Spectroscopic in Inorganic Chemistryr.takjoo.profcms.um.ac.ir/imagesm/1006/stories/...Inorganic of...

Electronic Absorption Spectroscopy

Spectroscopy in Inorganic Chemistry

Ferdo

wsi Univ

ersity

of Mash

had

Charge transfer

Ferdowsi University of Mashhad 2

SO42-

ClO4-


UV

O→S

O→Cl

MO4 Td d-d MnO4

2-

CrO42-

Ferdo

wsi Univ

ersity

of Mash

had

Charge transfer


MO4 Td

CrO42-


nb→π* (LMCT)

Oxygen Cr

Ferdo

wsi Univ

ersity

of Mash

had

Charge transfer


MO4 Td

MnO42-

CrO42-


Metal Oxygen Ferdo

wsi Univ

ersity

of Mash

had



Ferdo

wsi Univ

ersity

of Mash

had



MnO42-

Ferdo

wsi Univ

ersity

of Mash

had


Ferdo

wsi Univ

ersity

of Mash

had


CT from I- to ring antibonding orbital


Ferdo

wsi Univ

ersity

of Mash

had

Polarized absorption spectra



x

z axis of crystal

Plane polarized oscillator

Nicole prism

Source

z

y axis of crystal

Ferdo

wsi Univ

ersity

of Mash

had


Canadian Journal of Chemistry, 1974, 52(1): 174-181

Ferdo

wsi Univ

ersity

of Mash

had


Ferdo

wsi Univ

ersity

of Mash

had



b1g

b2u

eg

a2u

Eu A2u B2u b2ub1g egb1g a2ub1g

Cl

π

A1g

Ferdo

wsi Univ

ersity

of Mash

had

PtCl42-



1A1g→ 1A2u

1A1g→ 1Eu

1A1g→ 1B2u

Ferdo

wsi Univ

ersity

of Mash

had



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

Ferdo

wsi Univ

ersity

of Mash

had



∫ ΨeMzΨeex

=A1gA2uA2u=A1g

∫ ΨeMyΨe

ex =A1gEuEu=A1

∫ ΨeMxΨeex

=A1gEuB2u=0

forbidden

1A1g→ 1A2u

1A1g→ 1Eu

1A1g→ 1B2u

Ferdo

wsi Univ

ersity

of Mash

had

application


Electronic spectra 210 nm – 750 nm

Near IR spectra 800 nm – 2500 nm

Sample: solid liquid gas


Ferdo

wsi Univ

ersity

of Mash

had

Fingerprint



Ferdo

wsi Univ

ersity

of Mash

had

Fingerprint


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*


Ferdo

wsi Univ

ersity

of Mash

had


Ferdo

wsi Univ

ersity

of Mash

had

Fingerprint


Carbonyl compounds:


Ferdo

wsi Univ

ersity

of Mash

had

Fingerprint


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


n→π*

n→π*

Ferdo

wsi Univ

ersity

of Mash

had


Ferdo

wsi Univ

ersity

of Mash

had

Molecular addition compounds of

iodine


I2 σ2π4n4π*4 λmax= 520 nm (CCl4) π*→σ*

wavelenght


adso

rpti

on

Wavelength nm

New band at 250 nm Blue shift

I2:OH

Ferdo

wsi Univ

ersity

of Mash

had


vibrational-electronic spectrum of I2 in the region from 500-

650 nm displays a large number of well-defined bands

Ferdo

wsi Univ

ersity

of Mash

had


φ0 = aφcov. + bφel

Usually in adduct b>a (ground state)

a>b (excited state)


σ*

σ*

nb

π* π*

σ

I2 adduct base

CT

π*→σ*

then charge transfer: nb(base)→σ*(I2)

Ferdo

wsi Univ

ersity

of Mash

had


Ferdo

wsi Univ

ersity

of Mash

had

Effect of solvent polarity on charge-

transfer spectra


N-methylpyridinium iodid

Electronic Absorption Spectroscopy gas phase solution

Lone pair

Excited state pair

ET

Ferdo

wsi Univ

ersity

of Mash

had


methanol formaldehyde

Z (ET) 83.6 83.6

dielectric cons. 32.6 109.5


Ferdo

wsi Univ

ersity

of Mash

had

Structures of excited state



Ferdo

wsi Univ

ersity

of Mash

had

Optical rotary dispersion, circular

dichroism and magnetocircular

dichroism



Ferdo

wsi Univ

ersity

of Mash

had



Ferdo

wsi Univ

ersity

of Mash

had



Ferdo

wsi Univ

ersity

of Mash

had


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.


