Crystal structure of Ba2Co(BO3)2

N'Faoui, F.-E.; Aride, J.; Boukhari, A.; Taibi, M.; Saadi, M.; El Ammari, L.

doi:10.1107/S2056989019002597

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Volume 75| Part 3| March 2019| Pages 388-391

https://doi.org/10.1107/S2056989019002597

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Crystal structure of Ba₂Co(BO₃)₂

Fatima-Ezahra N'Faoui,^a ^* Jilali Aride,^a Ali Boukhari,^b M'Hamed Taibi,^a Mohamed Saadi ^b and Lahcen El Ammari ^b

^aLaboratoire de Physico-Chimie des Matériaux Inorganiques et Organiques, Centre des Sciences des Matériaux, Ecole Normale Supérieure, Mohammed V University in Rabat, Morocco, and ^bLaboratoire de Chimie Appliquée des Matŕiaux, Centre des Sciences des Matériaux, Faculty of Sciences, Mohammed V University in Rabat, Avenue Ibn Batouta, BP 1014, Rabat, Morocco
^*Correspondence e-mail: f_nfaoui43@yahoo.com

Edited by M. Weil, Vienna University of Technology, Austria (Received 28 January 2019; accepted 20 February 2019; online 22 February 2019)

Single crystals of dibarium cobalt(II) bis(orthoborate), Ba₂Co(BO₃)₂, have been obtained from the melt. The crystal structure is composed of two isolated (BO₃)³⁻ triangles linked to Co²⁺ cations. The resulting [CoO₅] square pyramids and the borate anions make up branched rows extending parallel to [010]. The barium cations occupy two sites in the voids of this arrangement and exhibit coordination numbers of nine each. A comparison with the structures of other A₂M(BO₃)₂ compounds reveals a unique five-coordination of the small metal M in the title compound instead of four- or six-coordination for the other A₂M(BO₃)₂ compounds with M = Cu, Zn, Mg, Ca, or Cd.

Keywords: cobalt borate; diborates; Ba₂Co(BO₃)₂; crystal structure; crystal growth; X-ray diffraction.

CCDC reference: 1898300

1. Chemical context

The crystal chemistry of borates differs from those of silicates, phosphates, sulfates, carbonates or nitrates due to the possibility of forming borate anions with trigonal–planar and tetrahedral configurations (Zhang et al., 2011a ; Filatov & Bubnova, 2000 ; Chen et al., 2005 ; Reshak, 2016 ). In general, borate compounds are applied in different fields, such as non-linear optical (NLO) materials (Becker, 1998 ), for photoluminescence (Mergen & Pekgözlü, 2013 ), for their optical properties (Zhang et al., 2011b ; Lv et al., 2018 ), or as ferroelectrics (Dhanasekaran, 2009 ; Murugan et al., 2001 ). The borate systems A₂M(BO₃)₂, where A = Ba, Sr, Pb and M = Cu, Mg, Cd, Ca, Zn, have been studied previously. For these compounds, several structures types have been reported that depend on the size and nature of the A and M atoms, as shown in Table 1.

Table 1
Lattice parameters (Å, °), space groups and references for A₂M(BO₃)₂ compounds

Formula	a	b	c	β	Z	Space group	Reference
Ba₂Ca(BO₃)₂	9.362 (2)	5.432 (2)	6.635 (2)	119.38 (1)	2	C2/m	Akella & Keszler (1995 )
Ba₂Cd(BO₃)₂	9.6305 (4)	5.3626 (3)	6.5236 (2)	118.079 (3)	2	C2/m	Zhang et al. (2011b)
Sr₂Mg(BO₃)₂	9.046 (4)	5.1579 (9)	6.103 (3)	118.691	2	C2/m	Chen et al. (2007 )
Ba₂Co(BO₃)₂	11.9784 (4)	5.3256 (2)	10.3220 (3)	117.494 (1)	4	C2/m	This work
α-Sr₂Cu(BO₃)₂	5.707 (1)	8.796 (2)	6.027 (1)	116.98	2	P2₁/c	Smith & Keszler (1989 )
Pb₂Cu(BO₃)₂	5.6311 (6)	8.7628 (9)	6.2025 (6)	115.706 (1)	2	P2₁/c	Pan et al. (2006 )
Ba₂Cu(BO₃)₂	8.023 (1)	11.290 (1)	13.889 (1)		8	Pnma	Smith & Keszler (1990 )
β-Sr₂Cu(BO₃)₂	7.612 (3)	10.854 (7)	13.503 (4)		8	Pnma	Smith & Keszler (1989)
Ba₂Zn(BO₃)₂	15.068 (2)	8.720 (2)	10.128 (3)		8	Pca2₁	Smith & Koliha (1994 )
Ba₂Mg(BO₃)₂	5.343 (2)	5.343 (2)	16.520 (3)		3	R $[\overline{3}]$ m	Kokh et al. (2017 )

