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ISSN: 2056-9890

High-pressure synthesis and crystal structure of SrGa4As4

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 GaIIIAs4 tetra­hedra or honeycomb-like layers built up from distorted ethane-like GaII2As6 units com­prising Ga—Ga bonds.

1. Chemical context

The ternary systems ATr–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[Kauzlarich, S. M. & Kuromoto, T. Y. (1991). Croat. Chem. Acta, 64, 343-352.]), as dimers, as chains (Stoyko et al., 2015[Stoyko, S., Voss, L., He, H. & Bobev, S. (2015). Crystals, 5, 433-446.]; He et al., 2012[He, H., Tyson, C., Saito, M. & Bobev, S. (2012). J. Solid State Chem. 188, 59-65.]), condensed to ethane-like Tr2As6 groups (Mathieu et al., 2008[Mathieu, J., Achey, R., Park, J., Purcell, K. M., Tozer, S. W. & Latturner, S. E. (2008). Chem. Mater. 20, 5675-5681.]; Goforth et al., 2009[Goforth, A. M., Hope, H., Condron, C. L., Kauzlarich, S. M., Jensen, N., Klavins, P., MaQuilon, S. & Fisk, Z. (2009). Chem. Mater. 21, 4480-4489.]; He et al., 2011[He, H., Stearrett, R., Nowak, E. R. & Bobev, S. (2011). Eur. J. Inorg. Chem. 2011, 4025-4036.]) or as large supertetra­hedral units (Weippert et al., 2019[Weippert, V., Haffner, A., Stamatopoulos, A. & Johrendt, D. (2019). J. Am. Chem. Soc. 141, 11245-11252.]). SrGa4As4 is the first high-pressure com­pound in this system and contains an unprecedented layer-like framework, thus expanding the structural variety of the ATr–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[link]). 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[Schimek, G. L., Pennington, W. T., Wood, P. T. & Kolis, J. W. (1996). J. Solid State Chem. 123, 277-284.]). 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[link]). 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[link]). 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[link]). 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 As1vi—Ga1A—Ga1Ai—As1iv and 119.3 (1)° for As2v—Ga1B—Ga1Bi—As2vii (for symmetry codes, see Fig. 4[link]). 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[Pauling, L. (1960). In The Nature of the Chemical Bond, 3rd ed. Ithaca: Cornell University Press.]). In com­parison, the trigonal pyramid around Ga1B is elongated, with Ga—As distances of 2.415 (4)–2.845 (2) Å.

[Figure 1]
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]
Figure 2
Edge- and corner-sharing GaAs4 tetra­hedra forming a layer with triangular voids viewed along [001].
[Figure 3]
Figure 3
Corner-sharing Ga2As6 dumbbells with disordered Ga positions forming a honeycomb-like layer viewed along [001].
[Figure 4]
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[link]. 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[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]) shows two clearly separated maxima justifying this approach. Structural data were standardized with STRUCTURE-TIDY (Gelato & Parthé, 1987[Gelato, L. M. & Parthé, E. (1987). J. Appl. Cryst. 20, 139-143.]).

Table 1
Experimental details

Crystal data
Chemical formula SrGa4As4
Mr 666.18
Crystal system, space group Trigonal, P3221
Temperature (K) 293
a, c (Å) 6.3615 (1), 16.5792 (2)
V3) 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[Bruker (2016). SAINT, APEX3 and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.])
Tmin, Tmax 0.446, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections 14966, 928, 918
Rint 0.034
(sin θ/λ)max−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
Δρmax, Δρmin (e Å−3) 0.51, −0.69
Absolute structure Flack x determined using 340 quotients [(I+) − (I)]/[(I+) + (I)] (Parsons et al., 2013[Parsons, S., Flack, H. D. & Wagner, T. (2013). Acta Cryst. B69, 249-259.])
Absolute structure parameter −0.024 (11)
Computer programs: SAINT (Bruker, 2016[Bruker (2016). SAINT, APEX3 and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]), APEX3 (Bruker, 2016[Bruker (2016). SAINT, APEX3 and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]), SUPERFLIP (Palatinus & Chapuis, 2007[Palatinus, L. & Chapuis, G. (2007). J. Appl. Cryst. 40, 786-790.]), EDMA (Palatinus et al., 2012[Palatinus, L., Prathapa, S. J. & van Smaalen, S. (2012). J. Appl. Cryst. 45, 575-580.]), SHELXL (Sheldrick, 2015[Sheldrick, G. M. (2015). Acta Cryst. C71, 3-8.]), DIAMOND (Brandenburg, 2014[Brandenburg, K. (2014). DIAMOND. Crystal Impact GbR, Bonn, Germany.]) and PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]).

