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The Various Packing Structures of Tb@C82 (I, II) Isomers in Their Cocrystals with Ni(OEP)
Wei Dong1, Qin Zhou1, Wangqiang Shen2
1Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin 150080, China.
Abstract:
Soot-containing terbium (Tb)-embedded fullerenes were prepared by evaporation of Tb4O7-doped graphite rods in an electric arc discharge chamber. After 1,2,4-trichlorobenzene extraction of the soot and rotary evaporation of the extract, a solid product was obtained and then dissolved into toluene by ultrasonication. Through a three-stage high-pressure liquid chromatographic (HPLC) process, Tb@C82 (I, II) isomers were isolated from the toluene solution of fullerenes and metallofullerenes. With the success of the growth of cocrystals of Tb@C82 (I, II) with Ni(OEP), the molecular structures of Tb@C82 (I) and Tb@C82 (II) were confirmed to be Tb@C(9)-C82 and Tb@Cs(6)-C82, respectively, based on crystallographic data from X-ray single-crystal diffraction. Moreover, it was found that Tb@C82 (I, II) isomers demonstrated different packing behaviors in their cocrystals with Ni(OEP). Tb@C(9)-C82 forms a 1:1 cocrystal with Ni(OEP), in which Tb@C(9)-C82 is aligned diagonally between the Ni(OEP) bilayers to form zigzag chains. In sharp contrast, Tb@Cs(6)-C82 forms a 2:2 cocrystal with Ni(OEP), in which Tb@Cs(6)-C82 forms a centrosymmetric dimer that is aligned linearly with Ni(OEP) pairs to form one-dimensional structures in the a-c lattice plane. In addition, the distance of a Ni atom in Ni(OEP) to the Cs(6)-C82 cage is much shorter than that to the C(9)-C82 one, indicative of a stronger π-π interaction between Ni(OEP) and the C82 carbon cage in the cocrystal of Tb@C(6)-C82 and Ni(OEP). Density functional theory calculations reveal that the regionally selective dimerization of Tb@C(6)-C82 is the result of a dominant unpaired spin existing on a particular C atom of the C(6)-C82 cage.
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