In this investigation we have isolated single crystals of Ba₂Co(BO₃)₂ from the melt. The new compound crystallizes in the monoclinic system in the same space-group type as some other A₂M(BO₃)₂ compounds, but with different cell parameters (Table 1).

2. Structural commentary

In the crystal structure of the title compound, except for the two oxygen atoms O1 and O3 that lie in general positions of the C2/m space group, all atoms are located on a mirror plane (Wyckoff position 4i).

The principal building units in the crystal structure are two trigonal–planar borate anions, one five-coordinate Co²⁺ cation and two nine-coordinate Ba²⁺ cations (Fig. 1). Relevant bond lengths and angles are collated in Table 2. The borate anions are isolated from each other. (B2O₃) anions and [CoO₅] polyhedra share one edge to form a {BCoO₆} group, whereas the (B1O₃) anion is connected through its corners to three different {BCoO₆} groups. This arrangement leads to the formation of branched rows extending parallel to [010], as shown in Fig. 2. The rows are linked by pairs of [BaO₉] polyhedra (Fig. 3) into a three-dimensional framework, as shown in Figs. 4 and 5.

Table 2
Selected geometric parameters (Å, °)

Ba1—O3	2.7232 (12)	Co1—O2^iv	2.0152 (18)
Ba1—O4	2.7266 (4)	Co1—O1	2.0432 (11)
Ba1—O1ⁱ	2.7697 (11)	Co1—O3	2.1043 (12)
Ba1—O4ⁱⁱ	2.8215 (19)	B1—O2	1.364 (3)
Ba1—O3ⁱ	2.9272 (12)	B1—O1	1.3943 (16)
Ba2—O3	2.7688 (12)	B1—O1^v	1.3943 (16)
Ba2—O1ⁱⁱⁱ	2.8064 (11)	B2—O4	1.377 (3)
Ba2—O2^iv	2.9009 (8)	B2—O3^vi	1.3920 (17)
Ba2—O1^iv	2.9668 (12)	B2—O3	1.3920 (17)
Ba2—O4ⁱⁱ	3.1360 (17)

O2—B1—O1	120.42 (9)	O4—B2—O3^vi	122.38 (9)
O2—B1—O1^v	120.42 (9)	O4—B2—O3	122.38 (9)
O1—B1—O1^v	119.16 (18)	O3^vi—B2—O3	115.18 (19)
Symmetry codes: (i) -x+1, -y, -z+1; (ii) $[-x+{\script{3\over 2}}, -y+{\script{1\over 2}}, -z+1]$ ; (iii) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, z]$ ; (iv) $[-x+{\script{3\over 2}}, -y+{\script{1\over 2}}, -z+2]$ ; (v) x, -y, z; (vi) x, -y+1, z.

Figure 1
The principal building units in the structure of the title compound with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) x, −y, z; (ii) x, y − 1, z; (iii) −x + 1, −y, −z + 1; (iv) −x + 1, y, −z + 1; (v) −x + $[{3\over 2}]$ , −y + $[{1\over 2}]$ , −z + 1; (vi) x + $[{1\over 2}]$ , −y + $[{1\over 2}]$ , z; (vii) x + $[{1\over 2}]$ , y − $[{1\over 2}]$ , z; (viii) −x + $[{3\over 2}]$ , −y + $[{1\over 2}]$ , −z + 2; (ix) −x + $[{3\over 2}]$ , −y − $[{1\over 2}]$ , −z + 2; (x) −x + $[{3\over 2}]$ , y − $[{1\over 2}]$ , −z + 2; (xi) x, −y + 1, z.]

Figure 2
Edge- and corner-sharing [CoO₅] and (BO₃) polyhedra forming branched rows parallel to [010].

