title: Fullerenium salts: a new class of C60-based compounds.
abstract: We report here on the preparation and characterization of a fullerenium salt in the solid state, where the fullerene is in the 2+ oxidized state. To succeed in this long-standing challenge, we exploit the oxidizing power of one of the strongest Lewis acids, AsF(5). The weak nucleophilic character of its conjugate base is essential in stabilizing the fullerene dication in a crystal lattice. High-resolution structural analysis of this compound, with the formula C(60)(AsF(6))(2), indicates that the highly reactive C(60)(2+) units are arranged according to a novel 1D "zigzag" polymer structure. The molecules are connected by an alternating sequence of four-membered carbon rings ([2 + 2] cycloaddition) and single C-C bonds. The long awaited high-T(c) superconductivity and magnetism, expected in a hole-doped C(60) compound, are replaced instead by a semiconducting behavior, quite probably originating from the reduced crystal and molecular symmetry upon polymerization. The small value of the energy gap (approximately 70 meV) suggests, nevertheless, the proximity of a metallic phase.
authors.affiliation: Dipartimento di Fisica, Università di Parma, Via G. Usberti 7/a, 43100 Parma, Italy. Mauro.Ricco@fis.unipr.it
authors.forename: Mauro
authors.initials: M
authors.lastname: Riccò
authors.forename: Daniele
authors.initials: D
authors.lastname: Pontiroli
authors.forename: Marcello
authors.initials: M
authors.lastname: Mazzani
authors.forename: Fabio
authors.initials: F
authors.lastname: Gianferrari
authors.forename: Massimo
authors.initials: M
authors.lastname: Pagliari
authors.forename: Angelo
authors.initials: A
authors.lastname: Goffredi
authors.forename: Michela
authors.initials: M
authors.lastname: Brunelli
authors.forename: Giorgia
authors.initials: G
authors.lastname: Zandomeneghi
authors.forename: Beat H
authors.initials: BH
authors.lastname: Meier
authors.forename: Toni
authors.initials: T
authors.lastname: Shiroka