Topochemical 3D polymerization of C60 under high pressure at elevated temperatures.
Fullerene C60 monomer crystals were compressed to a face-centered cubic (fcc) phase with a lattice parameter of a = 11.93(5) A and a micro-Vickers hardness of 4500 kg/mm2 using high-pressure and high-temperature conditions of 15 GPa at 500-600 degrees C. The hardness is compatible with that of cubic boron nitride (c-BN), suggesting the formation of a 3D C60 polymer. The single-crystal X-ray structural analysis revealed that each C60 molecule in the polymer was linked to the 12 nearest neighbors by [2+2] cycloaddition between the common pentagon-hexagon (56) edges. However, ab initio geometry optimization and molecular dynamics calculations suggested that the 3D polymer should have a rhombohedral structure with the space group of R containing [3+3] cycloaddition between the pentagons of C60 molecules within the plane perpendicular to the 3-fold axis. The higher apparent symmetry of fcc was observed as an averaged structure of different orientations of the rhombohedral structure. The R structure can be derived by only a slight rotation of each C60 unit in the (111) plane of the fcc structure. The band-structure calculation suggested that the 3D polymer (R) was a semiconductor; the activation energy for the electrical conductivity was experimentally determined to be 0.25 eV at 550 K.
Yamanaka
Shoji
S
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan.
Kini
Nagesh S
NS
Kubo
Akira
A
Jida
Saeko
S
Kuramoto
Hideaki
H
D003198:Computer Simulation; D003500:Cyclization; D004553:Electric Conductivity; D037741:Fullerenes / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D011108:Polymers / Q000138:chemical synthesis* / Q000737:chemistry; D011312:Pressure; D011789:Quantum Theory; D013696:Temperature; D013997:Time Factors; D014961:X-Ray Diffraction
D037741:Fullerenes; D011108:Polymers; C069837:fullerene C60