High-pressure synthesis and crystal structure of SrGa4As4

Weippert, V.; Johrendt, D.

doi:10.1107/S2056989019013562

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Volume 75| Part 11| November 2019| Pages 1643-1645

https://doi.org/10.1107/S2056989019013562

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High-pressure synthesis and crystal structure of SrGa₄As₄

Valentin Weippert ^a and Dirk Johrendt ^a ^*

^aLudwig-Maximilians-Universität München, Butenandtstrasse 5-13, D-81377 München, Germany
^*Correspondence e-mail: johrendt@lmu.de

Edited by M. Weil, Vienna University of Technology, Austria (Received 13 September 2019; accepted 4 October 2019; online 22 October 2019)

Strontium tetragallate(II,III) tetraarsenide, SrGa₄As₄, was synthesized in a Walker-type multianvil apparatus under high-pressure/high-temperature conditions of 8 GPa and 1573 K. The compound crystallizes in a new structure type (P3₂21, Z = 3) as a three-dimensional (3D) framework of corner-sharing SrAs₈ quadratic antiprisms with strontium situated on a twofold rotation axis (Wyckoff position 3b). This arrangement is surrounded by a 3D framework which can be described as alternately stacked layers of either condensed Ga^IIIAs₄ tetrahedra or honeycomb-like layers built up from distorted ethane-like Ga^II₂As₆ units comprising Ga—Ga bonds.

Keywords: crystal structure; strontium; gallium; arsenic; high-pressure synthesis.

CCDC references: 1957548; 1957548

1. Chemical context

The ternary systems A–Tr–As (A = Ca, Sr or Ba; Tr = Ga or In) contain numerous compounds with different crystal structures based on TrAs₄ tetrahedra which occur isolated (Kauzlarich & Kuromoto, 1991 ), as dimers, as chains (Stoyko et al., 2015 ; He et al., 2012 ), condensed to ethane-like Tr₂As₆ groups (Mathieu et al., 2008 ; Goforth et al., 2009 ; He et al., 2011 ) or as large supertetrahedral units (Weippert et al., 2019 ). SrGa₄As₄ is the first high-pressure compound in this system and contains an unprecedented layer-like framework, thus expanding the structural variety of the A–Tr–As family.

2. Structural commentary

SrGa₄As₄ crystallizes in the space group P3₂21 (No. 154) and constitutes a new structure type. Strontium is coordinated in a quadratic antiprismatic manner by eight As atoms (Fig. 1). The antiprisms are slightly distorted, with their quadratic planes twisted by ∼34° relative to each other instead of 45° for an ideal quadratic antiprism. Sr—As distances range from 3.2665 (4) to 3.4560 (4) Å. The SrAs₈ polyhedra are connected through common corners, each As atom shared by two quadratic antiprisms, building up a three-dimensional (3D) framework. A similar structural motif is known for RbAg₂SbS₄, which crystallizes in the space group P3₁21 (Schimek et al., 1996 ). The surrounding construct in the two crystal structures differs however. SrGa₄As₄ contains a 3D Ga/As framework that can be subdivided into two types of layers with an AB stacking sequence along the c axis. The first type is built up from corner- and edge-sharing GaAs₄ tetrahedra forming sheets with triangular voids (Fig. 2). The tetrahedra are distorted, with angles in the range of 100.790 (19)–127.996 (19)°, and have typical Ga—As distances of 2.4384 (5)–2.5470 (5) Å. The second layer type consists of distorted ethane-like Ga₂As₆ groups with nearly eclipsed conformations. The Ga₂As₆ groups are connected via common corners, forming a honeycomb-like sheet (Fig. 3). The Ga1A and Ga1B positions of the Ga–Ga dumbbell are disordered and were treated with split positions having an occupancy of 50% each (Fig. 4). The coordination of each of these Ga sites consists of three As atoms and one Ga atom forming trigonal pyramids, showing torsion angles of 114.5 (1)° for As1^vi—Ga1A—Ga1Aⁱ—As1^iv and 119.3 (1)° for As2^v—Ga1B—Ga1Bⁱ—As2^vii (for symmetry codes, see Fig. 4). The Ga—Ga distances range between 2.542 (8) and 2.572 (8) Å and are considered as Ga—Ga bonds, which is consistent with a charge-neutral compound. Ga—As distances between 2.477 (4) and 2.694 (2) Å for Ga1A are near to the covalent radii sum of 2.46 Å (Pauling, 1960 ). In comparison, the trigonal pyramid around Ga1B is elongated, with Ga—As distances of 2.415 (4)–2.845 (2) Å.

