A novel monoclinic phase of impurity-doped CaGa2S4 as a phosphor with high emission intensity

Suzuki, A.; Takizawa, T.; Hidaka, C.; Shigetaka, N.; Kitajima, I.

doi:10.1107/S1600536812019113

inorganic compounds

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Volume 68| Part 6| June 2012| Page i42

doi:10.1107/S1600536812019113

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A novel monoclinic phase of impurity-doped CaGa₂S₄ as a phosphor with high emission intensity

Akihiro Suzuki,^a ^* Takeo Takizawa,^a Chiharu Hidaka,^a Nomura Shigetaka ^b and Ittetsu Kitajima ^a

^aDepartment of Physics,College of Humanities and Sciences, Nihon University, 3-25-40 Sakura-josui, Setagaya-ku, Tokyo 156-8550, Japan, and ^bDepartment of Electrical Engineering, Faculty of Engineering, Tokyo University of Science, 1-14-6 Kudan-kita, Chiyoda-ku, Tokyo 102-0073, Japan
^*Correspondence e-mail: akihiro_k_s_z_b@yahoo.co.jp

(Received 13 March 2012; accepted 28 April 2012; online 12 May 2012)

In the solid-state synthesis of impurity-doped CaGa₂S₄, calcium tetrathiodigallate(III), a novel phosphor material (denominated as the X-phase), with monoclinic symmetry in the space group P2₁/a, has been discovered. Its emission intensity is higher than that of the known orthorhombic polymorph of CaGa₂S₄ crystallizing in the space group Fddd. The asymmetric unit of the monoclinic phase consists of two Ca, four Ga and eight S sites. Each of the Ca and Ga atoms is surrounded by seven and four sulfide ions, respectively, thereby sharing each of the sulfur sites with the nearest neighbours. In contrast, the corresponding sites in the orthorhombic phase are surrounded by eight and four S atoms, respectively. The photoluminescence peaks from Mn²⁺ and Ce³⁺ in the doped X-phase, both of which are supposed to replace Ca²⁺ ions, have been observed to shift towards the high energy side in comparison with those in the orthorhombic phase. This suggests that the crystal field around the Mn²⁺ and Ce³⁺ ions in the X-phase is weaker than that in the orthorhombic phase.

Related literature

For the crystal structure of the orthorhombic form of CaGa₂S₄, see: Eisenmann et al. (1983 ). For the emission properties of CaGa₂S₄, see: Peters & Baglio (1972 ); Georgobiani et al. (1995 ); Bessière et al. (2004 ); Takizawa & Hidaka (2008 ). For synthetic details, see: Boitier et al. (2009 ); Obonai et al. (2009 ). For the Mn²⁺ emission properties in various compounds, see: Barthou et al. (1994 ); Provenzano & White (1991 ); Wang et al. (2003 ). For crystallographic background, see: Carruthers & Watkin (1979 ).

Experimental

Crystal data

CaGa₂S₄
M_r = 307.76
Monoclinic, P 2₁ /a
a = 6.841 (3) Å
b = 27.069 (9) Å
c = 7.231 (3) Å
β = 109.413 (5)°
V = 1262.9 (8) Å³
Z = 8
Mo Kα radiation
μ = 10.52 mm⁻¹
T = 270 K
0.10 × 0.10 × 0.05 mm

Data collection

Rigaku Saturn724+ diffractometer
Absorption correction: multi-scan (REQABS; Jacobson, 1998 ) T_min = 0.417, T_max = 0.591
8869 measured reflections
2869 independent
256 reflections with F² > 2σ(F²)
R_int = 0.047

Refinement

R[F² > 2σ(F²)] = 0.038
wR(F²) = 0.050
S = 1.21
2869 reflections
127 parameters
Δρ_max = 2.64 e Å⁻³
Δρ_min = −3.10 e Å⁻³

