A Neutral Zwitterionic Molecular Solid

Abstract

We report on the acid ethylenedithiotetrathiafulvaleneamidoglycine (EDT-TTF-CO-NH-CH(2)-CO(2)H; 1; EDT-TTF=ethylenedithiotetrathiafulvalene) and the 1:1 adduct [(EDT-TTF)(·+)-CO-NH-CH(2)-(CO(2))(-)][(EDT-TTF)-CO-NH-CH(2)-(CO(2)H)]·CH(3)OH (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.

Hydrogen bond-promoted metallic state in a purely organic single-component conductor under pressure

“…At the moment, the detailed process of the formation of the minimal unit and the electrochemical crystallization is unclear. On the analogy of the formation of phosphonic-acid and amino-acid TTFs 45,46 , however, the process is possibly explained as follows; H 2 Cat-EDT-TTF is diacid. In the presence of bipyridine (see method), the monoanionic (HCat-EDT-TTF) À is generated.…”

“…Most studies of the molecular conductors based on hydrogen bond-functionalized TTF derivatives have focused on the tuning of the molecular self-assembly and the HOMO/LUMO energy levels 47,48 . In this context, several groups have recently reported that the introduction of the hydrogen bond has another important role, that is, the generation of the charge carriers 46,49 . Besides the carrier generation, our system demonstrates that the symmetric hydrogen bond constructs the new type of the purely organic single-component molecular conductors which are composed of highly symmetric molecular units.…”

Crystal structure and metallization mechanism of the π-radical metal TED

“…19 We adopted DFT calculations here, but it is known to provide essentially the same results with tight-binding calculations employing the extended Hückel approximation. 23 The anisotropy in the inter-TED transfer integrals is mirrored in the band structure, with a dispersive band along the G to A direction (aaxis), in contrast to a dispersionless one along the G to Z (caxis). The Fermi surface is predominantly one-dimensional (1D) along k a (a-axis) with a large open shape, reecting t a [ t b .…”

Two Closely Related Organic Charge-Transfer Complexes Based on Tetrathiafulvalene and 9H-fluorenone Derivatives. Competition between Hydrogen Bonding and Stacking Interactions

“…Regarding hydrogen bonding, it is well documented that, under favorable circumstances, such bonds are able to cooperate with CT interactions, to modulate the transport properties in the material [29]. The deliberate choice of engaging A and D precursors functionalized by strong hydrogen bond donor/acceptor groups remains a viable strategy in the field of organic conductors [30], and has indeed produced outstanding results [31,32]. Finally, even for complexes close to the neutral state, the spectroscopic determination of δ seems to afford reliable data.…”