M], [α]) as a function of
wavelength is termed optical rotatory dispersion (ORD)
spectroscopy.
Electronic Absorption Spectroscopy
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optical rotation
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Electronic Absorption Spectroscopy
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CD ORD absorption spectra
Electronic Absorption Spectroscopy
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The simplicity and low‐cost of the experiment and
instrumentation makes it ideal for this application. Circular
dichroism spectra on the other hand are better spectrally
resolved than ORD spectra, and consequently more suitable
for advanced spectral analysis.
Electronic Absorption Spectroscopy
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Transition moment integral (for electric dipol transition)
ƒ = ∫ ΨeMΨe dv =D
Transition moment integral (for electric and magnetic dipol)
R=[∫ ΨeMΨe dv][∫ ΨeMDΨe dv
Selection rules
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Electronic Absorption Spectroscopy
+x
-x
ex 2 ^
ex ^ ex
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application
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Nickel complex with Oh symmetry (Ni(pn)32+)
3A2g → 3T2g
3A2g → 3T1g(F)
3A2g → 3T1g(P)
Electronic Absorption Spectroscopy
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E 8C3 6C2 6C4 3C2 =(C4)2 i 6S4 8S6 3σh 6σd
linear,
rotations quadratic
A1g 1 1 1 1 1 1 1 1 1 1 x2+y2+z2
A2g 1 1 -1 -1 1 1 -1 1 1 -1
Eg 2 -1 0 0 2 2 0 -1 2 0 (2z2-x2-y2, x2-y2)
T1g 3 0 -1 1 -1 3 1 0 -1 -1 (Rx, Ry, Rz)
T2g 3 0 1 -1 -1 3 -1 0 -1 1 (xz, yz, xy)
A1u 1 1 1 1 1 -1 -1 -1 -1 -1
A2u 1 1 -1 -1 1 -1 1 -1 -1 1
Eu 2 -1 0 0 2 -2 0 1 -2 0
T1u 3 0 -1 1 -1 -3 -1 0 1 1 (x, y, z)
T2u 3 0 1 -1 -1 -3 1 0 1 -1
Electronic Absorption Spectroscopy
Character table for Oh point group
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3A2g → 3T2g
A2g T1g T2g =A1g + ….
3A2g → 3T1g(F)
3A2g → 3T1g(P)
Electronic Absorption Spectroscopy
εl - εr = 0.8
εl - εr =0.04
εl - εr = 0.04
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Electronic Absorption Spectroscopy
log
ε
ε l-
ε r
cm-1
A1→Ea
A1→ A2
A1→Eb
A1→ A1 forbidden
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magnetocircular dichroism
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Electronic Absorption Spectroscopy
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The Faraday Effect
Electronic Absorption Spectroscopy
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A-Terms:
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Electronic Absorption Spectroscopy
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C-Terms:
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Electronic Absorption Spectroscopy
Temperature dependent
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B-Terms:
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Electronic Absorption Spectroscopy
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Electronic Absorption Spectroscopy
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CT in RuO42-
Mcd used for assignment of spin-forbidden
electronic transition (low intensity)
Electronic Absorption Spectroscopy
t1π(O)→ex2-y2,z2(Re)
t2π(O)→ex2-y2,z2(Re)
A-term
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