7 Inorganic Chemistry-II (Metal-Ligand Bonding, Electronic Spectra and Magnetic Properties of Transition Metal Complexes) MODULE No

Web links

 http://www.slideshare.net/jaggu007/opticalrotatory-dispersion  http://www.slideshare.net/sujitpatel11/optical-rotatory-dispersion  http://www.analyticalchemistrygsu.com/2012/04/difference-between-optical-rotatory.html  http://www.docstoc.com/docs/113019213/Optical-Rotatory-Dispersion-and-Circular- Dichroism  http://dc126.4shared.com/doc/Ib7aZz9A/preview.html

Suggested Readings Miessler, G. L.; Tarr, D. A. (2003). Inorganic Chemistry (3rd ed.). Pearson Prentice Hall. ISBN 0-13-035471-6

Drago, R. S.Physical Methods In Chemistry. W.B. Saunders Company. ISBN 0721631843 (ISBN13: 9780721631844)

Mason, S. F. (1982). Molecular Optical Activity and the Chiral Discriminations.Cambridge University Press. ISBN 0521 24702 0

CHEMISTRY PAPER No.: 7 Inorganic Chemistry-II (Metal-Ligand Bonding, Electronic Spectra and Magnetic Properties of Transition Metal Complexes) MODULE No. 26: Assignment of Absolute Configuration of Chiral Coordination Complexes

Purcell, K. F.; Kotz, J. C. Inorganic Chemistry (India ed.). Cengage Learning . ISBN 978-81-315-1371-2

Geoffroy, G. L. Topics in Inorganic and Organometallic Stereochemistry, Volume 12, John Wiley & sons. ISBN 0-471-05292-2

Zelewsky, A.v. Stereochemistry of Coordination Compounds. John Wiley & sons. ISBN 0 471 95599 X(paper)

Glossary

A Absolute configuration: The spatial arrangement of the atoms of a chiral molecular entity (or group) with its stereochemical description.

Asymmetric

It is applied to a molecule totally lacking any symmetry.

Bidentate ligand

A bidentate ligand has two points at which it can attach to the central metal ion. For example ethylenediamine has two amine groups by which it can attach to the central metal ion.

Binuclear complex

Any coordination complex having two metal ions in the coordination sphere is called binuclear complex.

C Chromophore A chromophore is the part of a molecule responsible for its color. The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state

Complex Complex or coordination compound is formed when metal ion (central ion) reacts with molecules or ions which have free electron pairs (ligand). Metal ion and ligand are bonded with a polar covalent bond in which both electrons are given by the ligand.

Configuration: the spatial arrangement of ligands around the metal ion.

Conformation: The spatial arrangement of the atoms affording distinction between stereoisomers which can be interconverted by rotations about formally single bonds.

Coordination sphere The central metal ion plus the attached ligands of a coordination compound is called coordination sphere.

Diastereomers: Diastereomers are stereoisomers not related through a reflection operation. They are not mirror images of each other. These include geometrical isomers and non-enantiomeric optical isomers.

Dipole Moment

Dipole moment (μ) is the measure of net molecular polarity, which is the magnitude of the charge Q at either end of the molecular dipole times the distance r between the charges.Dipole moments tell us about the charge separation in a molecule. The larger the difference in electronegativities of bonded atoms, the larger the dipole moment. For example, NaCl has the highest dipole moment because it has an ionic bond (i.e. highest charge separation).

Dissymmetric: It is applied to a molecule that lacks a rotation-reflection (Sn) axis. As it lacks a Sn

axis, the dissymmetric molecule has neither a plane of symmetry (S1) nor a center of symmetry (S2).

In order for a molecule to have an enantiomer, it must not have a Sn axis. However, dissymmetric

molecule may have proper axis of rotation Cn (n>1).

Enantiomers

Enantiomers are two stereoisomers that are related to each other by a reflection: They are mirror images of each other, which are non-superimposable. Human hands are a macroscopic analog of stereoisomerism.

Ligands: an ion or molecule which donates electron density to a metal atom /ion to form a complex

Lone Pair: An electron pair in the valence shell of an atom which does not participate in bonding, i.e. it is associated with only one atom.

Monodentate ligand

A monodentate ligand has one point at which it can attach to the central atom. Many simple anions, or more accurately Lewis bases, can act as monodentate ligands, including, chloride ion (Cl-), hydroxide - ion (OH ), water (H2O), and ammonia (NH3).

Octahedral molecular geometry Octahedral molecular geometry (square bipyramidal shape) describes the shape of compounds where six atoms or ligands are symmetrically arranged around a central atom.

Proper rotation axis (Cn or Dn)

The rotation operations (both proper and improper) occur with respect to line called an axis of rotation. A proper rotation is performed by rotating the molecule 360°/n, where n is the order of the axis. If the resulting configuration is indistinguishable from the original, we say there exists an n-fold proper rotation axis (or Cn axis) in the molecule.

Refractive index

In optics the refractive index or index of refraction n of a substance (optical medium) is a dimensionless number that describes how light, or any other radiation, propagates through that medium. It is defined as

n= c/v

where c is the speed of light in vacuum and v is the speed of light in the substance. For example, the refractive index of water is 1.33, meaning that light travels 1.33 times slower in water than it does in vacuum.

