Instrument Centre for Solid-State NMR Spectroscopy, Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark.
J Magn Reson. 2010 Feb;202(2):173-9. doi: 10.1016/j.jmr.2009.11.001. Epub 2009 Nov 10.
A strategy, involving (i) sensitivity enhancement for the central transition (CT) by population transfer (PT) employing WURST inversion pulses to the satellite transitions (STs) in natural abundance (33)S MAS NMR for two different MAS frequencies (nu(r)=5.0 and 10.0kHz) at 14.1T and (ii) a (33)S static QCPMG experiment at 19.6T, has allowed acquisition and analysis of very complex solid-state (33)S CT NMR spectra for the disordered tetrathioperrhenate anion ReS(4)(-) in [(C(2)H(5))(4)N][ReS(4)]. This strategy of different NMR experiments combined with spectral analysis/simulations has allowed determination of precise values for two sets of quadrupole coupling parameters (C(Q) and eta(Q)) assigned to the two different S sites for the four sulfur atoms in the ReS(4)(-) anion in the ratio S1:S2=1:3. These sets of C(Q), eta(Q) values for the S1 and S2 site are quite similar and the magnitudes of the quadrupole coupling constants (C(Q)=2.2-2.5MHz) are a factor of about three larger than observed for other tetrathiometalates A(2)MS(4) (A=NH(4), Cs, Rb and M=W, Mo). In addition, the spectral analysis also leads to a determination of the chemical shift anisotropy (CSA) parameters (delta(sigma) and eta(sigma)) for the S1 and S2 site, however, with much lower precisions (about 20% error margins) compared to those for C(Q), eta(Q), because the magnitudes of the two CSAs (i.e., delta(sigma)=60-90ppm) are about a factor of six smaller than observed for the other tetrathiometalates mentioned above. This large difference in the magnitudes of the anisotropic parameters C(Q) and delta(sigma) for the ReS(4)(-) anion, compared to those for the WS(4)(2-) and MoS(4)(2-) anions determined previously under identical experimental conditions, accounts for the increased complexity of the PT-enhanced (33)S MAS spectra observed for the ReS(4)(-) anion in this study. This difference in C(Q) also contributes significantly to the intensity distortions observed in the outer wings of the CTs when employing PT from the STs under conditions of slow-speed MAS.
一种策略涉及到通过（i）在 14.1T 下使用 WURST 反转脉冲对天然丰度（33）S MAS NMR 中的卫星跃迁（ST）进行种群转移（PT），从而增强中央跃迁（CT）的灵敏度，以及（ii）在 19.6T 下进行（33）S 静态 QCPMG 实验，从而实现了无序四硫代过铼酸根阴离子 ReS（4）（-）在 [(C（2）H（5））（4）N][ReS（4）]中复杂的固态（33）S CT NMR 谱的采集和分析。这种不同 NMR 实验与光谱分析/模拟相结合的策略，允许确定分配给 ReS（4）（-）阴离子中四个硫原子的两个不同 S 位点的两组四极耦合参数（C（Q）和 eta（Q））的精确值，对于 S1：S2=1：3 的比例。这两组 S1 和 S2 位点的 C（Q）、eta（Q）值非常相似，四极耦合常数（C（Q）=2.2-2.5MHz）的大小比其他四硫代金属 A（2）MS（4）（A=NH（4），Cs，Rb 和 M=W，Mo）观察到的大约大三倍。此外，光谱分析还导致了对 S1 和 S2 位点的化学位移各向异性（CSA）参数（delta（sigma）和 eta（sigma））的确定，但是与 C（Q）、eta（Q）相比，精度要低得多（约 20%的误差幅度），因为这两个 CSA 的大小（即 delta（sigma）=60-90ppm）比上述提到的其他四硫代金属大约小六倍。与之前在相同实验条件下确定的 WS（4）（2-）和 MoS（4）（2-）阴离子相比，ReS（4）（-）阴离子的各向异性参数 C（Q）和 delta（sigma）的大小差异很大，这导致了研究中观察到的 ReS（4）（-）阴离子的增强 PT 的（33）S MAS 谱的复杂性增加。在慢速 MAS 条件下，从 ST 进行 PT 时，C（Q）的这种差异也会导致 CT 的外翼观察到的强度扭曲。
