Perfect and Defective13C-Furan-Derived Nanothreads from Modest-Pressure Synthesis Analyzed by13C NMR

Bryan S. Matsuura, Steven Huss, Zhaoxi Zheng, Shichen Yuan, Tao Wang, Bo Chen, John V. Badding, Dirk Trauner, Elizabeth Elacqua, Adri C.T. van Duin, Vincent H. Crespi, Klaus Schmidt-Rohr

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish (US)
Pages (from-to)9529-9542
Number of pages14
JournalJournal of the American Chemical Society
Volume143
Issue number25
DOIs
StatePublished - Jun 30 2021

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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