Hydrogen bond system and vibrational spectroscopy of the iron sulfate fibroferrite, Fe(OH)SO4•5H2O

The crystal structure of fibroferrite, Fe(OH)SO4•5H2O, was studied by means of single-crystal X-ray diffraction and vibrational (FTIR and Raman) spectroscopies. The new diffraction data allowed to successfully locate eleven H positions and to completely define the H bond system that ensures the cohesion of the Fe-O-S chains in the fibroferrite structure. Infrared and Raman spectra are presented for the first time for this compound and commented on the basis of the crystal structure and literature data for sulfate minerals. Both FTIR and Raman spectra show, in the fundamental water stretching region, a very broad absorption extending from 3600 to 2600 cm−1; peaks at 3522, 3411 and 3140 cm−1 can be resolved in the Raman pattern. The bands present in the lowwavenumber (<1300 cm−1) region are assigned on the basis of the literature data for similar substances, and the observed multiplicity is in agreement with a symmetry reduction of the sulfate ion in the structure of fibroferrite.