A new approach in 1D and 2D 13C high-resolution solid-state NMR spectroscopy of paramagnetic organometallic complexes by very fast magic-angle spinning
A new approach in 1D and 2D 13C high-resolution solid-state NMR spectroscopy of paramagnetic organometallic complexes by very fast magic-angle spinning
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DOI：
10.1021/ja0291742
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发表时间：
2003-03-26
影响因子：
15
通讯作者：
Chimon, S
中科院分区：
文献类型：
--
作者：
Ishii, Y;Wickramasinghe, NP;Chimon, S
讨论了利用超快幻角旋转(VFMAS)(旋转速度20 kHz)进行顺磁性金属有机化合物的13C高分辨固态核磁共振的新的一维和多维固态核磁共振方法。VFMAS去除了大部分13C−H和1H−1H偶极耦合，这些偶极耦合通常很难通过射频脉冲技术在顺磁复合体中消除，因为顺磁移位很大。在第一个系统的方法中，利用顺磁配合物的VFMA的独特功能，我们展示了一种获得分辨率良好的一维和多维13C SSNMR谱的方法，通过交叉极化和信号分配来增强灵敏度，以及偶极重新耦合方法在中等顺磁位移(∼800ppm)的非标记顺磁有机金属配合物中的应用。对1H频率为400.2−400.3 MHz的小分子非标记配位络合物粉末样品的实验结果表明，在VFMAS下可以获得高分辨率的~(13)C核磁共振谱，而不需要~1H去耦合。通过1H自旋交叉极化的高功率CP序列，利用VFMAS探头中的强射频场(∼100 kHz)，证实了13C SSMR的灵敏度增强。未标记的铜(II)(dl-丙氨酸)2·(H2O)和V(III)(乙酰丙酮)3(V(AcAc)3)的13C CPMAS谱表明，在VFMAS下，在几分钟内就可以获得少量(∼15 mg)非标记顺磁性有机金属配合物的高分辨谱。在铜(Ⅱ)(dl-丙氨酸)_2·(H_2O)上的实验表明，在VFMAS下，通过对1H和13C自旋施加同步−脉冲，可以实现顺磁性金属有机络合物的1H-π-13C偶极再耦合。结果还表明，根据偶极再耦合引起的~(13)C-−~1H偶极去相量，可以对顺磁络合物中的~(13)CH、~(13)CH_3和~(13)CO基团进行信号归属。此外，未标记的V(Acac)3的实验2D13C/1H化学位移相关谱显示出分辨良好的谱线，这些谱线与1D13C和1H谱重叠。用~(13)C-~(13)H偶极去相法结合~(13)C/~(13)H相关−对2D谱中不同化学基团的信号进行了区分。这些指定提供了关于固体中配位络合物中存在不等价配体的信息，而不需要单晶样品。
Novel 1D and multidimensional solid-state NMR (SSNMR) methods using very fast magic-angle spinning (VFMAS) (spinning speed > 20 kHz) for performing13C high-resolution SSNMR of paramagnetic organometallic complexes are discussed. VFMAS removes a majority of13C−H and1H−1H dipolar couplings, which are often difficult to remove by RF pulse techniques in paramagnetic complexes because of large paramagnetic shifts. In the first systematic approach using the unique feature of VFMAS for paramagnetic complexes, we demonstrate a means of obtaining well-resolved 1D and multidimensional13C SSNMR spectra, sensitivity enhancements via cross polarization, and signal assignments, and applications of dipolar recoupling methods for nonlabeled paramagnetic organometallic complexes of moderate paramagnetic shifts (∼800 ppm). Experimental results for powder samples of small nonlabeled coordination complexes at1H frequencies of 400.2−400.3 MHz show that highly resolved13C SSNMR spectra can be obtained under VFMAS, without requirements of1H decoupling. Sensitivity enhancement in13C SSNMR via cross polarization from1H spins was demonstrated with an amplitude-sweep high-power CP sequence using strong RF fields (∼100 kHz) available in the VFMAS probe.13C CPMAS spectra of nonlabeled Cu(II)(dl-alanine)2·(H2O) and V(III)(acetylacetonate)3(V(acac)3) show that it is possible to obtain high-resolution spectra for a small quantity (∼15 mg) of nonlabeled paramagnetic organometal complexes within a few minutes under VFMAS. Experiments on Cu(II)(dl-alanine)2·(H2O) demonstrated that1H−13C dipolar recoupling for paramagnetic organometal complexes can be performed under VFMAS by application of rotor-synchronous π-pulses to1H and13C spins. The results also showed that signal assignments for13CH,13CH3, and13CO groups in paramagnetic complexes are possible on the basis of the amount of13C−1H dipolar dephasing induced by dipolar recoupling. Furthermore, the experimental 2D13C/1H chemical-shift correlation NMR spectrum obtained for nonlabeled V(acac)3exhibits well-resolved lines, which overlap in 1D13C and1H spectra. Signals for different chemical groups in the 2D spectrum are distinguished by the13C−1H dipolar dephasing method combined with the 2D13C/1H correlation NMR. The assignments offer information on the existence of nonequivalent ligands in the coordination complex in solids, without requiring a single-crystal sample.