Skibsted J, Jakobsen H J
Department of Chemistry, University of Aarhus, Denmark.
Solid State Nucl Magn Reson. 1994 Feb;3(1):29-38. doi: 10.1016/0926-2040(94)90049-3.
23Na Magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra of pure phases for Na2MoO4, Na2MoO4 x 2H2O, Na2WO4, and Na2WO4 x 2H2O have led to the determination of accurate values for the quadrupole coupling parameters and isotropic chemical shifts for all Na sites. The analysis of the spectra involves a combination of simulations of the line shapes for the central transitions and the manifold of spinning sidebands for the satellite transitions. The spectral parameters for the pure phases represent a prerequisite for a correct assignment and quantitative evaluation of 23Na MAS spectra at different magnetic field strengths observed for mixtures of the anhydrous and dihydrate phases. Such phase mixtures are observed, for example, for some commercial samples of Na2MoO4 or may be generated by (i) exposure of the anhydrous phases to a humid atmosphere or (ii) gently heating the dihydrates. The quadrupole coupling parameters for the two Na sites in the dihydrates are tentatively assigned to the two crystallographically distinct Na atoms in the asymmetric unit by calculations of an approximate dependency of the electric field gradient tensor on the local geometry for the Na sites.
Na2MoO4、Na2MoO4·2H2O、Na2WO4和Na2WO4·2H2O纯相的23Na魔角旋转核磁共振（MAS NMR）光谱已确定了所有Na位点的四极耦合参数和各向同性化学位移的准确值。光谱分析涉及对中心跃迁的线形和卫星跃迁的旋转边带多重峰进行模拟。纯相的光谱参数是正确归属和定量评估在不同磁场强度下观察到的无水相和二水合物相混合物的23Na MAS光谱的前提条件。例如，在一些Na2MoO4商业样品中会观察到这种相混合物，或者可能通过以下方式产生：（i）将无水相暴露在潮湿气氛中，或（ii）轻轻加热二水合物。通过计算电场梯度张量对Na位点局部几何结构的近似依赖性，二水合物中两个Na位点的四极耦合参数被初步指定给不对称单元中两个晶体学上不同的Na原子。
