Ba₂VO₄Br

Single crystals of dibarium vanadate(V) bromide, Ba₂VO₄Br, were grown from a melt of Ba₃(VO₄)₂ and BaBr₂. Ba₂VO₄Br crystallizes in the space group Pbcm and is isotypic with the structure of chlorspodiosite, Ca₂PO₄Cl. Although the ionic radii in chlorspodiosite are different from those in dibarium vanadate bromide, the structures are very similar to one another. The V atom is coordinated by four O atoms, forming a slightly distorted tetra­hedron. The Ba atoms occupy two different sites and are coordinated by six O atoms and three or four Br atoms, depending on the site occupied.

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Structure description

This work is part of investigations or reinvestigations of compounds with the general formula A₂BO₄X (A = alkaline earth metal; B = P, As, V or other penta­valent atoms; X = halogen atom). The intention behind the current work is to understand conditions of the stability of the different structure types and to search for new structure types with this general formula.

The title compound Ba₂VO₄Br crystallizes isotypically with chlorspodiosite, Ca₂PO₄Cl (Mackay, 1953), despite of different ionic radii and the existence of other structure types with the same general formula (Haberkorn et al., 2014). The crystal structure of Ca₂PO₄Cl was published by Greenblatt et al. (1967). For an easier comparison of both structures, the atomic sites were normalized and sorted in the same manner as for the title compound (cf. Refinement section). The normalized atomic positions of Ca₂PO₄Cl and Ba₂VO₄Br are given within the Supporting information. The relative distances d/d_Shannon between the cations and the surrounding anions of both compounds are given in Tables 1 and 2, respectively. There are also `ideal' distances d_Shannon provided, calculated from the sum of the corresponding ionic radii (Shannon, 1976) using r_Ca²⁺,[8] = 1.12 Å, r_Ba²⁺,[8] = 1.42 Å, r_P⁵⁺,[4] = 0.29 Å, r_V⁵⁺,[4] = 0.355 Å, r_{O²⁻,[3–4]} = 1.37 Å, r_Cl¹⁻,[6] = 1.81 Å, and r_Br¹⁻,[6] = 1.96 Å.

Table 1
Selected relative inter­atomic distances in Ca₂PO₄Cl

Central atom	ligand	d1/dShannon	d2/dShannon	d3/dShannon	d4/dShannon	dShannon (Å)
Ca1	O^2−	2× 0.943	2× 1.001	2× 1.016	2× 1.677	2.49
	Cl^1−	2× 0.957	2× 1.482	2× 1.602		2.93
Ca2	O^2−	2× 0.967	2× 0.973	2× 1.066	2× 1.595	2.49
	Cl^1−	1× 0.947	1× 1.023	1× 1.424	1× 1.486	2.93
P	O^2−	2× 0.923	2× 0.934	2× 2.083		1.66
Values of dShannon were calculated from the sum of the corresponding ionic radii (Shannon, 1976).

Table 2
Selected relative inter­atomic distances in Ba₂VO₄Br

Central atom	ligand	d1/dShannon	d2/dShannon	d3/dShannon	d4/dShannon	dShannon (Å)
Ba1	O^2−	2× 0.981	2× 0.983	2× 0.993	2× 1.665	2.79
	Br^1−	2× 1.048	2× 1.182	2× 1.794		3.38
Ba2	O^2−	2× 0.964	2× 0.965	2× 1.022	2× 1.566	2.79
	Br^1−	1× 0.986	1× 1.078	1× 1.108	1× 1.578	3.38
V	O^2−	2× 0.992	2× 0.999	2× 2.165		1.73
Values of dShannon were calculated from the sum of the corresponding ionic radii (Shannon, 1976).

Four O atoms form in a similar manner marginally distorted tetra­hedra around B for both compounds (Fig. 1).

Figure 1 The crystal structure of Ba2VO4Br with VO4 anions displayed as coordination polyhedra.

