Metallic Crystal with a Three-Dimensional Narrow Band Based on an Aromatic Hydrocarbon Derivative

Abstract

The properties and crystal structures of molecular conductors depend on the intermolecular interactions between their planar parts of conjugated molecules. Such interactions frequently produce low-dimensional band structures that are susceptible to perturbation and to lose the electrical conductivity. Herein, we report an extended intermolecular interaction pattern in a newly synthesized charge-transfer complex (EtHAC)₂I₃, which includes ten ethyl groups around the periphery of its fused aromatic rings HAC. The (EtHAC)₂I₃ crystal contains columns of stable EtHAC radical cations with intercolumnar interactions by Et-Et contacts. Theoretical calculations indicate that intramolecular Et-HAC and intermolecular Et-Et interactions enable three-dimensional (3D) EtHAC network. Additionally, charge-transfer interactions via Et-I contacts lead to carrier doping to the EtHAC network. These effects are combined to produce a stable 3D metallic ground state, accounting for their high 3D electrical conductivity (ca. 10—2500 Scm^-1) down to ~2 K. The unique metallic properties of (EtHAC)₂I₃ are further corroborated by the calculated band structures with 3D metallic characteristics. The electron spin resonance spectra of (EtHAC)₂I₃ suggest that the highly mobile unpaired electrons behave as if they are free electrons with long relaxation times. These findings add a different strategy to develop the molecular conductors and magnets.