School of Chemistry, Southampton University, Southampton SO17 1BJ (United Kingdom).
Chemphyschem. 2013 Sep 16;14(13):3121-30. doi: 10.1002/cphc.201300269. Epub 2013 Jun 20.
We present a solid-state NMR study of H2 molecules confined inside the cavity of C70 fullerene cages over a wide range of temperatures (300 K to 4 K). The proton NMR spectra are consistent with a model in which the dipole-dipole coupling between the ortho-H2 protons is averaged over the rotational/translational states of the confined quantum rotor, with an additional chemical shift anisotropy δ(H)(CSA)=10.1 ppm induced by the carbon cage. The magnitude of the chemical shift anisotropy is consistent with DFT estimates of the chemical shielding tensor field within the cage. The experimental NMR data indicate that the ground state of endohedral ortho-H2 in C70 is doubly degenerate and polarized transverse to the principal axis of the cage. The NMR spectra indicate significant magnetic alignment of the C70 long axes along the magnetic field, at temperatures below ~10 K.
我们进行了一项固态核磁共振研究，在很宽的温度范围内（300 K 至 4 K）研究了 H2 分子在 C70 富勒烯笼内的空腔中的情况。质子 NMR 谱与一个模型一致，其中束缚量子转子的旋转/平移状态下，对 H2 分子中 o-H2 质子的偶极-偶极耦合进行了平均，同时由于碳笼引起了附加的化学位移各向异性 δ(H)(CSA)=10.1 ppm。化学位移各向异性的大小与笼内化学屏蔽张量场的 DFT 估计值一致。实验 NMR 数据表明，C70 中笼内 o-H2 的基态是双重简并的，并且沿笼的主轴横向极化。在温度低于约 10 K 时，NMR 谱表明 C70 长轴沿磁场的磁取向非常显著。