Figure 3
A pair of [BaO₉] polyhedra.

Figure 4
Projection of the crystal structure of Ba₂Co(BO₃)₂ along [001].

Figure 5
Projection of the crystal structure of Ba₂Co(BO₃)₂ approximately along [010], emphasizing the voids between the cobalt borate rows in which the barium cations are located.

The slight deviation of the boron atoms from a planar environment by oxygen atoms is reflected in the maximum deviation of 0.007 (3) Å for B1, compared with 0.019 (3) Å for B2. The average distances B1—O = 1.384 Å and B2—O = 1.387 Å are similar to those found in other A₂M(BO₃)₂ borates where B—O bonds vary between 1.325 and 1.411 Å and are in good agreement with the results of the analysis carried out by Zobetz (1982 ) on 225 B—O distances belonging to 75 BO₃ groups [1.370 (19) Å]. Addison et al. (1984 ) have proposed the parameter τ₅ to distinguish whether a five-coordinated atom is in a trigonal–bipyramidal or a square-pyramidal environment. With τ₅ = −0.01667α + 0.01667β = 0, where β > α are the two largest valence angles of the coordination polyhedron, namely α = O1—Co1—O3ⁱ = 157.75° and β = Oⁱ—Co1—O3 = 157.75° [symmetry code: (i) x, −y + 1, z], a square-pyramidal environment is realized for the Co²⁺ cation in the structure of the title compound. Each of the two barium cations is surrounded by nine oxygen atoms forming distorted polyhedra with average distances for Ba1—O and Ba2–O of 2.791 and 2.891 Å, respectively.

3. Comparison with related structures

Comparison of the crystal structure of the title compound with those of other orthoborates with formula type A₂M(BO₃)₂ listed in Table 1 reveals that the first three compounds crystallize in the monoclinic system with the same space group (C2/m) but a halved unit-cell volume. α-Sr₂Cu(BO₃)₂ and Pb₂Cu(BO₃)₂ also crystallize in the monoclinic system but in space group P2₁/c. The remaining compounds adopt an orthorhombic structure, except for the last, Ba₂Mg(BO₃)₂, which is hexagonal. In the crystal structures of all these borates, the small metal M has either a coordination number of four (CuO₄, ZnO₄) or six (CuO₆, MgO₆, CaO₆, CdO₆). Accordingly, it is important to note the originality of the title structure with its five-coordination of the cobalt cation instead of four- or six-coordination for M in the other A₂M(BO₃)₂ compounds. Moreover, the linkage of [CoO₅] polyhedra and one of the two (BO₃)^3– anions by sharing an edge is different from other A₂M(BO₃)₂ structures where [MO₄] or [MO₆] polyhedra are linked to the (BO₃)^3– anions only through their vertices.

4. Synthesis and crystallization

Single crystals of Ba₂Co(BO₃)₂ were isolated from the melt, starting from a mixture of Ba(NO₃)₂, Co(NO₃)₂·6H₂O and H₃BO₃ in a molar ratio of 2:1:2. The mixture was subjected to successive heat treatments at 673 K and at 1073 K. The obtained powder was melted at a temperature of 1433 K, followed by a slow cooling. The resulting product consisted of pink crystals corresponding to the title compound.

5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. The maximum and minimum remaining electron density peaks are at 0.47 Å from Ba1 and 1.08 Å from Co1, respectively.

Table 3
Experimental details

Crystal data
Chemical formula	Ba₂Co(BO₃)₂
M_r	451.23
Crystal system, space group	Monoclinic, C2/m
Temperature (K)	296
a, b, c (Å)	11.9784 (4), 5.3256 (2), 10.3220 (3)
β (°)	117.494 (1)
V (Å³)	584.10 (3)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	16.11
Crystal size (mm)	0.36 × 0.27 × 0.20

Data collection
Diffractometer	Bruker D8 VENTURE Super DUO
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.638, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	12996, 1392, 1391
R_int	0.032
(sin θ/λ)_max (Å⁻¹)	0.806

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.015, 0.031, 1.41
No. of reflections	1392
No. of parameters	62
Δρ_max, Δρ_min (e Å⁻³)	1.73, −1.12
Computer programs: APEX3 and SAINT (Bruker, 2016 ), SAINT, SHELXT2014/5 (Sheldrick, 2015a ), SHELXL2016/6 (Sheldrick, 2015b ), ORTEP-3 for Windows (Farrugia, 2012 ), DIAMOND (Brandenburg, 2006 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1898300

