Rietveld refinement of the mixed boracite Fe(1.59)Zn(1.41)B(7)O(13)Br.

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.

Related literature

The method of preparation was based on Schmid (1965 ▶). For related structures, see: Mao et al. (1991 ▶); Dowty & Clark (1972 ▶, 1973 ▶); Mendoza-Alvarez et al. (1985 ▶); Schindler & Hawthorne (1998 ▶); Knorr et al. (2007 ▶). For properties and potential applications of boracites, see: Campa-Molina et al. (1994 ▶, 2002 ▶); Dana (1951 ▶); Mathews et al. (1997 ▶); Smart & Moore (1992 ▶). For bond-valence parameters for oxides, see: Brese & O’Keeffe (1991 ▶).

Experimental

Crystal data

Fe1.59Zn1.41B7O13Br

M = 544.65

Trigonal,

a = 8.6081 (1) Å

c = 21.0703 (3) Å

V = 1352.12 (3) Å3

Z = 6

Cu Kα radiation

T = 300 K

Specimen shape: irregular

20 × 20 × 0.2 mm

Specimen prepared at 1173 K

Particle morphology: irregular, pale pink

Data collection

Bruker D8 Advance diffractometer

Specimen mounting: packed powder sample container

Specimen mounted in reflection mode

Scan method: step

2θmin = 8.1, 2θmax = 110.0°

Increment in 2θ = 0.02°

Refinement

R p = 0.018

R wp = 0.025

R exp = 0.014

R B = 0.06

S = 1.89

Profile function: pseudo-Voigt modified by Thompson et al. (1987 ▶)

397 reflections

18 parameters

Data collection: DIFFRAC/AT (Siemens, 1993 ▶); cell refinement: FULLPROF (Rodríguez-Carvajal, 2006 ▶; Rodriguez & Rodriguez-Carvajal, 1997 ▶, a strongly modified version of that described by Wiles & Young, 1981); data reduction: FULLPROF; method used to solve structure: coordinates were taken from an isotypic compound (Mao et al., 1991 ▶); program(s) used to refine structure: FULLPROF; software used to prepare material for publication: DIAMOND.

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809044407/br2119sup1.cif

Rietveld powder data: contains datablocks I. DOI: 10.1107/S1600536809044407/br2119Isup2.rtv

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Enhanced figure: interactive version of Fig. 4

Fe1.59Zn1.41B7O13Br	F(000) = 1546.0
Mr = 544.65	Dx = 4.013 Mg m−3
Trigonal, R3c	Cu Kα radiation, λ = 1.54175 Å
Hall symbol: R 3 -2"c	T = 300 K
a = 8.6081 (1) Å	Particle morphology: irregular
c = 21.0703 (3) Å	pale pink
V = 1352.12 (3) Å3	irregular, 20 × 20 mm
Z = 6	Specimen preparation: Prepared at 1173 K

Bruker D8 Advance diffractometer	Data collection mode: reflection
Radiation source: sealed X-ray tube, Cu Kα	Scan method: step
graphite	2θmin = 8.12°, 2θmax = 110.01°, 2θstep = 0.02°
Specimen mounting: packed powder sample container

Least-squares matrix: full with fixed elements per cycle	5240 data points
Rp = 0.018	Profile function: pseudo-Voigt modified by Thompson et al. (1987)
Rwp = 0.025	18 parameters
Rexp = 0.014	Weighting scheme based on measured s.u.'s
RBragg = 0.06	(Δ/σ)max = 0.02
R(F2) = 0.06	Background function: linear interpolation between a set of 72 background points with refinable heights
χ2 = 3.572

	x	y	z	Uiso*/Ueq	Occ. (<1)
Br	0.00000	0.00000	0.26670	0.0084 (9)
Zn	0.1488 (8)	0.3037 (3)	0.3347 (2)	0.0113 (8)	0.47000
Fe	0.1488 (8)	0.3037 (3)	0.3347 (2)	0.0113 (8)	0.53000
B1	−0.184 (1)	0.1519 (1)	−0.080 (1)	0.00304
B2	0.1130 (2)	−0.0902 (1)	−0.0259 (1)	0.00304
B3	0.00000	0.00000	0.105 (1)	0.00304
O1	0.00000	0.00000	−0.008 (1)	0.0025 (9)
O2	0.010 (1)	−0.157 (2)	0.107 (1)	0.0025 (9)
O3	0.282 (1)	0.274 (1)	−0.032 (1)	0.0025 (9)
O4	0.206 (1)	−0.006 (1)	−0.085 (1)	0.0025 (9)
O5	0.242 (1)	−0.059 (1)	0.024 (1)	0.0025 (9)

Zn—Br	2.680 (3)	B1—O4vii	1.451 (13)
Zn—Bri	3.412 (1)	B1—O5vi	1.49 (3)
Zn—O2ii	2.130 (4)	B2—O1	1.566 (3)
Zn—O3iii	2.081 (7)	B2—O3viii	1.452 (8)
Zn—O4iv	2.035 (4)	B2—O4	1.463 (18)
Zn—O5v	2.012 (7)	B2—O5	1.453 (17)
B1—O2vi	1.506 (14)	B3—O2	1.397 (14)
B1—O3vii	1.48 (2)	B3—O1	2.38 (3)
Zn—Br—Znvii	94.1 (2)	O2—B3—O2vii	119.9 (9)

Zn—Br	2.680 (3)
Zn—Bri	3.412 (1)
Zn—O2ii	2.130 (4)
Zn—O3iii	2.081 (7)
Zn—O4iv	2.035 (4)
Zn—O5v	2.012 (7)
B1—O2vi	1.506 (14)
B1—O3vii	1.48 (2)
B1—O4vii	1.451 (13)
B1—O5vi	1.49 (3)
B2—O1	1.566 (3)
B2—O3viii	1.452 (8)
B2—O4	1.463 (18)
B2—O5	1.453 (17)
B3—O2	1.397 (14)
B3—O1	2.38 (3)

O2—B3—O2vii

119.9 (9)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) ; (vii) ; (viii) .