Figure 1
The unit cell of SrGa₄As₄, viewed along [ $[\overline{1}]$ $[\overline{1}]$ 0], with the quadratic antiprismatic strontium coordination spheres shown as red polyhedra.

Figure 2
Edge- and corner-sharing GaAs₄ tetrahedra forming a layer with triangular voids viewed along [001].

Figure 3
Corner-sharing Ga₂As₆ dumbbells with disordered Ga positions forming a honeycomb-like layer viewed along [001].

Figure 4
Ga₂As₆ groups with disordered Ga positions having an occupancy of 50%. Displacement ellipsoids are drawn at the 95% probability level. [Symmetry codes: (i) −x + 2, −x + y + 1, −z + $[{5\over 3}]$ ; (ii) y, x, −z + 1; (iii) x, y + 1, z + 1; (iv) y + 1, x + 1, −z + 1; (v) y + 1, x, −z + 1; (vi) −y + 1, x − y + 1 z + $[{2\over 3}]$ ; (vii) −y + 1, x − y, z + $[{2\over 3}]$ ; (viii) −y + 2, x − y + 1, z + $[{2\over 3}]$ ; (ix) −x + 2, −x + y + 2, −z + $[{2\over 3}]$ .]

3. Synthesis and crystallization

The starting material SrAs was synthesized by heating stoichiometric amounts of Sr (Sigma–Aldrich, 99.95%) and As (Alfa Aesar, 99.99999+%) in alumina crucibles, sealed in silica ampules under an atmosphere of purified argon for 20 h at 1223 K. The title compound was obtained via high-pressure synthesis using a modified Walker-type multianvil set-up driven by a 1000 t hydraulic press (Voggenreiter, Mainleus, Germany). A Cr₂O₃-substituted (6%) MgO octahedron (Ceramic Substrates & Components, Isle of Wight, UK) with an edge length of 18 mm, housing a ZrO₂ sleeve with graphite sleeves (Schunk, Heuchelheim, Germany) for heating and a h-BN crucible (Henze, Kempten, Germany), was compressed with tungsten carbide cubes (Hawedia, Marklkofen, Germany) with an edge length of 11 mm. The starting materials SrAs (73.4 mg, 0.452 mmol), Ga (66.5 mg, 0.953 mmol, Alfa Aesar, 99.999%) and As (60.1 mg, 0.802 mmol) were mixed in a glove-box (H₂O, O₂ <1 ppm) and filled into the octahedron assembly. The reaction was carried out at 8 GPa and 1573 K, with a dwell time of 3 h. The temperature was increased and decreased over a period of 1 h. The assembly was opened in a glove-box, revealing crystals with a metallic luster.

The composition of SrGa₄As₄ was verified by EDX measurements using a a Carl Zeiss EVO-MA 10 instrument with a Bruker Nano EDX detector. The experimental values [Sr 12 (1) at%, Ga 44 (2) at% and As 45 (1) at%] are in excellent agreement with the expected values (Sr 11.1 at%, Ga 44.4 at% and As 44.4 at%) within the typical error of the method, and confirm the composition obtained from single-crystal X-ray diffraction data.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. The Ga1A and Ga1B positions were introduced as half-occupied split positions since one fully occupied position with a prolate ellipsoid caused residual densities in the order of 2.2 e Å⁻³. Upon exclusion of the Ga1A/Ga1B positions, the contour difference map in PLATON (Spek, 2009 ) shows two clearly separated maxima justifying this approach. Structural data were standardized with STRUCTURE-TIDY (Gelato & Parthé, 1987 ).

Table 1
Experimental details

Crystal data
Chemical formula	SrGa₄As₄
M_r	666.18
Crystal system, space group	Trigonal, P3₂21
Temperature (K)	293
a, c (Å)	6.3615 (1), 16.5792 (2)
V (Å³)	581.05 (2)
Z	3
Radiation type	Mo Kα
μ (mm⁻¹)	37.42
Crystal size (mm)	0.10 × 0.05 × 0.05

Data collection
Diffractometer	Bruker APEXII D8 Quest CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2016 )
T_min, T_max	0.446, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	14966, 928, 918
R_int	0.034
(sin θ/λ)_max (Å⁻¹)	0.657

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.012, 0.025, 1.17
No. of reflections	928
No. of parameters	52
Δρ_max, Δρ_min (e Å⁻³)	0.51, −0.69
Absolute structure	Flack x determined using 340 quotients [(I⁺) − (I⁻)]/[(I⁺) + (I⁻)] (Parsons et al., 2013 )
Absolute structure parameter	−0.024 (11)
Computer programs: SAINT (Bruker, 2016), APEX3 (Bruker, 2016), SUPERFLIP (Palatinus & Chapuis, 2007 ), EDMA (Palatinus et al., 2012 ), SHELXL (Sheldrick, 2015 ), DIAMOND (Brandenburg, 2014 ) and PLATON (Spek, 2009).