Data collection: CrystalClear (Rigaku/MSC and Rigaku, 2006 ); cell refinement: CrystalClear; data reduction: CrystalStructure (Rigaku/MSC and Rigaku, 2006); program(s) used to solve structure: SIR92 (Altomare et al., 1994 ); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003 ); molecular graphics: VESTA 3 (Momma & Izumi, 2011 ); software used to prepare material for publication: CrystalStructure (Rigaku/MSC and Rigaku, 2006).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536812019113/wm2605sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536812019113/wm2605Isup2.hkl

checkCIF report

Comment top

The alkaline earth thiodigallates MGa₂S₄ (M = Ca, Sr, Ba) have been studied as candidates for phosphor host materials because of their various emissions when doped with a rare earth element (Peters & Baglio, 1972; Georgobiani et al., 1995; Bessière et al., 2004; Takizawa & Hidaka, 2008). Especially, CaGa₂S₄ doped with Ce³⁺ and Eu²⁺ shows strong blue and green emissions. This compound normally belongs to the orthorhombic system, crystallizing in space group Fddd (Eisenmann et al., 1983). However, in the synthesis of CaGa₂S₄ using solid state reactions, a novel phosphor (we call it the X-phase) has unexpectedly appeared. In this paper, the crystal structure of the X-phase investigated by powder and single-crystal X-ray diffraction (XRD) measurements is reported.

Powder XRD patterns of the X-phase are shown in Fig. 1. This phase happened to be generated when doped with one of the impurities such as Mn, Ge, Sn, La, Ce, Nd, Sm, Dy, intentionally incorporated as an activator of fluorescence or phosphorescence. Thus it is expected that the X-phase is strongly related with the dopant. However, detailed conditions how to prepare the X-phase from a directed preparation route have not been clarified yet. From the analysis of the single-crystal XRD data, the chemical formula of the compound in the X-phase was shown to be CaGa₂S₄. The simulation of the powder XRD pattern corresponds well to the experimental pattern as shown in Fig. 1. Hence we can conclude that the X-phase is a newly found polymorph of CaGa₂S₄.

The unit cell of the X-phase is shown in Figs. 2 and 3; the asymmetric unit consists of two Ca sites, four Ga sites and seven S sites. Figs. 4 and 5 show the environment of the cation sites in the unit cell. In the X-phase, each Ca site is surrounded by seven sulfur atoms forming a distorted enneahedron. Each of the involved sulfur atoms is shared by the adjacent one or two Ca sites and by two Ga sites. The Ca—S distances range from 2.8261 (10) to 3.0823 (13) Å. Each Ga site is tetrahedrally surrounded by sulfur atoms which are also shared by adjacent two Ca sites and two Ga sites. The Ga—S distances and the S—Ga—S angles range from 2.2254 (11) to 2.3116 (11) Å and from 93.54 (3) to 124.12 (3) °, respectively. In the orthorhombic phase, each of the three Ca sites and the two Ga sites is in an eightfold and fourfold coordination environment, respectively, by sulfur atoms. Each of the sulfur atoms of these sites is shared by adjacent two Ca sites and two Ga sites. The Ca—S distances in this polymorph range from 2.970 to 3.130 Å. The Ga—S distances and the S—Ga—S angles range from 2.240 to 2.318 Å and from 96.6 to 125°. It should be noted that the coordination number of the Ca sites in the X-phase is reduced by one compared to that of the orthorhombic phase, while the Ga sites are tetrahedrally surrounded in both phases. Nevertheless, the framework built up from the GaS₄ tetrahedra and their connection modes (corner and edge-sharing) is quite different in the two phases.

The intensities of photoluminescence from Mn²⁺ and Ce³⁺ in the X-phase were about four and eight times higher than those in the orthorhombic phase. These emission peaks shifted toward the high energy side in comparison with those in the orthorhombic phase. Mn²⁺ and Ce³⁺ ions are known to be very sensitive with respect to the crystal field (Peters & Baglio, 1972; Provenzano & White, 1991; Barthou et al., 1994; Wang et al., 2003). Thus the observed shifts of the emission peaks are assumed to be caused by a weakened crystal field originating from the decrease in the coordination number of the Ca sites in the X-phase.

