CHEMISTRY MODULE No. : 21(Optical

Web links

 http://en.wikipedia.org/wiki/Coordination_complex  http://www.youtube.com/watch?v=g-U5v91GaNw  http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0m/s27-04- coordination-compounds.html  http://www.chem.purdue.edu/gchelp/cchem/iintro2.html  http://www.britannica.com/EBchecked/topic/136410/coordination- compound/277793/Enantiomers-and-diastereomers

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

Huheey, J. E.; Keiter, E. A.; Keiter, R. L.; Medhi, O. K. (2006). Inorganic Chemistry: principles of

Structure and reactivity (4th ed.). Pearson Education India. ISBN 978-81-7758-130-0

CHEMISTRY PAPER No.7: Inorganic Chemistry-II (Metal-Ligand Bonding, Electronic Spectra and Magnetic Properties of Transition Metal Complexes) MODULE No. : 21(Optical Isomerism)

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

Shriver, D. F.; Atkins, P. W. (2001). Inorganic Chemistry (4th ed.). Oxford University Press. pp. 227– 236. ISBN 0-8412-3849-9

Research papers/articles: 1. http://pubs.rsc.org/en/content/articlelanding/2014/cs/c3cs60189g#!divAbstract

Kumar, Prashant; Kumar Gupta, Rakesh and Pandey, Daya Shankar, Half-sandwich arene ruthenium complexes: synthetic strategies and relevance in catalysis, Chem. Soc. Rev., 43 (2014): 707-733

2. http://pubs.rsc.org/en/content/articlelanding/2013/cs/c2cs35270b#!divAbstract

Constable, Edwin C., Stereogenic metal centres – from Werner to supramolecular chemistry, Chem. Soc. Rev., 42(2013): 1637-1651

Glossary

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

Ambidentate ligands An ambidentate ligand has two different modes of attachment. Examples include NO2 (N or O), CN- (C or N), and SCN- (S or N).

Asymmetric

It is applied to a molecule totally lacking in symmetry.

Bidentate ligand CHEMISTRY PAPER No.7: Inorganic Chemistry-II (Metal-Ligand Bonding, Electronic Spectra and Magnetic Properties of Transition Metal Complexes) MODULE No. : 21(Optical Isomerism)

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.

Bridged polynuclear complexes

In some complexes, a ligand binds to two or more metal ions, linking them together to produce a bridge between two metal ions. These complexes are called Bridged polynuclear complexes. Bridging is indicated by the Greek letter mu (μ) appearing before the ligand name and separated by a hyphen. An example is sulfide in an iron-sulfur cluster.

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.

Counter ion Counter ion is the ion that accompanies an ionic species in order to maintain electric neutrality

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

CHEMISTRY PAPER No.7: Inorganic Chemistry-II (Metal-Ligand Bonding, Electronic Spectra and Magnetic Properties of Transition Metal Complexes) MODULE No. : 21(Optical Isomerism)

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).

Empirical formula

A formula that gives the simplest whole-number ratio of atoms in a compound. A simple example of

this concept is that the empirical formula of hydrogen peroxide, or H2O2, would simply be H.

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.

I Infrared spectroscopy

Infrared spectroscopy (IR spectroscopy) is the spectroscopy that deals with the infrared region of the electromagnetic spectrum that is light with a longer wavelength and lower frequency than visible light. The infrared portion of the electromagnetic spectrum is usually divided into three regions; the near-, mid- and far- infrared, named for their relation to the visible spectrum. The higher-energy near- IR, approximately 14000–4000 cm−1 (0.8–2.5 μm wavelength) can excite overtone or harmonic vibrations.

Ion exchange method

Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion exchangers'. Typical ion exchangers are ion exchange resins (functionalized porous or gel polymer), zeolites, montmorillonite, clay, and soil humus.

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. CHEMISTRY PAPER No.7: Inorganic Chemistry-II (Metal-Ligand Bonding, Electronic Spectra and Magnetic Properties of Transition Metal Complexes) MODULE No. : 21(Optical Isomerism)

Labile: readily or continually undergoing chemical, physical, or biological change or breakdown: unstable.