Supporting information

CCDC references: 1957548; 1957548

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S2056989019013562/wm5523sup1.cif

checkCIF report

Computing details top

Data collection: SAINT (Bruker, 2016); cell refinement: APEX3 (Bruker, 2016); data reduction: APEX3 (Bruker, 2016); program(s) used to solve structure: SUPERFLIP (Palatinus & Chapuis, 2007) and EDMA (Palatinus et al., 2012); program(s) used to refine structure: SHELXL (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2014); software used to prepare material for publication: PLATON (Spek, 2009).

Strontium tetragallate(II,III) tetraarsenide top

Crystal data top

SrGa₄As₄	D_x = 5.711 Mg m⁻³
M_r = 666.18	Mo Kα radiation, λ = 0.71073 Å
Trigonal, P3₂21	Cell parameters from 9912 reflections
a = 6.3615 (1) Å	θ = 3.7–30.4°
c = 16.5792 (2) Å	µ = 37.42 mm⁻¹
V = 581.05 (2) Å³	T = 293 K
Z = 3	Block, black
F(000) = 882	0.10 × 0.05 × 0.05 mm

Data collection top

Bruker APEXII D8 Quest CCD diffractometer	928 independent reflections
Radiation source: Iµ S	918 reflections with I > 2σ(I)
Goebel Mirror monochromator	R_int = 0.034
combined φ and ω scans	θ_max = 27.9°, θ_min = 3.7°
Absorption correction: multi-scan (SADABS; Bruker, 2016)	h = −8→8
T_min = 0.446, T_max = 0.746	k = −8→8
14966 measured reflections	l = −21→21

Refinement top

Refinement on F²	Primary atom site location: iterative
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.012	w = 1/[σ²(F_o²) + (0.0102P)² + 0.3943P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.025	(Δ/σ)_max < 0.001
S = 1.17	Δρ_max = 0.51 e Å⁻³
928 reflections	Δρ_min = −0.69 e Å⁻³
52 parameters	Absolute structure: Flack x determined using 340 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
0 restraints	Absolute structure parameter: −0.024 (11)

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	Occ. (<1)
Sr1	0.52374 (8)	0.000000	0.166667	0.01264 (11)
Ga1A	0.8090 (7)	0.9427 (8)	0.8779 (2)	0.0120 (4)	0.5
Ga1B	0.8516 (7)	0.9303 (8)	0.8920 (2)	0.0175 (5)	0.5
Ga2	0.27470 (8)	0.54448 (7)	0.00800 (2)	0.00988 (9)
As1	0.50915 (7)	0.49019 (6)	0.11634 (2)	0.00817 (8)
As2	0.86593 (6)	0.17439 (6)	0.00577 (2)	0.00838 (8)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Sr1	0.01406 (18)	0.0121 (2)	0.0111 (2)	0.00605 (12)	0.00104 (9)	0.00209 (17)
Ga1A	0.0136 (10)	0.0079 (6)	0.0131 (10)	0.0044 (6)	0.0032 (6)	0.0001 (6)
Ga1B	0.0184 (13)	0.0080 (7)	0.0206 (13)	0.0025 (7)	0.0107 (9)	−0.0018 (8)
Ga2	0.0105 (2)	0.00988 (18)	0.01119 (18)	0.00654 (16)	−0.00233 (16)	−0.00109 (14)
As1	0.00767 (16)	0.00801 (17)	0.00862 (16)	0.00376 (14)	−0.00032 (13)	0.00041 (12)
As2	0.00712 (16)	0.00890 (17)	0.00970 (17)	0.00444 (14)	0.00033 (13)	0.00055 (13)