The cation A occupies two different sites, one at Wyckoff position 4c (site symmetry 2..; Ca1 and Ba1), the other at Wyckoff position 4d (..m; Ca2 and Ba2). For Ca at the 4d sites (Ca2) in Ca₂PO₄Cl six O atoms form a distorted trigonal prism capped by two Cl atoms. Ca at the 4c site (Ca1) is also coord­inated by two Cl atoms and six O atoms. The eight atoms form an irregular polyhedron. Additional Cl atoms are much more distant and do not belong to the coordination polyhedra of Ca1 and Ca2.

Ba²⁺ requires more than twice the volume in comparison with Ca²⁺. Hence, the coordination numbers of the A-sites increase in Ba₂VO₄Br compared to Ca₂PO₄Cl. The Ba2 site is ninefold coordinated by six O atoms and three Br atoms, forming a distorted tricapped trigonal prism (Fig. 2). The distortion of the trigonal prism is very similar to that of Ca2 in Ca₂PO₄Cl. Ba1 has an irregular shaped coordination polyhedron consisting of six O atoms and four Br atoms (Fig. 3). As can be seen in the Voronoi polyhedron, two of these bromine ligands belong to the coordination sphere; nevertheless they are more distant than the other bromine ligands and their Ba—Br distance is 118% of the sum of the ionic radii.

Figure 2 The coordination polyhedron of Ba at the 4d site (Ba2) in Ba2VO4Br with inter­atomic distances. Displacement ellipsoids are drawn at the 99.8% probability level. [Symmetry codes: (i) x, y, −z + ; (ii) x, y − 1, −z + ; (iii) x, y − 1, z; (iv) −x, y − , −z + ; (v) −x, y − , z; (vi) −x + 1, y − , −z + .]

Figure 3 (a) The coordination polyhedron of Ba at the 4c site (Ba1) in Ba2VO4Br, (b) displacement ellipsoid plot (99.8% probability level) with inter­atomic distances and (c) Voronoi polyhedron. [Symmetry codes: (i) x, −y + , −z; (ii) −x + 1, −y + 1, −z; (iii) −x + 1, y − , z; (iv) −x + 1, y − , −z + ; (v) −x + 1, −y + 1, z − ; (vi) −x + 1, −y, −z; (vii) −x + 1, y + , z.]

The compounds Ca₂CrO₄Cl (Greenblatt et al., 1967), Ca₂VO₄Cl (Banks et al., 1970), and Ba₂VO₄Br crystallize in the same space group type Pbcm as Ca₂PO₄Cl and are isopointal. The similarity of Ca₂PO₄Cl to these compounds was numerically determined using the program COMPSTRU (de la Flor et al., 2016). The results are given in Table 3, where S is the degree of lattice distortion, d_max and d_av are the maximum and mean displacements of equivalent atoms and Δ is the measure of similarity taking atomic positions and lattice parameters into account. The structure of Ba₂VO₄Br is less similar to Ca₂PO₄Cl than the structures of the other compounds due to a larger difference of the ionic radii. The large volume of the unit cell of Ba₂VO₄Br (V_Ba2VO2Br/V_Ca2PO4Cl = 138%) causes high values of S and Δ. The displacement of the X atom of more than 1 Å enables higher coordination numbers of the A atoms for Ba₂VO₄Br. The mean displacement d_av is less than twice the value for Ca₂CrO₄Cl and demonstrates rather small displacements of the other sites. Despite different ionic radii and different coordination numbers of the A atoms, the structures of all these compounds are very similar and can be regarded as isotypic (Lima-de-Faria et al., 1990).

