29 Fullerene Chemistry By M.J. ROSSEINSKY Inorganic Chemistry Laboratory University of Oxford South Parks Road Oxford OX1 3QR UK 1 Introduction As in the years following the bulk synthesis of c60 in October 1990 1994 has seen a large amount of activity in fullerene chemistry and physics. This Report is a necessarily selectike account of the 1994 literature with the focus on fullerene-like carbons and their inorganic chemistry with a less thorough coverage of the rapidly developing field of organic derivitization of c60 and its homologues. The proceedings of a NATO AS1 and a book on molecular fullerene chemistry have 2 C, and the Higher Fullerenes Synthesis Separation and Physical Properties LDTOFMS has shown that 0.1ppm of C, is present in the Allende mete~rite.~ Although indications of an hcp as well as the fcc polymorph of C, have been known for some time 1994 saw the first preparation and crystallographic analysis of an hcp single crystal of C,,.4 A dynamic light scattering study showed that the hydrodynamic radius of C6 is 6.4 & 0.1 8 in ben~ene.~ 30-40 nm particles of C6 have been shown to be formed by vapour condensation in a flow system.‘ The effect of temperature and pressure have been the subject of considerable interest a molecular dynamics study indicates that c60 melts at above 4000 K.7 Synchrotron powder X-ray diffraction revealed that the threshold pressure for the onset of orientational ordering in space group Pa3 at room temperature is less than 0.5GPa.8 Application of more than 10GPa causes the lines to broaden and 23 GPa produces an amorphous ‘collapsed fullerite’ phase.’ Heating C, to higher temperature under 5 GPa pressure followed by quenching allowed isolation of metastable fcc (T = 3400 “C a = 13.6A) and rhombohedra1 phases (T= 5-800 “C,a = 9.22 A c = 24.6 A).In the toluene-insoluble ’ ‘Physics and Chemistry of the Fullerenes’ NATO AS1 Series C Vol. 443 ed. K. Prassides 1994. ‘The Chemistry of the Fullerenes’ A. Hirsch Thieme Verlag 1994. L. Becker J. L. Bada R. E. Winans and T.E. Bunch Nature 1994 372 507. J. L. de Boers S. van Smaalen V. Petricek M. Dusek M. A. Verheijen and G. Meijer Chem. Phys. Lett. 1994 219 469. * Q. Ying J. Marecek and B. Chu J. Chem. Phys. 1994 101 2665. A. S. Gurav T.T. Kodas L.-M.Wang E.I. Kauppinen and J. Joutsensaari Chem. Phys. Lett. 1994,218 304. ’ S. G. Kim and D. Tomanek Phys. Rev. Lett. 1994 72 2418. ’A. P. Jephcoat J.A. Hriljac L. W. Finger and D. E. Cox Europhys. Lett. 1994 25 429. J. Haines and J. M. Leger Solid State Comrnun. 1993 90 361. 577 578 M. J. Rosseinsky rhombohedra1 phase the close c6O-c60 centre to centre separation is accompanied by IR Raman and NMR signatures of the formation of c6o-c,o bonds." These phases revert to fcc c60 after heating to 300°C. The physical properties of c60 continue to attract attention. The orientational ordering transition at 260K is accompanied by a 1% reduction in the diamagnetic susceptibility showing a novel effect of a cooperative phase transition on a molecular property detailed ab initio calculations show that the diamagnetic susceptibility of C, is very sensitive to the molecular structure with a 0.07% change in C-C bond lengths producing a 1.2% change in the susceptibility.' Measurement of the picosecond absorption spectrum of a photoexcited c60 film revealed an optical absorption assigned to free (tl12< 15ps) and self-trapped (tlIz-250 ns)excitons.12 Exposure of a C, thin film to oxygen reduces the photoconductivity by several orders of magnitude as traps are created which reduce the carrier lifetime.' Photodiodes have been made from MEH-PPV sensitized with C,,.14 An A1/C6,/Au sandwich device has potential for application in the area of fast non-linear optoelectronic detectors.' Photo- and electro-luminescent emission from c60 have been studied.16 The 1.2K phosphores-cence of c60 has been assigned to both triplet state and shallow trap or exciton emission.Significant advances in the synthesis and purification of C6 and the higher fullerenes have been made. c60can be formed from the natural source camphor.' An improved chromatographic separation using a Norit-Elorit stationary phase and toluene followed by 1,2 dichlorobenzene eluants allows isolation of c60 and 98% pure C70 in one pass." Two different calixarenes can be used to isolate c60 by fractional precipitation.20 I3C CPMAS NMR has been used to study the fullerene-calixarene interaction in these complexes.2' A flash chromatography method for the isolation of gram quantities of C7 has been reported,22 while the differential solubilities of C6 and C70 in CS or o-xylene produces a simple method for the isolation of >99.5% pure c60 or >99% pure C7,.23 At 970 K vacuum effusion on a baffled distillation column with a linear temperature gradient has been shown to allow synthesis of 99.97% pure C60.24 lo Y.Iwasa T. Arima R. M. Fleming T. Siegrist 0.Zhou R. C. Haddon L. J. Rothberg K. B. Lyons H. L. Carter Jr. A. F. Hebard R. Tycko G. Dabbagh J. J. Krajewski G. A. Thomas and T. Yagi Science 1994 264 1570. I' (u) A. P. Ramirez R.C. Haddon 0.Zhou R. M. Fleming J. Zhang S. M. McClure and R. E. Smalley Science 1994,265.84;(b)W. Luo H. Wang R. S. Ruoff J. Cioslowski and S. Phelps,Phys. Rev. Lett. 1994 73 186. T. W. Ebbesen Y. Mochizuki K.Tanigaki and G. Hirua Europhys. Lett. 1994 25 503. l3 C.H. Lee G. Yu B. Kraabel D. Moses and V.I. Srdanov Phys. Rev. B 1994 49 10572. l4 G. Yu K. Pakbaz and A. J. Heeger Appl. Phys. Lett. 1995 64 3422. C.H. Lee G. Yu D. Moses and A.J. Heeger Appl. Phys. Lett. 1994,65 664. l6 H. J. Byrne A. T. Werner J. Anders W. K. Maser M. Kaiser L. Akselrod W. W. Ruhle A. Mittelbach and S. Roth J. Modern Optics 1994 41 1243. l7 D. J. Vandenheuvel 1. Y. Chan E. J. J. Groenen J Schmidt and G. Meijer Chem. Phys. Lett. 1994,231 111. K. Mukhopadhyay K. M. Krishna and M. Sharon Phys. Rev. Lett. 1994 72 3182. l9 R. Taylor G.J. Langley H. W. Kroto and D. R.M. Walton J. Chem. SOC. Chem. Commun. 1994 15. (a)J. L. Atwood G. A. Koutsantonis C. L. Raston Nuture 1994,368,229; (b)T.Suzuki K. Nakashima and S. Shinkai Chern. Lett. 1994 699. R. M. Williams J. M. Zwier J. W. Verhoeven G. H. Nachtegaal and A. P. M. Kentgens J. Am. Chem. SOC. 1994 116 6965. 22 W.A. Scrivens A.M. Cassell B. L. North and J. M. Toor J. Am. Chern. Soc. 1994 116 6939. 23 X. Zhou Z. Gu Y. Wu Y. Sun Z. Jin,Y. Xiong B. Sun,Y. Wu H. Fu,and J. Wang Curbon 1994,32,935. 24 R.D. Averitt J. M. Alford and N. J. Halas Appl. Phys. Lett. 1994 65 374. Fullerene Chemistry 579 Asymmetric osmylation allows resolution of c76 C,, and c84 c76 and C, are configurationally stable at the limit of their thermal stability.” The search for a rational synthesis of c60 continues and the preparation of C3oHl2 a hydrocarbon which constitutes half of c, and would dimerize to yield a ‘nonisolated pentagon’ D, C, isomer was achieved this year., The crystallography and polymorphism of C70 has been clarified a DSC study emphasized the importance of sample purity and indicates that both the majority equilibrium fcc and minority metastable hcp phases undergo two first order transitions associated with the successive freezing of rotation of the long molecular axis and spinning about that axis., Single crystal X-ray diffraction shows the C, molecules rotate freely in the hexagonal modification about the principal molecular axis (space group P6,/mm~).,~ Dilatometry showed three first order transitions in single crystals.29 Analysis of pulsed neutron diffraction measurements of the pair correlation function revealed C-C bond lengths of between 1.38 and 1.48A.30 Calorimetric determination of the heat of formation per C atom shows that C, (36.5 kJ mol-’) is more stable than c60 (38.8kJ mol-1).31 Helium pressure during fullerene synthesis strongly influences the fractions of the three known isolated pentagon isomers of C, which are formed with high pressure favouring the energetically most stable C, structure.32 Semi-empirical calculations on all 55 candidate isomers of c76 (those fitting the experimental 13C NMR) reveal the isolated pentagon D isomer as the most stable supporting the isolated pentagon rule.33 Both TEM and EELS studies show that C7 adopts an fcc structure.34 The electrochemistry of the D and D, isomers of c84 has been measured separately in pyridine each isomer displays five waves with the first three reversible in each cage.35 Laser ablation of C, films has provided evidence36 for two C , species a closed case fullerene (of D, or T symmetry) and a C, dimer whose structure is most probably the lowest energy dimer3 resulting from [2 + 21 cycloaddition of two 6 6 bonds.The area of gas-phase growth of fullerenes and metallocarbohedranes has been the subject of a recent review.3* 25 J.M. Hawkins M. Nambu and A. Meyer J. Am. Chem. SOC. 1994 116 7642. 