The Mo ¨ ssbauer spectrum of synthetic hureaulite: Fe 5 2+ (H 2 O) 4 (PO 4 H) 2 (PO 4 ) 2 Angel Bustamante & Enrico Mattievich & Helio S. de Amorim & Ivo Vencato & Ma ´ ximo M. Silveira Published online: 27 October 2006 # Springer Science + Bussiness Media B.V. 2006 Abstract The crystal structure of synthetic ferrous hureaulite, Fe 5 2+ (H 2 O) 4 (PO 4 H) 2 (PO 4 ) 2 , was refined from single-crystal X-ray data. It is monoclinic, space group C2/c, with a=17.487(4), b=9.017(2), c=9.338(2) A ˚ , b=96.27(3)-, V=1463.6(6) A ˚ 3 , Z=4 and D calc =3.327 g/cm 3 . This end member of the hureaulite series was crystallized under distinctly acidic conditions, by a method that gives perfect crystals, large enough for X-ray single crystal studies. The main feature of the hureaulite structure is that it has an equal number of normal (PO 4 ) 3+ and acid (PO 4 H) 2+ tetradentate groups. These are centered on Fe 2+ atoms and share corners with edge-linked octahedra, forming pentamer units. The five Fe 2+ atoms are distributed on three distinct sites in these units. This can be directly observed in the Mo ¨ ssbauer spectrum at 295 K, which contains three doublets whose relative intensities correspond to the 1:2:2 distributions of crystallographic sites. Key words iron phosphate . Hureaulite . Mo ¨ ssbauer Spectroscopy . X-ray refinement 1 Introduction Several works appeared recently on the synthetic phosphate series named hureaulite, Mn 5 – x Fe x (H 2 O) 4 (PO 4 H) 2 (PO 4 ) 2 ,0< x < 5, which in nature always has Hyperfine Interact (2005) 166:599–603 DOI 10.1007/s10751-006-9326-1 A. Bustamante (*) Facultad de Ciencias Fı ´sicas, Universidad Nacional Mayor de San Marcos Apto. Postal 14-0149 Lima-14, Peru e-mail: abustamanted@unmsm.edu.pe E. Mattievich Á H. S. de Amorim Á M. M. Silveria Instituto de Fı ´sica, Universidade Federal do Rio de Janeiro, P.O. Box: 68.528, 21945-970 Rio de Janeiro, RJ, Brazil I. Vencato Instituto de Fı ´sica, Universidade Federal de Goia ´s, P.O. Box 131, 74001-970 Goia ˆ nia, GO, Brazil