Transcript Optical Activity of Inorganic Complexes

Optical Activity of Inorganic
Complexes
Chem 510
Adam Daly
29-Oct-04
Why this topic?
• Every organic chemistry textbook…..
• Classical or Quantum phenomenon?
• “Of all the natural phenomenon observed
in nature, none has had so profound effect
on chemical thought as that of natural
optical rotatory power”.1
1. Lieher, A.D. J.Phys. Chem. 1964, 40, 1965
Outline
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Historical Look…
Introduction to Optical Activity
Theory of Optical Activity
Optical Activity and Group Theory
Character Tables – Hidden Treasures
Optical Activity – A historical note
• Early 1800’s polarized light in quartz crystals by
Arago, Biot
• Structural information of optically active tartaric
acid by Pasteur 1846-1860.
• Electromagnetic Equations by Maxwell 1860.
• Initial paper of the Journal of the American
Chemical Society (1879): “A method for the
detection of artificial or dextro-glucose in cane
sugar and the exact determination of cane-sugar
by the polariscope”.
History Cont.
• Quantum Mechanics…. 1920
– Rosenfeld’s theory of rotational strength: an
exact theory of chromophores that are small
relative to wavelength of light…. But the math
is tooooooo complicated!
– Much more but this is enough history….
Refer to: Charney, E. The molecular basis of
optical activity, John Wiley and Sons Inc.1979
Ch 1.
Electromagnetic Waves
• Linear polarized light contains two vectors
perpendicular to axis of propagation.
– Oscillating Electric and Magnetic Fields
• Superposition of Both Right and Left circularly
polarized light.
Charney, E. The molecular basis of optical activity,
John Wiley and Sons Inc.1979
Polarized Light
Lieher, A.D. J.Phys. Chem. 1964, 40, 665
Polarized Light
Davis, J.C. Advanced Physical Chemistry, John Wiley and Sons Inc.1965
Optical Rotation Model (Classically)
• Angle of rotation is attributed to the
difference in the indices of refraction of left
and right circularly polarized light.
• Elliptization (Circular Dichroism) of the
polarized light is attributed to the
absorption (extinction coefficients)
differences of left and right circularly
polarized light.
Optical Rotation
Lieher, A.D. J.Phys. Chem. 1964, 40, 665
Circular Dichroism
Classical Theory Cont.
• The index of refraction contains two terms:
– The index of refraction in a transparent medium…
the rotation term .
– The absorption (non-transparent) term where the
extinction coefficient differences appear… the
circular dichroism.
• The rotation term is labeled

The Beta term relates the response of the molecule in the radiation field. Zero
Beta, no optical activity.
Quantum Theory
• Beta: The chiral response parameter.
• Rotational Strength is related to the electric
transition moment and the magnetic transition
moment by
 * m(a, b)
  K *  Im 2
2
 ba 
Where (a,b) is:
 ab   b  a d
Where rotational strength is the term of *m(a,b) Rosenfeld
What to take from this…
• To have optical activity from Q.M. stand
point: the induced electric dipole () and
the induced magnetic dipole (m) must
have components that are parallel.
– So that the dot product is not zero.
• Where is this going…….
Group Theory and Quantum
Mechanics Connection
• Symmetry
– The electronic transition dipole moment integral
given by quantum mechanics is equal to:
 ab   b  a d
– To have a finite value this integral must be invariant
in the space integrated ! Ie.. Must not be affected
by the symmetry operations of the group.
Where A and B are states different energy states
Like 1A1g and 1T1g
Group Theory Takes Over
• The implication:  (transition dipole term)
belongs to or contains one of the totally
symmetric representations A.
• What about m?
• To have rotational strength be non-zero
both term must belong to the same totally
symmetric representation.
Lets Look at Some Character
Tables
• First: Groups with inversions or improper
rotations are not optically active.
• Second: Groups with degenerate states
– (x,y) and (Rx and Ry) on the same line can be
chiral with degeneracy removed.
• Third: Chiral group characteristics:
– (z and Rz in the same line gives transitions
that are naturally active).
What’s hot in this field?
• Predictive models based on ligands to give
rotational power.
• Synthesis of chiral catalysts and use of
optical activity/NMR for characterization.
Conclusions
• Optical activity has both classical and
quantum mechanical roots.
• Character tables give more info then first
suspected…!
• The foundation of inorganic/organic
structure and light interaction with matter
is conveyed in this theory.
References
• Lieher, A.D. J.Phys. Chem. 1964, 40, 665
• Charney, E. The molecular basis of optical activity, John
Wiley and Sons Inc.1979
• Jorge, F. Autschbach, J, Ziegler, T Inorg. Chem. 2003,
42, 8902-8910 (On the origin of the optical activity in the
d-d transition region of Tris-Didentate Co(III) and Rh(III)
complexes.
• Huyeey, J.E., Keiter, E.A. and Keiter, R.L. Inorganic
Chemistry, HarperCollins College Publishers, 4th Ed.
1993, pgs 62, 492-3.
• Davis, J.C. Advanced Physical Chemistry, John Wiley
and Sons Inc.1965