Neutron and x-ray diffraction evidence for a structural phase transition in the sulfur-based ambient-pressure organic superconductor bis(ethylenedithio)tetrathiafulvalene triiodide

Abstract

A low-temperature structural phase transition in the ambient-pressure organic superconductor, bis(ethylenedithio)tetrathiafulvalene triiodide, ${\mathrm{}(\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}-\mathrm{T}\mathrm{T}\mathrm{F})\mathrm{}}_2$ ${\mathrm{I}}_3$, abbreviated ${\mathrm{}\left(\mathrm{ET}\right)\mathrm{}}_2$ ${\mathrm{I}}_3$, has been observed from single-crystal x-ray diffraction and time-of-flight neutron diffraction data. Superlattice peaks with indices of $\mathrm{}\left(\mathrm{hkl}\right)\mathrm{}\pm q$, where $q=(0.08, 0.27, 0.205)$, appear when crystals are cooled below ∼200 K. This is the first example of an incommensurate modulated superstructure in the class of sulfur- and selenium-containing organic superconductors of which ${\mathrm{}\left(\mathrm{ET}\right)\mathrm{}}_2$ ${\mathrm{I}}_3$ is the first ambient-pressure S-based derivative.