Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo, 35131 Padova, Italy.
Philos Trans A Math Phys Eng Sci. 2013 Aug 5;371(1998):20110634. doi: 10.1098/rsta.2011.0634. Print 2013 Sep 13.
We have investigated the structure and nuclear magnetic resonance (NMR) spectroscopic properties of some dihydrogen endofullerene nitroxides by means of density-functional theory (DFT) calculations. Quantum versus classical roto-translational dynamics of H₂ have been characterized and compared. Geometrical parameters and hyperfine couplings calculated by DFT have been input to the Solomon-Bloembergen equations to predict the enhancement of the NMR longitudinal relaxation of H₂ due to coupling with the unpaired electron. Estimating the rotational correlation time via computed molecular volumes leads to a fair agreement with experiment for the simplest derivative; the estimate is considerably improved by recourse to the calculation of the diffusion tensor. For the other more flexible congeners, the agreement is less good, which may be due to an insufficient sampling of the conformational space. In all cases, relaxation by Fermi contact and Curie mechanisms is predicted to be negligible.
我们通过密度泛函理论（DFT）计算研究了一些双氢笼状富勒烯亚硝自由基的结构和核磁共振（NMR）光谱性质。对 H₂的量子与经典转子-平移动力学进行了特征化和比较。通过 DFT 计算的几何参数和超精细耦合已被输入到 Solomon-Bloembergen 方程中，以预测由于与未配对电子的耦合而导致 H₂的 NMR 纵向弛豫增强。通过计算的分子体积估算旋转相关时间可使最简单的衍生物与实验结果相当吻合；通过计算扩散张量可大大改善该估计值。对于其他更灵活的同系物，吻合度较差，这可能是由于构象空间的采样不足所致。在所有情况下，均预测 Fermi 接触和 Curie 机制的弛豫可以忽略不计。