Related literature top

For the crystal structure of the orthorhombic form of CaGa₂S₄, see: Eisenmann et al. (1983). For the emission properties of CaGa₂S₄, see: Peters & Baglio (1972); Georgobiani et al. (1995); Bessière et al. (2004); Takizawa & Hidaka (2008). For synthetic details, see: Boitier et al. (2009); Obonai et al. (2009). For the Mn²⁺ emission properties in various compounds, see: Barthou et al. (1994); Provenzano & White (1991); Wang et al. (2003). For crystallographic background, see: Carruthers & Watkin (1979).

Experimental top

A mixture of CaS (4 N) and Ga₂S₃ (6 N) was used as a starting material added with a small amount of a rare earth element (REE) or a transition metal (TM) as an activator. It was weighed to 0.5 g in total according to the formula Ca_1-_xM_xGa₂S₄ (M = REE or TM) (Boitier et al., 2009; Obonai et al., 2009). The mixture was carefully stirred to be homogenized under Ar atmosphere, and then sealed in a silica glass capsule under vacuum of 10 ^-4 Pa, where the inner surface of the capsule was coated with a carbon film to prevent the reaction between the starting materials and the container. It was sintered at 1411 K for 1 h. The X-phase samples were sometimes and unexpectedly synthesized and the detailed condition how and when the X-phase emerges has not been clarified yet.

Computing details top

Data collection: CrystalClear (Rigaku/MSC and Rigaku, 2006); cell refinement: CrystalClear (Rigaku/MSC and Rigaku, 2006); data reduction: CrystalStructure (Rigaku/MSC and Rigaku, 2006); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: VESTA 3 (Momma & Izumi, 2011); software used to prepare material for publication: CrystalStructure (Rigaku/MSC and Rigaku, 2006).

Figures top

	Fig. 1. Experimental and siumlated X-ray powder diffraction patterns of the X-phase of CaGa₂S₄ together with the known orthorhombic form for comparison.
	Fig. 2. The unit cell of the X-phase of CaGa₂S₄ viewed along [100].
	Fig. 3. The unit cell of the X-phase of CaGa₂S₄ viewed along [001].
	Fig. 4. The environment of the cation sites in the X-phase: Ca sites.
	Fig. 5. The environment of the cation sites in the X-phase: Ga sites.

calcium tetrathiodigallate(III) top

Crystal data top

CaGa₂S₄	F(000) = 1168.00
M_r = 307.76	D_x = 3.237 Mg m⁻³
Monoclinic, P2₁/a	Mo Kα radiation, λ = 0.71075 Å
Hall symbol: -P 2yab	Cell parameters from 3521 reflections
a = 6.841 (3) Å	θ = 3.2–27.5°
b = 27.069 (9) Å	µ = 10.52 mm⁻¹
c = 7.231 (3) Å	T = 270 K
β = 109.413 (5)°	Block, colorless
V = 1262.9 (8) Å³	0.10 × 0.10 × 0.05 mm
Z = 8

Data collection top

Rigaku Saturn724+ diffractometer	2869 independent reflections
Graphite monochromator	256 reflections with F² > 2σ(F²)
Detector resolution: 7.31 pixels mm^-1	R_int = 0.047
ω scans	θ_max = 27.5°
Absorption correction: multi-scan (REQABS; Jacobson, 1998)	h = −8→6
T_min = 0.417, T_max = 0.591	k = −35→26
8869 measured reflections	l = −9→9

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
R[F² > 2σ(F²)] = 0.038	Secondary atom site location: difference Fourier map
wR(F²) = 0.050	Chebychev polynomial with 3 parameters (Carruthers & Watkin, 1979) 6334.0000 8721.6900 0.0000
S = 1.21	(Δ/σ)_max < 0.001
2869 reflections	Δρ_max = 2.64 e Å⁻³
127 parameters	Δρ_min = −3.10 e Å⁻³

Crystal data top

CaGa₂S₄	V = 1262.9 (8) Å³
M_r = 307.76	Z = 8
Monoclinic, P2₁/a	Mo Kα radiation
a = 6.841 (3) Å	µ = 10.52 mm⁻¹
b = 27.069 (9) Å	T = 270 K
c = 7.231 (3) Å	0.10 × 0.10 × 0.05 mm
β = 109.413 (5)°

