Carbon Fullerenes

Formation Basic model –Clustering Chains, rings, tangled poly-cyclic structures or graphite sheets –Annealing (no collisions) Random cage, open cage, closed cage structures –Elimination of dangling bonds Fullerenes –Stone-Wales transformation »Migration of pentagons »Rearrangement to lower energy Critical parameters –Annealing time –Annealing temperature ms; K for the laser method 10 0 s; 1000 K for the arc discharge method

Formation Picture models –Pentagon road (1) Addition of dimers and trimers leaving pentagons as a deffect Reduction of dangling bonds, adjacent pentagons too much stress –Ring pentagon road (2) Stacking of proper size of C rings Pentagon annealing –Fullerene road (3) Linear chains up to C 10 Rings C 10 to C 20, fullerene from C 30, Addition of C 2 at two neighboring p-s –Ring annealing (4) Big rings, bi/tri-cyclic structures (C 60 + ) anneal under high T conditions –Chain annealing (5) Long chain with spiral structure –Graphite road (6) C 10 clusters, graphite sheet, curling –Nanotube road (7) Chips of carbon nanotubes 1

Formation Molecular dynamics (MD) simulations –Many-body potential function –Kinetic energy of clusters Classical mechanics translation, vibration and rotation –Clustering Collisions of atoms or clusters: grow and fragmentation of cluster Cooling: collisions with buffer gas and radiation Annealing between collisions T = 3000 K

Formation Temperature dependence of cluster structures Collision-free annealing of C 60 –Stone-Wales transformation

Formation Fullerene-like cage structures 2500<T<3500 –Extrapolation roughly agrees with experimental conditions

Formation Model of charges at bonds –Molecules: classical dynamics –Electrons: quantum mechanics Ground and excited states –Interaction potentials Covalent bonds, rotation, torsional vibration Interaction between atoms and electrons –bonding electron pairs at the centers of the covalent bonds –unshared electrons at approximately the same distance from the carbon atoms –Classical equations of motion for both Folding of flat carbon clusters –Unshared e – rearrange and form symmetrical sphere layer outside the fullerene C 24 flat cluster, 0 s Semispheroid, 50 ps Fullerene, 150 ps

Formation Another QM and MD simulation –Density functional theory Ring fusion spiral zipper mechanism –C atoms combine to C 2 and C 3 –n<10: linear chain C n sp hybrid prefer linear geometry –10<n<30: ring Energy gain in killing dangling bonds overcompensates for strain energy caused by folding –n>30: ring structure can grow in fullerene

Synthesis Graphite vaporization or ablation –Laser –Resistive heating –AC or DC arc Pyrolysis of hydrocarbons –Flame combustion –Laser –Torch or tube furnace Ion implantation Temperature of condensation and annealing –1000÷1500 K C 60 $30/gram The first published mass spectrum of carbon clusters in a supersonic beam produced by laser vaporization of a carbon target in a pulsed supersonic nozzle operating with a helium carrier gas.

Synthesis Laser vaporization of graphite –laser-vaporization supersonic cluster beam technique (Rice Univ., Texas) –1985: H. W. Kroto (Sussex Univ., Brighton) & R. E. Smalley (Rice) Experiment –Nd:YAG 300 mJ, 535 nm, 5ns –Rotating graphite disk –Plasma of vaporized carbon atoms K –High-density helium pulse Condensation and transport –“Integration cup” Adjusts the time of clustering –Supersonic expansion Frizzing out the reactions –Ionization by excimer laser –Mass spectrometer Fullerenes are made wherever carbon condenses. It just took us a little while to find out. Smalley

Synthesis Laser evaporation of doped carbon

Synthesis Resistive heating of graphite –Carbon rod in 100 torr helium –Kratschmer-Huffman 1990 –First macroscopic quantities of C 60 Carbon arc –AC or DC arc in 100 torr helium –60 Hz, 100÷200 A, 10÷20 V rms –Continuous graphite rod feedeing The generator design based on the Kratschmer-Huffman apparatus.

Synthesis Pyrolysis of hydrocarbons –Benzene, acetylene, toluene –Polycyclic aromatic hydrocarbons PAH Naphtalene –Mechanism Removal of hydrogen Curling of joined rings –Optimum conditions Very low pressure and high temperature Examples –Combustion of benzene Premixed flame of benzene and oxygen with argon 20 torr, C/O 0.995, 10% Ar, 1800 K –Acetylene/oxygen/argon flame Adding Cl 2 increases fullerene yield –Torch heating of naphtalene Heating torch Pyrolysing torch: propane/oxygen 1000 ºC –Laser pyrolysis Photosensitizer SF 6 + C 2 H 4 CO 2 laser 100÷180 W, 300 torr Mechanism of formation of a partial C 60 cage from naphthalene Pyrolysis apparatus

Synthesis Low-pressure benzene/oxygen diffusion flame –p = 12 ÷ 40 torr, T max = 1500 ÷1700 K –Precursor PAH Elimination of CO from oxidized PAH thought to be a source of C pentagons –Highest yield of fullerenes High soot formation High dilution with argon

Synthesis Atmospheric pressure combustion Oxy-acetylene torch (Ferrocene (C 10 H 10 Fe) – 60 ) Syringe injector Benzene, Dicyclopentadiene, Pyridine (C 5 H 5 N), Thiophene (C 4 H 4 S) Stainless steel plate on water-cooled brass block (< 800 K)

