Europium-doped barium bromide iodide

Single crystals of Ba_0.96Eu_0.04BrI (barium europium bromide iodide) were grown by the Bridgman technique. The title compound adopts the ordered PbCl₂ structure [Braekken (1932). Z. Kristallogr. 83, 222–282]. All atoms occupy the fourfold special positions (4c, site symmetry m) of the space group Pnma with a statistical distribution of Ba and Eu. They lie on the mirror planes, perpendicular to the b axis at y = ±0.25. Each cation is coordinated by nine anions in a tricapped trigonal prismatic arrangement.

Related literature

For details of crystal growth by the Bridgman technique, see: Robertson (1986). For structural details of isotypic compounds, see: PbCl₂ (Braekken, 1932); EuBrI (Liao et al., 2004); SrBrI (Hodorowicz & Eick, 1983); and BaBrCl (Hodorowicz et al., 1983). For structural details of PbFCl compounds, see: Liebich & Nicollin (1977). For the structure of compounds with similar compositions by powder diffraction, see Lenus et al. (2002). For the luminescent properties of some Eu²⁺-activated barium halides, see: Schweizer (2001); Crawford & Brixner (1991); Selling et al. (2007); Bourret-Courchesne et al. (2009).

Experimental

Crystal data

• Ba_0.96Eu_0.04BrI

• M_r = 344.70

• Orthorhombic, P n m a

• a = 8.684 (3) Å

• b = 5.0599 (19) Å

• c = 10.061 (4) Å

• V = 442.1 (3) ų

• Z = 4

• Mo Kα radiation

• μ = 24.97 mm⁻¹

• T = 153 K

• 0.14 × 0.09 × 0.06 mm

Data collection

• Bruker SMART 1000 CCD diffractometer

• Absorption correction: multi-scan (Blessing, 1995) T_min = 0.128, T_max = 0.316

• 2609 measured reflections

• 430 independent reflections

• 370 reflections with I > 2σ(I)

• R_int = 0.027

Refinement

• R[F² > 2σ(F²)] = 0.015

• wR(F²) = 0.033

• S = 1.02

• 430 reflections

• 21 parameters

• Δρ_max = 0.89 e Å⁻³

• Δρ_min = −0.78 e Å⁻³

Table 1
Selected bond lengths (Å)

I1—Ba1^i	3.6448 (10)
I1—Ba1^ii	3.6448 (10)
I1—Ba1^iii	3.7101 (9)
I1—Ba1^iv	3.7101 (9)
Ba1—Br1^v	3.2643 (10)
Ba1—Br1	3.2643 (10)
Ba1—Br1^vi	3.2931 (13)
Ba1—Br1^vii	3.3065 (14)
Symmetry codes: (i) -x+1, -y, -z; (ii) -x+1, -y+1, -z; (iii) ; (iv) ; (v) x, y+1, z; (vi) ; (vii) -x+2, -y, -z.

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.

Supporting information

S1. Comment

Barium mixed halides activated by Eu²⁺ have been extensively studied as X-ray phosphors (Schweizer, 2001; Crawford & Brixner, 1991) and scintillators for the detection of γ-rays (Selling et al., 2007). The F-based compounds of the form BaFX (X= Cl, Br, I) have a tetragonal, matlockite structure similar to PbFCl (Liebich & Nicollin, 1977). Among the other barium mixed halides, the structure of BaBrCl has been found to be the PbCl₂-type (Hodorowicz et al., 1983). Lenus et al. recently solved the structures of BaBrI and BaClI from X-ray powder diffraction data in the space groups P222₁ and Pbam respectively (Lenus et al., 2002). We have synthesized single crystals of Ba_0.96Eu_0.04BrI and present details of the structure. Eu is introduced as a dopant and substitute for Ba. The doping was not expected to change the structure of the parent material BaBrI. However, we determine the structure to have a space group Pnma, similar to that of isomorphous compounds EuBrI (Liao et al., 2004) and SrBrI (Hodorowicz & Eick, 1983), but not the structure published by Lenus et al. for powders of BaBrI (Lenus et al., 2002)

The title compound adopts the orthorhombic PbCl₂ structure. All atoms occupy the fourfold special positions (4c) of the space group D¹⁶_2h-Pnma. They lie on the mirror planes, perpendicular to the b axis at y = (±)0.25. Each Ba/Eu cation is coordinated by 9 anions in a tricapped trigonal prismatic arrangement (Fig. 1). The anions are not equidistant from the Ba cation but present in two different positions. The smaller bromide anions occupy one of the anionic positions at distances between 3.26 and 3.30 Å. The larger iodide anions occupy the second anionic position (distances 3.62 - 3.71 Å), giving a completely ordered structure for the anions. The same ordering has been observed in isomorphous compounds EuBrI (Liao et al., 2004) and SrBrI (Hodorowicz & Eick, 1983).