Data collection top

Rigaku Saturn724+ diffractometer	2869 independent reflections
Absorption correction: multi-scan (REQABS; Jacobson, 1998)	256 reflections with F² > 2σ(F²)
T_min = 0.417, T_max = 0.591	R_int = 0.047
8869 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.038	127 parameters
wR(F²) = 0.050	Δρ_max = 2.64 e Å⁻³
S = 1.21	Δρ_min = −3.10 e Å⁻³
2869 reflections

Special details top

Geometry. ENTER SPECIAL DETAILS OF THE MOLECULAR GEOMETRY

Refinement. Refinement was performed using reflections with F² > 2.0 σ(F²). The weighted R-factor (wR) and goodness of fit (S) are based on F². R-factor (gt) are based on F. The threshold expression of F² > 2.0 σ(F²) is used only for calculating R-factor (gt).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Ga1	0.41763 (6)	0.234320 (10)	0.54983 (6)	0.01027 (10)
Ga2	0.63163 (6)	0.150170 (10)	0.29040 (6)	0.01047 (10)
Ga3	−0.05236 (6)	0.052250 (10)	0.27118 (6)	0.01054 (10)
Ga4	0.23350 (6)	0.064220 (10)	0.01510 (6)	0.01095 (10)
Ca1	−0.44242 (12)	0.07086 (3)	−0.32662 (11)	0.0133 (2)
Ca2	0.09658 (12)	0.19323 (3)	0.04330 (11)	0.0145 (2)
S1	−0.08531 (14)	0.09720 (3)	−0.01062 (13)	0.0114 (2)
S2	−0.13487 (14)	0.09906 (4)	0.49207 (13)	0.0125 (2)
S3	0.24485 (13)	0.25319 (4)	0.75754 (13)	0.0128 (2)
S4	0.37219 (14)	0.15701 (3)	0.42780 (13)	0.0115 (2)
S5	0.28330 (14)	0.02921 (3)	0.31401 (13)	0.0112 (2)
S6	0.30654 (14)	0.27904 (3)	0.26168 (13)	0.0114 (2)
S7	−0.26440 (15)	−0.01372 (4)	0.21648 (14)	0.0157 (2)
S8	0.42875 (14)	0.13001 (3)	−0.02150 (13)	0.0118 (2)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ga1	0.0099 (2)	0.0137 (2)	0.0084 (2)	0.00054 (16)	0.00453 (16)	−0.00112 (16)
Ga2	0.0109 (2)	0.0120 (2)	0.0094 (2)	0.00015 (16)	0.00450 (16)	−0.00010 (16)
Ga3	0.0111 (2)	0.0126 (2)	0.0100 (2)	0.00015 (16)	0.00645 (16)	−0.00067 (16)
Ga4	0.0114 (2)	0.0141 (2)	0.0091 (2)	−0.00123 (17)	0.00581 (16)	−0.00087 (16)
Ca1	0.0127 (4)	0.0164 (4)	0.0114 (3)	−0.0016 (3)	0.0049 (3)	0.0007 (3)
Ca2	0.0146 (4)	0.0145 (4)	0.0140 (4)	−0.0003 (3)	0.0044 (3)	−0.0005 (3)
S1	0.0106 (4)	0.0161 (4)	0.0078 (4)	0.0007 (3)	0.0037 (3)	0.0016 (3)
S2	0.0153 (4)	0.0151 (5)	0.0084 (4)	0.0037 (3)	0.0056 (3)	−0.0004 (3)
S3	0.0074 (4)	0.0234 (5)	0.0088 (4)	0.0017 (3)	0.0043 (3)	−0.0004 (3)
S4	0.0134 (4)	0.0118 (4)	0.0114 (4)	−0.0002 (3)	0.0069 (3)	−0.0008 (3)
S5	0.0118 (4)	0.0151 (4)	0.0070 (4)	0.0024 (3)	0.0035 (3)	0.0015 (3)
S6	0.0135 (5)	0.0130 (4)	0.0094 (4)	0.0015 (3)	0.0062 (3)	0.0006 (3)
S7	0.0197 (5)	0.0167 (5)	0.0168 (5)	−0.0072 (3)	0.0142 (4)	−0.0073 (3)
S8	0.0124 (4)	0.0145 (4)	0.0093 (4)	−0.0029 (3)	0.0049 (3)	−0.0019 (3)

