Abstract
With the development of high-pressure apparatus, in situ characterization methods and theoretical calculations, high-pressure technology becomes a more and more important method to synthesize new compounds with unusual structures and properties. By compressing compounds containing unsaturated carbon atoms, novel poly-ionic polymers, graphanes and carbon nanothreads were obtained. Their compositions and structures were carefully studied by combining multiple cutting-edge technologies, like the in situ high-pressure X-ray and neutron diffraction, transmission electron microscopy, pair distribution function, solid-state nuclear magnetic resonance and gas chromatography-mass spectroscopy. The reaction mechanisms were investigated based on the crystal structure at the reaction threshold pressure (the pressure just before the reaction taking place), the long-range and short-range structure of the product, molecular structure of the intermediates, as well as the theoretical calculation. In this review, we will summarize the synthesis of carbon materials by compressing the unsaturated compounds and its reaction characteristics under extreme conditions. The topochemical reaction mechanism and related characterization methods of the molecular system will be highlighted. This review will provide a reference for designing chemical reaction and exploring novel carbon materials under high-pressure condition.
Highlights
Carbon is the fourth richest element in the universe after hydrogen, helium, and oxygen, which is widely studied by material scientists and organic chemists
By compressing CaC2, we found the electrical conductivity was enhanced by 107 -fold irreversibly and the band gap was compressed to 0 eV at 18 GPa (Figure 3a), which is attributed to the enhancement of the interaction between C2 2− units during compression and the polymerization of acetylide anions [63]
Benzene was widely studied in high-pressure chemistry, which was reported to react at the microscope (HRTEM) and fast Fourier transform (FFT) show it is consistent with a cubic unit cell withGPa lattice[99,100]
Summary
Carbon is the fourth richest element in the universe after hydrogen, helium, and oxygen, which is widely studied by material scientists and organic chemists. The molecules with unsaturated bonds can overcome the energy barriers and forms saturated, condensed and confined polymers with extended structures via polymerization, which is called pressure-induced polymerization (PIP). This inaugurates a new possibility to synthesize materials starting from molecular compounds. The high-pressure chemical reaction is closely related to the crystal structure of the reactant, including the relative orientations of molecules and the intermolecular distances. This review will provide some basic ideas about the unique reaction mechanisms of compounds containing unsaturated carbon atoms under high pressure and introduce several in situ characterization techniques for high-pressure chemical studies
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