Zeyer-Düsterer Michaela, Montagne Lionel, Palavit Gérard, Jäger Christian
Institute of Optics and Quantum Electronics, Friedrich Schiller University of Jena, Max-Wien-Platz1, D-07743 Jena, Germany.
Solid State Nucl Magn Reson. 2005 Jan;27(1-2):50-64. doi: 10.1016/j.ssnmr.2004.06.009.
17O enriched sodium borophosphate glasses were prepared from isotopically enriched NaPO3 and H3BO3. These glasses have been studied by 17O, 11B and 31P NMR including 17O and 11B multiple quantum magic angle sample spinning (MQMAS), 11B-31P heteronuclear correlation (HETCOR) NMR and 11B{31P} rotational echo double resonance (REDOR). For comparison, the crystalline borophosphates BPO4 and Na5B2P3O13 were included in the investigations. The latter compound shows three sharp 31P resonances at -0.2, -2 and -8 ppm and two BO4 sites that can only be resolved by MQMAS. The 17O NMR spectra were recorded using both the static echo method at medium magnetic field (9.4 T) as well as MAS and MQMAS methods at high field (17.6 T). In total, five oxygen sites were identified in these borophosphate glasses: P-O-P, Na...O-P, P-O-B, B-O-B, Na...O-B. However, these five sites are not present simultaneously in any of the glasses. The 17O MQMAS spectra prove that P-O-B links play a major role in borophosphate glasses. These results are confirmed by the complementary 11B MAS spectra that show the presence of asymmetric and symmetric trigonal groups BO3a and BO3s and two tetrahedral BO4 units. 11B{31P} REDOR NMR is used to give independent information to assign the 11B lines to structural units present in the glasses. These REDOR measurements reveal that B-O-P bonds are present for each borate unit, including the BO3 groups. Particularly, a structural proposal for the two different BO4 resonances is given in terms of a different number of bonded phosphate tetrahedra. The 31P MAS spectra are usually broad and not well resolved. It is shown by 11B-31P HETCOR NMR that a possible structural assignment of a 31P signal at about -20 ppm to Q2 units as in binary sodium phosphate glasses is wrong and that the phosphate tetrahedron belonging to this resonance must be connected to borate groups.
用同位素富集的NaPO₃和H₃BO₃制备了¹⁷O富集的硼磷酸钠玻璃。这些玻璃通过¹⁷O、¹¹B和³¹P核磁共振进行了研究，包括¹⁷O和¹¹B多量子魔角样品旋转（MQMAS）、¹¹B - ³¹P异核相关（HETCOR）核磁共振以及¹¹B{³¹P}旋转回波双共振（REDOR）。为了进行比较，研究中还包括了晶体硼磷酸盐BPO₄和Na₅B₂P₃O₁₃。后一种化合物在-0.2、-2和-8 ppm处显示出三个尖锐的³¹P共振峰，以及两个只能通过MQMAS分辨的BO₄位点。¹⁷O核磁共振谱使用中磁场（9.4 T）下的静态回波方法以及高磁场（17.6 T）下的MAS和MQMAS方法进行记录。在这些硼磷酸盐玻璃中总共鉴定出五个氧位点：P - O - P、Na...O - P、P - O - B、B - O - B、Na...O - B。然而，这五个位点在任何一种玻璃中都不同时存在。¹⁷O MQMAS谱证明P - O - B键在硼磷酸盐玻璃中起主要作用。互补的¹¹B MAS谱显示存在不对称和对称的三角基团BO₃a和BO₃s以及两个四面体BO₄单元，证实了这些结果。¹¹B{³¹P} REDOR核磁共振用于提供独立信息，以便将¹¹B谱线归属到玻璃中存在的结构单元。这些REDOR测量结果表明，每个硼酸盐单元（包括BO₃基团）都存在B - O - P键。特别是，根据与磷酸盐四面体键合数量的不同，给出了两种不同BO₄共振峰的结构提议。³¹P MAS谱通常很宽且分辨率不佳。¹¹B - ³¹P HETCOR核磁共振表明，将二元磷酸钠玻璃中约-20 ppm处的³¹P信号归属于Q₂单元的可能结构归属是错误的，并且属于该共振峰的磷酸盐四面体必须与硼酸盐基团相连。
