Fullerenes

fullerenes

1. DEPARTMENT OF CHEMISTRY TKMM COLLEGE NANGIARKULANGARA

2. FULLERENES

3. FULLERENE An allotrope of carbon The most famous fullerene is C 60 Discovered by H W Kroto and R Smalley at Rice University ,USA (1985) Popularly known as Buckministerfullerene in honour of the American architect Buckminister Fuller The shape of C 60 resembles the dome structure based on hexagons and pentagons designed by Fuller

4. The research group that discovered the fullerenes at Rice University in September of 1985. standing: Curl, kneeling (left to right): O’Brian, Smalley, Kroto and Heath Nobel Prize in chemistry in 1996

5. The shape of C 60 resembles the geodesic dome structure based on hexagons and pentagons designed by Fuller in 1960's FULLERENE C 60

6. fullerenes C 60 is also known as buckyball as it is a spherical clusture of carbon atoms arranged in a series of five and six membered rings to form a soccer ball shape Other relatively common clusters are C 70 , C 72 , C 74 , C 76 , C 80 , C 82 and C 84 (plenty of others, higher or lower than C 60 , exist too but less abundant in the experimentally produced mixture fullerene soot).

7. fullerenes C 70 C 60

8. Types of fullerenes Since the discovery of fullerenes in 1985, structural variations on fullerenes have evolved well beyond the individual clusters themselves. Examples include : buckyball clusters : smallest member is C 20 (unsaturated version of dodecahedrane ) and the most common is C 60 ; nanotubes : hollow tubes of very small dimensions, having single or multiple walls; potential applications in electronics industry; megatubes : larger in diameter than nanotubes and prepared with walls of different thickness; potentially used for the transport of a variety of molecules of different sizes; polymers : chain, two-dimensional and three-dimensional polymers are formed under high pressure high temperature conditions nano"onions " : spherical particles based on multiple carbon layers surrounding a buckyball core; proposed for lubricants; linked "ball-and-chain" dimers : two buckyballs linked by a carbon chain; fullerene rings .

9. STRUCTURE OF C 60 A truncated icosahedron structure Icosahedron - a polygon with 60 vertices and 32 faces , 12 of which are pentagonal and 20 hexagonal A carbon atom is present at each vertex Aromatic and has several resonance structures Pentegons are separated by hexagons –The isolated pentogon rule Valancies of each carbon atom are satisfied by two single and one double bond ( sp 2 hybridised carbon ) Fullerene cages are about 7-15 Å in diameter , and are one carbon atom thick

10. Bond Structure and Reactivity The bonding pattern of the C 60 fullerene , with yellow bonds representing double bonds and red bonds representing single bonds . The pentagonal rings contain only single bonds ; double bonds have a shorter bond length and lead to instability in the pentagonal ring . The limitations on double bond locations lead to poor delocalization of electrons, increasing the molecule’s reactivity. C 60 fullerene

11. C 60 fullerene C 60 form a normal face- centred cubic lattice The solid state NMR spectrum of shows that the solid is acting like a liquid and the molecules are tumbling on their lattice sites (gives a sharp line at 143ppm without any magic angle spinning , instead of a broad line as expected for a solid) X-ray diffraction shows this to be true C 60 fullerene show selectivity for intercalated ions as the tetrahedral and octahedral holes have significant size differences Cesium fits comfortably into octahedral holes but it is large to be accommodated in the tetrahedral holes

12. SYNTHESIS AND PURIFICATION OF FULLERENES Fullerenes are prepared by vapourising a graphite rod in a helium atmosphere Mixtures of fullerenes like C 60 , C 70 are formed which are separated by solvent extraction pure C 60 is isolated from this mixture by column chromatography

13. SYNTHESIS AND PURIFICATION OF FULLERENES ARC DISCHARGE METHOD A welding transformer, a chamber connected to a vacuum pump and some graphite rods are needed The graphite electrodes are brought into close contact with each other and an arc is struck in an atmosphere of He or Ar The soot generated is collected on water cooled surfaces After sustaining the arc for several minutes ,the vacuum is broken and soot is collected soxhlet extracted in toluene or benzene ,resulting in a dark reddish-brown solution which is a mixture of fullerenes

14. SYNTHESIS AND PURIFICATION OF FULLERENES The soluble material is subjected to chromatographic separation C 60 Can be collected by toluene as mobile phase C 70 Can be collected by toluene / o-dichlorobenzene as the eluant C 60 Solution is violet and C 70 solution is reddish brown in colour Higher fullerenes C 76 , C 78, C 82 etc require HPLC for separation Evaporation is also used as a method of purification (substantial difference in the onset of evaporation between C 60 and C 70 Calixarenes have been used in the purification of fullerenes

15. SYNTHESIS AND PURIFICATION OF FULLERENES

16. SYNTHESIS AND PURIFICATION OF FULLERENES Fullerenes have been found in flames ,upon chemical vapor deposition used to produce diamond Fullerenes can be synthesised from camphor Upon laser evaporation , highly unsaturted carbonaceous ring system produce C 60 There are several other exotic means of producing C 60

17. CHARACTERISTION OF FULLERENES Synthesis and purification were followed by the characterization of fullerenes in a veriety of technique XRD Mass spectrometry NMR spectroscopy UV/VIS spectroscopy IR spectroscopy RAMAN spectroscopy The predicted electronic structure was confirmed by HeI and HeII photoelectron spectroscopies

18. PROPERTIES OF FULLERENES Quite stable from chemical and physical points of view (breaking the balls requires temperatures of about 1000 °C). Highest tensile strength of any known 2D structure or element. Highest packing density of all known structures Impenetrable to all elements under normal circumstances, even to a helium atom with an energy of 5 eV .

19. PROPERTIES OF FULLERENES A black powdery material Forms deep magenta solution in benzene Very tough and thermally stable Exists as a discrete molecule unlike the other two allotropes of carbon (graphite and diamond) Can be compressed to lose 30% of its volume without destroying its carbon cage structure

20. APPLIATIONS OF FULLERENES As a lubricant due to its sherical structure -the bucky balls act as a molecular ball bearings As a superconductor when mixed with alkali metals Used as a soft ferromagnet (TDAE C 60 ) Used in electronic , microelectronic and non-linear optical devices Researchers have found that water-soluble derivatives of fullerenes inhibit the HIV-1 protease (enzyme responsible for the development of the virus) and are therefore useful in fighting the HIV virus that leads to AIDS .