Table 3
Similarity of Ca₂PO₄Cl to some isotypic compounds

Compound	Ca2CrO4Cl	Ca2VO4Cl	Ba2VO4Br
S	0.0092	0.0121	0.0561
dmax (Å)	0.3665	0.2445	1.1214
dav (Å)	0.1575	0.1278	0.2607
Δ	0.045	0.030	0.092

Synthesis and crystallization

Ba₂VO₄Br may be synthesized either via a solid-state reaction (ssr) of Ba₃(VO₄)₂ with BaBr₂ or via a melt of Ba₃(VO₄)₂ and an excess of BaBr₂. While the ssr supports the preparation of a polycrystalline mass, the melt enables the yield of single crystals. Both methods were used, but the synthesis of single crystals will be focused on here.

Single crystals of Ba₂VO₄Br were grown from a melt of BaBr₂ using as flux and as reacting agent. 0.4 mmol of Ba₃(VO₄)₂, 1.6 mmol BaBr₂·2H₂O, and 1.6 mmol NH₄Br were mixed and filled into a platinum crucible. NH₄Br was added to minimize the formation of hydroxides. After an initial step of slowly heating to 523 K allowing water to evaporate, the mixture was heated to 1173 K. This temperature was held for 2 h. Then the melt was allowed to cool down to 1053 K within 10 h, followed by cooling to room temperature with a higher cooling rate. The excess BaBr₂ was leached out with distilled water.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 4. The atomic coordinates were standardized by the program STRUCTURE TIDY (Gelato & Parthé 1987) as implemented in the program PLATON (Spek, 2009), though with a different sequence of the sites. The sites were sorted in the same order as the chemical symbols in the chemical formula. For sites with the same atom type these sites were arranged in alphabetical order of their Wyckoff letters. For sites with the same atom type and the same Wyckoff letter the sites were arranged according to increasing x.

Table 4
Experimental details

Crystal data
Chemical formula	Ba2VO4Br
Mr	469.52
Crystal system, space group	Orthorhombic, Pbcm
Temperature (K)	200
a, b, c (Å)	6.8103 (7), 7.8855 (9), 12.0131 (14)
V (Å^3)	645.14 (12)
Z	4
Radiation type	Mo Kα
μ (mm^−1)	19.61
Crystal size (mm)	0.04 × 0.04 × 0.03
Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015)
Tmin, Tmax	0.663, 0.749
No. of measured, independent and observed [I > 2σ(I)] reflections	32756, 2741, 2132
Rint	0.062
(sin θ/λ)max (Å^−1)	0.994
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.023, 0.042, 1.05
No. of reflections	2741
No. of parameters	42
Δρmax, Δρmin (e Å^−3)	1.63, −1.14
Computer programs: APEX2, SAINT (Bruker, 2012), SHELXT2014 (Sheldrick, 2015a), SHELXL2015 (Sheldrick, 2015b), DIAMOND (Brandenburg et al., 1999) and publCIF (Westrip, 2010).

Structural data

Computing details

Data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXT2014 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2015 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg et al., 1999); software used to prepare material for publication: publCIF (Westrip, 2010).

Dibarium vanadate(V) bromide

Crystal data

Ba2VO4Br	Dx = 4.834 Mg m^−3
Mr = 469.52	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbcm	Cell parameters from 5232 reflections
a = 6.8103 (7) Å	θ = 4.3–40.6°
b = 7.8855 (9) Å	µ = 19.61 mm^−1
c = 12.0131 (14) Å	T = 200 K
V = 645.14 (12) Å^3	Cuboid, colorless
Z = 4	0.04 × 0.04 × 0.03 mm
F(000) = 808

Data collection

Bruker APEXII CCD diffractometer	2132 reflections with I > 2σ(I)
Radiation source: sealed X-ray tube	Rint = 0.062
φ and ω scans	θmax = 44.9°, θmin = 3.0°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −13→13
Tmin = 0.663, Tmax = 0.749	k = −15→15
32756 measured reflections	l = −20→23
2741 independent reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0146P)^2] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.023	(Δ/σ)max = 0.001
wR(F^2) = 0.042	Δρmax = 1.63 e Å^−3
S = 1.05	Δρmin = −1.14 e Å^−3
2741 reflections	Extinction correction: SHELXL2015 (Sheldrick, 2015b), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
42 parameters	Extinction coefficient: 0.00114 (12)

