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

The crystal structure of iron(III) trinitrate hexa­hydrate is built up from [Fe(H₂O)₆]²⁺ octa­hedra and nitrate anions connected via hydrogen bonds. In iron(III) trinitrate penta­hydrate, one water mol­ecule in the coordination octa­hedron of the Fe^III atom is substituted by an O atom of a nitrate group. Iron(III) trinitrate tetra­hydrate represents the first example of a simple iron(III) nitrate with penta­gonal-bipyramidal coordination geometry, where two bidentate nitrate anions and one water mol­ecule form a penta­gonal plane.