About irontribromide: Equilibrium studies, crystal structure, and spectroscopic characterization

Iron(III) bromide has been thoroughly characterized by thermal, x-ray, and spectroscopic investigations on crystalline FeBr3 samples which were grown by CVD at higher bromine pressures. The thermodynamical data for equilibria between FeBr2, FeBr3 and Br-2 obtained by pressure measurements are in agr eement with chemical vapor transport experiments and confirm the statements of the literature to a high extent. Refinement of the crystal structure wi th single crystal data (a = 6.937(1) Angstrom; c = 18.375(4) Angstrom Z = 6 ) confirms the assignment to the rhombohedral BiI3 type (Spgr. R-3). On thi s base, the UV-VIS, FTIR and Raman spectra were interpreted. The totally sy mmetric stretching mode of FeBr3 (173 cm(-1)) in comparision to FeCl3 (282 cm(-1)) was found lower as to be expected by consideration of the mass infl uence alone. Impedance measurements on pure samples under ambient condition s showed low electronic conductivity (10(-8) Omega(-1) cm(-1)) but high cap acitive contributions, resulting from displacement polarisation. The invest igations gave no hints for neither a mixed valent "Fe3Br8" nor a substantia l phase width of the solid compounds FeBr2 and FeBr3.