Special details

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

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

	x	y	z	Uiso*/Ueq
Ba1	0.61644 (2)	0.2500	0.0000	0.00879 (3)
Ba2	0.11189 (2)	0.03912 (2)	0.2500	0.00733 (3)
V1	0.11728 (5)	0.2500	0.0000	0.00469 (6)
O1	0.03522 (17)	0.77707 (15)	0.11312 (11)	0.0074 (2)
O2	0.26812 (17)	0.08342 (15)	0.03175 (11)	0.0085 (2)
Br1	0.41944 (4)	0.41720 (4)	0.2500	0.01897 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ba1	0.00453 (5)	0.00797 (5)	0.01389 (7)	0.000	0.000	−0.00337 (4)
Ba2	0.01093 (5)	0.00591 (5)	0.00515 (6)	0.00088 (4)	0.000	0.000
V1	0.00453 (12)	0.00486 (12)	0.00467 (15)	0.000	0.000	0.00036 (10)
O1	0.0071 (4)	0.0097 (5)	0.0054 (5)	−0.0011 (3)	−0.0005 (4)	−0.0014 (4)
O2	0.0079 (4)	0.0073 (4)	0.0104 (6)	0.0013 (3)	0.0006 (4)	0.0012 (4)
Br1	0.01411 (11)	0.02987 (15)	0.01293 (13)	−0.00761 (10)	0.000	0.000

Geometric parameters (Å, º)