26 P. W. Rabideau A. H. Abdourazak H. E. Folsom Z. Marcinow A. Sygula and R. Sygula J. Am. Chem. Soc. 1994 116 7891. ” A. R. McGhie J. E. Fischer P. A. Heiney P. W. Stephens R. L. Cappelletti D. A. Neumann W. H. Mueller H. Mohn and H. U. Meer Phys. Rev. B Condens. Matter 1994 49 12614.28 E. Blanc H.-B. Buergi R.Restori D. Schwarzenbach P. Stellberg and P. Venugopalan. Europhys. Lett. 1994 27 359. 29 C. Meingast F. Gugenberger G. Roth M. Haluska and H. Kuzmany 2.Phys. B Condens. Matter 1994 95 61. 30 A.V. Nikolaev T.J.S.Dennis K. Prassides and A.K. Soper Chem. Phys. Lett. 1994 223 143. 31 H. D. Beckhaus S. Verevkin C. Ruchardt F. Diederich C. Thilgen H. U. Termeer H. Mohn and W. Muller Angew. Chem. Int. Ed. Engl. 1994 33 99. ‘2 T. Wakabayashi K. Kikuchi S. Suzuki H. Shiromaru Y. Achiba J. Phys. Chem. 1994 98 3090. 33 S.J. Austin P. W. Fowler G. Orlandi D. E. Manolopoulos and F. Zerbetto Chem. Phys. Lett. 1994,226 219. 34 J.F. Armbruster H.A. Romberg P. Schweiss P. Adelmann M. Knupfer J. Fink R.H. Michel J. Rockenberger and F.Hennrich 2. Phys. B Condens. Matter 1994 95 469. 35 P. Boulas M. T. Jones K. M. Kadish R. S. Ruoff D. C. Lorents and D. S. Tse J. Am. Chem. Soc. 1994 116 20. 36 J. M. Hunter J. L. Fye N. M. Boivin and M.F. Jarrold J. Phys. Chem. 1994 98 7440. 37 N. Matsuzawa A. Masafumi D. A. Dixon and G. Fitzgerald J. Phys. Chem. 1994 98 2555. 38 M.T. Bowers ACC. Chem. Res. 1994 27 324. M. J. Rosseinsky 3 Fullerene Chemistry Molecular Chemistry.-A review of the structure and reactivity of c60 has been published.39 The solubilization of fullerenes in aqueous media continues to attract attention (see also under Organic chemistry). Both molecular and colloidal (10nm diameter) C6 are found in aqueous micellar solutions of the non-ionic surfactant Triton X-100.40 The reaction of C6 in CS with a saturated solution of y-cyclodextrin in ethanolic water has been shown to provide a mild route to the 1 :1 inclusion complex which is water soluble (0.33 mg mL- I) and displays two reversible one- electron reductions of the C6 molecule when dis~olved.~~ NMR and UV-visible studies of the 2 1 and 1 :1 adducts of y-cyclodextrin with c60 in water have been rep~rted.~' y-Cyclodextrin can also solubilize C, in water,43 and polyvinylpyrrolidine can be used to solubilize c60 and C, in water.44 The reactivity of fullerenes with hydrogenating agents shows the expected addition across the 6 6 double bonds.C60H2" and C7,H2" products are formed by diimide reduction.45 Zinc/acid reduction also results in C6& and C6,H4.46 C6& was shown to react with one equivalent of BH3-THF to give six C6oH4 isomers.47 Equilibrium studies and ab initio calculations on C70 show that 1,2 addition (using BH in THF) is favoured and the 1,9 isomer of C7oHz is more stable than the other experimentally observed 7,8 isomer (Figure l).48 Fluorine reacts with c60 to yield products with a variety of stoichiometries and isomers and this year has seen some clarification of the effect of reaction conditions on product formation.Sodium fluoride mediated fluorination at 250 "C yields 60% of a single structure of C6oF48 (the two enantiomers are shown in Figure 2).49 XPS studies of fluorinated C6oF solids indicate the formation of CF and CF groups at high fluorination levels (c6oFs3) due to breaking of some C-C bonds in the cage and the presence of oxygen as epoxide in the contaminant C6,F,0,.50 The compound C60F48 is 1.38 v easier to reduce than c60 and forms C6oF4g - reduction to C6oFi is followed by fluoride loss to give C60F47- which can then be reduced to C6OF;T .51 The reactivity of c60 with other strongly oxidizing species has also been studied extensively.Reaction with AsF in SO yields a non-conducting solid with a body-centred tetragonal str~cture.~ The reaction of MoF6 with c60 gives oxidized 39 H. W. Kroto R. Taylor and D. R. M. Walton Pure Appi. Chem. 1994 66 2091. 40 A. Beeby J. Eastoe and R.K. Heenan J. Chem. Soc. Chem. Commun. 1994 173. 41 P. Boulas W. Kutner M. T. Jones and K. M. Kadish J. Phys. Chem. 1994 98 1282.42 T. Anderson G.Westman 0.Wennerstroem and M. Sundahl J. Chem.Soc. Perkin Trans. 2 1994 1097. 43 T. Anderson M. Sundahl G. Westman and 0.Wennerstrom Tetrahedron Lett. 1994 35 7103. 44 Y.N. Yamakashi T. Yagami K. Fukuhara S. Sueyoshi and N. Miyata J. Chem. SOC.,Chem. Commun. 1994 517. 45 A. G.Avent A. D. Darwish D. Heimbach H. W. Kroto M. F. Merdine J. P. Parson C. Remars R. Roers 0.Ohashi R. Taylor and D.R.M. Walton J. Chem. Soc. Perkin Trans. 2 1994 15. 46 C. C. Henderson C. M. Rohlfing R. A. Assink and P. A. Cahill Angew. Chem. Int. Ed. Engi. 1994,33,786. 47 M.S. Meier P. S. Corbin V.K. Vance M. Clayton M. Mollman and M. Poplawska Tetrahedron Lett. 1994 35 5789. 48 C.C. Henderson C. M. Rohlfing K.T. Gillen and P. A. Cahill Science 1994 264 397. 49 A.A. Gakh,A. A. Tuiman J. L. Adcock R. A. Sachleben and R.N. Compton J. Am. Chem. Soc. 1994,116 819. D. M. Cox S.D. Cameron A. Tuinman A. Gakh J. L. Adock R. N. Compton E. W. Hagaman K. KniaL J. E. Fischer R. M. Strongin M. A. Cichy and A. B. Smith 1.Am. Chem. SOC. 1994 116 1115. 51 F. Zhou G.J. Van Berkel and B.T. Donovan J. Am. Chem. Soc. 1994 116 5485. 52 W.R. Datars T. R. Chien R. K. Nkum and P. K. Ummat Phys. Rev. €3 Condens. Matter 1994,50,4937. Fullerene Chemistry Figure 1 The structure of 7,8-C7,H (Reproduced by permission from Science 1994 264 397) ss RR Figure 2 The RR and SS enantiomers of C,,F,,. Fluorine atoms are omitted in the Schlegel diagrams-the lettering corresponds to distinct 9F NMR resonances of Juorine hound to the indicated carbons.(Reproduced by permission from J. Am. Chem. SOC. 1994 116 820) 582 M. J. Rosseinsky products containing MoF,.,~ c60 has been shown to react with SO, either neat or in fuming sulfuric acid to initially form radical cations which are intermediates in the formation of C6,(S03) (x z 3.5) sultones with C-S bonds.54 NO gas multiply nitrates c60 in toluene solution.55 Ozonolysis yields a mixture of oxidized products with ketone ester and epoxide functionalities.s6 Binary molecular solids in which there is no charge-transfer between c6 and the other molecule have produced some interesting chemical and structural features though the compounds are of course electrically insulating. (P4)2C60 is the first example of host-guest chemistry of the P molecule which occupies trigonal prismatic sites between close packed c60 layers stacked in a simple hexagonal manner.57 C60’4C6H6 has been shown by single crystal X-ray diffraction at 104K to have a honeycomb-like arrangement of c60 stacks with the channels containing ben- zene-the authors suggest the structure may be considered as a macroscopically ordered nanocomposite of fullerene and benzene domains.58 As would be predicted by consideration of the electrode potentials for the relevant redox couples TTF type donors seem insufficiently reducing to form charge-transfer salts with c60.The 1:1 complex BDMT-TTeF :c60is insulating and the structural data indicate that there is no charge-transfer to c60 from the organic donor.s9 Octamethylene-TTF can also be crystallized as a 1 1adduct with c60-again the crystal structure and high resistivity indicate the absence of charge-tran~fer.’