New iron(III) nitrate hydrates: Fe(NO₃)₃·xH₂O with x = 4, 5 and 6

Acta Cryst. (2012). C68, i29-i33 (http://doi.org/h9z)

Two pentagonal–bipyramidal [Fe(NO₃)₂(H₂O)₃]⁺ units in Fe(NO₃)₃·4H₂O.

Crystals of lower hydrates of iron(III) nitrate were grown from melts or solutions in concentrated nitric acid. While iron(III) is coordinated by six oxygen atoms in the hexahydrate and the pentahydrate, the coordination number of iron(III) in Fe(NO₃)₃·4H₂O is enhanced to seven. Fe(NO₃)₃·4H₂O represents the first simple iron(III) salt with pentagonal-bipyramidal coordination geometry. In our research we are interested in the study of the phase formation in inorganic salt-water systems. We have started systematic investigations and further results will be published soon.