Besides their technological applications, endohedral fullerenes provide ideal conditions for investigating molecular dynamics in restricted geometries. A representative of this class of systems, Sc₃C₂@C₈₀ displays complex intramolecular dynamics. The motion of the ⁴⁵Sc trimer has a remarkable effect on its electron paramagnetic resonance (EPR) spectrum, which changes from a symmetric 22-peak pattern at high temperature to a single broad lineshape at low temperature. The scandium trimer consists of two equivalent and one inequivalent metal atom, due to the carbon dimer rocking through the Sc₃ triangle. We demonstrate through first-principles molecular dynamics (MD), EPR parameter tensor averaging, and spectral modelling that, at high temperatures, three-dimensional movement of the enclosed Sc₃C₂ moiety takes place, which renders the metal centers equivalent and their magnetic parameters effectively isotropic. In contrast, at low temperatures the dynamics becomes restricted to two dimensions within the equatorial belt of the I_h symmetric C₈₀ host fullerene. This restores the inequivalence of the scandium centers and causes their anisotropic hyperfine couplings to broaden the experimental spectrum.

中文翻译：

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棘轮旋转或快速旋转：EP ₃和Sc ₃ C ₂ @C _80的动力学

除了其技术应用外，内面富勒烯还为研究受限几何结构中的分子动力学提供了理想的条件。此类系统的代表，Sc ₃ C ₂ @C ₈₀显示复杂的分子内动力学。⁴⁵ Sc三聚体的运动对其电子顺磁共振（EPR）谱有显着影响，该谱从高温下的对称22峰图形变为低温下的单宽线形。the三聚体由两个等价和一个不等价的金属原子组成，这是由于碳二聚物摇摆通过Sc ₃三角形。我们通过第一性原理分子动力学（MD），EPR参数张量平均和光谱模型证明，在高温下，封闭的Sc ₃ C ₂部分发生了三维运动，这使金属中心等效并且它们的磁性参数有效各向同性。相反，在低温下，动力学在I _h对称C ₈₀主体富勒烯的赤道带内被限制为二维。这恢复了centers中心的不等价性，并导致它们的各向异性超精细偶联扩大了实验光谱。