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Terminal and bridging fluorine ligands in TiF4 as studied by 19F NMR in solids.
Solid State Nuclear Magnetic Resonance ( IF 3.2 ) Pub Date : 2019-05-20 , DOI: 10.1016/j.ssnmr.2019.05.007
Miwa Murakami 1 , Yasuto Noda 2 , K Takegoshi 2
Affiliation  

To examine bonding nature of fluorine ligands in a metal coordinated system, 19F high-resolution solid-state NMR has been applied to TiF4, which bears both bridging and terminal fluorines. Observed 12 isotropic signals are assigned to 12 crystallographically different fluorines (6 terminal and 6 bridging fluorines) in TiF4 by referring to the calculated isotropic shifts using density functional theory (DFT). The isotropic chemical shift (δiso) for terminal F (FT) appears at high frequency (420–480 ppm from δ(CCl3F) = 0 ppm) with large shielding anisotropy Δσ ∼ 850 ppm. Whereas the δiso and Δσ values for bridging F (FB) are moderate; δiso ∼ 0–25 ppm and Δσ ∼ 250 ppm. The origin of the observed high-frequency shift for FT is ascribed to the second-order paramagnetic shift with increased covalency, shorter Ti–F bonds, and smaller energy difference between the occupied and vacant orbitals. Examination of the orientation of the shielding tensor relative to the molecular structure shows that the most deshielded component of the shielding tensor is oriented along the Ti–F bond. The characteristic orientation is consistent with a Ti–F σ bond formed by dYZ of Ti and pz of F. Further, we show that the selectively observed spinning sideband patterns and the theoretical patterns with the calculated Δσ and η (shielding asymmetry) values are not consistent with each other for FB, indicating deficiency of the present DFT calculation in evaluating Δσ.



中文翻译:

通过19F NMR在固体中研究的TiF4中的末端和桥接氟配体。

为了检查金属配位体系中氟配体的键合性质,已将19 F高分辨率固态NMR应用于带有桥连和末端氟的TiF 4。通过参考使用密度泛函理论(DFT)计算的各向同性位移,将观察到的12个各向同性信号分配给TiF 4中的12个晶体学上不同的氟(6个末端氟和6个桥联氟)。各向同性化学位移(δ终端F(F)Ť)出现在高频(从420-480 ppm的δ(CCL 3 F)= 0 PPM)具有大的屏蔽各向异性Δσ〜850ppm的。尽管δ桥接F(F B)的Δσ值适中;δ 〜0-25 PPM和Δσ〜250ppm的。观测到的F T的高频位移的起因是由于二价顺磁位移具有更高的共价性,更短的Ti-F键以及被占据的轨道和空的轨道之间的能量差较小。检查屏蔽张量相对于分子结构的取向表明,屏蔽张量中最不屏蔽的成分沿Ti-F键取向。特征取向与由Ti和p z的d YZ形成的Ti–Fσ键一致此外,我们表明对于F B,选择性观察到的旋转边带模式和具有计算的Δσ和η(屏蔽不对称性)值的理论模式彼此不一致,表明当前的DFT计算在评估Δσ方面缺乏。

更新日期:2019-05-20
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