~ A detailed electron diffraction study of iodine de-intercalation from (12)2C60 suggests the reaction proceeds by shearing along { 1010) type planes.60 A beautiful reaction is the intercalation of c60 into graphite by displacement of pre-intercalated aromatic hydrocarbons.61 Further investigations of proposed noble metal fullerene polymers have been made with the preparation of amorphous C6oPt species6 and a detailed electron diffraction study of the C6,Pd system this revealed small crystals of Pd for n = 1 and for 25% of the n = 3 sample 10% of the Pd3C6 sample contains a = 11.38 bcc crystallites for which a structural model based on 3 perpendicular sets of linear chains is proposed.63 Reaction of (Na(crown)+ ),C& with [PPNICl in acetonitrile afford (PPN+),CiO and the single crystal X-ray structure is interpreted in terms of a Jahn-Teller distortion of the C$ anion.64 Electrocrystallized Ph4PC6,.Ph,C1 adopts a supercell of the CsCl ‘3 A.Harnwi G. Dondainas and J. Dupuis Mol. Cryst. Liq. Cryst. Sect. A 1994 245 301. s4 G. P. Miller M. A. Buretea M. M. Bernado C. S. Hsu and H. L. Fang J. Chem. SOC. Chem. Commun. 1994 274. ’’ S. Roy and S. Sarkar J. Chem. Soc. Chem. Commun. 1994 275. 56 R. Malhotra S. Kumar and A. Satyarn J. Chem. Soc. Chem. Commun. 1994 1339. ” (a) R. E. Douthwaite M.L.H. Green S.J. Heyes M. J. Rosseinsky and J.F.C. Turner J. Chem.Soc. Chem. Commun. 1994 1367; (b)I. W. Locke A. D. Darwish H. W. Kroto K. Prassides R. Taylor and D. R. M. Walton Chem. Phys. Lett. 1994 225 186. 58 H. B. Buergi R. Restori P. Schwarzenbach A. L. Balch J. W. Lee B. C. Noll and M. M. Olrnstead Chem. Muter. 1994 6 1325. 59 (a)P. Wang W.-J. Lee I. Shcherbakova M. P. Cava and R. M. Metzger Synth. Met. 1994,64,319 (6)G. Saito T. Terarnoto A. Otsuka Y. Sugita T. Ban M. Kusunoki and K. Sakaguchi Synth. Met. 1994,64 359. 6o X. B. Zhang X. F. Zhang S. Amelinckx and H. Werner Appl. Phys. A 1994 58(2) 107. 61 B.A. Averill T. E. Sutto and J. M. Fabre Mol. Cryst. Liq. Cryst. Sect. A 1994 244 77. H. Nagashima Y. Kato H. Yarnaguchi E. Kimura T. Kawanishi M. Kato Y. Saito M. Haga and K. Ttoh Chem. Lett. 1994 1207.63 J. M. Cowley M.-Q. Liu B. L. Ramakrishna T. S. Peace A. K. Wertsching and M. R. Pena Carbon 1994 32 746. 64 P. Paul Z. Xie R. Bau P.D. W. Boyd and C. A. Reed J. Am. Chem. Soc. 1994 116 4145. Fullerene Chemistry Figure 3 The crystal structure of Ph,PC,,.Ph,PCI showing the pseudocubic sub-lattice of phosphorous atoms; for clarity the phenyl rings are omitted (Reproduced from J. Chem. SOC.,Chem. Commun. 1994,403) structure with c60 and C1-ordered in the anionic positions (Figure 3).65 EPR measurements have shown that Ph4PC,,.Ph,PI undergoes a dynamic Jahn-Teller distortion which becomes static below 140 K.66 Alkali Metal Ful1erides.-Several review articles have been published .6 There have been important developments in this area with a new superconductor with the highest T (40K)yet discovered for a molecular system and the structural characterization of a new family of polymers.Those who do not regard this field as chemistry should take note! The monotonic increase of T (superconducting transition temperature) with lattice parameter in the A3C6 family means that cS3c60 has long been sought. It was finally synthesized by Palstra et al. 68 by reduction of c60 with Cs metal dissolved in liquid h5 U. Bilow and M. Jansen J. Chem. Soc. Chem. Commun. 1994 403. 66 B. Gotschy M. Keil H. Klos and 1. Rystau Solid State Commun. 1994 92 935. 67 A. P.Ramirez,Superconductivity Rev. 1994,1,1(56);M. Gelfand Superconductivity Rev. 1994,1,103;M. L. Cohen Phil. Mag. B,1994,70 627. 6R T. T. M. Palstra 0.Zhou Y.Iwasa P. E. Sulewski R. M. Fleming B. R. Zegarski Solid State Commun. 1994 92 71. 584 M.J. Rosseinsky ammonia followed by deammoniation under vacuum at 150"C. However the crystal chemistry of this metastable system is complex with both body centred cubic (bcc) A15 and defect A,C, structures being formed. The value of T reaches a maximum of 40 K under 15 kbar of hydrostatic pressure. The increase of T under pressure is particularly important as it is counter to the conventional BCS theory and the observed pressure dependence of T in the lower transition temperature A,C,O systems. The very existence of monoanionic A,C, phases (A = K Rb Cs) has been controversial for some time. RblC, has the face-centred cubic (fcc) rock-salt- structure with the Rb' cation on the octahedral site of the fcc array at high temperature and recent work has revealed that this may be conserved by quenching to low temperat~re.,~ Slow cooling however leads to an orthorhombic compound in which one lattice parameter (9.31A) implies very short contacts between the C, molecules.Structure refinement7' shows the material contains one dimensional polymer chains in which the C, units are connected by 1.44 A inter molecular bonds between 6:6 bonds on adjacent molecules (Figure 4). The polymer is a one dimensional metal at high temperatures and undergoes a spin density wave transition at low temperature. Polymer formation occurs from the high temperature phase where the dynamically disordered anions can adopt relative orientations which allow the [2 + 21 cycloaddition reaction to occur.Similar polymerization is seen for CsIC6, and in rapidly cooled K,C,,. Single crystals of K'C, can be grown by a vapour phase route.71 Non-superconducting Li,CsC, has orientationally disordered C:; anions and a spherical harmonic orientation distribution function analysis indicates the observed scattering density is consistent with covalent Li *. * C bonding.72 The structural influence of sodium on the tetrahedral site in a cubic close packed C, array is to produce at room temperature the orientational order found in C, itself below 260 K-this was shown by powder neutron diffraction in N~,CSC,,;~~ the transition to a high temperature disordered phase occurs at 299K.74 Several studies on the physical properties of superconducting A3C, compounds have been reported.Preparation of 85Rb- and 87Rb- (isotopically pure) Rb3C, allowed the demonstration of a zero isotope effect once again ruling out alkali-metal C, optic modes from the pairing mechanism.75 13C NMR T,Tmeasurements (which allow an estimate of N(E,) in a Fermi liquid picture) confirm a previously proposed weak to medium coupling BCS electron-phonon coupling mechanism involving phonons with a frequency above 600 K and a Stoner parameter of 3 eV spin-' carbon-'.76 A debate in the literature concerning the true conduction electron spin hy 0.Chauvet G. Oszlany L. Forro P. W. Stephens M. Tegze G. Faigel and A. Janossy Phys. Rev. Lett. 1994 72 2721. 'O P. W. Stephens G.Bortel G. Faigel M. Tegze A. Janossy S. Pekker G. Oszlanyi and L. Forro Nuture 1994 370 636. S. Pekker A. Janossy L. Mihaly 0.Chauvet M. Carrad and L. Forro Science 1994 265 1077. 72 I. Hirosawa K. Prassides J. Mizuki K. Tanigaki M. Gevaert A. Lappas and J. K. Cockcroft Science 1994 264 1294. 73 K. Prassides C. Christides I. M. Thomas J. Mizuki K. Tanigaki I. Hirosawa and T. W. Ebbesen Science 1994,263 950. 74 K. Tanigaki I. Hirosawa T. Manako J.S. Tsai J. Mizuki and T. W. Ebbesen Phys. Rev. B Condens. Mutter 1994 49 12 307. l5 B. Burk V. H. Crespi A. Zettl and M. L. Cohen Phys. Rev. Lett. 1994 72 3706. 