Spectroscopic and magnetic properties of FeOCl intercalated with organosulfur electron donors

In an effort to develop a new type of low-dimensional conductor, the intercalation chemistry of FeOCl with tetrathiolene molecules has been explored. New intercalation compounds of the organic electron donors TTF (tetrathiafulvalene), TMTTF (tetramethyltetrathiafulvalene), TTN (tetrathianaphthalene), and TTT (tetrathiatetracene) with the inorganic host FeOCl were prepared by direct reaction of solutions of the organosulfur compounds with solid FeOCl. The new phases obtained were FeOCl(TTF)_1/8.5, FeOCl(TMTTF)_1/13, FeOCl(TTN)_1/9(tol)_1/22, and FeOCl(TTT)_1/9(tol)_1/23. X-ray powder diffraction data are consistent with the tetrathiolene molecule being oriented perpendicular to the layers, with the exception of FeOCl(TMTTF)_1/13, in which the TMTTF molecule is oriented parallel to the host layers. Detailed wideline ¹H and cross polarization magic angle spinning (CPMAS) ¹³C NMR studies carried out on FeOCl(TTF)_1/8.5 and related model compounds indicate that there is more than one type of ordering of the TTF molecules characterized by different average TTF environments and/or dynamics. The pressed powder electrical conductivity of FeOCl intercalated with these tetrathiolenes is 10³-10⁵ times that of the pristine material (σ_RTFeOCl ∼ 10^-7 (Ω-cm)^-1). The temperature dependence of the conductivity is consistent with FeOCl and the intercalates being semiconductors with apparent bandgaps of 0.6 eV and ca. 0.3-0.4 eV, respectively. Infrared spectra indicate that the tetrathiolene molecules exist as radical cations within the layers. Mössbauer spectra are consistent with reduction of 4-6% of the Fe³⁺ in FeOCl to Fe²⁺ upon intercalation.