Perfect and Defective 13 C-Furan-Derived Nanothreads from Modest-Pressure Synthesis Analyzed by 13 C NMR
Perfect and Defective 13 C-Furan-Derived Nanothreads from Modest-Pressure Synthesis Analyzed by 13 C NMR
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通过 13 C NMR 分析中压合成中完美和有缺陷的 13 C-呋喃衍生纳米线
DOI：
10.1021/jacs.1c03671
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发表时间：
2021
影响因子：
15
通讯作者：
van Duin, Adri C.
中科院分区：
文献类型：
--
作者：
Matsuura, Bryan S.;Huss, Steven;Zheng, Zhaoxi;Yuan, Shichen;Wang, Tao;Chen, Bo;Badding, John V.;Trauner, Dirk;Elacqua, Elizabeth;van Duin, Adri C.
利用固体核磁共振技术研究了13 C4-呋喃缓慢压缩所产生的纳米线的分子结构。光谱编辑显示>95%的碳原子与一个氢（C-H）键合，并且存在2-4%的CH 2、0.6%的C = O和<0.3%的CH 3基团。烯烃占CH部分的18%，而捕获的未反应的呋喃占7%。二维（2D）~（13）C-~（13）C和~（13）H-~（13）C NMR确定了不对称O-CH-CH-CH-CH-环中12%的碳原子和对称O-CH-CH-CH-CH-环中24%的碳原子。虽然前者代表缺陷或链端，但后者中的一些似乎形成重复的螺纹段。在高度有序的、完全饱和的纳米线片段中发现了大约10%的碳原子。异常缓慢的13 C自旋交换与网站以外的完美的线程段记录的长度至少为14债券，小宽度的完美的线程信号也意味着一个相当长的，规则的结构。碳在完美的线程进行相对缓慢的自旋晶格弛豫，表明缓慢的自旋交换与其他线程和较小的振幅运动。通过部分反转恢复，有选择地观察和分析了完整螺纹的信号。交换NMR的中心带检测排除了先前认为的具有四种不同C-H键取向的顺螺纹，相反，这与反螺纹一致。通过量子化学计算，13 C的化学位移与反螺纹很好地匹配，但对于更复杂的结构，如yn/反螺纹，则不匹配。这些观察结果代表了完全饱和纳米线的原子级结构的第一次直接测定。
The molecular structure of nanothreads produced by the slow compression of13C4-furan was studied by advanced solid-state NMR. Spectral editing showed that >95% of carbon atoms were bonded to one hydrogen (C—H) and that there were 2–4% CH2, 0.6% C═O, and <0.3% CH3groups. Alkenes accounted for 18% of the CH moieties, while trapped, unreacted furan made up 7%. Two-dimensional (2D)13C–13C and1H–13C NMR identified 12% of all carbon in asymmetric O—CH═CH—CH—CH— and 24% in symmetric O—CH—CH═CH—CH— rings. While the former represented defects or chain ends, some of the latter appeared to form repeating thread segments. Around 10% of carbon atoms were found in highly ordered, fully saturated nanothread segments. Unusually slow13C spin-exchange with sites outside the perfect thread segments documented a length of at least 14 bonds; the small width of the perfect-thread signals also implied a fairly long, regular structure. Carbons in the perfect threads underwent relatively slow spin–lattice relaxation, indicating slow spin exchange with other threads and smaller amplitude motions. Through partial inversion recovery, the signals of the perfect threads were observed and analyzed selectively. Previously consideredsyn-threads with four different C—H bond orientations were ruled out by centerband-only detection of exchange NMR, which was, on the contrary, consistent withanti-threads. The observed13C chemical shifts were matched well by quantum-chemical calculations foranti-threads but not for more complex structures likesyn/anti-threads. These observations represent the first direct determination of the atomic-level structure of fully saturated nanothreads.