76 Y. Maniwa T. Saito A. Ohi K. Mizoguchi K. Kume K. Kikuchi I. Ikemoto S. Suzuki and Y. Achiba J. Phys. SOC.Jpn. 1994 63 11 39. Fullerene Chemistry r 1 ~=14.233 m -1.44kO.15 1.9W0.15 f-/=\ A >i( 3 1 2 Figure 4 Polymer chains in Rb,C, (Reproduced by permission from Nature 1994 370 636) resonance signal from Rb3C, has beg~n.~~'',~ An STM investigation of Rb3C, has revealed effective grain sizes of a few hundred nanometers which is important in " (a)M.Kosaka K. Tanigaki I. Hirosawa Phys. Rev. Lett. (Comment) 1994 72 3130; (h) A. Janossy 0. Chauvet S. Pekker J. R. Cooper L. Forro M. Tegze and G.Faigel Phys. Rev. Lett. (Reply) 1994,72(19) 3131. 586 M.J. Rosseinsky interpreting the small superconducting shielding fractions which are often observed.78 Studies of the environmental stability of the superconducting fullerides indicate that though very unstable to dry air oxygen and water,79 the application of Si and %/A1 protective layers to Rb,C, films can maintain superconducting properties in air for up to 8 hours.80 Direct information on phase equilibria in the Na-C, binary phase diagram has been provided by a high temperature solid state electrochemical study showing solid solution in NaXC6 for 2 < x < 3 and for 3.3 < x < 11." A lower temperature polymer electrolyte solid state electrochemical study indicates several line phases in this composition range.82 Lithium fullerides prepared by low temperature elec- trochemistry have been characterized by electron diffra~tion.~ The electronic properties of the fullerides have been the major points of interest thus far but the catalytic activity of the M6C60 phases (M = Cs K Na) to H,-D exchange and ethene hydrogenation which is comparable to that of the noble metals suggests this will be a profitable area for future PES studies indicate that none of the phases (prepared at high temperature in contrast to reference 68) are metallic at room temperature-slow caesium diffusion was also noted.8 Though fullerides with metal concentrations which require filling the t, band for Li and Na have been known for some time all the previous evidence indicated that no more than six potassium cations could be intercalated into c60.However photoemis- sion studies of c60 deposited on K multilayers indicates population of the t, band corresponding to 6 < x < 12.86 Alkaline earth metal fullerides with x > 3 also have the C, t, levels occupied in a naive ionic view of the bonding.However resonant PES shows that Ba6C60 has 25% Ba character at the Fermi energy with strong metalkarbon hybridization with both the t, and t, levels.87 The Sr-C, system has been identified as the only fulleride in which fcc and bcc phases coexist (x = 3 bcc A15 and fcc phases coexist). Sr,C, (bcc) has been shown to be superconducting at 4 K.** As separation techniques improve more studies of the intercalation chemistry of higher fullerenes can be expected. No new superconductors have emerged yet. Preliminary structural work on the K,C, phase diagram reveals a dependence on the starting polymorph (hcp or fcc) at low x with both C70 modifications yielding a potassium saturated fcc K9C70 phase89 and in contrast with the bcc 78 H.P. Lang V. Thommen-Geiser K. Lueders M. Kraus M. Baenitz and H.-J. Guentherodt Mol. Cryst. Liq. Cryst. Sect. A 1994 245 289. 79 D. R. Riley D. Jurbergs J. P. Zhou J. Zhao and J. T. McDevitt Solid State Commun. 1994 88 431. 80 N. Okuda H. Kugai T. Uemura K. Okura Y. Ueba and K. Tada Jpn. J.Appl. Phys. Part 1,1994,33(4A) 1851. 81 J. H. Kim A. Petric P.K. Ummat and W.R. Datars J. Phys. Condens. Mutter 1994 6 5387. 82 S. Lemont J. Ghanbaja and D. Billaud Muter. Res. Bull. 1994 29 465. 113 S. Lemont J. Ghanbaja and D. Billaud Mol. Cryst. Liq. Cryst. A 1994 244 203. 84 S. Serizawa I. Gabrielova T. Fujimoto T. Shido and M. Ichikawa J. Chem. SOC.,Chem. Commun. 1994 799. 85 J. M. Gildemeister and G.K.Wertheim Chem. Phys. Lett. 1994 220 181. 86 L.Q. Jiang and B.E. Koel Phys. Rev. Lett. 1994 72 140. (17 M. Knupfer F. Stepniak and J. H. Weaver Phys. Rev. B,1994 49 7620. 88 A. R. Kortan N. Kopylov E. Ozdas A. P. Ramirez R. M. Fleming and R. C. Haddon Chem. Phys. Lett. 1994 223 50 1. 89 M. Kobayashi Y. Akahama H. Kawamura H. Shimohara H. Sato and Y. Saito Phys. Rev. B,1993,48 16877. 90 M. Kobayashi Y. Akahama H. Kawamura H. Shimohara H. Sato and Y. Saito Fullerene Sci. Technol. 1993 1 449. Fullerene Chemistry structures of the metal-saturated A& phases formed by these metals. Alternative more rapid synthetic routes than the gas-phase metal vapour plus C, solid reactions have been sought. Solution routes still involved extended heating to desolvate the metal cations.The decamethylmanganocenide anion has allowed isolation of the solvated fulleride Na(THF),C,,,91 and has been used to prepare K3C,,.92 The compound Na,C,,(THF) (x r 0.4 y z 2.2) is a further solvated sodium fulleride which is metallic at room temperat~re.~~ K3C, can be prepared in under 60 seconds total reaction time using a microwave-induced argon plasma.94 TDAE C, and Magnetic Fullerene Compounds.-The salt TDAE C, (TDAE is tetrakisdimethylaminoethylene) continues to attract attention in view of the magnetic transition at 16 K. A dependence of T on preparation technique has been observed with a maximum T of 24 K in materials which appear from Raman spectroscopy to be non-stoichi~metric.~~ Microwave conductivity measurements show both the magni- tude S cm-') and temperature dependence of the conductivity are non-metallic ruling out explanations of the magnetic transition based on itinerant electron^.^ The methyl protons of the TDAE molecule show a strongly temperature dependent NMR chemical shift but the shift observed below T is much smaller than would arise from ferromagnetic ordering of all the C; EPR measurements also indicate a smaller than expected local field below Tc.98The EPR line is homogeneously broadened above 16 K and inhomogeneously broadened below the tran~ition.~~ The existence of a spontaneous magnetization below 15K has been revealed by ac susceptibility (the non-zero value of the imaginary part of the susceptibility indicates non-zero ordered moments) and precise dc measurements of hysteresis (a coercive field of 1.6 G is measured at 5 K).lo0 The search for other amines which might produce charge-transfer salts with similar properties continues.The tertiary amines 1,8- diazabicyclo (5.4.0)undec-7-ene (DBU) and 1,5-diazabicyclo (5.3.0) non-5-ene (DBN) afford moisture- and air-sensitive 2 1 salts when reacted with C, in toluene. The DBU salt exhibits a cusp in XTat 70K while the DBN salt has a Weiss constant of -4 K.'" Organic Chemistry.-The area of methanofullerene chemistry (addition of carbenes or their equivalents to c60)has been active and is the subject of a comprehensive review.' O2 The competition between the 'open' methanoannulene fulleroid formed by 5 :6 addition and the cyclopropane 6 :6 methanofullerene is illustrated by the addition of MeCO,C,H,CHN, which yields the 5,6 fulleroid initially this then thermally isomerizes to the more stable methanofullerene.Interestingly addition of a third 91 R.E. Douthwaite A. R. Brough and M. L.H. Green .I. Chem. SOC. Chem. Commun. 1994 267. 92 X. Liu W.C. Wan S. M. Owens and W. E. Broderick J. Am. Chem. Soc. 1994 116 5489. 93 H. Kobayashi H. Tomita H. Moriyama A. Kobayashi and T. Watanabe J. Am. Chem. SOC. 1994,116 3153. 94 R. E. Douthwaite M. L. H. Green and M. J. Rosseinsky J. Chem. SOC.,Chem. Commun. 1994 2027. 95 D. Mihailovic K. Lutar A. Hassanien P. Cevc and P. Venturini Solid Stute Commun. 1994,89 209. 96 A. Schilder H. Klos 1. Rystau w. Schuetz and B. Gotschy Phys. Rev. Lett.1994 73 1299. 97 R. Blinc J. Dolinsek D. Arcon D. Mihailovic and P. Venturini Solid State Commun. 1994 89 487. 