Geometric parameters (Å, º) top

Sr1—As2	3.2665 (4)	Ga1A—As1^xii	2.477 (4)
Sr1—As2ⁱ	3.2666 (4)	Ga1A—As2^xiii	2.503 (4)
Sr1—As1ⁱ	3.2739 (4)	Ga1A—Ga1B^xiv	2.5444 (13)
Sr1—As1	3.2739 (4)	Ga1A—Ga1A^xiv	2.572 (8)
Sr1—As1ⁱⁱ	3.3048 (4)	Ga1A—As1^xv	2.694 (2)
Sr1—As1ⁱⁱⁱ	3.3048 (4)	Ga1B—As2^xiii	2.415 (4)
Sr1—Ga1B^iv	3.312 (4)	Ga1B—As1^xii	2.515 (4)
Sr1—Ga1B^v	3.312 (4)	Ga1B—Ga1B^xiv	2.542 (8)
Sr1—Ga1A^vi	3.346 (4)	Ga1B—As2^xvi	2.845 (2)
Sr1—Ga1A^vii	3.346 (4)	Ga2—As2^viii	2.4384 (5)
Sr1—Ga2^viii	3.3505 (4)	Ga2—As1	2.4668 (5)
Sr1—Ga2^ix	3.3506 (4)	Ga2—As2^xvii	2.4868 (5)
Sr1—As2^x	3.4560 (4)	Ga2—As1^viii	2.5470 (5)
Sr1—As2^xi	3.4560 (4)	Ga2—Ga2^viii	2.9844 (8)

