A hexagonal polymorph of Fe(HPO3H)3

Iron tri(hydrogenphosphite), Fe(HPO3H)3, crystallizes in both a monoclinic and a hexagonal space group. In this report the structure determination of the hexagonal variant is described: space group P63, a = 8.1690(2) A, c = 6.9300(2) A. The structure is slightly disordered, Fe3+ being partially replaced by Al3+, and is very close to that of Fe2(HPO3)3. The only significant difference is that one half of the FeO6 octahedra is missing and that its density is reduced by one half.