Extending carbon chemistry at high-pressure by synthesis of CaC2 and Ca3C7 with deprotonated polyacene- and para-poly(indenoindene)-like nanoribbons

Abstract

Metal carbides are known to contain small carbon units similar to those found in the molecules of methane, acetylene, and allene. However, for numerous binary systems ab initio calculations predict the formation of unusual metal carbides with exotic polycarbon units, [C6] rings, and graphitic carbon sheets at high pressure (HP). Here we report the synthesis and structural characterization of a HP-CaC2 polymorph and a Ca3C7 compound featuring deprotonated polyacene-like and para-poly(indenoindene)-like nanoribbons, respectively. We also demonstrate that carbides with infinite chains of fused [C6] rings can exist even at conditions of deep planetary interiors ( ~ 140 GPa and ~3300 K). Hydrolysis of high-pressure carbides may provide a possible abiotic route to polycyclic aromatic hydrocarbons in Universe.

Synthesis of LaCN3, TbCN3, CeCN5, and TbCN5 Polycarbonitrides at Megabar Pressures

“…containing N 4 4– , N 6 6– , N 8 6– anions, , N 6 rings, − N 18 macrocycle, infinite one-dimensional (1D)-polynitrogen chains, ,− and two-dimensional (2D)-polynitrogen layers , ) as well as polycarbides (i.e. containing graphene-, polyacene-, and para-poly­(indenoindene)-like ribbons − ) were discovered. Recently discovered binary carbon nitrides C 3 N 4 and CN 2 , built of CN 4 tetrahedra and synthesized at pressures above 70 GPa, possess many remarkable physical properties, such as superhardness, ultraincompressibility, photoluminescence, piezoelectricity, and superconductivity, making these multifunctional materials candidates for technological applications, considering that they are recoverable to ambient conditions.…”