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Acta Cryst. (2009). E65, i83-i84  [ doi:10.1107/S1600536809044407 ]

Rietveld refinement of the mixed boracite Fe1.59Zn1.41B7O13Br

S. Ulloa-Godínez, I. Rosales, L. Bucio, M. H. Farías and J. Campa-Molina

Abstract: The structural characterization of the new iron-zinc heptaborate bromide with composition Fe1.59Zn1.41B7O13Br, prepared by chemical transport is reported. A rigid-body model with constrained generalized coordinates was defined in order to hold the positions of the B atoms at reasonable interatomic distances that typically would reach unacceptable values because of the weak scattering power of boron. There are three independent sites for the B atoms of which two are tetrahedrally coordinated. The bond-valence sum around the third B atom, located on a threefold rotation axis, was calculated considering two cases of coordination of boron with oxygens: trigonal-planar and tetrahedral. The contribution of the fourth O atom to the bond-valence sum was found to be only 0.06 v.u., indicating the presence of a very weak bond in the right position to have a distorted tetrahedral coordination in favour of the trigonal-planar coordination for the third B atom. X-ray fluorescence (XRF) was used to determinate the Fe/Zn ratio.

Online 31 October 2009


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