Carbynes: carriers of primordial noble gases in meteorites

Exploring the Growth Dynamics of Size-Selected Carbon Atomic Wires with In Situ UV Resonance Raman Spectroscopy

Short carbon atomic wires, the prototypes of the lacking carbon allotrope carbyne, represent the fundamental 1D system and the first stage in carbon nanostructure growth, which still exhibits many open points regarding their growth and stability. An in situ UV resonance Raman approach is introduced for real-time monitoring of the growth of carbon atomic wires during pulsed laser ablation in liquid without perturbing the synthesis environment. Single-chain species' growth dynamics are tracked, achieving size selectivity by exploiting the peculiar optoelectronic properties of carbon wires and the tunability of synchrotron radiation. Diverse solvents are systematically explored, finding size- and solvent-dependent production rates linked to the solvent's C/H ratio and carbonization tendency. Carbon atomic wires' growth dynamics reveal a complex interplay between formation and degradation, leading to an equilibrium. Water, lacking in carbon atoms and reduced polyynes solubility, yields fewer wires with rapid saturation. Organic solvents exhibit enhanced productivity and near-linear growth, attributed to additional carbon from solvent dissociation and low relative polarity. Exploring the dynamics of the saturation regime provides new insights into advancing carbon atomic wires synthesis via PLAL. Understanding carbon atomic wires' growth dynamics can contribute to optimizing PLAL processes for nanomaterial synthesis.

Twisting of Alkynes towards a Carbon Double Helix

The carbon allotrope exhibiting only one-dimensional sp-hybridized carbon atoms is called carbyne. However, its existence is very controversial. Studies on model compounds for carbyne revealed that many oligoalkynes show not a straight, but a bent structure of the carbon chain. Here, we question whether it would also be possible to obtain a more complex structure from carbyne, such as a dimeric double helix. Based on quantum chemical calculations, we show that only a small energetic expense is needed for the formation of a double helix starting from oligoalkyne chains. In some cases, the double helix-like conformation is more stable than the corresponding conformation with a parallel arrangement of the acetylene chains. Furthermore, model systems were synthesized in which two diphenyl oligoalkyne chains are fixed and twisted by a chiral imidazole-containing clamp. A structural investigation of these model systems was performed based on UV and CD spectroscopy and quantum chemical calculations. The observed twisting in these model systems can be regarded as the first small step towards an imaginable carbon double helix.

Massive dihydrogen uptake by anionic carbon chains

The remarkable capacity of anionic and dianionic carbon chains to bind dihydrogen compared to their neutral moieties has been established theoretically and these one dimensional anions could be utilized in developing novel H₂ storage materials.

Non-covalent intermolecular carbon-carbon interactions in polyynes

Polyynes, the smaller analogues of one dimensional infinite chain carbon allotrope carbyne, have been studied for the type and strength of the intermolecular interactions in their dimer and tetramer complexes using density functional theory. The nature of end group functionalities and the chain length of the polyynes are varied to assess their role in modulating the non-covalent interaction energy. As seen in molecular electrostatic potential analysis, all the polyyne complexes showed a multitude of non-covalent CC interactions, resulting from complementary electrostatic interactions between relatively electron rich formal triple bond region of one monomer and the electron deficient formal single bond region of the other monomer. This type of paired (C[triple bond, length as m-dash]C)(C-C) bonding interaction, also characterized using quantum theory of atoms-in-molecules, increases with increase in the monomer chain length leading to substantial increase in interaction energy (Eint); -1.07 kcal mol(-1) for the acetylene dimer to -45.83 kcal mol(-1) for the 50yne dimer. The magnitude of Eint increases with substitutions at end positions of the polyyne and this effect persists even up to 50 triple bonds, the largest chain length analyzed in this paper. The role of CC interactions in stabilizing the polyyne dimers is also shown by sliding one monomer in a dimer over the other, which resulted in multiple minima with a reduced number of CC interactions and lower values of Eint. Furthermore, strong cooperativity in the CC bond strength in tetramers is observed as the interaction energy per monomer (Em) of the polyyne is 2.5-2.8 times higher compared to that of the dimer in a test set of four tetramers. The huge gain in energy observed in large polyyene dimers and tetramers predicts the formation of polyyne bundles which may find use in the design of new functional molecular materials.

Carbyne with finite length: The one-dimensional sp carbon

Carbyne is the one-dimensional allotrope of carbon composed of sp-hybridized carbon atoms. Definitive evidence for carbyne has remained elusive despite its synthesis and preparation in the laboratory. Given the remarkable technological breakthroughs offered by other allotropes of carbon, including diamond, graphite, fullerenes, carbon nanotubes, and graphene, interest in carbyne and its unusual potential properties remains intense. We report the first synthesis of carbyne with finite length, which is clearly composed of alternating single bonds and triple bonds, using a novel process involving laser ablation in liquid. Spectroscopic analyses confirm that the product is the structure of sp hybridization with alternating carbon-carbon single bonds and triple bonds and capped by hydrogen. We observe purple-blue fluorescence emissions from the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of carbyne. Condensed-phase carbyne crystals have a hexagonal lattice and resemble the white crystalline powder produced by drying a carbyne solution. We also establish that the combination of gold and alcohol is crucial to carbyne formation because carbon-hydrogen bonds can be cleaved with the help of gold catalysts under the favorable thermodynamic environment provided by laser ablation in liquid and because the unique configuration of two carbon atoms in an alcohol molecule matches the elementary entity of carbyne. This laboratory synthesis of carbyne will enable the exploration of its properties and applications.