As2—Sr1—As2ⁱ	120.45 (2)	Ga1A^xiv—Ga1B—As2^xvi	89.08 (12)
As2—Sr1—As1ⁱ	134.533 (8)	As2^xiii—Ga1B—Sr1^xviii	142.90 (10)
As2ⁱ—Sr1—As1ⁱ	78.453 (9)	As1^xii—Ga1B—Sr1^xviii	67.51 (9)
As2—Sr1—As1	78.453 (9)	Ga1B^xiv—Ga1B—Sr1^xviii	67.43 (7)
As2ⁱ—Sr1—As1	134.533 (8)	Ga1A^xiv—Ga1B—Sr1^xviii	72.45 (15)
As1ⁱ—Sr1—As1	119.39 (2)	As2^xvi—Ga1B—Sr1^xviii	63.55 (6)
As2—Sr1—As1ⁱⁱ	79.285 (11)	As2^xiii—Ga1B—Sr1^xv	67.96 (9)
As2ⁱ—Sr1—As1ⁱⁱ	74.128 (11)	As1^xii—Ga1B—Sr1^xv	137.34 (9)
As1ⁱ—Sr1—As1ⁱⁱ	66.217 (5)	Ga1B^xiv—Ga1B—Sr1^xv	68.95 (7)
As1—Sr1—As1ⁱⁱ	150.471 (11)	Ga1A^xiv—Ga1B—Sr1^xv	64.32 (16)
As2—Sr1—As1ⁱⁱⁱ	74.128 (11)	As2^xvi—Ga1B—Sr1^xv	119.38 (13)
As2ⁱ—Sr1—As1ⁱⁱⁱ	79.284 (11)	Sr1^xviii—Ga1B—Sr1^xv	136.38 (13)
As1ⁱ—Sr1—As1ⁱⁱⁱ	150.470 (11)	As2^xiii—Ga1B—Sr1^xix	100.06 (10)
As1—Sr1—As1ⁱⁱⁱ	66.217 (5)	As1^xii—Ga1B—Sr1^xix	39.58 (5)
As1ⁱⁱ—Sr1—As1ⁱⁱⁱ	124.89 (2)	Ga1B^xiv—Ga1B—Sr1^xix	118.30 (16)
As2—Sr1—Ga1B^iv	51.25 (5)	Ga1A^xiv—Ga1B—Sr1^xix	125.48 (7)
As2ⁱ—Sr1—Ga1B^iv	73.07 (5)	As2^xvi—Ga1B—Sr1^xix	138.21 (12)
As1ⁱ—Sr1—Ga1B^iv	109.71 (7)	Sr1^xviii—Ga1B—Sr1^xix	101.86 (10)
As1—Sr1—Ga1B^iv	126.49 (6)	Sr1^xv—Ga1B—Sr1^xix	98.42 (5)
As1ⁱⁱ—Sr1—Ga1B^iv	44.67 (7)	As2^xiii—Ga1B—Sr1^xiii	30.22 (6)
As1ⁱⁱⁱ—Sr1—Ga1B^iv	81.77 (7)	As1^xii—Ga1B—Sr1^xiii	86.93 (10)
As2—Sr1—Ga1B^v	73.07 (5)	Ga1B^xiv—Ga1B—Sr1^xiii	155.24 (14)
As2ⁱ—Sr1—Ga1B^v	51.25 (5)	Ga1A^xiv—Ga1B—Sr1^xiii	146.47 (15)
As1ⁱ—Sr1—Ga1B^v	126.49 (6)	As2^xvi—Ga1B—Sr1^xiii	80.65 (8)
As1—Sr1—Ga1B^v	109.71 (7)	Sr1^xviii—Ga1B—Sr1^xiii	128.07 (9)
As1ⁱⁱ—Sr1—Ga1B^v	81.77 (7)	Sr1^xv—Ga1B—Sr1^xiii	93.16 (8)
As1ⁱⁱⁱ—Sr1—Ga1B^v	44.67 (7)	Sr1^xix—Ga1B—Sr1^xiii	80.08 (6)
Ga1B^iv—Sr1—Ga1B^v	45.14 (14)	As2^viii—Ga2—As1	127.996 (19)
As2—Sr1—Ga1A^vi	111.75 (6)	As2^viii—Ga2—As2^xvii	101.790 (19)
As2ⁱ—Sr1—Ga1A^vi	123.12 (5)	As1—Ga2—As2^xvii	107.308 (18)
As1ⁱ—Sr1—Ga1A^vi	48.02 (5)	As2^viii—Ga2—As1^viii	112.107 (18)
As1—Sr1—Ga1A^vi	74.76 (5)	As1—Ga2—As1^viii	100.790 (19)
As1ⁱⁱ—Sr1—Ga1A^vi	95.97 (6)	As2^xvii—Ga2—As1^viii	104.987 (18)
As1ⁱⁱⁱ—Sr1—Ga1A^vi	138.60 (6)	As2^viii—Ga2—Ga2^viii	160.190 (16)
Ga1B^iv—Sr1—Ga1A^vi	135.24 (5)	As1—Ga2—Ga2^viii	54.718 (14)
Ga1B^v—Sr1—Ga1A^vi	174.30 (10)	As2^xvii—Ga2—Ga2^viii	94.821 (13)
As2—Sr1—Ga1A^vii	123.12 (5)	As1^viii—Ga2—Ga2^viii	52.245 (14)
As2ⁱ—Sr1—Ga1A^vii	111.75 (6)	As2^viii—Ga2—Sr1^xx	66.554 (14)
As1ⁱ—Sr1—Ga1A^vii	74.76 (5)	As1—Ga2—Sr1^xx	164.526 (19)
As1—Sr1—Ga1A^vii	48.02 (5)	As2^xvii—Ga2—Sr1^xx	70.850 (14)
As1ⁱⁱ—Sr1—Ga1A^vii	138.60 (6)	As1^viii—Ga2—Sr1^xx	65.805 (12)
As1ⁱⁱⁱ—Sr1—Ga1A^vii	95.97 (7)	Ga2^viii—Ga2—Sr1^xx	109.825 (18)
Ga1B^iv—Sr1—Ga1A^vii	174.30 (10)	As2^viii—Ga2—Sr1^xxi	65.922 (13)
Ga1B^v—Sr1—Ga1A^vii	135.23 (5)	As1—Ga2—Sr1^xxi	62.098 (13)
Ga1A^vi—Sr1—Ga1A^vii	45.20 (14)	As2^xvii—Ga2—Sr1^xxi	126.697 (18)
As2—Sr1—Ga2^viii	43.223 (9)	As1^viii—Ga2—Sr1^xxi	128.043 (18)
As2ⁱ—Sr1—Ga2^viii	161.548 (17)	Ga2^viii—Ga2—Sr1^xxi	112.066 (16)
