Glycine Residue Twists HOMO¿HOMO Interactions in a Molecular Conductor

Abstract

We report on radical cation salts of EDT-TTF cores bearing a glycine residue with hydrogenosulfate, [HSO4−], or the amphoteric para- carboxybenzenesulfonate, [HO2C-C6H4-SO3−]. In (EDT-TTF-CO-NHCH2-CO2H)2+[HSO4−], orthogonal pairs of oxygen atoms of the tetrahedral sulfonate anions engage in hydrogen bonds building the two-dimensional (2D) chess-board pattern of orthogonal dimers typical of a κ-phase 2D metal. We find by tight-binding and density functional theory analysis of the band structure that, as a result of the structure-directing role of the Gly residue, HOMO···HOMO interactions in (EDT-TTF-CO-NHCH2-CO2H)2+- [HSO4−] are twisted away from the usual in-plane isotropy of κ-phases toward a very uncommon quasi-one-dimensional electronic structure with electronic localization. Transport measurements confirm the highly conducting, yet weakly localized regime. The ability of para-carboxybenzenesulfonate to act as a bimolecular, dianionic unit of double spatial extension is fulfilled in (EDT-TTF-CO-NHCH2-CO2H)22+[HO2C-C6H4-SO3−]2, where the charge is balanced by diamagnetic dimers leaving no carrier left available in the lattice.