Islam M Tauhidul, Chantler Christopher T, Cheah Mun Hon, Tantau Lachlan J, Tran Chanh Q, Best Stephen P
School of Physics, University of Melbourne, Australia.
ANU College of Medicine, Biology and Environment, Australian National University, Australia.
J Synchrotron Radiat. 2015 Nov;22(6):1475-91. doi: 10.1107/S1600577515014976. Epub 2015 Oct 24.
High-accuracy transmission XAFS determined using the hybrid technique has been used to refine the geometries of bis(N-n-propyl-salicylaldiminato) nickel(II) (n-pr Ni) and bis(N-i-propyl-salicylaldiminato) nickel(II) (i-pr Ni) complexes which have approximately square planar and tetrahedral metal coordination. Multiple-scattering formalisms embedded in FEFF were used for XAFS modelling of the complexes. Here it is shown that an IFEFFIT-like package using weighting from experimental uncertainty converges to a well defined XAFS model. Structural refinement of (i-pr Ni) was found to yield a distorted tetrahedral geometry providing an excellent fit, χr(2) = 2.94. The structure of (n-pr Ni) is best modelled with a distorted square planar geometry, χr(2) = 3.27. This study demonstrates the insight that can be obtained from the propagation of uncertainty in XAFS analysis and the consequent confidence which can be obtained in hypothesis testing and in analysis of alternate structures ab initio. It also demonstrates the limitations of this (or any other) data set by defining the point at which signal becomes embedded in noise or amplified uncertainty, and hence can justify the use of a particular k-range for one data set or a different range for another. It is demonstrated that, with careful attention to data collection, including the correction of systematic errors with statistical analysis of uncertainty (the hybrid method), it is possible to obtain reliable structural information from dilute solutions using transmission XAFS data.
使用混合技术测定的高精度透射XAFS已用于优化双（N-正丙基-水杨醛亚胺基）镍（II）（n-pr Ni）和双（N-异丙基-水杨醛亚胺基）镍（II）（i-pr Ni）配合物的几何结构，这些配合物具有近似平面正方形和四面体的金属配位。FEFF中嵌入的多重散射形式用于配合物的XAFS建模。在此表明，使用来自实验不确定性加权的类似IFEFFIT的程序包收敛于一个定义明确的XAFS模型。发现（i-pr Ni）的结构精修产生了扭曲的四面体几何结构，拟合效果极佳，χr(2)=2.94。（n-pr Ni）的结构最好用扭曲的平面正方形几何结构建模，χr(2)=3.27。本研究证明了从XAFS分析中的不确定性传播可获得的见解，以及在假设检验和从头开始分析替代结构时可获得的相应置信度。它还通过定义信号嵌入噪声或放大不确定性的点来证明该（或任何其他）数据集的局限性，因此可以为一个数据集使用特定的k范围或为另一个数据集使用不同范围提供依据。结果表明，通过仔细关注数据收集，包括用不确定性的统计分析校正系统误差（混合方法），使用透射XAFS数据从稀溶液中获得可靠的结构信息是可能的。