Supporting information


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
SrGa4As4Dx = 5.711 Mg m3
Mr = 666.18Mo Kα radiation, λ = 0.71073 Å
Trigonal, P3221Cell parameters from 9912 reflections
a = 6.3615 (1) Åθ = 3.7–30.4°
c = 16.5792 (2) ŵ = 37.42 mm1
V = 581.05 (2) Å3T = 293 K
Z = 3Block, black
F(000) = 8820.10 × 0.05 × 0.05 mm
Data collection top
Bruker APEXII D8 Quest CCD
diffractometer
928 independent reflections
Radiation source: Iµ S918 reflections with I > 2σ(I)
Goebel Mirror monochromatorRint = 0.034
combined φ and ω scansθmax = 27.9°, θmin = 3.7°
Absorption correction: multi-scan
(SADABS; Bruker, 2016)
h = 88
Tmin = 0.446, Tmax = 0.746k = 88
14966 measured reflectionsl = 2121
Refinement top
Refinement on F2Primary atom site location: iterative
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.012 w = 1/[σ2(Fo2) + (0.0102P)2 + 0.3943P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.025(Δ/σ)max < 0.001
S = 1.17Δρmax = 0.51 e Å3
928 reflectionsΔρmin = 0.69 e Å3
52 parametersAbsolute structure: Flack x determined using 340 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
0 restraintsAbsolute 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
xyzUiso*/UeqOcc. (<1)
Sr10.52374 (8)0.0000000.1666670.01264 (11)
Ga1A0.8090 (7)0.9427 (8)0.8779 (2)0.0120 (4)0.5
Ga1B0.8516 (7)0.9303 (8)0.8920 (2)0.0175 (5)0.5
Ga20.27470 (8)0.54448 (7)0.00800 (2)0.00988 (9)
As10.50915 (7)0.49019 (6)0.11634 (2)0.00817 (8)
As20.86593 (6)0.17439 (6)0.00577 (2)0.00838 (8)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Sr10.01406 (18)0.0121 (2)0.0111 (2)0.00605 (12)0.00104 (9)0.00209 (17)
Ga1A0.0136 (10)0.0079 (6)0.0131 (10)0.0044 (6)0.0032 (6)0.0001 (6)
Ga1B0.0184 (13)0.0080 (7)0.0206 (13)0.0025 (7)0.0107 (9)0.0018 (8)
Ga20.0105 (2)0.00988 (18)0.01119 (18)0.00654 (16)0.00233 (16)0.00109 (14)
As10.00767 (16)0.00801 (17)0.00862 (16)0.00376 (14)0.00032 (13)0.00041 (12)
As20.00712 (16)0.00890 (17)0.00970 (17)0.00444 (14)0.00033 (13)0.00055 (13)
Geometric parameters (Å, º) top
Sr1—As23.2665 (4)Ga1A—As1xii2.477 (4)
Sr1—As2i3.2666 (4)Ga1A—As2xiii2.503 (4)
Sr1—As1i3.2739 (4)Ga1A—Ga1Bxiv2.5444 (13)
