High-Pressure Behavior of C₂I₂ and Polymerization to a Conductive Polymer

Abstract

Crystalline diiodoacetylene (C 2 I 2 ) was synthesized and then studied under high-pressure conditions using synchrotron X-ray diffraction, Raman/infrared spectroscopies, and first-principles calculations. At ∼0.3 GPa, the starting tetragonal (P4 2 /n) phase, which is stabilized by donor−acceptor interactions, transforms into a new orthorhombic structure (Cmca) that is more densely packed and analogous to the low-temperature phase of acetylene. Above approximately 4 GPa, compressed C 2 I 2 molecules in the Cmca structure begin to polymerize to form a predominantly sp 2 amorphous carbon network that maintains a significant fraction of C−I bonds. Transport measurements reveal that the polymeric material is electrically conducting. The magnitude of the electrical conductivity is similar to Br-doped polyacetylene and undoped trans-polyacetylene at 8 GPa and 1 atm, respectively. Elemental analyses performed on recovered samples show that the iodine concentration varies with specific processing conditions. Optimization of the pressure-induced polymerization pathway could allow for enhanced electrical properties to be realized, in addition to postpolymerization functionalization using the weak C−I bonds.

Controlled Single-Crystalline Polymerization of C10H8·C10F8 under Pressure

“…High-pressure polymerization reactions have received recent interest. Examples include high-pressure studies of benzene, − pyridine, aniline, diiododiacetylene, , acetylene, and cubane . The principal methods toward controlling polymerization include kinetically-aided slow compression, host-guest topochemistry, and crystal engineering/cocrystallization. ,, In several cases, ordered materials are produced during the pressure-induced polymerization process, yet it is not always clear how reactions will proceed based upon the initial configuration of molecules within the precursor phase.…”

From Molecules to Carbon Materials—High Pressure Induced Polymerization and Bonding Mechanisms of Unsaturated Compounds

“…A mixed amorphous and crystalline hydrocarbons were obtained when heating the co-crystal at 30 GPa and 200℃. The high-resolution transmission electron microscope (HRTEM) and fast Fourier transform (FFT) show it is consistent with a cubic unit cell with lattice parameter a ≈ 4.2 Å which matches the structure of i-carbon [96]. Considering the presence of the hydrogen atoms, the K4-CH is a promising candidate structure.…”

“…The Raman and IR spectrum data show that the samples begin to polymerize above 4 GPa with the color darkening and completely opaque. The formation of new C-C, conjugated C=C and C=C=C, as well as the weakened C-I stretching mode, were observed in the IR spectrum, which suggests the formation of an extended aromatic or conjugated C=C system [96]. The polymerized products exhibit good electrical conductivity, which provides insights into the synthesis of new conductive materials.…”

Calcium Carbide: Versatile Synthetic Applications, Green Methodology and Sustainability

“…An interesting application of acetylenic proton exchange for the synthesis of diiodoacetylene has been reported recently. [ 22 ] Acetylene 1 generated from calcium carbide and water is transferred to a vessel containing KI solution. Then, NaOI (produced by reaction of KI with sodium hypochlorite) reacts with acetylene via exchange‐type interaction giving diiodoacetylene 2 (Scheme 3) suitable for the synthesis of conducting polymers.…”

“…Then, NaOI (produced by reaction of KI with sodium hypochlorite) reacts with acetylene via exchange‐type interaction giving diiodoacetylene 2 (Scheme 3) suitable for the synthesis of conducting polymers. [ 22 ]…”