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989019002597/wm5486sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989019002597/wm5486Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX3 (Bruker, 2016); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT; program(s) used to solve structure: SHELXT2014/5 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2016/6 (Sheldrick, 2015b); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012), DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Dibarium cobalt(II) bis(orthoborate) top

Crystal data top

Ba₂Co(BO₃)₂	F(000) = 788
M_r = 451.23	D_x = 5.131 Mg m⁻³
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71073 Å
a = 11.9784 (4) Å	Cell parameters from 1392 reflections
b = 5.3256 (2) Å	θ = 3.4–35.0°
c = 10.3220 (3) Å	µ = 16.11 mm⁻¹
β = 117.494 (1)°	T = 296 K
V = 584.10 (3) Å³	Block, colourless
Z = 4	0.36 × 0.27 × 0.20 mm

Data collection top

Bruker D8 VENTURE Super DUO diffractometer	1392 independent reflections
Radiation source: INCOATEC IµS micro-focus source	1391 reflections with I > 2σ(I)
HELIOS mirror optics monochromator	R_int = 0.032
Detector resolution: 10.4167 pixels mm^-1	θ_max = 35.0°, θ_min = 3.4°
φ and ω scans	h = −19→18
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	k = −8→8
T_min = 0.638, T_max = 0.746	l = −16→16
12996 measured reflections

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.004P)² + 1.2571P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.015	(Δ/σ)_max = 0.001
wR(F²) = 0.031	Δρ_max = 1.73 e Å⁻³
S = 1.41	Δρ_min = −1.12 e Å⁻³
1392 reflections	Extinction correction: SHELXL-2016/6 (Sheldrick, 2015b), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
62 parameters	Extinction coefficient: 0.0101 (3)

Special details top

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 (Å²) top

	x	y	z	U_iso*/U_eq
Ba1	0.59046 (2)	0.000000	0.39992 (2)	0.00733 (4)
Ba2	0.82861 (2)	0.000000	0.84816 (2)	0.00846 (4)
Co1	0.61032 (3)	0.500000	0.79447 (3)	0.00765 (6)
B1	0.5939 (2)	0.000000	0.9373 (2)	0.0065 (3)
B2	0.6356 (2)	0.500000	0.5684 (3)	0.0073 (3)
O1	0.53712 (10)	0.2258 (2)	0.87137 (12)	0.00920 (18)
O3	0.63351 (11)	0.2793 (2)	0.63947 (13)	0.01062 (18)
O2	0.70464 (16)	0.000000	1.0636 (2)	0.0151 (3)
O4	0.64458 (17)	0.500000	0.4400 (2)	0.0120 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ba1	0.00848 (6)	0.00626 (6)	0.00619 (6)	0.000	0.00250 (4)	0.000
Ba2	0.00697 (6)	0.00742 (6)	0.00910 (6)	0.000	0.00210 (4)	0.000
Co1	0.01018 (11)	0.00530 (11)	0.00871 (12)	0.000	0.00542 (10)	0.000
B1	0.0076 (8)	0.0057 (8)	0.0067 (8)	0.000	0.0038 (7)	0.000
B2	0.0073 (8)	0.0066 (8)	0.0079 (8)	0.000	0.0034 (7)	0.000
O1	0.0105 (4)	0.0064 (4)	0.0101 (4)	0.0006 (3)	0.0043 (4)	0.0018 (3)
O3	0.0151 (5)	0.0069 (4)	0.0094 (4)	−0.0003 (4)	0.0052 (4)	0.0006 (3)
O2	0.0105 (6)	0.0134 (7)	0.0127 (7)	0.000	−0.0020 (6)	0.000
O4	0.0197 (7)	0.0079 (6)	0.0132 (7)	0.000	0.0118 (6)	0.000

