Marichal C, Kempf J Y, Maigret B, Hirschinger J
Institut de Chimie, UMR 50 CNRS, Université Louis Pasteur, Strasbourg, France.
Solid State Nucl Magn Reson. 1997 Mar;8(1):33-46. doi: 10.1016/s0926-2040(96)01265-9.
51V Magic-angle-spinning (MAS) NMR has been applied to V2O5 at two different magnetic field strengths (4.7 and 7.1 T). Both the magnitude and relative orientation of the quadrupole and chemical shift (CS) tensors have been determined by iterative fitting of the 51V MAS NMR lineshapes at the two magnetic field strengths. The reliability of the results is discussed. Moreover, it is shown that previous low-field single-crystal data are fully consistent with the high-field powder-sample MAS NMR results provided that a slight noncoincidence between the CS tensor and the crystal frame axes is considered. The electric field gradient tensor at the vanadium and lithium sites is subsequently used to test several electronic structure calculation at an ab initio Hartree-Fock level in V2O5 and gamma-LiV2O5 crystals. It is shown that a wide distribution of oxygen charges must be considered to describe the particular environment of each type of oxygen atoms. Furthermore, this analysis supports the fact that the vanadyl bond is likely a short ionic bond. NMR is found to be a valuable experimental tool to get insight into the nature of chemical bonds in vanadium oxides.
51V魔角旋转（MAS）核磁共振已应用于在两种不同磁场强度（4.7和7.1 T）下的V2O5。通过对两种磁场强度下的51V MAS NMR线形进行迭代拟合，确定了四极张量和化学位移（CS）张量的大小和相对取向。讨论了结果的可靠性。此外，结果表明，只要考虑CS张量与晶体框架轴之间的轻微不重合，先前的低场单晶数据与高场粉末样品MAS NMR结果完全一致。随后，利用钒和锂位点处的电场梯度张量在V2O5和γ-LiV2O5晶体的从头算Hartree-Fock水平上测试了几种电子结构计算。结果表明，必须考虑氧电荷的广泛分布来描述每种类型氧原子的特殊环境。此外，该分析支持钒氧基键可能是短离子键这一事实。发现核磁共振是深入了解钒氧化物中化学键性质的有价值的实验工具。