As1ⁱ—Sr1—Ga2^viii	118.760 (14)	Sr1^xx—Ga2—Sr1^xxi	131.844 (12)
As1—Sr1—Ga2^viii	45.205 (10)	As2^viii—Ga2—Sr1^xvii	94.008 (14)
As1ⁱⁱ—Sr1—Ga2^viii	105.550 (10)	As1—Ga2—Sr1^xvii	87.434 (14)
As1ⁱⁱⁱ—Sr1—Ga2^viii	86.374 (9)	As2^xvii—Ga2—Sr1^xvii	33.956 (10)
Ga1B^iv—Sr1—Ga2^viii	93.55 (5)	As1^viii—Ga2—Sr1^xvii	137.041 (15)
Ga1B^v—Sr1—Ga2^viii	110.30 (5)	Ga2^viii—Ga2—Sr1^xvii	105.802 (10)
Ga1A^vi—Sr1—Ga2^viii	75.33 (5)	Sr1^xx—Ga2—Sr1^xvii	97.358 (11)
Ga1A^vii—Sr1—Ga2^viii	81.05 (6)	Sr1^xxi—Ga2—Sr1^xvii	93.202 (9)
As2—Sr1—Ga2^ix	161.548 (17)	As2^viii—Ga2—Sr1	154.513 (14)
As2ⁱ—Sr1—Ga2^ix	43.223 (9)	As1—Ga2—Sr1	29.480 (10)
As1ⁱ—Sr1—Ga2^ix	45.205 (10)	As2^xvii—Ga2—Sr1	84.221 (13)
As1—Sr1—Ga2^ix	118.759 (14)	As1^viii—Ga2—Sr1	89.655 (14)
As1ⁱⁱ—Sr1—Ga2^ix	86.374 (9)	Ga2^viii—Ga2—Sr1	37.413 (11)
As1ⁱⁱⁱ—Sr1—Ga2^ix	105.549 (10)	Sr1^xx—Ga2—Sr1	137.673 (13)
Ga1B^iv—Sr1—Ga2^ix	110.30 (5)	Sr1^xxi—Ga2—Sr1	90.483 (9)
Ga1B^v—Sr1—Ga2^ix	93.55 (5)	Sr1^xvii—Ga2—Sr1	77.087 (5)
Ga1A^vi—Sr1—Ga2^ix	81.05 (6)	As2^viii—Ga2—Sr1^xxii	123.013 (14)
Ga1A^vii—Sr1—Ga2^ix	75.33 (5)	As1—Ga2—Sr1^xxii	78.871 (13)
Ga2^viii—Sr1—Ga2^ix	154.42 (2)	As2^xvii—Ga2—Sr1^xxii	117.500 (15)
As2—Sr1—As2^x	69.230 (6)	As1^viii—Ga2—Sr1^xxii	22.713 (10)
As2ⁱ—Sr1—As2^x	150.543 (8)	Ga2^viii—Ga2—Sr1^xxii	37.772 (10)
As1ⁱ—Sr1—As2^x	76.839 (11)	Sr1^xx—Ga2—Sr1^xxii	88.357 (8)
As1—Sr1—As2^x	72.738 (10)	Sr1^xxi—Ga2—Sr1^xxii	111.288 (14)
As1ⁱⁱ—Sr1—As2^x	81.367 (9)	Sr1^xvii—Ga2—Sr1^xxii	141.184 (8)
As1ⁱⁱⁱ—Sr1—As2^x	129.115 (8)	Sr1—Ga2—Sr1^xxii	73.220 (6)
Ga1B^iv—Sr1—As2^x	100.60 (6)	Ga2—As1—Ga1A^xii	114.64 (6)
Ga1B^v—Sr1—As2^x	140.87 (6)	Ga2—As1—Ga1B^xii	105.91 (6)
Ga1A^vi—Sr1—As2^x	43.14 (7)	Ga1A^xii—As1—Ga1B^xii	9.02 (9)
Ga1A^vii—Sr1—As2^x	76.71 (7)	Ga2—As1—Ga2^viii	73.038 (18)
Ga2^viii—Sr1—As2^x	42.823 (9)	Ga1A^xii—As1—Ga2^viii	96.32 (10)
Ga2^ix—Sr1—As2^x	120.222 (14)	Ga1B^xii—As1—Ga2^viii	96.14 (9)
As2—Sr1—As2^xi	150.543 (8)	Ga2—As1—Ga1A^vii	98.03 (9)
As2ⁱ—Sr1—As2^xi	69.230 (6)	Ga1A^xii—As1—Ga1A^vii	141.90 (4)
As1ⁱ—Sr1—As2^xi	72.738 (10)	Ga1B^xii—As1—Ga1A^vii	147.27 (17)
As1—Sr1—As2^xi	76.839 (11)	Ga2^viii—As1—Ga1A^vii	112.22 (9)
As1ⁱⁱ—Sr1—As2^xi	129.114 (8)	Ga2—As1—Sr1	128.755 (16)
As1ⁱⁱⁱ—Sr1—As2^xi	81.366 (9)	Ga1A^xii—As1—Sr1	102.71 (6)
Ga1B^iv—Sr1—As2^xi	140.87 (6)	Ga1B^xii—As1—Sr1	111.12 (6)
Ga1B^v—Sr1—As2^xi	100.60 (6)	Ga2^viii—As1—Sr1	68.989 (12)
Ga1A^vi—Sr1—As2^xi	76.71 (7)	Ga1A^vii—As1—Sr1	67.39 (9)
Ga1A^vii—Sr1—As2^xi	43.14 (7)	Ga2—As1—Sr1^xxi	76.628 (13)
Ga2^viii—Sr1—As2^xi	120.222 (14)	Ga1A^xii—As1—Sr1^xxi	73.33 (8)
Ga2^ix—Sr1—As2^xi	42.823 (9)	Ga1B^xii—As1—Sr1^xxi	67.82 (8)
As2^x—Sr1—As2^xi	117.382 (19)	Ga2^viii—As1—Sr1^xxi	139.977 (16)
As1^xii—Ga1A—As2^xiii	114.84 (16)	Ga1A^vii—As1—Sr1^xxi	97.23 (9)
As1^xii—Ga1A—Ga1B^xiv	119.2 (2)	Sr1—As1—Sr1^xxi	150.472 (11)