Geometric parameters (Å, º) top

Ba1—O3	2.7232 (12)	Ba2—O1^viii	2.9668 (12)
Ba1—O3ⁱ	2.7232 (12)	Ba2—O1^x	2.9668 (11)
Ba1—O4ⁱⁱ	2.7266 (4)	Ba2—O4^v	3.1360 (17)
Ba1—O4	2.7266 (4)	Co1—O2^viii	2.0152 (18)
Ba1—O1ⁱⁱⁱ	2.7697 (11)	Co1—O1^xi	2.0432 (11)
Ba1—O1^iv	2.7697 (11)	Co1—O1	2.0432 (11)
Ba1—O4^v	2.8215 (19)	Co1—O3^xi	2.1043 (12)
Ba1—O3ⁱⁱⁱ	2.9272 (12)	Co1—O3	2.1043 (12)
Ba1—O3^iv	2.9272 (12)	B1—O2	1.364 (3)
Ba2—O3ⁱ	2.7688 (12)	B1—O1	1.3943 (16)
Ba2—O3	2.7688 (12)	B1—O1ⁱ	1.3943 (16)
Ba2—O1^vi	2.8064 (11)	B2—O4	1.377 (3)
Ba2—O1^vii	2.8064 (11)	B2—O3^xi	1.3920 (17)
Ba2—O2^viii	2.9009 (8)	B2—O3	1.3920 (17)
Ba2—O2^ix	2.9009 (8)

O3—Ba1—O3ⁱ	66.22 (5)	O1^vi—Ba2—O2^viii	75.01 (4)
O3—Ba1—O4ⁱⁱ	117.61 (5)	O1^vii—Ba2—O2^viii	134.17 (4)
O3ⁱ—Ba1—O4ⁱⁱ	52.88 (4)	O3ⁱ—Ba2—O2^ix	64.04 (4)
O3—Ba1—O4	52.88 (4)	O3—Ba2—O2^ix	123.27 (4)
O3ⁱ—Ba1—O4	117.61 (5)	O1^vi—Ba2—O2^ix	134.17 (4)
O4ⁱⁱ—Ba1—O4	155.16 (8)	O1^vii—Ba2—O2^ix	75.01 (4)
O3—Ba1—O1ⁱⁱⁱ	160.05 (3)	O2^viii—Ba2—O2^ix	133.25 (7)
O3ⁱ—Ba1—O1ⁱⁱⁱ	117.76 (3)	O3ⁱ—Ba2—O1^viii	154.99 (3)
O4ⁱⁱ—Ba1—O1ⁱⁱⁱ	73.21 (5)	O3—Ba2—O1^viii	112.17 (3)
O4—Ba1—O1ⁱⁱⁱ	123.99 (4)	O1^vi—Ba2—O1^viii	66.44 (4)
O3—Ba1—O1^iv	117.76 (3)	O1^vii—Ba2—O1^viii	96.47 (3)
O3ⁱ—Ba1—O1^iv	160.05 (3)	O2^viii—Ba2—O1^viii	48.15 (4)
O4ⁱⁱ—Ba1—O1^iv	123.99 (4)	O2^ix—Ba2—O1^viii	103.68 (4)
O4—Ba1—O1^iv	73.21 (5)	O3ⁱ—Ba2—O1^x	112.17 (3)
O1ⁱⁱⁱ—Ba1—O1^iv	51.46 (5)	O3—Ba2—O1^x	154.99 (3)
O3—Ba1—O4^v	77.18 (4)	O1^vi—Ba2—O1^x	96.47 (3)
O3ⁱ—Ba1—O4^v	77.18 (4)	O1^vii—Ba2—O1^x	66.44 (4)
O4ⁱⁱ—Ba1—O4^v	77.69 (4)	O2^viii—Ba2—O1^x	103.68 (4)
O4—Ba1—O4^v	77.69 (4)	O2^ix—Ba2—O1^x	48.15 (4)
O1ⁱⁱⁱ—Ba1—O4^v	122.58 (4)	O1^viii—Ba2—O1^x	58.98 (4)
O1^iv—Ba1—O4^v	122.58 (4)	O3ⁱ—Ba2—O4^v	71.41 (4)
O3—Ba1—O3ⁱⁱⁱ	100.43 (3)	O3—Ba2—O4^v	71.41 (4)
O3ⁱ—Ba1—O3ⁱⁱⁱ	68.02 (4)	O1^vi—Ba2—O4^v	66.68 (4)
O4ⁱⁱ—Ba1—O3ⁱⁱⁱ	70.32 (4)	O1^vii—Ba2—O4^v	66.68 (4)
O4—Ba1—O3ⁱⁱⁱ	130.98 (4)	O2^viii—Ba2—O4^v	112.77 (4)
O1ⁱⁱⁱ—Ba1—O3ⁱⁱⁱ	66.20 (3)	O2^ix—Ba2—O4^v	112.77 (4)
O1^iv—Ba1—O3ⁱⁱⁱ	92.16 (3)	O1^viii—Ba2—O4^v	132.76 (3)
O4^v—Ba1—O3ⁱⁱⁱ	142.41 (3)	O1^x—Ba2—O4^v	132.76 (3)
O3—Ba1—O3^iv	68.02 (4)	O2^viii—Co1—O1^xi	104.04 (5)
O3ⁱ—Ba1—O3^iv	100.43 (3)	O2^viii—Co1—O1	104.04 (5)
O4ⁱⁱ—Ba1—O3^iv	130.98 (4)	O1^xi—Co1—O1	91.26 (6)
O4—Ba1—O3^iv	70.32 (4)	O2^viii—Co1—O3^xi	93.78 (6)
O1ⁱⁱⁱ—Ba1—O3^iv	92.16 (3)	O1^xi—Co1—O3^xi	97.30 (4)
O1^iv—Ba1—O3^iv	66.20 (3)	O1—Co1—O3^xi	157.75 (5)
O4^v—Ba1—O3^iv	142.41 (3)	O2^viii—Co1—O3	93.78 (6)
O3ⁱⁱⁱ—Ba1—O3^iv	61.09 (5)	O1^xi—Co1—O3	157.75 (5)
O3ⁱ—Ba2—O3	64.99 (5)	O1—Co1—O3	97.30 (4)
O3ⁱ—Ba2—O1^vi	138.10 (4)	O3^xi—Co1—O3	67.90 (6)
O3—Ba2—O1^vi	100.67 (4)	O2—B1—O1	120.42 (9)
O3ⁱ—Ba2—O1^vii	100.67 (3)	O2—B1—O1ⁱ	120.42 (9)
O3—Ba2—O1^vii	138.10 (4)	O1—B1—O1ⁱ	119.16 (18)
O1^vi—Ba2—O1^vii	62.72 (5)	O4—B2—O3^xi	122.38 (9)
O3ⁱ—Ba2—O2^viii	123.27 (4)	O4—B2—O3	122.38 (9)
O3—Ba2—O2^viii	64.04 (4)	O3^xi—B2—O3	115.18 (19)

