Ulloa-Godínez Sandra, Rosales Ivonne, Bucio Lauro, Farías Mario H, Campa-Molina Jorge
Acta Crystallogr Sect E Struct Rep Online. 2009 Oct 31;65(Pt 11):i83-i84. doi: 10.1107/S1600536809044407.
The structural characterization of the new iron-zinc hepta-borate bromide with composition Fe(1.59)Zn(1.41)B(7)O(13)Br, 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 inter-atomic 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 tetra-hedrally 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 tetra-hedral 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.
报道了通过化学传输法制备的组成为Fe(1.59)Zn(1.41)B(7)O(13)Br的新型溴化铁锌七硼酸盐的结构表征。定义了一个具有约束广义坐标的刚体模型，以便将B原子的位置保持在合理的原子间距离，因为硼的散射能力较弱，这些距离通常会达到不可接受的值。B原子有三个独立的位置，其中两个是四面体配位。考虑到硼与氧的两种配位情况：三角平面和四面体，计算了位于三重旋转轴上的第三个B原子周围的键价和。发现第四个O原子对键价和的贡献仅为0.06 v.u.，这表明在正确的位置存在一个非常弱的键，有利于第三个B原子的三角平面配位而形成扭曲的四面体配位。采用X射线荧光(XRF)法测定Fe/Zn比。