The Eu content of 4% has been determined from the refinement of the structure. The presence of divalent Eu is also confirmed by measuring the emission curve under X-ray excitation. The characteristic 4f⁶5 d¹ → 4f⁷transition of Eu²⁺ was observed. A detailed study of the luminescent properties is currently underway and will be presented in a future publication (Bourret-Courchesne et al., 2009).

Related literature

For details of the synthesis by the Bridgman technique, see: Robertson (1986). For structural details of isomorphous compounds, see: PbCl₂ (Braekken, 1932); EuBrI (Liao et al., 2004); SrBrI (Hodorowicz & Eick, 1983); and BaBrCl (Hodorowicz et al., 1983). For structural details of PbFCl compounds, see: Liebich & Nicollin (1977). For the structure of compounds with similar compositions by powder diffraction, see Lenus et al. (2002). For the luminescent properties of some Eu²⁺-activated barium halides, see Schweizer (2001); Crawford & Brixner (1991); Selling et al. (2007); Bourret-Courchesne et al. (2009).

S2. Experimental

Single crystals with the composition Ba_0.96Eu_0.04BrI were grown by the vertical Bridgman techniques. BaBr₂, BaI₂, EuBr₂ and EuI₂ were obtained commerically, mixed in the molar ratio 0.48: 0.48: 0.02: 0.02 and sealed in a quartz ampoule under a dynamic vacuum of 1.10 ^–6 Torr. The sealed ampoule, about 1 cm in diameter, was heated in a 24 zone Mellen furnace to a temperature of 1123 K and directionally cooled to provide a growth rate of 1 mm/hour. The reactants and products are moisture-sensitive and all manipulations were carried out inside an Argon-filled glove box. The crystal obtained is colorless.

S3. Refinement

The doping of Eu(ii) on the Ba(ii) site was modeled with a fractional Eu atom fixed in the same location and with the same thermal parameters as the Ba(ii) atom. The relative occupancy factor refined to 0.963 (13) Ba, 0.037 (13) Eu.

Computing details

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

Fig. 1. Arrangement of anions around each Ba atom. The displacement ellipsoids are given at 50% probability. The symmetry codes are: (i) -x + 1, -y, -z; (ii) -x + 1, -y + 1, -z; (iii) -x + 3/2, -y + 1, z + 1/2; (iv) -x + 3/2, -y, z + 1/2; (v) x, y + 1, z; (vi) -x + 3/2, -y, z - 1/2; (vii) -x + 2, -y, -z; (viii) -x + 3/2, -y + 1, z - 1/2; (ix) x, y - 1, z.

barium europium bromide iodide

Crystal data

Ba0.96Eu0.04BrI	F(000) = 576.7
Mr = 344.70	Dx = 5.179 Mg m^−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 1548 reflections
a = 8.684 (3) Å	θ = 4.5–25.4°
b = 5.0599 (19) Å	µ = 24.97 mm^−1
c = 10.061 (4) Å	T = 153 K
V = 442.1 (3) Å^3	Block, colourless
Z = 4	0.14 × 0.09 × 0.06 mm

Data collection

Bruker SMART 1000 CCD diffractometer	430 independent reflections
Radiation source: fine-focus sealed tube	370 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.027
Detector resolution: 8.192 pixels mm^-1	θmax = 25.0°, θmin = 3.1°
φ and ω scans	h = −9→10
Absorption correction: multi-scan (Blessing, 1995)	k = −6→5
Tmin = 0.128, Tmax = 0.316	l = −11→11
2609 measured reflections

Refinement

Refinement on F^2	Primary atom site location: heavy-atom method
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.02P)^2] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.015	(Δ/σ)max = 0.001
wR(F^2) = 0.033	Δρmax = 0.89 e Å^−3
S = 1.02	Δρmin = −0.78 e Å^−3
430 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
21 parameters	Extinction coefficient: 0.0151 (5)
0 restraints

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

The doping of Eu(ii) on the Ba(ii) site was modeled with a fractional Eu atom fixed in the same location and with the same thermal parameters as the Ba(ii) atom. The relative occupancy factor refined to 0.963 (13) Ba, 0.037 (13) Eu.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
I1	0.52804 (5)	0.2500	0.16976 (4)	0.01285 (18)
Ba1	0.76955 (4)	0.2500	−0.12472 (4)	0.01213 (17)	0.963 (13)
Eu1	0.76955 (4)	0.2500	−0.12472 (4)	0.01213 (17)	0.037 (13)
Br1	0.85573 (8)	−0.2500	0.06634 (6)	0.0107 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.0119 (3)	0.0139 (3)	0.0128 (2)	0.000	0.00011 (16)	0.000
Ba1	0.0110 (3)	0.0126 (3)	0.0128 (2)	0.000	−0.00069 (15)	0.000
Eu1	0.0110 (3)	0.0126 (3)	0.0128 (2)	0.000	−0.00069 (15)	0.000
Br1	0.0096 (4)	0.0119 (5)	0.0105 (3)	0.000	−0.0008 (2)	0.000

