Solid-state (79/81)Br NMR and gauge-including projector-augmented wave study of structure, symmetry, and hydration state in alkaline earth metal bromides.
Solid-state (79/81)Br NMR and gauge-including projector-augmented wave study of structure, symmetry, and hydration state in alkaline earth metal bromides.
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对碱土金属溴化物的结构、对称性和水合状态进行固态 (79/81)Br NMR 和包括投影仪的增强波研究。
DOI：
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发表时间：
2010
影响因子：
2.9
通讯作者：
D. L. Bryce
中科院分区：
文献类型：
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作者：
C. Widdifield;D. L. Bryce
溴-79/81固体核磁共振（SSNMR）光谱是一种表征无机体系中溴离子局部结构和对称性的工具。获得CaBr(2)、SrBr(2)、BaBr(2)、MgBr(2)的基准实验（79/81）Br SSNMR数据。6 h (2) O, SrBr(2)。6 h (2) O, BaBr(2)。2H(2)O和CaBr(2)利用Solomon回波和/或QCPMG脉冲序列在11.75和21.1 t磁场下的xH(2)O，分析线形分析提供了（79/81）Br电场梯度（EFG）张量参数(包括（79）Br四极耦合常数，C(Q)((79)Br)，在CaBr(2)中高达75.1(5)MHz)，化学位移张量参数（包括最大的各向异性），以及张量主轴系统的相对取向。这些数据用结构和对称性来解释。我们的研究结果表明，尽管有相当大的四极性相互作用，离子溴体系应该通常可以通过（79/81）Br SSNMR进行表征。（79/81）Br SSNMR光谱的分辨能力，用样品具有多达四个磁不等效的位置，并通过一个罕见的（79）Br魔角自旋核磁共振在非立方晶格中的一个Br的例子说明。通过C(Q)和δ (iso)的剧烈变化，溴-79/81 SSNMR光谱被证明对水合物（即伪多态性）的存在很敏感。这些变化在一定程度上是诊断性的，混合物的成分是CaBr(2)。第一次确定了xH(2)O。因此，该技术应适用于表征其他未知的混合物或多态性。在发现（79）Br核四极共振数据不足的重要情况下，注意并纠正。GIPAW DFT计算结果通常与实验（79/81）Br SSNMR观测结果非常吻合。最后，证明了即使考虑了Sternheimer反屏蔽效应，也不能用点电荷模型定量地描述Br核上EFG的起源。
Bromine-79/81 solid-state NMR (SSNMR) spectroscopy is established as a tool to characterize the local structure and symmetry about bromide ions in inorganic systems. Benchmark experimental (79/81)Br SSNMR data are acquired for CaBr(2), SrBr(2), BaBr(2), MgBr(2).6H(2)O, SrBr(2).6H(2)O, BaBr(2).2H(2)O, and CaBr(2).xH(2)O using the Solomon echo and/or QCPMG pulse sequences in magnetic fields of 11.75 and 21.1 T. Analytical line-shape analysis provides (79/81)Br electric field gradient (EFG) tensor parameters (including (79)Br quadrupolar coupling constants, C(Q)((79)Br), of up to 75.1(5) MHz in CaBr(2)), chemical shift tensor parameters (including the largest reported anisotropy), and the relative orientation of the tensor principal axis systems. These data are interpreted in terms of structure and symmetry. Our results indicate that ionic bromide systems should be generally accessible to characterization by (79/81)Br SSNMR despite sizable quadrupolar interactions. The resolving capabilities of (79/81)Br SSNMR spectroscopy are illustrated, using samples which possess up to four magnetically inequivalent sites, and through a rare example of (79)Br magic-angle spinning NMR for a Br in a noncubic lattice. Bromine-79/81 SSNMR spectroscopy is demonstrated to be sensitive to the presence of hydrates (i.e., pseudopolymorphism), via drastic changes in C(Q) and delta(iso). The changes are diagnostic to an extent that the composition of the mixture CaBr(2).xH(2)O is determined for the first time. This technique should therefore be applicable to characterize other unknown mixtures or polymorphs. Important instances where (79)Br nuclear quadrupole resonance data were found to be deficient are noted and corrected. GIPAW DFT computations are shown to be generally in very good agreement with the experimental (79/81)Br SSNMR observations. Finally, it is demonstrated that the origin of the EFG at the Br nuclei cannot be described quantitatively using a point charge model, even after including Sternheimer antishielding effects.