As2^xiii—Ga1A—Ga1B^xiv	121.43 (16)	Ga2—As1—Sr1^xvii	65.908 (13)
As1^xii—Ga1A—Ga1A^xiv	127.04 (14)	Ga1A^xii—As1—Sr1^xvii	161.16 (10)
As2^xiii—Ga1A—Ga1A^xiv	112.61 (17)	Ga1B^xii—As1—Sr1^xvii	156.82 (8)
Ga1B^xiv—Ga1A—Ga1A^xiv	8.82 (9)	Ga2^viii—As1—Sr1^xvii	101.547 (13)
As1^xii—Ga1A—As1^xv	87.94 (10)	Ga1A^vii—As1—Sr1^xvii	32.12 (9)
As2^xiii—Ga1A—As1^xv	107.20 (13)	Sr1—As1—Sr1^xvii	89.333 (9)
Ga1B^xiv—Ga1A—As1^xv	95.81 (13)	Sr1^xxi—As1—Sr1^xvii	89.018 (12)
Ga1A^xiv—Ga1A—As1^xv	99.49 (15)	Ga1B^xxiii—As2—Ga2^viii	109.16 (6)
As1^xii—Ga1A—Sr1^xv	151.81 (10)	Ga1B^xxiii—As2—Ga2^xxiv	107.80 (10)
As2^xiii—Ga1A—Sr1^xv	70.77 (10)	Ga2^viii—As2—Ga2^xxiv	111.741 (17)
Ga1B^xiv—Ga1A—Sr1^xv	72.42 (16)	Ga1B^xxiii—As2—Ga1A^xxiii	8.97 (10)
Ga1A^xiv—Ga1A—Sr1^xv	67.40 (7)	Ga2^viii—As2—Ga1A^xxiii	100.47 (6)
As1^xv—Ga1A—Sr1^xv	64.59 (7)	Ga2^xxiv—As2—Ga1A^xxiii	110.18 (10)
As1^xii—Ga1A—Sr1^xviii	64.22 (9)	Ga1B^xxiii—As2—Ga1B^iv	88.49 (12)
As2^xiii—Ga1A—Sr1^xviii	128.43 (8)	Ga2^viii—As2—Ga1B^iv	133.38 (9)
Ga1B^xiv—Ga1A—Sr1^xviii	63.92 (16)	Ga2^xxiv—As2—Ga1B^iv	102.40 (9)
Ga1A^xiv—Ga1A—Sr1^xviii	68.55 (7)	Ga1A^xxiii—As2—Ga1B^iv	96.31 (10)
As1^xv—Ga1A—Sr1^xviii	123.83 (13)	Ga1B^xxiii—As2—Sr1	127.93 (10)
Sr1^xv—Ga1A—Sr1^xviii	135.95 (13)	Ga2^viii—As2—Sr1	70.223 (14)
As1^xii—Ga1A—Sr1^xix	44.97 (5)	Ga2^xxiv—As2—Sr1	120.879 (15)
As2^xiii—Ga1A—Sr1^xix	105.82 (11)	Ga1A^xxiii—As2—Sr1	128.03 (10)
Ga1B^xiv—Ga1A—Sr1^xix	127.80 (7)	Ga1B^iv—As2—Sr1	65.20 (9)
Ga1A^xiv—Ga1A—Sr1^xix	135.48 (17)	Ga1B^xxiii—As2—Sr1^xxii	71.67 (8)
As1^xv—Ga1A—Sr1^xix	46.51 (6)	Ga2^viii—As2—Sr1^xxii	73.974 (13)
Sr1^xv—Ga1A—Sr1^xix	107.02 (6)	Ga2^xxiv—As2—Sr1^xxii	66.325 (12)
Sr1^xviii—Ga1A—Sr1^xix	104.00 (10)	Ga1A^xxiii—As2—Sr1^xxii	66.09 (8)
As1^xii—Ga1A—Sr1^xiii	85.55 (10)	Ga1B^iv—As2—Sr1^xxii	151.44 (9)
As2^xiii—Ga1A—Sr1^xiii	29.68 (6)	Sr1—As2—Sr1^xxii	143.341 (12)
Ga1B^xiv—Ga1A—Sr1^xiii	149.64 (10)	Ga1B^xxiii—As2—Sr1^xxv	21.56 (6)
Ga1A^xiv—Ga1A—Sr1^xiii	140.99 (16)	Ga2^viii—As2—Sr1^xxv	128.411 (14)
As1^xv—Ga1A—Sr1^xiii	102.85 (10)	Ga2^xxiv—As2—Sr1^xxv	103.930 (14)
Sr1^xv—Ga1A—Sr1^xiii	94.16 (9)	Ga1A^xxiii—As2—Sr1^xxv	30.44 (6)
Sr1^xviii—Ga1A—Sr1^xiii	120.80 (7)	Ga1B^iv—As2—Sr1^xxv	68.27 (8)
Sr1^xix—Ga1A—Sr1^xiii	81.80 (6)	Sr1—As2—Sr1^xxv	120.158 (9)
As2^xiii—Ga1B—As1^xii	116.66 (16)	Sr1^xxii—As2—Sr1^xxv	88.418 (8)
As2^xiii—Ga1B—Ga1B^xiv	125.23 (17)	Ga1B^xxiii—As2—Sr1^xxvi	139.37 (9)
As1^xii—Ga1B—Ga1B^xiv	117.83 (16)	Ga2^viii—As2—Sr1^xxvi	97.627 (13)
As2^xiii—Ga1B—Ga1A^xiv	116.7 (2)	Ga2^xxiv—As2—Sr1^xxvi	32.041 (11)
As1^xii—Ga1B—Ga1A^xiv	126.56 (18)	Ga1A^xxiii—As2—Sr1^xxvi	142.22 (10)
Ga1B^xiv—Ga1B—Ga1A^xiv	8.90 (9)	Ga1B^iv—As2—Sr1^xxvi	94.88 (8)
As2^xiii—Ga1B—As2^xvi	80.20 (9)	Sr1—As2—Sr1^xxvi	89.306 (7)
As1^xii—Ga1B—As2^xvi	102.75 (11)	Sr1^xxii—As2—Sr1^xxvi	87.812 (8)
Ga1B^xiv—Ga1B—As2^xvi	93.10 (15)	Sr1^xxv—As2—Sr1^xxvi	130.398 (9)

