Institut des Molécules et Matériaux du Mans (IMMM), UMR 6283 CNRS, Le Mans Université, Le Mans, Cedex 9, France.
Dalton Trans. 2019 Jan 2;48(2):587-601. doi: 10.1039/c8dt03241f.
Solid state NMR signals are very sensitive to the local environment of the observed nucleus; however, their interpretation is not straightforward. On the other hand, first-principles DFT calculations of NMR parameters can now be applied to periodic compounds to predict NMR parameters. Thus, ab initio calculations can help to interpret the NMR spectra exhibited by complex materials, to assign NMR lines to structural environments, and even to enlighten the environmental factors influencing the NMR parameters for a given nucleus. Both techniques have been applied to crystalline compounds of the KF-YF3 binary system, γ-K3YF6, K2YF5, KYF4, β-KY2F7 and α-KY3F10, which present a variety of YFn and KFm polyhedra. First, the structure of K2YF5 was refined in the Pnma space group and, for all compounds, atomic positions were optimized by DFT. The 19F, 89Y and 39K NMR spectra have been recorded and the measured NMR parameters are compared to those calculated from the first-principles DFT method, allowing unambiguous assignments of NMR lines to crystallographic sites. Linear correlations between the experimental δiso and calculated σiso values for the three nuclei are used to predict the theoretical 19F spectra of KYF4 (24 F sites) and β-KY2F7 (19 F sites) as well as the 39K spectrum of KYF4 (6 K sites). For 89Y and 39K, both computational and experimental results show a decrease of the isotropic chemical shift values when the cation coordination number increases. Above all, 89Y isotropic chemical shift values correlate with the number of K atoms present in the Y second coordination sphere. For 19F, the combination of isotropic chemical shift and chemical shift anisotropy allows for distinguishing four kinds of F environments.
固态 NMR 信号对观察核的局部环境非常敏感；然而，其解释并不直接。另一方面，现在可以将第一性原理 DFT 计算应用于周期性化合物以预测 NMR 参数。因此，从头算计算可以帮助解释复杂材料的 NMR 谱，将 NMR 线分配给结构环境，甚至阐明影响给定核 NMR 参数的环境因素。这两种技术都已应用于 KF-YF3 二元体系的结晶化合物，γ-K3YF6、K2YF5、KYF4、β-KY2F7 和 α-KY3F10，它们呈现出各种 YFn 和 KFm 多面体。首先，在 Pnma 空间群中精修 K2YF5 的结构，并且对于所有化合物，通过 DFT 优化原子位置。记录了 19F、89Y 和 39K NMR 谱，并且将测量的 NMR 参数与从第一性原理 DFT 方法计算的参数进行比较，从而可以将 NMR 线明确地分配给晶体学位点。三个核的实验 δiso 和计算 σiso 值之间的线性相关性用于预测 KYF4（24 F 位）和 β-KY2F7（19 F 位）的理论 19F 谱以及 KYF4 的 39K 谱（6 K 位）。对于 89Y 和 39K，计算和实验结果均表明当阳离子配位数增加时，各向同性化学位移值减小。最重要的是，89Y 各向同性化学位移值与第二配位球中存在的 K 原子数相关。对于 19F，各向同性化学位移和化学位移各向异性的组合可用于区分四种 F 环境。