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

Lattice parameters (Å, °), space groups and references for A₂M(BO₃)₂ compounds top

Formula	a	b	c	β	Z	Space group	Reference
Ba₂Ca(BO₃)₂	9.362 (2)	5.432 (2)	6.635 (2)	119.38 (1)	2	C2/m	Akella & Keszler (1995)
Ba₂Cd(BO₃)₂	9.6305 (4)	5.3626 (3)	6.5236 (2)	118.079 (3)	2	C2/m	Zhang et al. (2011b)
Sr₂Mg(BO₃)₂	9.046 (4)	5.1579 (9)	6.103 (3)	118.691	2	C2/m	Chen et al. (2007)
Ba₂Co(BO₃)₂	11.9784 (4)	5.3256 (2)	10.3220 (3)	117.494 (1)	4	C2/m	This work
α-Sr₂Cu(BO₃)₂	5.707 (1)	8.796 (2)	6.027 (1)	116.98	2	P2₁/c	Smith & Keszler (1989)
Pb₂Cu(BO₃)₂	5.6311 (6)	8.7628 (9)	6.2025 (6)	115.706 (1)	2	P2₁/c	Pan et al. (2006)
Ba₂Cu(BO₃)₂	8.023 (1)	11.290 (1)	13.889 (1)		8	Pnma	Smith & Keszler (1990)
β-Sr₂Cu(BO₃)₂	7.612 (3)	10.854 (7)	13.503 (4)		8	Pnma	Smith & Keszler (1989)
Ba₂Zn(BO₃)₂	15.068 (2)	8.720 (2)	10.128 (3)		8	Pca2₁	Smith & Koliha (1994)
Ba₂Mg(BO₃)₂	5.343 (2)	5.343 (2)	16.520 (3)		3	R3m	Kokh et al. (2017)

Acknowledgements

The authors thank the Faculty of Science, Mohammed V University in Rabat, Morocco, for the X-ray data collection.

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