A Neutral Zwitterionic Molecular Solid

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. Electrostatic envelope: Two neutral chemical objects with ionizable residues, one of which is a π‐conjugated zwitterion, self‐assemble in a two‐dimensional array (see picture). It is predicted that the carriers are probably localized, yet the system is highly conducting. Although not part of the conducting network, a rattling proton deeply impinges on the collective behavior of the holes.