Sr1—As13.2739 (4)Ga1A—Ga1Axiv2.572 (8)
Sr1—As1ii3.3048 (4)Ga1A—As1xv2.694 (2)
Sr1—As1iii3.3048 (4)Ga1B—As2xiii2.415 (4)
Sr1—Ga1Biv3.312 (4)Ga1B—As1xii2.515 (4)
Sr1—Ga1Bv3.312 (4)Ga1B—Ga1Bxiv2.542 (8)
Sr1—Ga1Avi3.346 (4)Ga1B—As2xvi2.845 (2)
Sr1—Ga1Avii3.346 (4)Ga2—As2viii2.4384 (5)
Sr1—Ga2viii3.3505 (4)Ga2—As12.4668 (5)
Sr1—Ga2ix3.3506 (4)Ga2—As2xvii2.4868 (5)
Sr1—As2x3.4560 (4)Ga2—As1viii2.5470 (5)
Sr1—As2xi3.4560 (4)Ga2—Ga2viii2.9844 (8)
As2—Sr1—As2i120.45 (2)Ga1Axiv—Ga1B—As2xvi89.08 (12)
As2—Sr1—As1i134.533 (8)As2xiii—Ga1B—Sr1xviii142.90 (10)
As2i—Sr1—As1i78.453 (9)As1xii—Ga1B—Sr1xviii67.51 (9)
As2—Sr1—As178.453 (9)Ga1Bxiv—Ga1B—Sr1xviii67.43 (7)
As2i—Sr1—As1134.533 (8)Ga1Axiv—Ga1B—Sr1xviii72.45 (15)
As1i—Sr1—As1119.39 (2)As2xvi—Ga1B—Sr1xviii63.55 (6)
As2—Sr1—As1ii79.285 (11)As2xiii—Ga1B—Sr1xv67.96 (9)
As2i—Sr1—As1ii74.128 (11)As1xii—Ga1B—Sr1xv137.34 (9)
As1i—Sr1—As1ii66.217 (5)Ga1Bxiv—Ga1B—Sr1xv68.95 (7)
As1—Sr1—As1ii150.471 (11)Ga1Axiv—Ga1B—Sr1xv64.32 (16)
As2—Sr1—As1iii74.128 (11)As2xvi—Ga1B—Sr1xv119.38 (13)
As2i—Sr1—As1iii79.284 (11)Sr1xviii—Ga1B—Sr1xv136.38 (13)
As1i—Sr1—As1iii150.470 (11)As2xiii—Ga1B—Sr1xix100.06 (10)
As1—Sr1—As1iii66.217 (5)As1xii—Ga1B—Sr1xix39.58 (5)
As1ii—Sr1—As1iii124.89 (2)Ga1Bxiv—Ga1B—Sr1xix118.30 (16)
As2—Sr1—Ga1Biv51.25 (5)Ga1Axiv—Ga1B—Sr1xix125.48 (7)
As2i—Sr1—Ga1Biv73.07 (5)As2xvi—Ga1B—Sr1xix138.21 (12)
As1i—Sr1—Ga1Biv109.71 (7)Sr1xviii—Ga1B—Sr1xix101.86 (10)
As1—Sr1—Ga1Biv126.49 (6)Sr1xv—Ga1B—Sr1xix98.42 (5)
As1ii—Sr1—Ga1Biv44.67 (7)As2xiii—Ga1B—Sr1xiii30.22 (6)
As1iii—Sr1—Ga1Biv81.77 (7)As1xii—Ga1B—Sr1xiii86.93 (10)
As2—Sr1—Ga1Bv73.07 (5)Ga1Bxiv—Ga1B—Sr1xiii155.24 (14)
As2i—Sr1—Ga1Bv51.25 (5)Ga1Axiv—Ga1B—Sr1xiii146.47 (15)
As1i—Sr1—Ga1Bv126.49 (6)As2xvi—Ga1B—Sr1xiii80.65 (8)
As1—Sr1—Ga1Bv109.71 (7)Sr1xviii—Ga1B—Sr1xiii128.07 (9)
As1ii—Sr1—Ga1Bv81.77 (7)Sr1xv—Ga1B—Sr1xiii93.16 (8)
As1iii—Sr1—Ga1Bv44.67 (7)Sr1xix—Ga1B—Sr1xiii80.08 (6)
Ga1Biv—Sr1—Ga1Bv45.14 (14)As2viii—Ga2—As1127.996 (19)
As2—Sr1—Ga1Avi111.75 (6)As2viii—Ga2—As2xvii101.790 (19)
As2i—Sr1—Ga1Avi123.12 (5)As1—Ga2—As2xvii107.308 (18)
As1i—Sr1—Ga1Avi48.02 (5)As2viii—Ga2—As1viii112.107 (18)
As1—Sr1—Ga1Avi74.76 (5)As1—Ga2—As1viii100.790 (19)
