Hansen Michael Ryan, Jakobsen Hans J, Skibsted Jørgen
Instrument Centre for Solid-State NMR Spectroscopy, Department of Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark.
Inorg Chem. 2003 Apr 7;42(7):2368-77. doi: 10.1021/ic020647f.
29Si chemical shift anisotropy (CSA) data have been determined from (29)Si MAS NMR spectra recorded at 14.1 T for a number of synthetic calcium silicates and calcium silicate hydrates. These are beta- and gamma-Ca(2)SiO(4), Ca(3)SiO(4)Cl(2), alpha-dicalcium silicate hydrate (alpha-Ca(2)(SiO(3)OH)OH), rankinite (Ca(3)Si(2)O(7)), cuspidine (Ca(4)Si(2)O(7)F(2)), wollastonite (beta-Ca(3)Si(3)O(9)), pseudowollastonite (alpha-Ca(3)Si(3)O(9)), scawtite (Ca(7)(Si(6)O(18))CO(3).2H(2)O), hillebrandite (Ca(2)SiO(3)(OH)(2)), and xonotlite (Ca(6)Si(6)O(17)(OH)(2)). The (29)Si MAS NMR spectra of rankinite and wollastonite clearly resolve manifolds of spinning sidebands from two and three Si sites, respectively, allowing the CSA parameters to be obtained with high precision for each site. For the (29)Si Q(1) sites in rankinite and cuspidine, the CSA asymmetry parameters (eta(sigma) approximately 0.6) contrast the general expectation that sorosilicates should possess small eta(sigma) values as a result of the nearly axially symmetric environments of the SiO(4) tetrahedra. The (29)Si CSA parameters provide an improved insight into the electronic and geometric environments for the SiO(4) tetrahedra as compared to the values solely for the isotropic chemical shift. It is shown that the shift anisotropy (delta(sigma)) and the CSA asymmetry parameter (eta(sigma)) allow a clear distinction of the different types of condensation of SiO(4) tetrahedra in calcium silicates. This relationship may in general be valid for neso-, soro-, and inosilicates. The CSA data determined in this work may form a valuable basis for (29)Si MAS NMR studies of the structures for tobermorites and calcium silicate hydrate phases resulting from hydration of Portland cements.
通过在14.1 T下记录的29Si 魔角旋转核磁共振（MAS NMR）谱，已测定了多种合成硅酸钙和硅酸钙水合物的29Si化学位移各向异性（CSA）数据。这些物质包括β - 和γ - Ca₂SiO₄、Ca₃SiO₄Cl₂、α - 二水硅酸钙（α - Ca₂(SiO₃OH)OH）、透辉石（Ca₃Si₂O₇）、尖晶石（Ca₄Si₂O₇F₂）、硅灰石（β - Ca₃Si₃O₉）、假硅灰石（α - Ca₃Si₃O₉）、钙板石（Ca₇(Si₆O₁₈)CO₃·2H₂O）、硅钙石（Ca₂SiO₃(OH)₂）和硬硅钙石（Ca₆Si₆O₁₇(OH)₂）。透辉石和硅灰石的29Si MAS NMR谱分别清晰地分辨出了来自两个和三个硅位点的自旋边带流形，从而能够高精度地获取每个位点的CSA参数。对于透辉石和尖晶石中的29Si Q¹位点，CSA不对称参数（ησ约为0.6）与一般预期相反，一般认为由于SiO₄四面体的近轴对称环境，链硅酸盐应具有较小的ησ值。与仅基于各向同性化学位移的值相比，29Si CSA参数能更深入地了解SiO₄四面体的电子和几何环境。结果表明，位移各向异性（δσ）和CSA不对称参数（ησ）能够清晰地区分硅酸钙中不同类型的SiO₄四面体缩聚。这种关系通常可能对孤岛状、链状和环状硅酸盐有效。本工作中测定的CSA数据可能为对由波特兰水泥水化产生的雪硅钙石和硅酸钙水合物相结构的29Si MAS NMR研究形成有价值的基础。