Synthesis and properties of long [n]cumulenes (n ≥ 5)

This review highlights the synthesis and reactivity of longer [n]cumulenes (n ≥ 5) and summarizes their electronic and structural properties.

Carbyne forms of carbon: do they exist?

Almost 15 years have passed since carbynes entered the literature as new forms of elemental carbon. They recently attracted attention as possible interstellar dust constituents and as carriers of presolar noble gases in meteorites. Their existence and that of the related mineral chaoite are questioned, and a reevaluation of previous data is suggested.

Electronic absorption and resonance Raman spectra of large linear carbon clusters isolated in solid argon

Neutral and anionic carbon clusters have been generated via a laser-induced graphite-based plasma and deposited in a solid argon matrix. Anionic clusters were formed from neutral clusters by using crossed electron/carbon cluster beams. Thermal annealing (to 36 K) resulted in the aggregation of the smaller carbon species, leading to the formation of long chain neutral and anionic clusters. Spectroscopic measurements in the ultraviolet, visible, near-infrared and infrared regions revealed a series of bands attributable to a homologous set of odd-numbered C5-C29 neutral clusters and even-numbered C6(-)-C36- anionic clusters. Good agreement is found for the band positions of carbon chains containing odd C15-C21 neutrals and even C6(-)-C22- anions, with species previously identified by Maier and coworkers using mass selection or laser vaporization, followed by neon matrix isolation. Resonance Raman frequencies for the neutral C17, C21 and C23 species are shown to be consistent with the above attributions. Density functional theory calculations agree well with the observed bands. It is found that certain low frequency Raman stretching frequencies decrease in a predictable way with increasing chain length. Comparison of the 0(0)0 absorption transitions of the even C18(-)-C36- anionic clusters with the 'unidentified' infrared (UIR) interstellar emission bands suggests that the electronic emission from specific long chain carbon anions may contribute to the some of the UIR bands.

Stable isotope measurements of meteorites and cosmic dust grains

Although it was well known that a high 13 C abundance was a common feature of the spectra of evolved stars, it took over 50 years to find evidence of carbonaceous instellar dust, which might have been ejected from such objects, in the Solar System. However, it is now established that dust probably produced in novae and red giants can be located in primitive meteorites and the latest state of knowledge in respect of such components is reviewed herein. Nitrogen isotopic measurements have been helpful in distinguishing another form of dust that is carbonaceous but does not have a distinctive 13 C abundance. Likewise they suggest a non-carbonaceous material (possibly a sulphide) present in the meteorite Bencubbin could be a relict of supernovae outbursts. None of the components seen in meteorites can be detected in deep-sea spheres or stratospheric grains to provide a link between interstellar matter and comets. Until now interstellar dust has been the realm of observing astronomers and theoretians; stable isotope measurements are responsible for recognizing a material which it should be possible to isolate and study in the laboratory.

13C NMR spectroscopy of the insoluble carbon of carbonaceous chondrites

13C NMR spectra have been obtained of the insoluble carbon residues resulting from HF-digestion of three carbonaceous chondrites, Orgueil (C1), Murchison (CM2), and Allende (CV3). Spectra obtained using the cross polarization magic-angle spinning technique show two major features attributable respectively to carbon in aliphatic/olefinic structures. The spectrum obtained from the Allende sample was weak, presumably as a consequence of its low hydrogen content. Single pulse excitation spectra, which do not depend on 1H-13C polarization transfer for signal enhancement were also obtained. These spectra, which may be more representative of the total carbon in the meteorite samples, indicate a greater content of carbon in aromatic/olefinic structures. These results suggest that extensive polycyclic aromatic sheets are important structural features of the insoluble carbon of all three meteorites. The Orgueil and Murchison materials contain additional hydrogenated aromatic/olefinic and aliphatic groups.

Interstellar Carbon in Meteorites

The Murchison and Allende chondrites contain up to 5 parts per million carbon that is enriched in carbon-13 by up to + 1100 per mil (the ratio of carbon-12 to carbon-13 is approximately 42, compared to 88 to 93 for terrestrial carbon). This "heavy" carbon is associated with neon-22 and with anomalous krypton and xenon showing the signature of the s-process (neutron capture on a slow time scale). It apparently represents interstellar grains ejected from late-type stars. A second anomalous xenon component ("CCFXe") is associated with a distinctive, light carbon (depleted in carbon-13 by 38 per mil), which, however, falls within the terrestrial range and hence may be of either local or exotic origin.

Graphitic carbon in the Allende meteorite: a microstructural study

High-resolution transmission electron microscopy, shows that carbon in the Allende carbonaceous chondrite meteorite is predominantly a poorly crystalline graphite. Such material is of interest as an important carrier of the isotopically anomalous noble gases found in carbonaceous chondrites.

Carbynes in Meteorites: Detection, Low-Temperature Origin, and Implications for Interstellar Molecules

Carbon from the Allende meteorite is not graphite but carbyne (triply bonded elemental carbon), inasmuch as on heating to 250 degrees to 330 degrees C it releases mainly triply bonded fragments: -(C identical withC)(n),- with n = 1 to 5, and -(C identical withC)(n)-CN, with n = 1 to 3. Although carbynes have been known to form only by condensation of carbon vapor above 2600 K or by explosive shock of > 600 kilobars, it is found that they also form metastably by the reaction 2CO --> CO(2) + C (solid) at 300 degrees to 400 degrees C in the presence of a chromite catalyst. Such low-temperature formation by surface catalysis may be the dominant source of carbynes on the earth and in meteorites, and a major source of interstellar carbynes and cyanopolyacetylenes.