A Neutral Zwitterionic Molecular Solid

Abstract

We report on the acid ethylenedithiotetrathiafulvaleneamidoglycine (EDT‐TTF‐CO‐NH‐CH₂‐CO₂H; 1; EDT‐TTF=ethylenedithiotetrathiafulvalene) and the 1:1 adduct [(EDT‐TTF)^.+‐CO‐NH‐CH₂‐(CO₂)⁻][(EDT‐TTF)‐CO‐NH‐CH₂‐(CO₂H)]⋅CH₃OH (2), a new type of hydrogen‐bonded, 1:1 acid/zwitterion hybrid embrace of redox peptidics into a two‐dimensional architecture, an example of a system deliberately fashioned so that oxidation of π‐conjugated cores toward the radical‐cation form would interfere with the activity of the appended ionizable residues in the presence of a templating base during crystal growth. First‐principles calculations demonstrate that, notwithstanding preconceived ideas, a metallic state is more stable than the hole‐localized alternatives for a neat 1:1 neutral acid/zwitterion hybrid. The inhomogeneous Coulomb field associated with proton‐shared, interstacks OH⋅⋅⋅O hydrogen bonds between the ionizable residues distributed on both sides of the two‐dimensional π‐conjugated framework leads, however, to a weak hole localization responsible for the activated but high conductivity of 1 S cm⁻¹. This situation is reminiscent of the role of the environment on electron transfer in tetraheme cytochrome c, in which the protonation state of a heme propionate becomes paramount, or ion‐gated transport phenomena in biology. These observations open rather intriguing opportunities for the construction of electronic systems at the interface of chemistry and biology.