Geometric parameters (Å, º)

I1—Ba1	3.6299 (11)	Ba1—Br1^vii	3.3065 (14)
I1—Ba1^i	3.6448 (10)	Ba1—I1^i	3.6448 (10)
I1—Ba1^ii	3.6448 (10)	Ba1—I1^ii	3.6448 (10)
I1—Ba1^iii	3.7101 (9)	Ba1—I1^vi	3.7101 (9)
I1—Ba1^iv	3.7101 (9)	Ba1—I1^viii	3.7101 (9)
Ba1—Br1^v	3.2643 (10)	Br1—Ba1^ix	3.2643 (10)
Ba1—Br1	3.2643 (10)	Br1—Ba1^iv	3.2930 (13)
Ba1—Br1^vi	3.2931 (13)	Br1—Ba1^vii	3.3065 (14)
Ba1—I1—Ba1^i	107.950 (19)	Br1—Ba1—I1^ii	140.69 (2)
Ba1—I1—Ba1^ii	107.950 (19)	Br1^vi—Ba1—I1^ii	69.416 (14)
Ba1^i—I1—Ba1^ii	87.92 (3)	Br1^vii—Ba1—I1^ii	136.041 (16)
Ba1—I1—Ba1^iii	100.44 (2)	I1—Ba1—I1^ii	72.051 (19)
Ba1^i—I1—Ba1^iii	151.463 (16)	I1^i—Ba1—I1^ii	87.92 (3)
Ba1^ii—I1—Ba1^iii	86.09 (3)	Br1^v—Ba1—I1^vi	138.42 (2)
Ba1—I1—Ba1^iv	100.44 (2)	Br1—Ba1—I1^vi	72.00 (3)
Ba1^i—I1—Ba1^iv	86.09 (3)	Br1^vi—Ba1—I1^vi	68.31 (2)
Ba1^ii—I1—Ba1^iv	151.463 (16)	Br1^vii—Ba1—I1^vi	68.457 (18)
Ba1^iii—I1—Ba1^iv	85.99 (3)	I1—Ba1—I1^vi	136.767 (14)
Br1^v—Ba1—Br1	101.62 (3)	I1^i—Ba1—I1^vi	78.07 (2)
Br1^v—Ba1—Br1^vi	129.163 (17)	I1^ii—Ba1—I1^vi	137.726 (19)
Br1—Ba1—Br1^vi	129.163 (17)	Br1^v—Ba1—I1^viii	72.00 (3)
Br1^v—Ba1—Br1^vii	70.719 (16)	Br1—Ba1—I1^viii	138.42 (2)
Br1—Ba1—Br1^vii	70.718 (16)	Br1^vi—Ba1—I1^viii	68.31 (2)
Br1^vi—Ba1—Br1^vii	119.523 (18)	Br1^vii—Ba1—I1^viii	68.457 (18)
Br1^v—Ba1—I1	69.62 (2)	I1—Ba1—I1^viii	136.767 (14)
Br1—Ba1—I1	69.62 (2)	I1^i—Ba1—I1^viii	137.726 (19)
Br1^vi—Ba1—I1	125.42 (3)	I1^ii—Ba1—I1^viii	78.07 (2)
Br1^vii—Ba1—I1	115.06 (2)	I1^vi—Ba1—I1^viii	85.99 (3)
Br1^v—Ba1—I1^i	140.69 (2)	Ba1—Br1—Ba1^ix	101.62 (3)
Br1—Ba1—I1^i	72.41 (2)	Ba1^ix—Br1—Ba1^iv	118.69 (2)
Br1^vi—Ba1—I1^i	69.416 (14)	Ba1—Br1—Ba1^vii	109.282 (16)
Br1^vii—Ba1—I1^i	136.041 (16)	Ba1^ix—Br1—Ba1^vii	109.282 (16)
I1—Ba1—I1^i	72.051 (19)	Ba1^iv—Br1—Ba1^vii	99.06 (2)
Br1^v—Ba1—I1^ii	72.41 (2)

Symmetry codes: (i) −x+1, −y, −z; (ii) −x+1, −y+1, −z; (iii) −x+3/2, −y+1, z+1/2; (iv) −x+3/2, −y, z+1/2; (v) x, y+1, z; (vi) −x+3/2, −y, z−1/2; (vii) −x+2, −y, −z; (viii) −x+3/2, −y+1, z−1/2; (ix) x, y−1, z.