Magnetic Moment

The magnetic moment (or magnetic dipole moment) of an object is a measure of the object's tendency to align with a magnetic field. It is a vector quantity, with the positive direction defined by the way the object responds to a magnetic field: The object will tend to align itself so that its magnetic moment vector is parallel to the magnetic field lines. There are two sources for a magnetic moment: the motion of electric charge and spin angular momentum. For example, a loop of wire with a current running through it will have a magnetic moment proportional to the current and area of the loop, pointing in the direction of your right thumb if your fingers are curling in the direction of the current. Alternatively, an electron, which is a spin-1/2 fermion, has an intrinsic magnetic moment proportional to its spin.

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.

Piano-stool compounds

A complex that has four different ligands with one of them being a cyclic polyhapto hydrocarbon ligand acts as a chiral half-sandwich complex with an asymmetric metal center like an asymmetric carbon atom.

Polyhapto ligand

Hapticity (represented by η) refers to the number of contiguous atoms that comprise a donor site and attach to a metal center. Butadiene forms both η2 and η4 complexes depending on the number of carbon atoms that are bonded to the metal.

Proper rotation axis (Cn or Dn)

CHEMISTRY PAPER No.7: Inorganic Chemistry-II (Metal-Ligand Bonding, Electronic Spectra and Magnetic Properties of Transition Metal Complexes) MODULE No. : 21(Optical Isomerism)

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.

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

trans effect

trans effect is the labilization (making unstable) of ligands that are trans to certain other ligands, which can thus be regarded as trans-directing ligands.

Time-Lines

Timelines Image Description

Late 17th century Christiaan Huygens discovers plane- polarized light

CHEMISTRY PAPER No.7: Inorganic Chemistry-II (Metal-Ligand Bonding, Electronic Spectra and Magnetic Properties of Transition Metal Complexes) MODULE No. : 21(Optical Isomerism)

1815 Jean Baptiste Biot was among the first to uncover the optically active phenonmen, but there were many others who made significant contributions to what is known today. He was filtering out the light so that he could monitor its behavior, then realized that polarized light passing through certain substances can be rotated. The substance that he first tested was a sugar solution. http://jeanbont.pbworks.com/w/page/3 7083486/L'histoire%20d'isom%C3%A 8res%20optiques

1853 Louis Pasteur was the first who demonstrated chiral molecules. Pasteur separated the left and right crystal of tartaric acid from each other to form two piles of crystals: in solution one form rotated light to the left, the other to the right, while an equal mixture of the two forms cancelled each other's effect, and does not rotate the polarized light. http://en.wikipedia.org/wiki/Louis_Pas teur

1874 Jacobus van't Hoff accounted for the phenomenon of optical activity by assuming that the chemical bonds between carbon atoms and their neighbors were directed towards the corners of a regular tetrahedron. This three-dimensional structure perfectly accounted for the isomers found in nature. He proposed the tetrahedral carbon atom. He pointed out that http://jeanbont.pbworks.com/w/page/3 when CH4 was converted to CH3Y 7083486/L'histoire%20d'isom%C3%A (Y can be Cl, Br, OH) only one 8res%20optiques structure existed (absence of isomers). Also, regarding CH2YZ, only one structure existed.

CHEMISTRY PAPER No.7: Inorganic Chemistry-II (Metal-Ligand Bonding, Electronic Spectra and Magnetic Properties of Transition Metal Complexes) MODULE No. : 21(Optical Isomerism)

1894 Hermann Emil Louis Fischer identified 16 stereoisomers of sugar (aldohexoses- C6H1206). He also invented D and L glucose. D stands for dextrorotatory-clockwise and L for levorotatory-counterclockwise. He also invented Fisher projections to distinguish the three dimensional

http://en.wikipedia.org/wiki/Hermann shapes of isomers. _Emil_Fischer

1911 Alfred Werner extended optical isomerism to coordination complexes. He resolved [Co(en)2Cl2]Cl into its optical isomers.

Source: http://en.wikipedia.org/wiki/Alfred_ Werner

CHEMISTRY PAPER No.7: Inorganic Chemistry-II (Metal-Ligand Bonding, Electronic Spectra and Magnetic Properties of Transition Metal Complexes) MODULE No. : 21(Optical Isomerism)