Ba1—O2^i	2.7383 (12)	Ba2—O1^x	2.6919 (12)
Ba1—O2	2.7383 (12)	Ba2—O1^xi	2.6919 (12)
Ba1—O1^ii	2.7423 (12)	Ba2—O2	2.8510 (14)
Ba1—O1^iii	2.7423 (12)	Ba2—O2^xii	2.8510 (14)
Ba1—O2^iv	2.7706 (12)	Ba2—Br1^vii	3.3334 (4)
Ba1—O2^v	2.7706 (12)	Ba2—Br1	3.6436 (4)
Ba1—Br1^vi	3.5437 (4)	Ba2—Br1^viii	3.7440 (5)
Ba1—Br1	3.5437 (4)	V1—O2	1.7107 (12)
Ba1—Br1^iii	3.9958 (4)	V1—O2^i	1.7107 (12)
Ba1—Br1^vii	3.9958 (4)	V1—O1^xiii	1.7236 (13)
Ba2—O1^viii	2.6885 (13)	V1—O1^ix	1.7236 (13)
Ba2—O1^ix	2.6885 (13)
O2^i—Ba1—O2	59.94 (5)	Br1^iii—Ba1—Br1^vii	172.988 (9)
O2^i—Ba1—O1^ii	141.36 (4)	O1^viii—Ba2—O1^ix	75.41 (5)
O2—Ba1—O1^ii	135.87 (4)	O1^viii—Ba2—O1^x	146.830 (14)
O2^i—Ba1—O1^iii	135.87 (4)	O1^ix—Ba2—O1^x	95.16 (4)
O2—Ba1—O1^iii	141.36 (4)	O1^viii—Ba2—O1^xi	95.16 (4)
O1^ii—Ba1—O1^iii	60.21 (5)	O1^ix—Ba2—O1^xi	146.830 (14)
O2^i—Ba1—O2^iv	79.03 (4)	O1^x—Ba2—O1^xi	75.30 (6)
O2—Ba1—O2^iv	132.99 (4)	O1^viii—Ba2—O2	128.03 (4)
O1^ii—Ba1—O2^iv	67.20 (4)	O1^ix—Ba2—O2	59.41 (3)
O1^iii—Ba1—O2^iv	84.07 (4)	O1^x—Ba2—O2	66.72 (4)
O2^i—Ba1—O2^v	132.99 (4)	O1^xi—Ba2—O2	136.73 (4)
O2—Ba1—O2^v	79.03 (4)	O1^viii—Ba2—O2^xii	59.41 (3)
O1^ii—Ba1—O2^v	84.07 (4)	O1^ix—Ba2—O2^xii	128.03 (4)
O1^iii—Ba1—O2^v	67.20 (4)	O1^x—Ba2—O2^xii	136.73 (4)
O2^iv—Ba1—O2^v	147.03 (5)	O1^xi—Ba2—O2^xii	66.72 (4)
O2^i—Ba1—Br1^vi	74.48 (3)	O2—Ba2—O2^xii	133.74 (5)
O2—Ba1—Br1^vi	67.15 (3)	O1^viii—Ba2—Br1^vii	123.92 (3)
O1^ii—Ba1—Br1^vi	140.94 (3)	O1^ix—Ba2—Br1^vii	123.92 (3)
O1^iii—Ba1—Br1^vi	83.03 (3)	O1^x—Ba2—Br1^vii	87.96 (3)
O2^iv—Ba1—Br1^vi	125.25 (3)	O1^xi—Ba2—Br1^vii	87.96 (3)
O2^v—Ba1—Br1^vi	68.76 (3)	O2—Ba2—Br1^vii	71.22 (2)
O2^i—Ba1—Br1	67.15 (3)	O2^xii—Ba2—Br1^vii	71.21 (2)
O2—Ba1—Br1	74.48 (3)	O1^viii—Ba2—Br1	69.09 (3)
O1^ii—Ba1—Br1	83.03 (3)	O1^ix—Ba2—Br1	69.09 (3)
O1^iii—Ba1—Br1	140.94 (3)	O1^x—Ba2—Br1	137.70 (3)
O2^iv—Ba1—Br1	68.76 (3)	O1^xi—Ba2—Br1	137.70 (3)
O2^v—Ba1—Br1	125.25 (3)	O2—Ba2—Br1	71.65 (2)
Br1^vi—Ba1—Br1	135.507 (11)	O2^xii—Ba2—Br1	71.65 (2)
O2^i—Ba1—Br1^iii	61.79 (3)	Br1^vii—Ba2—Br1	71.673 (8)
O2—Ba1—Br1^iii	111.52 (3)	O1^viii—Ba2—Br1^viii	79.58 (3)
O1^ii—Ba1—Br1^iii	111.98 (3)	O1^ix—Ba2—Br1^viii	79.58 (3)
O1^iii—Ba1—Br1^iii	74.43 (3)	O1^x—Ba2—Br1^viii	67.38 (3)
O2^iv—Ba1—Br1^iii	59.84 (3)	O1^xi—Ba2—Br1^viii	67.38 (3)
O2^v—Ba1—Br1^iii	122.49 (3)	O2—Ba2—Br1^viii	113.09 (3)
Br1^vi—Ba1—Br1^iii	65.431 (8)	O2^xii—Ba2—Br1^viii	113.09 (2)
Br1—Ba1—Br1^iii	111.683 (8)	Br1^vii—Ba2—Br1^viii	148.359 (12)
O2^i—Ba1—Br1^vii	111.52 (3)	Br1—Ba2—Br1^viii	139.968 (10)
O2—Ba1—Br1^vii	61.79 (3)	O2—V1—O2^i	106.18 (8)
O1^ii—Ba1—Br1^vii	74.43 (3)	O2—V1—O1^xiii	116.27 (6)
O1^iii—Ba1—Br1^vii	111.98 (3)	O2^i—V1—O1^xiii	106.33 (6)
O2^iv—Ba1—Br1^vii	122.49 (3)	O2—V1—O1^ix	106.33 (6)
O2^v—Ba1—Br1^vii	59.84 (3)	O2^i—V1—O1^ix	116.27 (6)
Br1^vi—Ba1—Br1^vii	111.683 (8)	O1^xiii—V1—O1^ix	105.90 (8)
Br1—Ba1—Br1^vii	65.431 (8)

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