95Mo magic angle spinning NMR at high field: improved measurements and structural analysis of the quadrupole interaction in monomolybdates and isopolymolybdates.
95Mo magic angle spinning NMR at high field: improved measurements and structural analysis of the quadrupole interaction in monomolybdates and isopolymolybdates.
复制标题
高场 95Mo 魔角旋转 NMR：改进单钼酸盐和同聚钼酸盐中四极相互作用的测量和结构分析。
DOI：
10.1021/jp0519621
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
Z. Gan
中科院分区：
文献类型：
--
作者：
J. d'Espinose de Lacaillerie;F. Barberon;K. Romanenko;O. Lapina;L. Polles;R. Gautier;Z. Gan
本研究利用魔角旋转（MAS）核磁共振在19.6 t的定向场下，方便准确地测量了各种钼酸盐中的95Mo四极耦合，54 MHz的共振频率足够高，可以去除声环伪影，光谱可以用通常的化学位移和四极线形状进行分析。对于单钼酸盐和钼酸盐，四极耦合主导了核磁共振响应，并且四极参数的测量精度优于以往的低场研究。此外，尽管钼配位的对称性较低，但通过从头算密度泛函理论（DFT）计算已知结构的电场梯度，建立了这种测量对探测钼环境的有用性。实验核磁共振数据与精细结构完全吻合。在异多酸盐中，共振是无形状的，由于大而低对称的单位细胞，DFT计算是不可能的。然而，从旋转侧带分析或MQMAS光谱中获得了经验但清晰的核磁共振特征。由于提高了基线和高场的灵敏度，这是第一次成为可能。随着17 T以上核磁共振谱仪的推广，预测95Mo MAS核磁共振将发展成为催化中负载钼酸盐等不明确结构的常规表征工具。
In this study, 95Mo quadrupole couplings in various molydbates were measured easily and accurately with magic angle spinning (MAS) NMR under a directing field of 19.6 T. The resonance frequency of 54 MHz was sufficiently high to remove acoustic ringing artifacts, and the spectra could be analyzed in the usual terms of chemical shift and quadrupolar line shapes. For monomolybdates and molybdite, the quadrupole coupling dominated the NMR response, and the quadrupole parameters could be measured with better accuracy than in previous lower field studies. Moreover, despite the low symmetry of the molybdenum coordination, the usefulness of such measurements to probe molybdenum environments was established by ab initio density functional theory (DFT) calculations of the electric field gradient from known structures. The experimental NMR data correlated perfectly with the refined structures. In isopolymolybdates, the resonances were shapeless and DFT calculations were impossible because of the large and low symmetry unit cells. Nevertheless, empirical but clear NMR signatures were obtained from the spinning sidebands analysis or the MQMAS spectra. This was possible for the first time thanks to the improved baseline and sensitivity at high fields. With the generalization of NMR spectrometers operating above 17 T, it was predicted that 95Mo MAS NMR could evolve as a routine characterization tool for ill-defined structures such as supported molybdates in catalysis.