As1ii—Sr1—Ga1Avi95.97 (6)As2xvii—Ga2—As1viii104.987 (18)
As1iii—Sr1—Ga1Avi138.60 (6)As2viii—Ga2—Ga2viii160.190 (16)
Ga1Biv—Sr1—Ga1Avi135.24 (5)As1—Ga2—Ga2viii54.718 (14)
Ga1Bv—Sr1—Ga1Avi174.30 (10)As2xvii—Ga2—Ga2viii94.821 (13)
As2—Sr1—Ga1Avii123.12 (5)As1viii—Ga2—Ga2viii52.245 (14)
As2i—Sr1—Ga1Avii111.75 (6)As2viii—Ga2—Sr1xx66.554 (14)
As1i—Sr1—Ga1Avii74.76 (5)As1—Ga2—Sr1xx164.526 (19)
As1—Sr1—Ga1Avii48.02 (5)As2xvii—Ga2—Sr1xx70.850 (14)
As1ii—Sr1—Ga1Avii138.60 (6)As1viii—Ga2—Sr1xx65.805 (12)
As1iii—Sr1—Ga1Avii95.97 (7)Ga2viii—Ga2—Sr1xx109.825 (18)
Ga1Biv—Sr1—Ga1Avii174.30 (10)As2viii—Ga2—Sr1xxi65.922 (13)
Ga1Bv—Sr1—Ga1Avii135.23 (5)As1—Ga2—Sr1xxi62.098 (13)
Ga1Avi—Sr1—Ga1Avii45.20 (14)As2xvii—Ga2—Sr1xxi126.697 (18)
As2—Sr1—Ga2viii43.223 (9)As1viii—Ga2—Sr1xxi128.043 (18)
As2i—Sr1—Ga2viii161.548 (17)Ga2viii—Ga2—Sr1xxi112.066 (16)
As1i—Sr1—Ga2viii118.760 (14)Sr1xx—Ga2—Sr1xxi131.844 (12)
As1—Sr1—Ga2viii45.205 (10)As2viii—Ga2—Sr1xvii94.008 (14)
As1ii—Sr1—Ga2viii105.550 (10)As1—Ga2—Sr1xvii87.434 (14)
As1iii—Sr1—Ga2viii86.374 (9)As2xvii—Ga2—Sr1xvii33.956 (10)
Ga1Biv—Sr1—Ga2viii93.55 (5)As1viii—Ga2—Sr1xvii137.041 (15)
Ga1Bv—Sr1—Ga2viii110.30 (5)Ga2viii—Ga2—Sr1xvii105.802 (10)
Ga1Avi—Sr1—Ga2viii75.33 (5)Sr1xx—Ga2—Sr1xvii97.358 (11)
Ga1Avii—Sr1—Ga2viii81.05 (6)Sr1xxi—Ga2—Sr1xvii93.202 (9)
As2—Sr1—Ga2ix161.548 (17)As2viii—Ga2—Sr1154.513 (14)
As2i—Sr1—Ga2ix43.223 (9)As1—Ga2—Sr129.480 (10)
As1i—Sr1—Ga2ix45.205 (10)As2xvii—Ga2—Sr184.221 (13)
As1—Sr1—Ga2ix118.759 (14)As1viii—Ga2—Sr189.655 (14)
As1ii—Sr1—Ga2ix86.374 (9)Ga2viii—Ga2—Sr137.413 (11)
As1iii—Sr1—Ga2ix105.549 (10)Sr1xx—Ga2—Sr1137.673 (13)
Ga1Biv—Sr1—Ga2ix110.30 (5)Sr1xxi—Ga2—Sr190.483 (9)
Ga1Bv—Sr1—Ga2ix93.55 (5)Sr1xvii—Ga2—Sr177.087 (5)
Ga1Avi—Sr1—Ga2ix81.05 (6)As2viii—Ga2—Sr1xxii123.013 (14)
Ga1Avii—Sr1—Ga2ix75.33 (5)As1—Ga2—Sr1xxii78.871 (13)
Ga2viii—Sr1—Ga2ix154.42 (2)As2xvii—Ga2—Sr1xxii117.500 (15)
As2—Sr1—As2x69.230 (6)As1viii—Ga2—Sr1xxii22.713 (10)
As2i—Sr1—As2x150.543 (8)Ga2viii—Ga2—Sr1xxii37.772 (10)
As1i—Sr1—As2x76.839 (11)Sr1xx—Ga2—Sr1xxii88.357 (8)
As1—Sr1—As2x72.738 (10)Sr1xxi—Ga2—Sr1xxii111.288 (14)
As1ii—Sr1—As2x81.367 (9)Sr1xvii—Ga2—Sr1xxii141.184 (8)
