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His research interests include reactive cation and superacid chemistry with inert carborane counterions, ionic liquids, bioinorganic chemistry, spin-coupling phenomena, fullerene chemistry, and new carbon-or porphyrin-based materials. He is a Sloan Fellow, a Dreyfus Teacher−Scholar Awardee, and a Guggenheim Fellow. Robert Bolskar received his B.S. degree in Chemistry from Carroll College in Waukesha, WI, in 1992. He earned his Ph.D. degree at the University of Southern California in Los Angeles under the direction of Christopher Reed in 1997, investigating the synthetic redox chemistry of fullerene anions and cations. In 1998 he moved to the University of California, Riverside, as Managing Research Associate. He is currently Senior Chemist at TDA Research in Wheat Ridge, CO. His research interests include the chemistry and physics of fullerene compounds, supramolecular chemistry, strongly oxidizing systems, and electrophilic cations.

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“…Nevertheless, polymer phases of A 3 C 60 (and A 4 C 60 ) have been proposed. [396][397][398] E. Features of C 60 4-and C 60 …”

Section: Features Of the C 60 3-epr Spectrummentioning

confidence: 99%

Discrete Fulleride Anions and Fullerenium Cations

2000

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Singly or doubly bonded dimers [1][2][3][4] and polymer chains, [5][6][7][8] as well as two-dimensional (2D) [9][10][11] and even three-dimensional [12][13][14] networks of C 60 molecules have been reported. The free energy of different structures is often very similar, resulting in an abundance of phase transitions which can be induced by temperature or pressure variations, light irradiation, or chemical doping as in alkali fullerides.…”

Section: Introductionmentioning

confidence: 99%

Low Band Gap and Ionic Bonding with Charge Transfer Threshold in the Polymeric Lithium Fulleride Li₄C₆₀

Macovez¹,

Savage

Schiessling

et al. 2008

J. Phys. Chem. C

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Low band gap and ionic bonding with charge transfer, threshold in the polymeric lithium fulleride Li(4)C(60) Macovez, Roberto; Savage, Rebecca; Schiessling, Joachim; Kamaras, Katalin; Rudolf, Petra; Venema, L.C. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. September 22, 2007; In Final Form: NoVember 19, 2007 We demonstrate the growth of crystalline Li 4 C 60 films. The low-energy electron diffraction pattern of the films indicates the formation of polymer chains in the plane of the surface, consistent with the reported crystal structure. Electron energy loss and photoemission spectra identify the Li 4 C 60 polymer as a low band gap semiconductor, with a relatively strong coupling of electrons to low-frequency stretching modes of the polymer bonds and alkali phonons. No evidence is found for hybridization between the Li-and fullerenederived electronic states. Instead, a partial charge transfer takes place, which is the same for different Li concentrations. This result rationalizes the stability of the polymer phase over a wide range of stoichiometries.

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“…Indeed, Li x C 60 can easily form compounds with x > 6 [5], whereas in Na 4 C 60 the fullerene molecules form a 2D planar polymer, with the molecular units linked by four single C-C bonds [6]. As commonly observed in singly bonded C 60 polymers [7], the latter system too was reported to be metallic [6,8]. Li 4 C 60 , though, represents a different situation.…”

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confidence: 99%

Recovering metallicity inA4C60: The case of monomericLi4C6

et al. 2007

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The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remarkable feature for a member of the A4C60 family (A = alkali metal), invariably found to be insulators. Structural and resonance technique investigations on Li4C60 at T ¿ 600 K, show that its fcc structure is associated with a complete (4e − ) charge transfer to C60 and a sparsely populated Fermi level. These findings not only emphasize the crucial role played by lattice symmetry in fulleride transport properties, but also re-dimension the role of Jahn-Teller effects in band structure determination.PACS numbers: 61.48.+c, 76.30.Pk, 76.60.Cq, 78.30.Na In recent years the competition between Coulomb repulsion, kinetic energy, Jahn-Teller effect, and Hund's coupling rules has been subject of intensive research in the domain of alkali-doped fullerenes. Apparently, most of the phenomena, including high-T c superconductivity in A 3 C 60 , seem to be relatively well understood. Nevertheless, the reason why A 4 C 60 are in general nonmagnetic insulators [1, 2] is still puzzling and remains subject of strong controversy. The situation is made even more complex as, differently from fcc A 3 C 60 , the A 4 C 60 arising from large-size alkali metals (A = K, Rb, Cs) adopt a bct structure [3]. Hence, the natural suggestion that the difference in lattice structure favors the metallicity in the former and an insulating behavior in the latter, with the coupling to H g Jahn-Teller phonons accounting for the lack of magnetic ordering in A 4 C 60 [4]. Doping the C 60 with the significantly smaller Li + and Na + alkali ions leads to interesting deviations from the standard behavior. Indeed, Li x C 60 can easily form compounds with x > 6 [5], whereas in Na 4 C 60 the fullerene molecules form a 2D planar polymer, with the molecular units linked by four single C-C bonds [6]. As commonly observed in singly bonded C 60 polymers [7], the latter system too was reported to be metallic [6,8]. Li 4 C 60 , though, represents a different situation. At normal conditions, it is a 2D polymer displaying a novel architecture based on the coexistence of single and double bonds oriented along two perpendicular directions within the polymer plane [9]. Although the presence of single bonds could suggest a metallic behavior, NMR, Raman and ESR spectroscopy show beyond doubt the diamagnetic and insulating character of this polymer [10]. Important questions hence arise both regarding the role of structure, as well as of polymerization in depressing the electron delocalization and destroying the expected metallicity.In this article we try to answer these questions by a thorough investigation of the high temperature monomeric Li 4 C 60 phase, obtained by thermally induced depolymerization which takes place above 590K. First we show that, in spite of its stoichiometry, the Li 4 C 60 monomeric phase retains a closed packed (fcc) cubic structure, and therefore can be directly compared to other, well known A 3 C 60 fcc systems. Subsequently, as revealed from the ESR l...

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Effect of Charge State on Polymeric Bonding Geometry: The Ground State ofNa2RbC60

Cited by 101 publications

References 26 publications

Discrete Fulleride Anions and Fullerenium Cations

Discrete Fulleride Anions and Fullerenium Cations

Low Band Gap and Ionic Bonding with Charge Transfer Threshold in the Polymeric Lithium Fulleride Li₄C₆₀

Recovering metallicity inA4C60: The case of monomericLi4C6

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Effect of Charge State on Polymeric Bonding Geometry: The Ground State ofNa2RbC60

Cited by 101 publications

References 26 publications

Discrete Fulleride Anions and Fullerenium Cations

Discrete Fulleride Anions and Fullerenium Cations

Low Band Gap and Ionic Bonding with Charge Transfer Threshold in the Polymeric Lithium Fulleride Li4C60

Recovering metallicity inA4C60: The case of monomericLi4C6

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Low Band Gap and Ionic Bonding with Charge Transfer Threshold in the Polymeric Lithium Fulleride Li₄C₆₀