Deblonde Gauthier J-P, Coelho-Diogo Cristina, Chagnes Alexandre, Cote Gérard, Smith Mark E, Hanna John V, Iuga Dinu, Bonhomme Christian
PSL Research University , Chimie ParisTech-CNRS, Institut de Recherche de Chimie Paris, 11 rue Pierre et Marie Curie, 75005 Paris, France.
ERAMET Research , Hydrometallurgy department, 1 avenue Albert Einstein, F-78193 Trappes, France.
Inorg Chem. 2016 Jun 20;55(12):5946-56. doi: 10.1021/acs.inorgchem.6b00345. Epub 2016 Jun 1.
This work determines the potential of solid-state NMR techniques to probe proton, alkali, and niobium environments in Lindqvist salts. Na7HNb6O19·15H2O (1), K8Nb6O19·16H2O (2), and Na8Ta6O19·24.5H2O (3) have been studied by solid-state static and magic angle spinning (MAS) NMR at high and ultrahigh magnetic field (16.4 and 19.9 T). (1)H MAS NMR was found to be a convenient and straightforward tool to discriminate between protonated and nonprotonated clusters AxH8-xM6O19·nH2O (A = alkali ion; M = Nb, Ta). (93)Nb MAS NMR studies at different fields and MAS rotation frequencies have been performed on 1. For the first time, the contributions of NbO5Oμ2H sites were clearly distinguished from those assigned to NbO6 sites in the hexaniobate cluster. The strong broadening of the resonances obtained under MAS was interpreted by combining chemical shift anisotropy (CSA) with quadrupolar effects and by using extensive fitting of the line shapes. In order to obtain the highest accuracy for all NMR parameters (CSA and quadrupolar), (93)Nb WURST QCPMG spectra in the static mode were recorded at 16.4 T for sample 1. The (93)Nb NMR spectra were interpreted in connection with the XRD data available in the literature (i.e., fractional occupancies of the NbO5Oμ2H sites). 1D (23)Na MAS and 2D (23)Na 3QMAS NMR studies of 1 revealed several distinct sodium sites. The multiplicity of the sites was again compared to structural details previously obtained by single-crystal X-ray diffraction (XRD) studies. The (23)Na MAS NMR study of 3 confirmed the presence of a much larger distribution of sodium sites in accordance with the 10 sodium sites predicted by XRD. Finally, the effect of Nb/Ta substitutions in 1 was also probed by multinuclear MAS NMR ((1)H, (23)Na, and (93)Nb).
本研究确定了固态核磁共振（NMR）技术用于探测Lindqvist盐中质子、碱金属和铌环境的潜力。通过在高磁场和超高磁场（16.4和19.9 T）下的固态静态和魔角旋转（MAS）NMR对Na7HNb6O19·15H2O（1）、K8Nb6O19·16H2O（2）和Na8Ta6O19·24.5H2O（3）进行了研究。发现（1）H MAS NMR是区分质子化和非质子化簇AxH8-xM6O19·nH2O（A = 碱金属离子；M = Nb、Ta）的便捷直接工具。对1进行了不同磁场和MAS旋转频率下的（93）Nb MAS NMR研究。首次在六铌酸盐簇中清晰地区分了NbO5Oμ2H位点和NbO6位点的贡献。通过结合化学位移各向异性（CSA）和四极效应并对线形进行广泛拟合，解释了MAS下获得的共振的强烈展宽。为了获得所有NMR参数（CSA和四极参数）的最高精度，在16.4 T下以静态模式记录了样品1的（93）Nb WURST QCPMG谱。结合文献中可用的XRD数据（即NbO5Oμ2H位点的占有率）对（93）Nb NMR谱进行了解释。对1的1D（23）Na MAS和2D（23）Na 3QMAS NMR研究揭示了几个不同的钠位点。再次将这些位点的多重性与先前通过单晶X射线衍射（XRD）研究获得的结构细节进行了比较。对3的（23）Na MAS NMR研究证实了根据XRD预测的10个钠位点，存在更大的钠位点分布。最后，还通过多核MAS NMR（（1）H、（23）Na和（93）Nb）探测了1中Nb/Ta取代的影响。
