Guest Solvent Substitution in a Partially Oxidized Zwitterionic Neutral Radical Conductor: Impact on π-Electron Interactions and Charge-Disproportionation Transitions

We report the synthesis and characterization of a new analog crystal of the partially oxidized tetrathiafulvalene (TTF)-based zwitterionic neutral radical 1• incorporating 1,3-dioxolane (DOL), namely 1•·2DOL (DOLcryst). Although DOLcryst is isostructural to the tetrahydrofuran (THF)-containing analog 1•·2THF (THFcryst) at room temperature, the two crystals diverge upon cooling and adopt different low-temperature (LT) phases. Comparative structural and physical analyses reveal that this divergence originates from a structural difference between THF and DOL, namely the substitution of a CH2 unit in THF by an oxygen atom in DOL. This seemingly subtle difference modulates solvent ordering and solvent–TTF electrostatic interactions within the conducting layers, giving rise to distinct charge-disproportionation patterns of the TTF π-skeletons in the LT phases. These findings demonstrate that guest solvent substitution in this zwitterionic neutral radical crystal directly impacts partially oxidized π-electron interactions and associated phase transitions. This feature contrasts with conventional charge-transfer salts, where solvent molecules reside in insulating counter-anion layers and influence the π-electron system indirectly.