BEDT-TTF Salts Formed with Tetrahedrally Coordinated Zinc(II) Complex Anions

Article abstract of DOI:10.1021/acs.cgd.6b01294

Twelve kinds of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) cation radical salts with tetrahedrally coordinated zinc(II) complex anions were obtained by electrocrystallization; most of them were produced via the additional reaction of Lewis-basic cyano-containing anions [N(CN)₂^-, C(CN)₃^-, and Au(CN)₂^-] with ZnX₂ (X = Cl^-, Br^-, and SCN^-) that occurred during electrocrystallization. On the basis of the charge and arrangement of ET molecules, these salts were predominantly categorized into four groups: (A) isolated ET^?+ dimers or tetramers, (B) infinite ET^?+ ribbon, (C) infinite layers either with a peculiar ET^0.5+ arrangement of ET molecules with partial charges other than +0.5, and (D) infinite layers of ET^0.5+ molecules. In A, zinc(II) complex anions including a unidentate-coordinated C(CN)₃ or Au(CN)₂ group spatially interrupt the infinite arrangement of ET molecules. The ET^?+ ribbon in B runs parallel to the pseudopolymeric chain of disordered Zn[C(CN)₃]₂Br₂^2- ions. In C, two salts are semiconductive, whereas the remaining two salts behave as metallic at room temperature and undergo a metal-insulator transition on cooling. The ET molecules in D are arranged in a θ₄₂₊₄₀-like packing motif, due to the nonplanar anionic layers. All salts are semiconductive and exhibit a gradual evolution in their superstructures with cooling associated with charge disproportionation.