Rotation-reflection (Sn) axis

It is also called improper axis of rotation. An improper rotation is performed by rotating the molecule 360°/n followed by reflection through the plane perpendicular to the rotation axis. If the resulting configuration is indistinguishable from the original, we say there exists an n-fold improper rotation

axis (or Sn axis) in the molecule.

Stereoisomers

Stereoisomers are isomeric molecules that have the same molecular formula and sequence of bonded atoms (constitution), but that differ only in the three-dimensional orientations of their atoms in space. This contrasts with structural isomers, which share the same molecular formula, but the bond connections and/or their order differ(s) between different atoms/groups—molecules that are stereoisomers of each other are the same structural isomer as each other

Time-Lines

Timelines Image Description

1811 Optical activity was first observed by François Jean Dominique Arago in the form of colours in sunlight that had passed along the optic axis of a quartz crystal placed between crossed polarizers.

http://en.wikipedia.org/wiki/Fran%C3 %A7ois_Arago 1812 Jean-Baptiste Biot established that the colours were due to two distinct effects: optical rotation and optical rotatory dispersion. In 1815, He observed optical activity for the ﬁrst time in organic compounds such as natural oils and terpenes, or solutions of camphor http://en.wikipedia.org/wiki/Jean_Bapt and cane sugar. iste_Biot

1822 The English astronomer, Sir John F.W. Herschel discovered that different crystal forms of quartz rotate the linear polarization in different directions.

http://en.wikipedia.org/wiki/John_Hers chel 1825 Augustin-Jean Fresnel’s celebrated theory of optical rotation followed from his discovery of circularly polarized light. He obtained circularly polarized light by means of a rhombus of glass, known as a Fresnel rhomb, having obtuse angles of 126° and acute angles of 54°.

http://en.wikipedia.org/wiki/Augustin- Jean_Fresnel

1847 Wilhelm Karl Ritter von Haidinger reported the differential absorption of circularly polarized light by amethyst crystals.

http://en.wikipedia.org/wiki/Wilhelm_ Karl_Ritter_von_Haidinger 1895–96 Aimé Auguste Cotton later observed Circular Dichroism of copper and chromium tartrate solutions.

http://www.ipnl.in2p3.fr/delphi/laktine h/monitorat/public_html/cotton/cotton. html

1898 Thomas Martin Lowry noted the change in optical rotation on nitro-d- camphor with time and invented the term mutarotation to describe this phenomenon. In 1935, he wrote a monograph on Optical Rotatory Power. http://en.wikipedia.org/wiki/Martin_L In 1929,Werner Kuhn later very owry carefully repeated Cotton’s work with the key compound, potassium chromium(III) tartrate and found it fully correct. In 1933, S. Mitchell in his treatise on the Cotton effect simply shows an inverted CD curve similar to cotton work.

Early 1950s A revolution in the study of optically active molecules was brought about through the introduction of instrument to measure optical rotatory dispersion: The Roussel- Juoan dichograph, based around the Pockel cell, a tetragonal crystal of monoammonium phosphate. http://www.jascoinc.com/products/spe

ctroscopy/circular-dichroism The Japan Spectroscopic Corporation, subsequently made Jasco CD instruments are described by the company as ‘spectropolarimeters’ despite their now being designed to primarily measure CD not ORD. 1960 Carl Djerassi, Steroid chemistry was one of the first areas to benefit by optical rotatory dispersion, mainly as a result of the pioneering work of Djerassi.

http://en.wikipedia.org/wiki/Carl_Djer assi

1914 The ﬁrst Werner complex for which both ORD and CD data through an absorption band were obtained, namely, potassium (trisoxalato)iridate(III) dihydrate, K3[Ir(C2O4)3]·2 H2O by M. Delepine

1923 Israel Lifshitz started a series of papers called “Investigations of Rotatory Dispersion”. In the first paper, he presented and discussed ORD data of complexes of Cr(III), Co(III), Ni(II), and UO22− ions with 3- nitrocamphor optically active camphor derivatives, including nitrocamphor. These compounds exhibited Cotton effects in the visible range. 1928 F. M. Jaeger extended the chiroptical studies to cobalt complexes with 1,2- diamino ligands, and he reported the Cotton effects in [Co(rac-trans-1,2- diaminocyclopentane)3]Cl3 · 4H2O at 470 nm and in [Co(rac-trans-1,2- rac-trans-1,2- diaminocyclopentane)(en)2]Br3·2H2 diaminocyclopentane O at 500 nm .

1934 Werner Kuhn reinvestigated Werner complexes, making use of advanced instrumentation. With potassium (trisoxalato)cobaltate(III), for example, the Cotton effect at  = 600 nm was measured both in rotatory dispersion and in circular dichroism

1965 Von P. Crabbé used Optical Rotatory Dispersion and Circular Dichroism in Organic Chemistry

1972 Von P. Crabbé used ORD and CD in Chemistry and Biochemistry