98 P. Cevc R. Blinc V. Erzen D. Arcon B. Zalar D. Mihailovic and P. Venturini Solid Stute Commun. 1994 90,543. '' P. Cevc R. Blinc D. Arcon D. Mihailovic P. Venturini S. K. Hoffmann and W. Hilczer Europhys. Lett. 1994 26 707. loo S. Atsushi T. Suzuki R.J. Whitehead and Y. Maruyama Chem. Phys. Lett. 1994 223 517. H. Klos I. Rystau W. Schuetz B. Gotschy A. Skiebe and A. Hirsch Chem. Phys. Lett. 1994,224,333. F. Diederich L. Isaacs and D. Philp Chem. Sac. Rev. 1994 23 227. M.J. Rosseinsky electron to the fulleroid isomerizes it to the methan~fullerene.'~~ A combined experimental and PM3 computational study of the preference for the 6,6-closed methanofullerene and 5,6-open fulleroid over the 6,6-open and 5,6-closed isomers indicates that the preservation of [5] radialene type bonding found in C, is decisive in favouring the two observed isomers (see Figure 5(a) for depictions of these struc- tures).' O4 A single crystal X-ray diffraction study has confirmed the cyclopropane structure for 6,6-closed methano-bridged fullerenes [(3,4-dimethyoxyphenyl)-phenyl-methanolC, (Figure 5),with the bridgehead C(ltC(2) bond of 1.6114(7) 8 clearly indicating the bonding to be cyclopropane-like.' O5 Synchrotron powder X-ray diffraction shows that the 6,5 open annulene isomer of C6 ,H undergoes orientational ordering to Pa3 symmetry at 290K.'06 Successive carbene addition allows the isolation of regioisomers of bis and tris adducts of C, and di(ethoxycarbony1) rnethylene,lo7 which may be converted into water-soluble malonic acid derivatives by treatment with sodium hydride.'08 Diethynylmethanobuckminster fullerene en- visaged as a building block for joint cyclo[n]carbon-fullerene molecular carbon allotropes has been prepared.'" These species may be coupled using CuCl to produce dimeric methanofullerenes linked by butadiynyl groups.' lo Reaction of diazomethane with C70 in toluene produces a mixture of isomeric pyrazolines which are thermally convertable into annulenes (C70 has eight types of bond and four distinct 6:6 bonds).'' Aziridines are formed by nitrene addition across the 6:6 junction of C, (N-aminophthalimide + Pb(OAc) in chlorobenzene) to yield mono to tetra adducts in contrast to reactions with alkyl azido reagents which yield open azafulleroids.' l2 Reaction with the azide Me(OCH,CH,),N attaches a short hydrophilic chain to the hydrophobic c60molecule forming an open azaannulene structure by addition across a 6:5 junction the molecule is amphiphilic and forms monomolecular films on spreading toluene solutions at the air-water interface.' l3 The 6 :6 junction aziridine urethane C60NC0,CH,CH is prepared by addition of the azidoformic ester:' l4 the supermesityl group can also be attached as a 6,6 aziridine via the azidoformate.This can be thermally converted into the isomeric oxazole in which 0 and N bind vicinally to the carbons of the 6 :6 junction (Figure 6)." One-step cycloaddition of a dendritic azide (M 3429 amu) yields an open annulene monosubstituted C, azafulleroid (Figure 7) with a glass transition temperature of 325 K.' l6 Amino-acid and amido M.Eiermann F. Wudl M. Prato and M. Maggini J. Am. Chem. Sac. 1994 116 8364. F. Diederich L. Isaacs and D. Philp J. Chem. SOC.,Perkin Truns. 2 1994 391. J. Osterodt M. Nieger and F. Voegtle J. Chem. Soc. Chem. Commun. 1994 1607. lo6 A. N. Lommen P. A. Heiney G. B. M. Vaughan P. W. Stephens D. Liu D. Li A. L. Smith A. R. McGhie and R. M. Strongin Phys. Rev. B Condens. Mutter 1994 49(18) 12 572. I"' A. Hirsch 1. Lamparth and H. R. Karfunkel Angew. Chem. Int. Ed. Engl. 1994 33 437. lox I. Lamparth and A. Hirsch J. Chem. SOC. Chem. Commun. 1994 1727. Io9 Y. An Y. Rubin C. Schaller and S.W.McElvany J. Org. Chem. 1994 59 2927. 'lo H. L. Anderson R. Faust Y. Rubin and F. Diederich Angew. Chem. Int. Ed. Engl. 1994 33 1366. l1 A. B. Smith R. M. Strongin L. Brard G. T. Furst W. J. Romanow K. G.Owens and R. J. Goldschmidt J. Chem. SOC. Chem. Commun. 1994 2187. 'I2 S. Kuwashima M. Kubota K. Kushida T. Ishida T. Ishida M. Ohoshi and T. Nogami Tetrahedron Lett. 1994 35 4371. 'I3 C. J. Hawker P. M. Saville and J. W. White J. Org. Chem. 1994 59 3503. 'I4 T. Ishida K. Tanaka and T. Nogami Chem. Lett. 1994 561. 'I5 M. R. Banks J. I. G. Cadogan I. Gosney P.K. G. Hodgson P. R. R. Langridge-Smith and D. W.H. Rankin J. Chem. SOC.,Chem. Commun. 1994 1365. C. J. Hawker K. L. Wooley and J. M. J. Frechet J. Chem. SOC.,Chem. Commun. 1994 925. Fullerene Chemistry 6-6 closed 5-6 open 6-6 open 5-6 closed R = Ph R = 3,4-(MeO),Ph (a) P Figure 5 (a) The possible structures of a rnethanofullerene; (b) The crystal structure of [(3,4-dimethyoxypheny1)-phenylmethano]C,,.2CHC13.Relevant bond lengths are C(lkC(2)= 161.4(7)pm C(lFC(61) = 151.0(7)pm and C(2kC(61) = 151.5(7)pm. The angles C(61)-C(2)-C(l) = 57.6" C(61)-C(l)-C(2) = 57.9(3)" C(l)-C(61rC(2) = 64.5(3)" and C(62)-C(61FC(68) = 115.4(4)O (Reproduced from J. Chern. Soc. Chern. Cornrnun. 1994 1607) derivatives are readily synthesized by addition of diazoamides both ring-closed and ring-opened isomers are formed and are separable by HPLC." Calix[8]arene may be attached to C, via polyether chain azide addition to yield the azafullerene."' Racemic and enantiopure fullero-3,4-prolines have been prepared and converted into the protonated amino acids."' 1,2 and 1,4 isomers of C, azacrown ethers have been prepared.' 2o N-acylated fulleropyrrolidines including a perfluorinated deriva- 11' A.Skiebe and A. Hirsch J. Chem. SOC.,Chem. Commun. 1994 335. 'IR M. Takeshita T. Suzuki and S. Shinkai J. Chem. SOC.,Chem. Commun. 1994 2587. 'I9 M. Maggini G. Scorrano A. Bianco C. Toniolo R. P. Sijbesma F. Wudl and M. Prato J. Chern. Soc. Chem. Commun. 1994 305. l2O S. N. Davey D. A. Leigh A. E. Moody L. W. Tetler and F.A. Wade J. Chem. Soc. Chem. Commun. 1994 391. M. J. Rosseinsky ) ) folc, i,Bu"Li,OoC,C0Cl2 lW% 1 2 ii NaN (2 equ.) wet acetone (0.05%),reflux 100% I 3 Scheme 1 \L 4 5 6 7 Figure 6 Reaction of the azidoformate 3 with C, yields the aziridine 4.which is thermally converted into the isomeric oxazole 5 (Reproduced from J. Chem. Soc. Chem. Commun. 1994 1365) tive have been prepared from the previously known N-H compound.121 The perfluorinated material forms monomolecular Langmuir-Blodgett films by spreading toluene solutions on water.' 22 Similar azomethine ylid addition chemistry affords 12' M. Maggini A. Karlsson L. Pasimeni G.Scorrano M. Prato and L. Valli Tetrahedron Lett. 1994,35 2985. lZ2 M. Maggini L. Pasimeni M. Prato G. Scorrano and L. Valli Langrnuir 1994 10 4164. Fullerene Chemistry 591 -N2 + -heat i 170.0 150.0 130.0 110.0 60.0 70.0 50.0 6 148.0 146.0 1u.a 1420 140.0 13.0 136.0 134.0 6 Figure 7 Synthetic scheme for a dendritic fullerene.The 13C NMR spectrum of the product (a) is shown together with an expanded section (6 133-149) showing resonances due to the fullerene moiety (b) (Reproduced from J. Chem. SOC. Chem. Commun. 1994 925) 592 M.J. Rosseinsky ferrocenyl fulleropyrrolidines as does reaction with the acyl chloride of ferrocene with the unfunctionalied pyrr01idine.l~~ The reaction of c60 with the tertiary amine 1,8-diazabicyclo [5.4.0]undec-7-ene gives a diamagnetic DBU c60 addition product via radical recombination of the ions formed in an initial electron-transfer step.' 24 Electrospray ionization mass spec- trometry shows that reaction of c60 with isobutylamine in air results in formation of oxygenated C6,0,(RNH2), with rn = 6 dominant while no oxygen is incorporated in a slower amine-only addition reaction under an inert atmosphere.' 25 1,3-diphenylnit-rilinine undergoes 1,3-dipolar cycloaddition with C, to form a pyrazoline dia- dduct.'26 The monoadduct of piperazine with c60 forms Langmuir-Blodgett films at the air-water interface with weak SHG (Second Harmonic Generation) activity.' 