C~4~0, C~4~0^+, Nb@C~4~0^+, NbC~3~9^+, Nb@C~4~0H~4^+的 量子化学研究

用量子化学从头计算方法研究了C~4~0,C~4~0^+,Nb@C~4~0^+,NbC~3~9^+,Nb@C~4~0H~4^+的几何构型、电子结构和C~2~8一样,C~4~0(T~d)基态也为^5A~2态,笼骨架上具有四个悬挂键。计算结果表明C~4~0和C~4~0^+比NbC~3~9^+和Nb@C~4~0^+稳定,与实验结果一致。

Quantum chemical study of C~4~0, C~4~0^+, Nb@C~4~0^+, NbC~3~9^+, Nb@C~4~0H~4^+

Ab initio Hartree - Fock calculations were performed on the equilibrium geometries and electronic structures of a series of endohedral, exohedral and endohedral - exohedral complexes of C40. The C40(Td) cage is found to have four unpaired electrons with a 5A2 open - shell ground state and have four dangling bonds. C40(Td) behaves as a sort of hollow superatom with an effective valence of 4,both toward the outside and inside of the carbon cage, so it is possible to form the endohedral metallofullerene Nb@ C40,exohedral complex C40H4 and endohedral - exohedral complex Nb@C40H4 from C40. From the values of binding energies per atom,it's found that C40( Td) is more stable than C40( C3v), while C40+(C3v) is more stable than C40+( Td) . In networked metallofullerenes NbC39+, Nb is connected directly with three carbon atom, forming three Nb - C single bonds with the Nb atom protruding from the surface of the carbon cage. Our Calculated results show that C40 and C40+ are more stable than NbC39+, and NbC39+ is more stable than Nb@C40+.The results are consistent with the experimental results.Through the comparison of the C40 series clusters with the C28 and related compounds,we have found that there are many similarities between C40 and C28 . Our calculated results may shed light on other endohedral and exhedral complexes of fullerenes and networked type metallofullerenes in general.