Fischer Andreas, Eickerling Georg, Scherer Wolfgang
Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg, Germany.
Molecules. 2021 Jul 14;26(14):4270. doi: 10.3390/molecules26144270.
Similar to classical , aspherical deformations of the electron density in the atomic core region can result in in refinements using a Hansen-Coppens multipolar model (HCM), especially when highly precise experimental datasets with resolutions far beyond sin(θ)/λ ≤ 1.0 Å are employed. These shifts are about two orders of magnitude smaller than their counterparts caused by valence shell deformations, and their underlying deformations are mainly of dipolar character for 1st row atoms. Here, we analyze the resolution dependence of core asphericity shifts in α-boron. Based on theoretical structure factors, an appropriate Extended HCM (EHCM) is developed, which is tested against experimental high-resolution (sin()/ ≤ 1.6 Å) single-crystal diffraction data. Bond length deviations due to core asphericity shifts of α-boron in the order of 4-6·10 Å are small but significant at this resolution and can be effectively compensated by an EHCM, although the correlation of the additional model parameters with positional parameters prevented a free refinement of all core model parameters. For high quality, high resolution data, a proper treatment with an EHCM or other equivalent methods is therefore highly recommended.
与经典情况类似，原子核区域电子密度的非球形变形会导致在使用汉森 - 科彭斯多极模型（HCM）进行精修时出现[相关问题]，特别是当使用分辨率远超过sin(θ)/λ ≤ 1.0 Å的高精度实验数据集时。这些位移比价壳层变形引起的位移小约两个数量级，并且对于第一行原子，其潜在变形主要具有偶极特征。在此，我们分析了α - 硼中核心非球形位移的分辨率依赖性。基于理论结构因子，开发了一种合适的扩展HCM（EHCM），并针对实验高分辨率（sin(θ)/λ ≤ 1.6 Å）单晶衍射数据进行了测试。α - 硼由于核心非球形位移导致的键长偏差约为4 - 6·10 Å，在该分辨率下虽小但很显著，并且可以通过EHCM有效补偿，尽管额外模型参数与位置参数的相关性阻止了所有核心模型参数的自由精修。因此，对于高质量、高分辨率数据，强烈建议使用EHCM或其他等效方法进行适当处理。