27 Nitrile oxides form 1,3-dipolar adducts to the 6:6 ring fusions of C7, and three separable isomers are formed.'28 Diels-Alder chemistry of c60 was well developed before 1994; the first use of the related ene reaction in functionalizing the molecule was reported this year producing a monoadduct with 3,5-di-t-butyl-4-(trimethylsiloxy)allylben~ene'~~ and 4-ally1 an- isole.' 30 8-methoxyheptafulvene has been reported to undergo [8 + 2) cycloaddition with c60 across a 6 :6 bond to give a tetrahydroazulenofullerene.'31 Ring-opened benzocyclobutenol undergoes Diels-Alder addition across the 6 :6 bond to give monosubstituted 1,9-dihydrofullerenes and the resulting alcohol is readily functional- ized.' 32 Diels-Alder adducts with tropones' 33 and ~ycloheptatriene'~~ are formed under high pressure and hydroquinone functionalized c6o's have been prepared.' The use of a remote tether to promote regiospecific functionalization of C, was demonstrated using multiple Diels-Alder additions of 1,3 butadienes attached via a methanofullerene carboxylic acid to give tris adducts across the 6 :6 bonds.136Mono Diels-Alder adducts of o-quinodimethane with C, and c76 have been isolated.' 37 (Trimethylsily1)ethynyl and phenylethynyl-fullerenes have been prepared by reac- tion with the lithium acetylide salts in refluxing toluene followed by acid addition yielding mono- and bis-adducts which have similar electrochemistry to C, itself.' 38 The compounds HC,,CH,SiMe,Y and C6,(CH2SiMe2Y) (Y = Me H CH=CH,,Ph,O'Pr) have been prepared from the Grignard reagents in THF and 123 M.Maggini A. Karlsson G. Scorrano G. Sandona G. Farnia and M. Prato J. Chem. SOC. Chem. Commun. 1994,647. 124 A. Skiebe A. Hirsch H. Klos and B. Gotschy Chem. Phys. Lett. 1994 220 138. 125 S. R. Wilson and Y. Wu Org. Mass Spectr. 1994 29 186. 126 S. Muthu P. Marutharnuthu R. Ragunathan P. R.Rao and C. K. Mathews Tetrahedron Lett. 1994,35 1763. 127 L. B. Can D. J. Zhou C. P. Luo C. H. Huang T. K. Li J. Bai X. S. Zhao and X. H. Xai J. Phys. Chem. 1994 98 12459. 128 M. S. Meier M. Poplawska A. L. Cornpton J. P. Shaw J. P. Selegue and T.F. Guarr J.Am. Chem. Soc. 1994 116 7044. 129 K. Kornatsu Y. Murata N. Sugita and T.S. M. Wan Chem. Lett. 1994 635. 130 S. Wu L. H. Shu and K.N. Fan Tetrahedron Lett. 1994 35 919. 131 E. Beer M. Feuerer A. Knorr A. Miclach and J. Daub Angew. Chem. Int. Ed. Engl. 1994 33 1087. 132 X. Zhang and C.S. Foote J. Org. Chem. 1994 59 5235. 133 H. Takeshita J.-F. Liu N. Kato A. Mori and R. Isobe J. Chem. SOC. Perkin Trans. 1 1994 1433. 134 J.-F. Liu N. Kato A. Mori H. Takeshita and R. Isobe Bu//.Chem. Soc. Jpn. 1994 67 1507.135 W. Bidell R. E. Douthwaite M. L. H. Green A. H. H. Stephens and J. F. C. Turner J. Chem. SOC. Chem. Commun. 1994 1641. 136 L. Isaacs R.F. Haldimann and F. Diederich Angew. Chem. Int. Ed. Engl. 1994 33 2339. 137 A. Herrrnann F. Diederich,C. Thilgen,H. U.Terrneer,and W.H. Muller Helu. Chim. Acta. 1994,77,1689. 138 K. Kornatsu Y. Murata N. Takirnoto S. Mori N. Sugita and T. S.M. Wan J.Org. Chem.,1994,59,6101. F ullerene Chemistry 593 toluene respectively :the unexpected formation of the latter suggests that the addition reactions may have radical as well as simply nucleophilic character.' 39 EPR has been used to study the regiochemistry of radical addition to C,,140 and 141 GO-Hydrolysis of polycyclosulfated fullerenes (see section on Molecular Chemistry) yields polyhydroxylated fullerenes (C,,(OH), n z 10-1 2)14 and hydrolysis of the product obtained on treating c60 with an excess of BH,-THF complex yields water soluble fullerols.143 Organometallic Chemistry.-C,,O has been shown to react with Ir(CO)Cl(PPh,) to afford a monoadduct in which the iridium complex adds to the C-C bond at one of the 6:6 ring junctions adjacent to the epoxide (Figure S).144 Treatment of Rh(acac)(C,H,) successively with c60 and pyridine affords Rh(acac)(C,H,N) q2C60.145c60 platinum and iridium organometallics may be prepared by elimination of HCl from species such as PtHCl(PPh,) in the presence of c60 to yield PtC,o(PPh,),.146 Electronic structure calculations have been used to rationalize the reactivity of C, with organometallics.147 A review of the organometallic chemistry of the fullerenes has been p~b1ished.l~' Reaction of a mixture of the D, and D isomers of C, with Ir(CO)Cl(PPh,) affords ~2-C,,IrCOC1(PPh,),.4c6H6 with the D, isomer of C, found predominantly in the product. The CS4 is bound via a 6 6 junction connecting two pentagons (Figure 9)-the selective crystallization of the less abundant D, isomer is ascribed to its increased tendency to adduct formation due to its more localized .n bonding.'49 The reaction of a tenfold excess of Ir(CO)Cl(PMe,) with c60 affords the bis adduct q2C,o[Ir(CO)Cl(PMe,)2]2 where the two iridium groups are 'para' at opposite ends of the fullerene.'50 4 Polymers High pressure polymerization of c60 and the formation of alkali metal fulleride polymers is covered in Section 2 and under Alkali Metal Fullerides Diels-Alder addition of a cyclopentadiene functionalized polymer to c60 allows reversible attachment of c6 to a polymer support.' Polychlorostyrene doped with 10% c60 undergoes a thousand-fold conductivity enhancement when the fullerene is partly reduced to C;0.152 Problems of multiple addition and subsequent cross-linking in c60 139 H.Nagashima H. Terasaki E. Kimura K. Nakajima and K. Itoh J. Org. Chem. 1994 59 1246. 140 J. R. Morton F. Negri and K. F. Preston Can. J. Chem. 1994 72 776. 14' R. Borghi L. Lunazzi G. Placucci P. J. Krusic D. A. Dixon and L. B. Knights Jr. J. Phys. Chem. 1994 98 5395. 14' L. Y. Chiang L.-Y. Wang J. W. Swirczewski S.Soleel and S. Cameron J. Org. Chem. 1994 59 3960. 143 N.S. Schneider A.D. Darwish H. W. Kroto R. Taylor and D. R. M. Walton J. Chem. SOC.. Chem. Commun. 1994,463. 144 A.L. Balch D.A. Costa J. W. Lee B.C. Noll and M.M. Olmstead Inorg. Chem. 1994 33 2071. 145 Y. Ishii H. Hoshi Y. Hamada and M. Hidai Chem. Lett. 1994 801. 146 S. Schreiner T.N. Gallaher and H. K. Parsons Inorg. Chem. 1994 33 3021. 14' (a)D. L. Lichtenberger L. J. Wright N. E. Gruhn and M. E. Rempe J.Organomet. Chem. 1994,478,213; (h)J.A. Lopez and C. Mealli J. Organomet. Chem. 1994 478 161. 148 J.R. Bowser Adv.Organomet. Chem. 1994 36 57. 149 A. L. Balch A. S. Ginwalla J. W. Lee B. C. Noll and M. M. Olmstead J.Am. Chem. SOC.,1994,116,2227. 150 A. L. Balch J. W. Lee B.C. Noll and M. M.Olmstead Inorg. Chem. 1994 33 5238. 15' K. I. Guhr M. D. Greaves and V. M. Rotello J. Am. Chem. SOC.,1994 116 5997. 15' S. E. Down D. R. Rosseinsky and R. S. Whitehouse J. Electroanal. Chem. 1994 365 311. M.J. Rosseinsky Figure 8 Crystal structure of q2-C,,01r(CO)Cl(PPh,) 50% thermal contours are shown for all atoms and only lhe ips0 carbons of the phenyl rings are shown. Relevant bond lengths are O(1tC(3) 1.445( 12)A O(1 bC(4) 1.462( 12)A C(3)-C(4) 1.480( 1 1)A Ir-C( 1) 2.168(7)A Ir-C(2) 2.174(7)A C(lbC(2) lSOO(1l)A. Bond angles of interest are C(3)-0(1)-C(4) 61.6(6)’ 0(1kC(3)-C(4) 59.9(6)” O(l)-C(4)-C(3) 58.8(6)0 C(l)-Ir-C(2) 40.4(3)0 (Reproduced by permission from Znorg. Chem. 1994 33 2071) copolymer formation can be overcome by cycloaddition of azido-substituted polysty- renes to c60 to give polymers which retain the electronic properties of the fullerene and the solubility and processability of the polystyrene.’ 53 Five mole percent c60doping of poly(0-trimethylsily1)phenylacetyleneenhances the photoconductivity.’54 Thermal breaking of the intermolecular C-C bonds in photopolymerized c60 proceeds with an activation energy of 1.25eV.”’ C, is also photopolymerizable albeit with greater difficulty this is ascribed to a reduction in the number of reactive double bonds to the five in each polar cap of the C, molecule.’56 The C,,(OH) (n = 10-12) fullerols (see under Organic Chemistry) derived from hydrolysis of sulfonation products of c60 may be condensed with excess diisocyanate (to prevent cross-linking) to give a dendritic polymer with six linear urethane connected polyether arms.’ s7 Soluble polyarylamine sulfone polymers with the c61 fulleroid pendant group have been prepared.58 5 Electrochemistry Electrochemical studies in o-dichlorobenzene show that the C; anion is a weak base while reduction to the dianion results in a marked increase in basicity (pK 153 C. J. Hawker Macromolecules 1994 27 4836. 154 K. Yoshino T. Akashi K. Yoshimoto S. Morita R. Sugimoto and A. A. Zakhidov Solid State Commun. 1990 90 41. 155 Y. Wang J. M. Holden X.-X. Bi and P.C. Eklund Chem. Phys. Lett. 1994 217 413. 156 A. M. Rao M. Menon K.-A. Wang P. C. Eklund K. R. Subbaswamy D. S. Cornet M. A. Duncan and I. J. Amster Chem. Phys. Lett. 1994 224 106. 157 L.Y. Chiang L. Y. Wang S. M. Tseng J. S. Wu and K. H. Hsich J. Chem. Soc. Chem. Commun. 1994 2675. 158 M. Berrada Y. Hashimoto and S. Miyata Chem. Muter. 1994 6 2023. Fullerene Chemistry Figure 9 The structure of (q2-C,,)Ir(CO)Cl(PPh,),. The principal twofold axis of an ideal D, symmetry molecule bisects the C(32bC(53)and C(42kC(43)bonds while the other twofold axes pass through the midpoints of the C-C bonds between the other hatched carbons. The C(32)-C(53) bond (1.455(6)A),which coordinates the iridium is considerably longer than the C(42bC(43)bond (1.332(11)A)at the opposite pole of the fullerene (Reproduced by permission from J. Am. Chem. SOC. 1994 116 2227) HC60 s 3.4 fO.1).I5' Electrochemical and EPR studies have indicated that the C& anion is diamagnetic while dynamic Jahn-Teller distortions are suggested for the Ci0 and (22; anions.' 6o X-Ray diffraction evidence exists for electrochemical intercalation of Bu,N+ cations into c60 films from acetonitrile solutions.'" Up to five reversible electrochemical reductions may be observed in c60trapped in electropolymerized films on Pt or C disk electrodes.162 The electrochemistry of methanofullerenes and [4 + 21 cycloaddition products have been studied.63 The effect of substituent electronegativ- ity on the electrochemistry of monosubstituted fullerenes is in accord with their electronegativity implying that inductive rather than resonance effects are important and more electronegative systems can be prepared simply by adding electron- withdrawing groups to the m01ecule.l~~ 6 Endohedral Fullerenes A considerable amount of progress has been made towards the bulk isolation and structural characterization of these molecules.A review of theory and experiment to the end of 1993 is available.' 65 The mechanism of endohedral metallofullerene formation in the gas-phase has been proposed to be the nucleation of polycyclic polyne 159 D. E. Cliffel and A. J. Bard J. Phys. Chem. 1994 98 8140. 160 M. M. Khaled R. T. Carlin P. C. Trulove G. R.Eaton,and S. S. Eaton,J. Am. Chem. SOC.,1994,116,3465. 161 K. Tomura M. Nishizawa D. Takemura T. Matsue and I. Uchida Chem. Lett. 1994 1365. A. Deronzier J.-C. Moutet and P. Seta J. Am. Chem. SOC. 1994 116 5019. 163 F. Arias Q. Xie L. Echegoyen Y. Wu Q. Lu and S.R.Wilson J. Am. Chem. SOC. 1994 116 6388. 164 T. Suzuki Y. Maruyama T. Akasaka W. Ando K. Kobayashi and S. Nagase J. Am. Chem. SOC.,1994 116 1359. 16' D.S. Bethune R.D. Johnson J.R. Salen M.S. De Vries and C.S. Yannoni Nature 1993 366 123. 596 M.J. Rosseinsky rings around a metal atom followed by conversion into the metallofullerene on the basis of quadrupole mass spectrometry studies.' Formation of endohedral species by insertion of the guest into the pre-formed fullerene via low energy formation of a nine-membered ring 'window' through breaking a pentagon-hexagon bond has been suggested by theoretical ~alculations,'~~ and exposing c60 to 2000 atmosphere of He Ne Ar Kr and Xe at 620 "C leads to formation of 0.1YOof endohedral species such as Xe@C, (and C70) consistent with such a mechanism.'68 The 3He NMR spectra indicate diamagnetic ring currents in c60and C70 from the 6 ppm and 29 ppm shielding of He in He(@C6 and He@C7 relative to the free atom.'69 The chemical shift of the 3He in He@C6 can be accurately cal~ulated.'~~ This NMR technique has also been used to follow organic reactions of fullerenes,'71 and mass spectrometry has been used to show helium encapsulation by derivatized fullerenes.' 72 Laser ablation of C6,/La203 mixtures gives evidence for formation of La@C, by a 'window' mechani~m.'~~ Ion drift tube techniques have indicated that NbC (n = 28-50) species with even values of n are endohedral but n odd species are fullerenes with metal atoms as part of the cage structure showing that networked metallofullerenes are a stable third class of f~l1erene.I~~ The separation and extraction of endohedral species from soot generated by arc erosion of metal oxide impregnated rods is a key aspect of endohedral fullerene chemistry-250 "C extraction with toluene under high pressure (16.5atm) produces 0.3% mass yield of a species rich in La@C (n = 82 is d~minant).'~~ Single stage HPLC allows the isolation of one isomer of La@C, whose near infrared spectrum is consistent with the formulation La3fC823-.176 Spark erosion of rods with a 1 :100 ratio of Y203 to C followed by HPLC on polystyrene and 'buckyclutcher' columns allows isolation of Y@c82 whose cyclic voltammetry shows one oxidation and three + reduction waves indicating a charge distribution Y3 (@jC; .'77 Automated anaerobic HPLC with polystyrene columns can be used for large-scale separation of Sc@C2 and Y@2 from the faster running empty cage fullerenes (200mg in 16hrs) while on-line EPR monitoring allows identification of paramagnetic Y @C, and sc3@c82 to mark the metallofullerene fraction; Y@c82 and Sc3@& can be isolated from the M@C2 metallogullerene fraction using a 'buckyclutcher' HPLC column.' 78 D.E. Clemmer K. B. Shelimov and M. F. Jarrold Nature 1994 367 718. 16' R. L. Murray and G. E. Scuseria Science 1994 263 791. M. Saunders H. A. Jimenez-Vazquez R. J. Cross S. Mroczkowski M. L. Cross D. E. Giblin and R. J. Poreda J. Am. Chem. Soc. 1994 116 2193. 16' M. Saunders H.A. Jimenez-Vazquez R.J. Cross S.Mroczkowski M.L. Cross D.E. Giblin R.J. Poredan D. I. Freedberg and F. A. L. Anet Nature 1994 367 256. J. Cioslowski J. Am. Chem. SOC. 1994 116 3619. 17' M. Saunders H. A. Jimenez-Vazquez B. W. Bangerter R. J. Cross S. Mroczkowski D. I. Freedberg and F.A. L. Anet J. Am. Chem. SOC. 1994 116 3621. 172 S.N. Davey D.A. Leigh A. E. Moody and L. W. Tetler J. Chem. Soc. Chem. Commun. 1994 I. 173 R. Huang H. Li W. Lu and S. Yang Chem. Phys. Lett. 1994 228 111. 174 D. E. Clemmer J. M. Hunter K. B. Shelimov and M. F. Jarrold Nature 1994 372 2488. 175 C. Capp T.D. Wood A.G. Marshall and J.V. Coe J. Am. Chem. Soc. 1994 116 4987. 17' K. Yamamoto H. Funasaka T. Takahashi and T. Akasaka J. Phys. Chem. 1994 98 2008. 177 K. Kikuchi Y. Nakao S. Suzuki Y. Achiba T. Suzuki and Y.Maruyama J. Am. Chem. Soc. 1994,116 9367(10). (a)S. Stevenson H. C. Dorn P. Burbank K. Harich J. Haynes Jr. C. H. Kiang J. R. Salem M. S. De Vries P. H. M. van Loosdrecht R. D. Johnson C.S. Yannoni and D. S. Bethune Anal. Chem. 1994,66 2675; (b)S. Stevenson H. C.Dorn P. Burbank K. Harich J. Haynes Jr. C. H. Kiang J. R. Salem M. S. De Vries P. H. M. van Loosdrecht R. D. Johnson C. S. Yannoni and D. S. Bethune Anal. Chem. 1994 66 2680. Fullerene Chemistry I I I I I 1 1 1 I I 3280 3300 3320 33LO 3360 3380 3-500 31.20 31.1.0 3460 H/G LD-TOF-MS (355 nm) L. 600 800 1000 1200 1400 m/ Figure 10 (a) EPR spectrum and (h) laser desorption time-ofjight mass spectrum of Sc,(u C, (Reproduced by permission from J. Phys. Chem.1994 98 8597) Improved separation techniques have allowed more detailed physical characteriz- ation of these species. PES studies of La@C, solid films indicate that the lanthanide is in the +3 state (though electronic structure calculations predict strong covalency and 1.49 8 displacement of the lanthanide from the centre of the cage) but the solid is non-metallic despite the radical nature of the molecule.'79 An EPR study of Sc3(uC,2 revealed 22 symmetric hyperfine lines about g = 1.9985 consistent with an equilateral triangle of Sc atoms within the C, isomer ofC, (EPR and mass spectra shown Figure lo).' 