Synthesis DC arc torch dissociation of C 2 Cl 4 (tetrachlorethylene) Operating conditions: Torch power: 56 kW He flow rate: 225 slm C 2 Cl 4 feed rate: 0.29 mol/min

Synthesis Ion implantation –Carbon ions 120 keV –Copper substrates 700÷1000 ºC –Thin film (diamond, fullerenes, onions) –Endohedral fullerenes Evaporation of fullerene (C 60 ) onto a substrate Ions of dopant 60

Solid State C 60 - Fullerite Face-centered cubic (fcc) –The most densely packed structure –Lattice constant a = Ǻ – Weak Van der Waals bonds Soft –Molecules spin nearly freely around centers Simple cubic (sc) –T<261 K –Fixed rotational axis 4 C 60 molecules arranged at vertices of tetraeder, spinning around different but fixed axis –Weak coulombic interaction Fixed orientation of molecules –T<90 K: molecules entirely frozen Polymeric –Covalent bonds –Photo-excitation, molecular collisions, high-pressure/temperature, ionization –Insolvable in toluene

Purification Extraction from carbon soot –C n<100 solvable in aromatic solvents Toluene, benzene, hexane, chloroform –C 60 magenta –C 70 dark red –C n>100 high boiling-solvents trichlorbenzene Separation by chromatograph

Derivatives Intercalation (fullerides) –Octahedral or tetrahedral inter. sites –Alkali or alkaline-earth metal atoms Na, K, Rb, Cs, Ca, Sr and Ba) –Charge transfer to the cage –Superconductors –Polymers Ba 6 C 60 7 K K 3 C K Rb 3 C K Cs 3 C K Cs 2 RbC K Polymerized Rb 1 C 60 C 60 -Fullerene tetrakis(dimethylamino)ethylene - ferromagnet

Derivatives Heterofullerenes –Substitution of an impurity atom with a different valence for C on the cage B, N, BN Nb C 59 X (X=B,N): nonlinear optical properties –Deformation of the electronic structure, strong enhancement of chemical activity –Radicals which can be stabilized by dimerization Azafullerenes: (a) C 59 N, (b) C 59 HN, and (c) (C 59 N) 2 C 48 N 12

Derivatives Exohedral –Covalent addition of atom or molecule –Hydrogenation C 60 H 18, C 60 H 36 –Fluorination C 60 F 36, C 70 F 34, C 60 F 60 (teflon balls) –Oxidation –Organic groups and complexes C 60 Cl 6 (eta2-C70-Fullerene)-carbonyl-chloro- bis(triphenylphosphine)-iridium

Derivatives Endohedral –Synthesis Evaporation of doped carbon –Arc, laser Ion implantation Noble gases –without overlap of Van der Waals radii Metallofullerenes –B, Al, Ga, Y, In, La –Stabilize cages not fulfilling isolated pentagon’s rule (n<60) –With permanent dipole moment form di/trimers and large aggregates on metal surfaces and C 60 films Alkali metals Lanthanide metals N, P (Group V) Synthesis of microcapsules for medical applications 60 60

Properties C 60 electron affinity EA = 2.65 eV (Cl 3.62, ) –more electronegative than hydrocarbons Dissolves in common solvents like benzene, toluene, hexane Readily sublimes in vacuum around 400°C Low thermal conductivity Pure C 60 is an electrical insulator C 60 doped with alkali metals shows a range of electrical conductivity: –Insulator (K 6 C 60 ) to superconductor (K 3 C 60 ) < 30 K Interesting magnetic and optical properties –Ferromagnetism At high pressure C 60 transfoms to diamond C 60 soft and compressible brown/black odorless powder/solid Flexible chemical reactivity breathing vibrational mode Pentagonal pinch mode

Properties Simulation of C 60 -C 240 collision Simulation of C 60 melting Kinetic energy = 10 eVKinetic energy = 100 eVKinetic energy = 300 eV David Tomanek Theoretical Condensed Matter Physics Michigan State University

Potential applications Lubrication –Molecular-sized ball bearing Not economical Superconductors –Intercalation metal fullerides (Semi)Conductors –Excellent conductors when compressed Photoconductors –add conducting properties to other polymers as a function of light intensity Optical Limiters –C 60 and C 70 solutions absorb high intensity light: protection for light- sensitive optical sensors Atom Encapsulation –Radioactive waste encapsulation 82 Rh-C 60 polymer with vacancies Excess spin density Dipole moment of magnitude Debye per C 60 unit

Potential applications Diamond films –Smoother than vaporizing graphite Novel polymers Optoelectronic nanomaterials and buliding blocks for nanotechnology –Endohedral fullerenes –Nanobots Medical applications –Magnetic Resonance Imaging markers Metal organic complex (toxic Ga) –contrast agents, tracers –anti-viral (even anticancer) agents –neuroprotective agents –fullerene-based liposome drug delivery systems –deployment of fullerene therapeutics to targeting vehicles Water soluble tail (red & gray) Encapsulates 2 gadolinium metal atoms (purple) and 1 scandium (green) attached to central nitrogen atom H 2 O molecules (red & yellow) MRI fullerene contrasting agent

Potential applications Potential AIDS inhibitor –HIV reproduces by growing long protein chains –Protein is cut in the active site of enzyme HIV-protease –Derivative of C 60 has been synthesized that is soluable in water Model of C 60 docked in the binding site of HIV-1 protease