论文标题
$^{31} $ p nmr研究中的分子旋转的冻结
Freezing of molecular rotation in a paramagnetic crystal studied by $^{31}$P NMR
论文作者
论文摘要
我们提出了一项详细的$^{31} $ P核电磁共振（NMR）研究分子旋转的研究[Cu（pz）$ _ {2} $（2-hopy）$ _ {2} $] c $ _5 $ h $ _4 $ nho。在这里，PF $ _6 $旋转模式的冻结通过温度依赖性第二光谱时刻的几种速度升高，伴随着纵向和横向核自旋 - 延伸速率的宽峰。基于bloembergen-purcell-pound（BPP）理论的分析将相关的激活能量量化为$ e_ {a}/k_ {b} $ = 250和1400 k。此外，$^{31} $ p吸收线的第二光谱时刻的各向异性是$ $ $^$ $的$ $ $ $ $ $的$ 3。模式，并且与实验数据非常吻合。 Whereas the anisotropy of the frequency shift and enhancement of nuclear spin-relaxation rates is driven by the molecular rotation with respect to the dipole fields stemming from the Cu ions, the second spectral moment is determined by the intramolecular interaction of nuclear $^{19}$F and $^{31}$P moments in the presence of the distinct rotation modes.
We present a detailed $^{31}$P nuclear magnetic resonance (NMR) study of the molecular rotation in the compound [Cu(pz)$_{2}$(2-HOpy)$_{2}$](PF$_{6}$)$_{2}$, where pz = C$_4$H$_4$N$_2$ and 2-HOpy = C$_5$H$_4$NHO. Here, a freezing of the PF$_6$ rotation modes is revealed by several steplike increases of the temperature-dependent second spectral moment, with accompanying broad peaks of the longitudinal and transverse nuclear spin-relaxation rates. An analysis based on the Bloembergen-Purcell-Pound (BPP) theory quantifies the related activation energies as $E_{a}/k_{B}$ = 250 and 1400 K. Further, the anisotropy of the second spectral moment of the $^{31}$P absorption line was calculated for the rigid lattice, as well as in the presence of several sets of PF$_6$ reorientation modes, and is in excellent agreement with the experimental data. Whereas the anisotropy of the frequency shift and enhancement of nuclear spin-relaxation rates is driven by the molecular rotation with respect to the dipole fields stemming from the Cu ions, the second spectral moment is determined by the intramolecular interaction of nuclear $^{19}$F and $^{31}$P moments in the presence of the distinct rotation modes.