8o The first crystallographic information concerning endohedral fullerenes comes from an electron diffraction and lattice imaging study of SC~(~C,~ which is hexagonal close packed with c/a = 1.63 (the ideal value) and the intermolecular separation in the close packed layer is 11.2 A equal to that of hollow C,,.I8' (Figure 11).A simple model for the bonding in endohedral fullerenes has been devised and used to predict stable endohedral species.Is2 D. M. Pokier M. Knupfer J.H. Weaver W. Andreoni. K. Laasonen M. Parincllo D. S. Bethune K. Kikuchi and Y. Achiba Phys. Rev. B 1994 49 11403. H. Shimohara M. Inakuma N. Hayashi H. Sato Y. Saito and S. Bandow,J. Phys. Chem. 1994,98,8597. '*'R. Beyers C.H. Kiang R.D. Johnson J.R. Salem M.S. de Vries C.S. Yannoni D. S. Bethune H.C. Dorn P. Burbank K. Harich and S. Stevenson Nature 1994 370 196. K. Jackson E. Kaxiras and M. R. Pederson J. Phys. Chem. 1994 98 7805.M. J. Rosseinsky Figure 11 (a) High resolution TEM lattice image of Sc2(dC,,; (b) is a Fourierfiltered image to bring out the periodicities in the original image; c and d are simulated images of 6.78 thick Sc,iu C, and C, crystals at 5008 deforus. In c and d three different orientations of the molecules are superimposed to simulate the orientational disorder present in the crystals (Reproduced by permission from Nature 1994 370 196) 7 Carbon Nanotubes Following the many studies reported in 1993 preparative work has concentrated on the synthesis ofhigh purity monodisperse tube samples to allow the unambiguous study of chemical and physical properties. Chemical opening and filling of the tubes has been achieved. A review of the area has been published in 1994.183 The carbon nanoparticles which typically compose 1/3 of the sample under all-carbon rod erosion can be burnt off in air or oxygen at 750 "C over 30 minutes leaving 1% by mass of the sample as pure open nan0t~bes.l~~ Perfect tubes longer than 40pm can be grown using a water cooled copper cathode together with the graphite anode preventing defect formation due to sintering together of the tubes at high temperat~re."~ The outside of closed tubes can be wet and the inside of open tubes filled by substances with low surface tension (<200 mNm- ')-this allows the interior of the tubes to be wetted by water and organic solvents.'86 Transition metal la3 T.W. Ebbesen Annu. Rev. Mater. Sci. 1994 24 235. T. W. Ebbesen P. M. Ajayan H.Hiura and K. Tanigaki Nature 1993 367,519. D.T. Colbert J. Zhang S. M. McClure P. Niklaev. Z. Chen J.H. Hafner D. W. Owens P.G. Kotula. C. B. Carter J. H. Weaver A.G. Rinzler and R. E. Smalley. Science 1994 266 1218. E. Dujardin T. W. Ebbesen. H. Hiura and K. Tanigaki Science 1994 265 1850. Fullerene Chemistry 599 catalysts co-evaporated from the anode increase the density of single-walled tubes this was first demonstrated using Co :C composite rods.'87 The single-walled tubes occur both as web-like deposits in the chamber when a mixed Co/Pt catalyst is used,'" and in the soot with Fe/Ni and Co/Ni catalysts.'89 Arc evaporation of Sc-C composite rods allows encapsulation of Sc,5C19 crystallites within the nanot~bes."~ The composition of the soot as well as the cathode carbon is a sensitive function of the catalytic metal-palladium and enhances the percentage of C70 and other higher fullerenes formed in comparison with pure graphite while platinum produces a high nanotube density in the cathode carbon.lgl The quenching of hot carbon vapour onto a -30 "C flat graphite substrate produces carbon cones up to 24 nm long which all have the same 19"cone angle shown to be the smallest of the five possible opening angles for graphitic cones.lg2 An important development is the chemical opening and filling193 of the nanotubes by nitric acid oxidation-pitaxially grown crystals of nickel can be formed and there is much scope for future development.Intercalation by potassium and rubidium into nanotubes can be achieved by vapour phase reaction-the results imply a highly defective structure for the tubes resembling turbostratic graphite rather than concentric hollow ~y1inders.l~~ 0.2 wt% Ruthenium particles (3-7 nm) supported on the external surfaces of the tubes are highly selective in catalysing the reduction of cinnamaldehyde to cinnamyl alcohol.' 95 Magnetic and electron transport measurements on 'as made' tubes seem to imply that the microscopic electronic structure is similar to that of graphite.The diamagnetic susceptibility is larger than that of graphite,' and quite isotropic when measured parallel or perpendicular to the axis of an aligned bundle of tubes.' 97 The semi-metallic nature of the tubes was quantitatively addressed by transport and magnetotransport measurements using contacts made to individual bundles of tubes with an STM198-a fit to p(r)indicates that the band overlap (3.7 meV) is ten times smaller than in graphite (40meV) resulting in fewer carriers and a larger low-temperature resistivity.The Hall voltage is always positive indicating p-type carriers. '99 EPR measurements indicate that neither potassium nor iodine 'doping' can introduce carriers,200 in contrast to graphite. The 1580cmp1 E, vibrational mode of graphite also appears in the Raman spectrum of the nanotubes.200 Mixing of the cr* and n* states of a flat graphite sheet on IK7C.H. Kiang W.A. Goddard R. Beyers J. R. Salem and D. S. Bethune J. Phys. Chem. 1994,98,6612. J. M. Lambert P. M. Ajayan P.Bernier J. M. Planeix V. Brotons B. Coq and J. Castaing Chem. Phys. Lett. 1994 226 364. lS9 S. Seraphin and D. Zhou Appl. Phys. Lett. 1994 64 2087. 190 Y. Saito M. Okuda T. Yoshikawa S. Bandow S. Yamamuro K. Wakoh. K. Sumiyama and K. Suzuki Jpn. J. Appl. Phys. 2 Lett. 1994 33 L186. 19' S. Seraphin D. Zhou J. Jias M. A. Minke S. Wang T. Yadav and J. C. Withers Chem. Phys. Lett. 1994 217 191. 19' M. Ge and K. Sattler Chem. Phys. Lett. 1994 220 192. 193 M. L. H. Green P. J. F. Harris and S.C. Tsang Nuture 1994 372 159. 194 0.Zhou R. M. Fleming D. W. Murphy C. H. Chen R.C. Haddon A. P. Ramirez and S. H. Glarum Science 1994 265 84. 195 J. M. Planeix N. Coustel B. Coq V. Brotons P. S. Krumbhar R. Dutarte P. Geneste P. Bernier and P. M. Ajayan J. Am. Chem.Soc. 1994 116 7935. 19' J. Heremans C.H. Olk and D. T. Morelli Phys. Rea. B 1994 49. 15 122. 197 X. K. Wang R. P.H. Chang A. Patashinski and J.B. Ketterson J. Muter. Res. 1994 9 1578. 19' L. Langer L. Stockman J. P. Heremans V. Bayot C. H. Olk C. Van Haesendonck Y. Bruynseraede and J.-P. Issi J. Muter. Res. 1994 9 927. 199 S.N. Song. X. K. Wang. R. P. H. Chang and J. B. Ketterson Phys. Ret.. Lett. 1994 72 697. K. Tanaka,T. Sato,T. Yamabe K. Okahara,K. Uchida M. Yumura H. Niino,S. Ohshima Y. Kuriki K. Yase. and F. Ikazaku Chem. Phys. Lett. 1994 223 65. M. J. Rosseinsky folding into a tube in the LDA can significantly reduce the gaps predicted for small radius tubes by tight-binding calculations.201 BN also displays a tendency to curl and form onion-like structures under electron beam irradiation; however complete closure of the spheres does not occur.2o2 '"' X.Blase L. X. Benedict E. L. Shirley and S.G. Louie,.Phys. Rev. Lett. 1994 72 1878. '02 F. Banhart M. Zwanger and H.J. Muhr Chem. Phys. Lett. 1994 231 98.