Constraining Carbon Nanothread Structures by Experimental and Calculated Nuclear Magnetic Resonance Spectra

Abstract

A one-dimensional (1D) sp carbon nanomaterial with high lateral packing order, known as carbon nanothreads, has recently been synthesized by slowly compressing and decompressing crystalline solid benzene at high pressure. The atomic structure of an individual nanothread has not yet been determined experimentally. We have calculated the C nuclear magnetic resonance (NMR) chemical shifts, chemical shielding tensors, and anisotropies of several axially ordered and disordered partially saturated and fully saturated nanothreads within density functional theory and systematically compared the results with experimental solid-state NMR data to assist in identifying the structures of the synthesized nanothreads. In the fully saturated threads, every carbon atom in each progenitor benzene molecule has bonded to a neighboring molecule (i.e., 6 bonds per molecule, a so-called "degree-6" nanothread), while the partially saturated threads examined retain a single double bond per benzene ring ("degree-4"). The most-parsimonious theoretical fit to the experimental 1D solid-state NMR spectrum, constrained by the measured chemical shift anisotropies and key features of two-dimensional NMR spectra, suggests a certain combination of degree-4 and degree-6 nanothreads as plausible components of this 1D sp carbon nanomaterial, with intriguing hints of a [4 + 2] cycloaddition pathway toward nanothread formation from benzene columns in the progenitor molecular crystal, based on the presence of nanothreads IV-7, IV-8, and square polymer in the minimal fit.

Local Structure and Bonding of Carbon Nanothreads Probed by High-Resolution Transmission Electron Microscopy

“…The interplanar spacings of the first-order reflections in SAED patterns are 5.7 ± 0.1 Å, which is consistent with the spacings predicted for several candidate degree-6 nanothread structures ( Figures S2-S5), when accounting for thermal expansion and beam-induced dilation of the lattice; these include the structures favored by a detailed solid-state NMR analysis. [26][27] The other reflections in Figure 4a index close to the Figure 1. Nanothread Carbon K-edge Electron Energy−Loss Spectrum.…”

The effects of morphology and temperature on the tensile characteristics of carbon nitride nanothreads

“…To date, more than 50 enumerated DNTs with the chemical formula ((CH)6) have been proposed, and some of them have been experimentally synthesized in lab-settings 4,30,31 . As a consequence of unique properties of DNTs, there are attempts to derivatize the DNTs.…”

Perfect and Defective 13C-Furan-Derived Nanothreads from Modest-Pressure Synthesis Analyzed by 13C NMR

“…33 It takes advantage of structurally characteristic 13 C and 1 H chemical shifts, which are also amenable to ab initio quantum-chemical simulations. 34 Unlike in vibrational spectra, peak areas in NMR are quantitative if the experiment has been performed appropriately, which means that relative concentrations of different moieties can be determined. Modern NMR involves much more than just taking "the" 13 C NMR spectrum.…”