C1sshakeup spectrum ofC60

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

“…Similar closely spaced lines were also observed in the Raman 36 and IR 45 spectra of a high-pressure high-temperature tetragonal C 60 polymer, where intense modes are also visible at frequencies corresponding to the 38 and 48 meV modes. Densely spaced modes were also observed in the 50-100 meV energy range in the orthorhombic phase of pressure-polymerized C 60 (both in Raman 46 and IR 47 ) and in IR studies on orthorhombic RbC 60 and CsC 60 . 48,49 The point symmetry in these phases is D 2h , which contains more symmetry elements than the C 2h group of Li 4 C 60 .…”

“…39 A Raman-active mode related to a stretching vibration of the polymer bonds was observed at 14.6 meV in photopolymerized C 60 . 40 This energy is close to that of the softest mode in the HREEL spectrum of Li 4 C 60 (16.5 …”

“…This is only partially due to the reduced radius of the intercalant, which allows multiple filling of the larger intercalation sites and diffusion into smaller interstices. 22 Stoichiometries up to x ) 28 have been observed in Li-doped C 60 with the formation of Li clusters in the largest interstitial voids between the fullerene molecules. 23 Such high alkali concentrations are clearly not compatible with a total charge transfer from the intercalant species.…”

“…17,24,25 For low Li concentrations x ∼ 1, a tendency toward phase segregation was reported, 20,26 also observed in Na fullerides, 27 with the formation of alkali-poor regions and of a polymeric phase tentatively assigned an orthorhombic (one-dimensional (1D)) symmetry. 26 Photoemission studies on Li-doped C 60 films with alkali concentration x e 1 have suggested the coexistence of two phases, 28,29 of which one would be a dimer phase analogous to that observed in the stoichiometric AC 60 fullerides at low temperature (A ) K, Rb, Cs). At intermediate Li concentrations, the aforementioned (monoclinic) 2D-polymer phase is present in the bulk at room temperature, which transforms into a metallic monomer phase at higher temperature.…”

“…9,15 In Mg fullerides, the formation of a rhombohedral phase is reported, 16 while the 2D polymer phase of Na 4 C 60 consists of planar rectangular networks where each molecule forms four single bonds within the plane. 10 The rectangular polymer networks in Li-doped C 60 were initially thought to consist of [2 + 2]-cycloaddition bonds. 17,18 However, more recent studies [19][20][21] have shown that the bonding motif is mixed, with [2 + 2]cycloaddition bonds in one direction and single bonds in the orthogonal direction.…”