Solid-State 137Ba NMR Spectroscopy: An Experimental and Theoretical Investigation of 137Ba Electric Field Gradient Tensors and Their Relation to Structure and Symmetry

详细信息    查看全文

• 作者：Hiyam Hamaed ; Eric Ye ; Konstantin Udachin ; Robert W. Schurko
• 刊名：Journal of Physical Chemistry B
• 出版年：2010
• 出版时间：May 13, 2010
• 年：2010
• 卷：114
• 期：18
• 页码：6014-6022
• 全文大小：360K
• 年卷期：v.114,no.18(May 13, 2010)
• ISSN：1520-5207

文摘

Ultrawideline ¹³⁷Ba SSNMR spectra of several barium-containing systems (barium nitrate, barium carbonate, barium chlorate monohydrate, barium chloride dihydrate, anhydrous barium chloride, and barium hydrogen phosphate) were acquired at two different magnetic field strengths (9.4 and 21.1 T) using frequency-stepped techniques. The recently reported WURST−QCPMG pulse sequence (O’Dell et al. Chem. Phys. Lett. 2008, 464, 97−102) is shown to be very useful for rapidly acquiring high signal-to-noise ¹³⁷Ba SSNMR spectra. The breadths of the second-order quadrupolar-dominated spectra and experimental times are notably reduced for experiments conducted at 21.1 T. Analytical simulations of the ¹³⁷Ba SSNMR spectra at both fields yield the quadrupolar parameters, and in select cases the barium chemical shift anisotropies (CSAs). Quadrupolar interactions dominate the ¹³⁷Ba powder patterns, with quadrupolar coupling constants, C_Q(¹³⁷Ba), ranging from 7.0 to 28.8 MHz. The ¹³⁷Ba electric field gradient (EFG) parameters extracted from these spectra are correlated to the local environments at the barium sites, via consideration of molecular symmetry and structure, and first principles calculations of ¹³⁷Ba EFG tensors performed using CASTEP software. The rapidity with which ¹³⁷Ba SSNMR spectra can be acquired using the WURST pulse sequence and/or at ultrahigh magnetic fields and the sensitivity of the ¹³⁷Ba EFG tensor parameters to the changes in the barium environment suggest that ¹³⁷Ba SSNMR has great potential for structural characterization of a variety of barium-containing materials.