TEMPERATURE-DEPENDENCE OF THERMAL MOTION IN CRYSTALLINE ANTHRACENE
TEMPERATURE-DEPENDENCE OF THERMAL MOTION IN CRYSTALLINE ANTHRACENE
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DOI：
10.1107/s0108768190008382
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发表时间：
1990-12-01
期刊：
影响因子：
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通讯作者：
DUNITZ, JD
中科院分区：
文献类型：
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作者：
BROCK, CP;DUNITZ, JD
在 94 至 295 K 的六个温度下测量了蒽 C14H10 的单晶 X 射线衍射数据。通过传统的最小二乘技术在每个温度下对 C 和 H 原子的位置和位移参数进行了细化。 得出的 C 原子在六个温度下的各向异性位移参数针对内部模式的贡献进行了校正，然后进行分析以确定描述刚体分子运动的平动 (T) 和解放 (L) 张量。 尽管所得的 T 和 L 张量与之前在室温下测量和计算的结果非常吻合，但 L 张量随晶体冷却的收缩似乎有些反常。 意想不到的行为集中在与长分子轴相关的 L 成分中，由于分子几何形状的原因，该成分的确定性相对较差。 因此，虽然不能排除一些微妙的、依赖于温度的结构变化的可能性，例如分子重新定向，但也不能认可它。 这项研究强调了所研究分子的几何形状如何限制衍射方法确定的刚体热运动描述的质量。
Single-crystal X-ray diffraction data for anthracene, C14H10, have been measured at six temperatures from 94 to 295 K. Positional and displacement parameters for C and H atoms were refined at each temperature by conventional least-squares techniques. The derived anisotropic displacement parameters for the C atoms at each of the six temperatures were corrected for the contributions of the internal modes and were then analyzed to determine translational (T) and librational (L) tensors describing the rigid-body molecular motion. Although the resulting T and L tensors agree well with those measured and calculated previously at room temperature, the shrinkage of the L tensor with crystal cooling appears somewhat anomalous. The unexpected behavior is concentrated in the component of L associated with the long molecular axis, a component that is, as a consequence of the molecular geometry, relatively poorly determined. Therefore, while the possibility of some subtle, temperature-dependent structural change, such as a molecular reorientation, cannot be ruled out, neither can it be endorsed. This study underlines how the geometry of the molecule being studied can limit the quality of the rigid-body thermal-motion description determined by diffraction methods.