5 research outputs found
Constraining Carbon Nanothread Structures by Experimental and Calculated Nuclear Magnetic Resonance Spectra
A one-dimensional
(1D) sp<sup>3</sup> 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 <sup>13</sup>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<sup>3</sup> 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
Constraining Carbon Nanothread Structures by Experimental and Calculated Nuclear Magnetic Resonance Spectra
A one-dimensional
(1D) sp<sup>3</sup> 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 <sup>13</sup>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<sup>3</sup> 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
Constraining Carbon Nanothread Structures by Experimental and Calculated Nuclear Magnetic Resonance Spectra
A one-dimensional
(1D) sp<sup>3</sup> 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 <sup>13</sup>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<sup>3</sup> 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
Constraining Carbon Nanothread Structures by Experimental and Calculated Nuclear Magnetic Resonance Spectra
A one-dimensional
(1D) sp<sup>3</sup> 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 <sup>13</sup>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<sup>3</sup> 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
Mechanochemical Synthesis of Carbon Nanothread Single Crystals
Synthesis
of well-ordered reduced dimensional carbon solids with
extended bonding remains a challenge. For example, few single-crystal
organic monomers react under topochemical control to produce single-crystal
extended solids. We report a mechanochemical synthesis in which slow
compression at room temperature under uniaxial stress can convert
polycrystalline or single-crystal benzene monomer into single-crystalline
packings of carbon nanothreads, a one-dimensional sp<sup>3</sup> carbon
nanomaterial. The long-range order over hundreds of microns of these
crystals allows them to readily exfoliate into fibers. The mechanochemical
reaction produces macroscopic single crystals despite large dimensional
changes caused by the formation of multiple strong, covalent C–C
bonds to each monomer and a lack of reactant single-crystal order.
Therefore, it appears not to follow a topochemical pathway, but rather
one guided by uniaxial stress, to which the nanothreads consistently
align. Slow-compression room-temperature synthesis may allow diverse
molecular monomers to form single-crystalline packings of polymers,
threads, and higher dimensional carbon networks