Stevensson Baltzar, Lv Peng, Edén Mattias
Physical Chemistry Division, Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm SE-106 91, Sweden.
MOE Frontiers Science Center for Rare Isotopes, Lanzhou University, Lanzhou 730000, PR China.
J Phys Chem B. 2024 Dec 19;128(50):12651-12667. doi: 10.1021/acs.jpcb.4c06721. Epub 2024 Dec 10.
We discuss the prospects for accurate B magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectral deconvolutions for reaching beyond the readily extracted borate speciations offered by the integrated resonances of the coexisting B and B species of the respective BO and BO network groups in borosilicate (BS) glasses. We critically review hitherto proposed B and B NMR-peak assignments relating to their neighboring Si, B and B species, as quantified by MAS NMR spectral deconvolution. Guidance to these resonance assignments was offered from double-quantum-single-quantum (2Q-1Q) B MAS NMR experiments that inform about the B-O-B network linkages. The NMR spectral deconvolutions from two BS glass series with low nonbridging oxygen (NBO) contents and fixed molar ratios / = {1.0, 2.0} but variable network-modifying cations of alkali metals and Mg revealed a dominance of B-O-Si linkages, yet with a significant dependence on the BO population of the glass, which was rationalized by the different propensities for B-O-{Si, B, B} linkage formation. For BS glasses with comparable B and Si contents, we recommend three-peak deconvolutions of the B spectral region, whose B(Si) sites differ in their (average) numbers of B-O-Si and 4 - B-O-B bonds, where B may assume B B. We also discuss the structural origin of the two rather arbitrarily classified "ring" and "non-ring" B entities, where 2Q-1Q B NMR suggests the former to primarily constitute BO groups that coexist with BO moieties in (superstructural) ring units largely devoid of bonds to Si, whereas the "non-ring" B sites involve linkages to all of B, B, and Si, with B-O-Si linkages prevailing. The limitations of B NMR spectral deconvolutions are discussed, including the remaining challenges in analyzing NBO-rich BS glasses.
我们讨论了通过精确的硼魔角旋转（MAS）核磁共振（NMR）光谱去卷积来超越硼硅酸盐（BS）玻璃中各自BO和BO网络基团共存的B和B物种的综合共振所提供的易于提取的硼酸盐形态的前景。我们批判性地回顾了迄今为止提出的与相邻的Si、B和B物种相关的B和B NMR峰归属，这些归属通过MAS NMR光谱去卷积进行了量化。双量子 - 单量子（2Q - 1Q）B MAS NMR实验为这些共振归属提供了指导，该实验揭示了B - O - B网络连接情况。对两个具有低非桥氧（NBO）含量且固定摩尔比/ = {1.0, 2.0}但碱金属和Mg的网络改性阳离子可变的BS玻璃系列进行的NMR光谱去卷积显示，B - O - Si连接占主导，但很大程度上依赖于玻璃中的BO含量，这可以通过B - O - {Si, B, B}连接形成的不同倾向来解释。对于具有可比B和Si含量的BS玻璃，我们建议对B光谱区域进行三峰去卷积，其B(Si)位点在B - O - Si和4 - B - O - B键的（平均）数量上有所不同，其中B可能为B或B。我们还讨论了两种相当随意分类的“环”和“非环”B实体的结构起源，其中2Q - 1Q B NMR表明前者主要构成BO基团，这些基团与（超结构）环单元中的BO部分共存，这些环单元在很大程度上没有与Si的键，而“非环”B位点涉及与所有B、B和Si的连接，其中B - O - Si连接占主导。讨论了B NMR光谱去卷积的局限性，包括分析富含NBO的BS玻璃时仍然存在的挑战。
