Trevorah Ryan M, Chantler Christopher T, Schalken Martin J
School of Physics , University of Melbourne , Parkville , VIC 3010 , Australia.
J Phys Chem A. 2020 Feb 27;124(8):1634-1647. doi: 10.1021/acs.jpca.9b10619. Epub 2020 Feb 12.
We present a new technology for analyzing the molecular structure and in particular subtle conformational differences in Ni complexes using X-ray absorption spectroscopy (XAS), enabling tighter and more robust constraints of structure and dynamic bond lengths. Self-absorption and attenuating effects have a large impact in fluorescence X-ray absorption spectroscopy (XAS), compromising accuracy and insight in structural and advanced analyses. We correct for these dominant systematic effects. We investigate nickel(II) complexes, that is, bis(--propyl-salicylaldiminato) nickel(II), "-pr", and bis(--propyl-salicylaldiminato) nickel(II), "-pr", in 15 mM solutions with 0.1% w/w Ni. One is "square-planar" and one is "tetrahedral", with identical coordination numbers. We identify two key sources of uncertainty and provide robust estimates for them, reflecting the quality of the data, and provide meaningful estimates of χ suitable for hypothesis testing. We apply significance and model testing for fluorescence data, with direct uncertainty estimates. Two new peaks are revealed in the X-ray absorption fine structure (XAFS) at ≈ 4.4 and 5.4 Å. The high intrinsic accuracy of our processed data allows these features to be well modeled and yields deeper potential insight. Three important notions in the field are addressed: resolvability of shell radii, estimation of the number of independent data points in least-squares or Bayesian analysis, and the effect of uncertainties on the determined structure and the determinability of key structural parameters. Conventional XAFS fitting requires a and a . The origin of these limits is explained from the data, in a quantitative manner. Being able to distinguish the isomers spectroscopically and structurally places strong demands on the data, the uncertainties, and the model interpretation, and this article reports success in this subtle structural identification. Two nearby shells-the innermost two shells-are identified quantitatively, well below the conventional aliasing limit. This illustrates the application of new technology to gain new insight.
我们展示了一种新技术，用于使用X射线吸收光谱（XAS）分析镍配合物的分子结构，特别是其细微的构象差异，从而能够对结构和动态键长进行更严格、更可靠的约束。自吸收和衰减效应在荧光X射线吸收光谱（XAS）中具有很大影响，会损害结构分析和高级分析的准确性和深入性。我们对这些主要的系统效应进行了校正。我们研究了镍（II）配合物，即15 mM溶液中含0.1% w/w镍的双（-丙基-水杨醛亚胺基）镍（II），“-pr”，以及双（-丙基-水杨醛亚胺基）镍（II），“-pr”。其中一个是“平面正方形”，另一个是“四面体”，配位数相同。我们确定了两个关键的不确定来源，并对其进行了可靠的估计，反映了数据的质量，并提供了适用于假设检验的有意义的χ估计值。我们对荧光数据应用显著性和模型检验，并进行直接的不确定度估计。在X射线吸收精细结构（XAFS）中，在约4.4和5.4 Å处发现了两个新峰。我们处理后的数据具有很高的固有精度，使得这些特征能够得到很好的建模，并产生更深入的潜在见解。本文讨论了该领域的三个重要概念：壳层半径的可分辨性、最小二乘法或贝叶斯分析中独立数据点数量的估计，以及不确定性对确定结构和关键结构参数可确定性的影响。传统的XAFS拟合需要一个 和一个 。从数据中以定量方式解释了这些限制的起源。能够在光谱和结构上区分异构体对数据、不确定性和模型解释提出了很高的要求，本文报告了在这种细微结构识别方面的成功。定量识别了两个相邻的壳层——最里面的两个壳层，远低于传统的混叠极限。这说明了新技术在获得新见解方面的应用。
