The Various Packing Structures of Tb@C (I, II) Isomers in Their Cocrystals with Ni(OEP).

Soot-containing terbium (Tb)-embedded fullerenes were prepared by evaporation of TbO-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@C (I, II) isomers were isolated from the toluene solution of fullerenes and metallofullerenes. With the success of the growth of cocrystals of Tb@C (I, II) with Ni(OEP), the molecular structures of Tb@C (I) and Tb@C (II) were confirmed to be Tb@C(9)-C and Tb@C(6)-C, respectively, based on crystallographic data from X-ray single-crystal diffraction. Moreover, it was found that Tb@C (I, II) isomers demonstrated different packing behaviors in their cocrystals with Ni(OEP). Tb@C(9)-C forms a 1:1 cocrystal with Ni(OEP), in which Tb@(9)-C is aligned diagonally between the Ni(OEP) bilayers to form zigzag chains. In sharp contrast, Tb@C(6)-C forms a 2:2 cocrystal with Ni(OEP), in which Tb@C(6)-C 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 C(6)-C cage is much shorter than that to the C(9)-C one, indicative of a stronger π-π interaction between Ni(OEP) and the C carbon cage in the cocrystal of Tb@C(6)-C and Ni(OEP). Density functional theory calculations reveal that the regionally selective dimerization of Tb@C(6)-C is the result of a dominant unpaired spin existing on a particular C atom of the C(6)-C cage.