Polymerized Structures of Small Fullerenes

The paper continues our earlier researches [3] and the main purpose is theoretical investigations of possibility of existence of stable high symmetry polymerized structures of small fullerenes C2o, C24, C28 and C32. 

The geometrical parameters of equilibrium configurations of small fullerenes isolated molecules C , their dimers (Cn)2 and cuban-like clusters(Cn)8 are obtained for n = 20, 24, 28, 32. The Cuban like clusters can be considered as fragments of polymerized crystal structures with simple cubic symmetry. Total energy, heat of formation, energies of HOMO and LUMO orbitals, density of one-electron states (DOS) are determined for equilibrium configurations of all these objects. All the computations are performed by help of pocket PC Gamess in frames of optimized semi-empirical PM3-basis [4-5],... 

The results PM3-calculations of the geometry and electronic structures cuban-like clusters (Cn)8 (for n = 20, 24, 28, 32) show the possibility of existence of polymerized cubic crystal structures on the base of small fullerenes. 

Polymeric fullerene materials can be obtained by many methods, for example by irradiation with electrons or ions, treatment in a plasma generator, doping with alkali metals [9,28,46], direct chemical synthesis [47], or mechanical milling [29]. Because of the small penetration depth of light fullerenes can only be photopolymerized as thin films, but bulk photopolymer can be obtained by polymerization in solution [48,49]. Diffraction studies show that photopolymers usually have a disordered fee structure. Although some ordered films have been... 

Now polymerized structures on basis of big and small fullerenes with different dimensionality and symmetry are the subjects a lot of theoretical and experimental investigations. 

Initially polymeric KC and RbC o were thought to be isostructural. Indeed, the lattice parameters of the three AC o polymers with A=K, Rb, Cs are similar [58]. However, the strong dilferences in the physical properties, in particular the magnetic susceptibilities, electrical conductivities [10] and MAS spectra [59] indicated some undetected structural differences. Brouet et al. [60] suggested from an analysis of MAS spectra that the main difference is in the relative orientation of neighboring C<,o chains. The MAS spectrum shifts are determined in principle both by inter and intra fullerene interactions and are sensitive to small structural differences. Some of the 16 inequivalent C lines of the polymer are well resolved and it was found that the C MAS spectra of polymeric RbCgo and CsCgo on the one hand, and polymeric KC o on the other, are very different (Fig. 13). 

---