Intercalation of Tetrathiafulvalene and Related Molecules into FeCl

Abstract

Intercalation of tetrathiafulvalene (TTF), tetramethyltetrathiafulvalene (TMTTF), tetrathiatetracene (ITT), and tetrathianaphthalene into FeOCl increases the electrical conductivity (pressed powder) by ~10³ over that of pristine FeOCl (~10^-6 (Ω-cm)^-1). Standard four-probe single crystal conductivity measurements on the FeOCl.TTF_1/9 intercalate show that conductivity in the plane of the FeOCl layers ~10³ times greater than that perpendicular to the plane. These novel low-dimensional materials are semiconductors with band gaps of 0.30 – 0.45 eV. EXAFS spectroscopy and X-ray powder diffraction studies of the TTF, TTT and TTN intercalates provide a consistent picture of the orientation of the intercalated radical cations within the FeOCl layers. The intercalants are tilted at an angle 0 from the perpendicular to the FeOCl layers (θ = 25 ± 5° for TTF, 30 ± 5° for TTT, TTN). For the TTT and TTN intercalates, the radical cations are tilted at an additional angle θ (θ = 31 ± 5°) from the plane of the FeOCl layers. The synthesis, physical properties, and structures of these and other FeOCl intercalates will be discussed and compared to those of known organic metals.