Symmetry codes: (i) x−y, −y, −z+1/3; (ii) x, y−1, z; (iii) x−y+1, −y+1, −z+1/3; (iv) y, x−1, −z+1; (v) −x+y+1, −x+1, z−2/3; (vi) y−1, x−1, −z+1; (vii) −x+y, −x+1, z−2/3; (viii) y, x, −z; (ix) −x+y, −x, z+1/3; (x) y, x−1, −z; (xi) −x+y+1, −x+1, z+1/3; (xii) y, x, −z+1; (xiii) x, y+1, z+1; (xiv) −x+2, −x+y+1, −z+5/3; (xv) −y+1, x−y+1, z+2/3; (xvi) y+1, x, −z+1; (xvii) x−1, y, z; (xviii) −y+1, x−y, z+2/3; (xix) −y, x−y, z+2/3; (xx) −y, x−y, z−1/3; (xxi) x, y+1, z; (xxii) −y+1, x−y, z−1/3; (xxiii) x, y−1, z−1; (xxiv) x+1, y, z; (xxv) −y+1, x−y−1, z−1/3; (xxvi) x+1, y+1, z.

Acknowledgements

We thank Lucien Eisenburger for assistance with the high pressure synthesis. Funding for this research was provided by Deutsche Forschungsgemeinschaft.

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