As1iii—Sr1—As2x129.115 (8)Sr1—Ga2—Sr1xxii73.220 (6)
Ga1Biv—Sr1—As2x100.60 (6)Ga2—As1—Ga1Axii114.64 (6)
Ga1Bv—Sr1—As2x140.87 (6)Ga2—As1—Ga1Bxii105.91 (6)
Ga1Avi—Sr1—As2x43.14 (7)Ga1Axii—As1—Ga1Bxii9.02 (9)
Ga1Avii—Sr1—As2x76.71 (7)Ga2—As1—Ga2viii73.038 (18)
Ga2viii—Sr1—As2x42.823 (9)Ga1Axii—As1—Ga2viii96.32 (10)
Ga2ix—Sr1—As2x120.222 (14)Ga1Bxii—As1—Ga2viii96.14 (9)
As2—Sr1—As2xi150.543 (8)Ga2—As1—Ga1Avii98.03 (9)
As2i—Sr1—As2xi69.230 (6)Ga1Axii—As1—Ga1Avii141.90 (4)
As1i—Sr1—As2xi72.738 (10)Ga1Bxii—As1—Ga1Avii147.27 (17)
As1—Sr1—As2xi76.839 (11)Ga2viii—As1—Ga1Avii112.22 (9)
As1ii—Sr1—As2xi129.114 (8)Ga2—As1—Sr1128.755 (16)
As1iii—Sr1—As2xi81.366 (9)Ga1Axii—As1—Sr1102.71 (6)
Ga1Biv—Sr1—As2xi140.87 (6)Ga1Bxii—As1—Sr1111.12 (6)
Ga1Bv—Sr1—As2xi100.60 (6)Ga2viii—As1—Sr168.989 (12)
Ga1Avi—Sr1—As2xi76.71 (7)Ga1Avii—As1—Sr167.39 (9)
Ga1Avii—Sr1—As2xi43.14 (7)Ga2—As1—Sr1xxi76.628 (13)
Ga2viii—Sr1—As2xi120.222 (14)Ga1Axii—As1—Sr1xxi73.33 (8)
Ga2ix—Sr1—As2xi42.823 (9)Ga1Bxii—As1—Sr1xxi67.82 (8)
As2x—Sr1—As2xi117.382 (19)Ga2viii—As1—Sr1xxi139.977 (16)
As1xii—Ga1A—As2xiii114.84 (16)Ga1Avii—As1—Sr1xxi97.23 (9)
As1xii—Ga1A—Ga1Bxiv119.2 (2)Sr1—As1—Sr1xxi150.472 (11)
As2xiii—Ga1A—Ga1Bxiv121.43 (16)Ga2—As1—Sr1xvii65.908 (13)
As1xii—Ga1A—Ga1Axiv127.04 (14)Ga1Axii—As1—Sr1xvii161.16 (10)
As2xiii—Ga1A—Ga1Axiv112.61 (17)Ga1Bxii—As1—Sr1xvii156.82 (8)
Ga1Bxiv—Ga1A—Ga1Axiv8.82 (9)Ga2viii—As1—Sr1xvii101.547 (13)
As1xii—Ga1A—As1xv87.94 (10)Ga1Avii—As1—Sr1xvii32.12 (9)
As2xiii—Ga1A—As1xv107.20 (13)Sr1—As1—Sr1xvii89.333 (9)
Ga1Bxiv—Ga1A—As1xv95.81 (13)Sr1xxi—As1—Sr1xvii89.018 (12)
Ga1Axiv—Ga1A—As1xv99.49 (15)Ga1Bxxiii—As2—Ga2viii109.16 (6)
As1xii—Ga1A—Sr1xv151.81 (10)Ga1Bxxiii—As2—Ga2xxiv107.80 (10)
As2xiii—Ga1A—Sr1xv70.77 (10)Ga2viii—As2—Ga2xxiv111.741 (17)
Ga1Bxiv—Ga1A—Sr1xv72.42 (16)Ga1Bxxiii—As2—Ga1Axxiii8.97 (10)
Ga1Axiv—Ga1A—Sr1xv67.40 (7)Ga2viii—As2—Ga1Axxiii100.47 (6)
As1xv—Ga1A—Sr1xv64.59 (7)Ga2xxiv—As2—Ga1Axxiii110.18 (10)
As1xii—Ga1A—Sr1xviii64.22 (9)Ga1Bxxiii—As2—Ga1Biv88.49 (12)
As2xiii—Ga1A—Sr1xviii128.43 (8)Ga2viii—As2—Ga1Biv133.38 (9)
Ga1Bxiv—Ga1A—Sr1xviii63.92 (16)Ga2xxiv—As2—Ga1Biv102.40 (9)