Ferdo

wsi Univ

ersity

of Mash

had


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.


Ferdo

wsi Univ

ersity

of Mash

had



Ferdo

wsi Univ

ersity

of Mash

had



Ferdo

wsi Univ

ersity

of Mash

had

optical rotation



Ferdo

wsi Univ

ersity

of Mash

had



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

Ferdo

wsi Univ

ersity

of Mash

had

circular dichroism


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.


kl - kr

c εl - εr =

K: absorption coefficient

I=I010-kd d:Sample thickness

I: intensity

εl - εr

or θ

λ Ferdo

wsi Univ

ersity

of Mash

had

CD


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


Ferdo

wsi Univ

ersity

of Mash

had

CD


Elliptically polarized not plane polarized


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]

Ferdo

wsi Univ

ersity

of Mash

had


CD varies as a function of wavelength, and that a CD

spectrum may exhibit both positive and negative peaks


Ferdo

wsi Univ

ersity

of Mash

had



Ferdo

wsi Univ

ersity

of Mash

had



Ferdo

wsi Univ

ersity

of Mash

had


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.


Ferdo

wsi Univ

ersity

of Mash

had


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.


Ferdo

wsi Univ

ersity

of Mash

had



Ferdo

wsi Univ

ersity

of Mash

had



Ferdo

wsi Univ

ersity

of Mash

had

Optical rotary dispersion


Measuring optical rotation (or [M], [α]) as a function of

wavelength is termed optical rotatory dispersion (ORD)

spectroscopy.


Ferdo

wsi Univ

ersity

of Mash

had

optical rotation



Ferdo

wsi Univ

ersity

of Mash

had


CD ORD absorption spectra


Ferdo

wsi Univ

ersity

of Mash

had


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.


Ferdo

wsi Univ

ersity

of Mash

had

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



+x

-x

ex 2 ^

ex ^ ex

Ferdo

wsi Univ

ersity

of Mash

had

application


Nickel complex with Oh symmetry (Ni(pn)32+)

3A2g → 3T2g

3A2g → 3T1g(F)

3A2g → 3T1g(P)


Ferdo

wsi Univ

ersity

of Mash

had


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


Character table for Oh point group

Ferdo

wsi Univ

ersity

of Mash

had


3A2g → 3T2g

A2g T1g T2g =A1g + ….

3A2g → 3T1g(F)

3A2g → 3T1g(P)


εl - εr = 0.8

εl - εr =0.04

εl - εr = 0.04

Ferdo

wsi Univ

ersity

of Mash

had



log

ε

ε l-

ε r

cm-1

A1→Ea

A1→ A2

A1→Eb

A1→ A1 forbidden

Ferdo

wsi Univ

ersity

of Mash

had

magnetocircular dichroism



Ferdo

wsi Univ

ersity

of Mash

had


The Faraday Effect


Ferdo

wsi Univ

ersity

of Mash

had

A-Terms:



Ferdo

wsi Univ

ersity

of Mash

had

C-Terms:



Temperature dependent

Ferdo

wsi Univ

ersity

of Mash

had

B-Terms:



Ferdo

wsi Univ

ersity

of Mash

had



Ferdo

wsi Univ

ersity

of Mash

had


CT in RuO42-

Mcd used for assignment of spin-forbidden

electronic transition (low intensity)


t1π(O)→ex2-y2,z2(Re)

t2π(O)→ex2-y2,z2(Re)

A-term

Ferdo

wsi Univ

ersity

of Mash

had

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Spectroscopic in Inorganic Chemistryr.takjoo.profcms.um.ac.ir/imagesm/1006/stories/...Inorganic of...

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