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The crystal structure of (H3O)Fe(SO4)2

Juraj Majzlan 1Cristian E. Botez Peter Stephens Boris Kiefer 

1. Univ.Freiburg, Freiburg, Germany

Abstract

(H3O)Fe(SO4)2 is a compound that precipitates from the most acidic solutions in the system Fe2O3-SO3-H2O. We have solved the structure of this phase from synchrotron powder X-ray diffraction (XRD) data in the space group P-1. The lattice parameters are a = 4.8087(1) Å, b = 8.3180(1) Å, c = 8.3034(1) Å, α = 70.181(1)º, β = 90.276(1)º, and γ = 89.993(1)º. The unit cell volume is 312.44(1) Å3. (H3O)Fe(SO4)2 has layered structure in which the layers are built by FeO6 octahedra and SO4 tetrahedra. Three oxygen ions in the SO4 unit are bridging and provide bonding to the Fe3+ ions within the layers. The fourth oxygen ion points into the interlayer space where the H3O+ ions are located. The structure of (H3O)Fe(SO4)2 belongs to the yavapaiite (KFe(SO4)2) family of layered structures with octahedral-tetrahedral layers and interlayer cations and can be interpreted as a triclinic distortion of the structures of CsFe(SO4)2 or RbFe(SO4)2. The partial refinement (excluding H atoms) was augmented and supported by static ab-initio calculations. The orientation of the hydronium ions and the hydrogen bond scheme was obtained from ab-initio molecular dynamics simulations. These calculations revealed that all hydrogen atoms participate in hydrogen bonding and the hydrogens of the alternating H3O+ groups are oriented “up” or “down” toward the Fe-SO4 layers. The ab-initio molecular dynamic simulations were performed at 300 K for 4.5 ps. The H3O+ groups re-arrange their orientation in time.

 

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Related papers

Presentation: Oral at 11th European Powder Diffraction Conference, Microsymposium 8, by Juraj Majzlan
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-03-22 22:23
Revised:   2009-06-07 00:48