Ga1Axiv—Ga1A—Sr1xviii68.55 (7)Ga1Axxiii—As2—Ga1Biv96.31 (10)
As1xv—Ga1A—Sr1xviii123.83 (13)Ga1Bxxiii—As2—Sr1127.93 (10)
Sr1xv—Ga1A—Sr1xviii135.95 (13)Ga2viii—As2—Sr170.223 (14)
As1xii—Ga1A—Sr1xix44.97 (5)Ga2xxiv—As2—Sr1120.879 (15)
As2xiii—Ga1A—Sr1xix105.82 (11)Ga1Axxiii—As2—Sr1128.03 (10)
Ga1Bxiv—Ga1A—Sr1xix127.80 (7)Ga1Biv—As2—Sr165.20 (9)
Ga1Axiv—Ga1A—Sr1xix135.48 (17)Ga1Bxxiii—As2—Sr1xxii71.67 (8)
As1xv—Ga1A—Sr1xix46.51 (6)Ga2viii—As2—Sr1xxii73.974 (13)
Sr1xv—Ga1A—Sr1xix107.02 (6)Ga2xxiv—As2—Sr1xxii66.325 (12)
Sr1xviii—Ga1A—Sr1xix104.00 (10)Ga1Axxiii—As2—Sr1xxii66.09 (8)
As1xii—Ga1A—Sr1xiii85.55 (10)Ga1Biv—As2—Sr1xxii151.44 (9)
As2xiii—Ga1A—Sr1xiii29.68 (6)Sr1—As2—Sr1xxii143.341 (12)
Ga1Bxiv—Ga1A—Sr1xiii149.64 (10)Ga1Bxxiii—As2—Sr1xxv21.56 (6)
Ga1Axiv—Ga1A—Sr1xiii140.99 (16)Ga2viii—As2—Sr1xxv128.411 (14)
As1xv—Ga1A—Sr1xiii102.85 (10)Ga2xxiv—As2—Sr1xxv103.930 (14)
Sr1xv—Ga1A—Sr1xiii94.16 (9)Ga1Axxiii—As2—Sr1xxv30.44 (6)
Sr1xviii—Ga1A—Sr1xiii120.80 (7)Ga1Biv—As2—Sr1xxv68.27 (8)
Sr1xix—Ga1A—Sr1xiii81.80 (6)Sr1—As2—Sr1xxv120.158 (9)
As2xiii—Ga1B—As1xii116.66 (16)Sr1xxii—As2—Sr1xxv88.418 (8)
As2xiii—Ga1B—Ga1Bxiv125.23 (17)Ga1Bxxiii—As2—Sr1xxvi139.37 (9)
As1xii—Ga1B—Ga1Bxiv117.83 (16)Ga2viii—As2—Sr1xxvi97.627 (13)
As2xiii—Ga1B—Ga1Axiv116.7 (2)Ga2xxiv—As2—Sr1xxvi32.041 (11)
As1xii—Ga1B—Ga1Axiv126.56 (18)Ga1Axxiii—As2—Sr1xxvi142.22 (10)
Ga1Bxiv—Ga1B—Ga1Axiv8.90 (9)Ga1Biv—As2—Sr1xxvi94.88 (8)
As2xiii—Ga1B—As2xvi80.20 (9)Sr1—As2—Sr1xxvi89.306 (7)
As1xii—Ga1B—As2xvi102.75 (11)Sr1xxii—As2—Sr1xxvi87.812 (8)
Ga1Bxiv—Ga1B—As2xvi93.10 (15)Sr1xxv—As2—Sr1xxvi130.398 (9)
Symmetry codes: (i) xy, y, z+1/3; (ii) x, y1, z; (iii) xy+1, y+1, z+1/3; (iv) y, x1, z+1; (v) x+y+1, x+1, z2/3; (vi) y1, x1, z+1; (vii) x+y, x+1, z2/3; (viii) y, x, z; (ix) x+y, x, z+1/3; (x) y, x1, 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, xy+1, z+2/3; (xvi) y+1, x, z+1; (xvii) x1, y, z; (xviii) y+1, xy, z+2/3; (xix) y, xy, z+2/3; (xx) y, xy, z1/3; (xxi) x, y+1, z; (xxii) y+1, xy, z1/3; (xxiii) x, y1, z1; (xxiv) x+1, y, z; (xxv) y+1, xy1, z1/3; (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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