Geometric parameters (Å, º) top

Ga1—S3	2.2569 (11)	Ga4—S8	2.2936 (9)
Ga1—S3ⁱ	2.2685 (8)	Ca1—S1	2.8261 (10)
Ga1—S4	2.2522 (8)	Ca1—S2^iv	2.9260 (14)
Ga1—S6	2.3090 (9)	Ca1—S4^v	2.9500 (11)
Ga2—S2ⁱⁱ	2.2458 (9)	Ca1—S5^v	2.8814 (10)
Ga2—S4	2.3116 (11)	Ca1—S5ⁱⁱⁱ	2.9095 (11)
Ga2—S6ⁱ	2.3048 (9)	Ca1—S7^vi	2.8480 (14)
Ga2—S8	2.2868 (8)	Ca1—S8^vii	3.0823 (13)
Ga3—S1	2.3190 (10)	Ca2—S1	2.8522 (11)
Ga3—S2	2.2526 (11)	Ca2—S3^iv	3.0538 (13)
Ga3—S5	2.2989 (10)	Ca2—S3^viii	2.9762 (10)
Ga3—S7	2.2513 (10)	Ca2—S4	2.9599 (10)
Ga4—S1	2.3062 (10)	Ca2—S6	2.9059 (11)
Ga4—S5	2.2795 (10)	Ca2—S6^ix	3.0127 (14)
Ga4—S7ⁱⁱⁱ	2.2254 (11)	Ca2—S8	3.0033 (13)

S5···S7^x	3.4654 (14)	S7···S5^x	3.4654 (14)

S3—Ga1—S3ⁱ	98.37 (3)	S3^iv—Ca2—S6^ix	130.31 (3)
S3—Ga1—S4	115.87 (4)	S3^iv—Ca2—S8	76.03 (3)
S3—Ga1—S6	113.19 (3)	S3^viii—Ca2—S4	158.30 (4)
S3ⁱ—Ga1—S4	112.04 (3)	S3^viii—Ca2—S6	97.31 (3)
S3ⁱ—Ga1—S6	118.40 (3)	S3^viii—Ca2—S6^ix	73.81 (3)
S4—Ga1—S6	99.93 (3)	S3^viii—Ca2—S8	130.42 (3)
S2ⁱⁱ—Ga2—S4	104.61 (3)	S4—Ca2—S6	73.08 (2)
S2ⁱⁱ—Ga2—S6ⁱ	106.99 (3)	S4—Ca2—S6^ix	85.13 (3)
S2ⁱⁱ—Ga2—S8	124.12 (3)	S4—Ca2—S8	71.28 (3)
S4—Ga2—S6ⁱ	117.90 (3)	S6—Ca2—S6^ix	78.97 (3)
S4—Ga2—S8	98.16 (3)	S6—Ca2—S8	106.10 (3)
S6ⁱ—Ga2—S8	105.82 (3)	S6^ix—Ca2—S8	152.63 (3)
S1—Ga3—S2	110.72 (3)	Ga3—S1—Ga4	85.00 (3)
S1—Ga3—S5	93.54 (3)	Ga3—S1—Ca1	112.55 (3)
S1—Ga3—S7	113.14 (3)	Ga3—S1—Ca2	116.58 (3)
S2—Ga3—S5	122.11 (3)	Ga4—S1—Ca1	120.51 (4)
S2—Ga3—S7	105.79 (4)	Ga4—S1—Ca2	89.07 (3)
S5—Ga3—S7	111.40 (3)	Ca1—S1—Ca2	124.13 (3)
S1—Ga4—S5	94.40 (3)	Ga2^vii—S2—Ga3	100.25 (3)
S1—Ga4—S7ⁱⁱⁱ	120.06 (3)	Ga2^vii—S2—Ca1^xi	89.39 (3)
S1—Ga4—S8	105.16 (3)	Ga3—S2—Ca1^xi	123.91 (4)
S5—Ga4—S7ⁱⁱⁱ	115.87 (3)	Ga1—S3—Ga1^ix	102.30 (3)
S5—Ga4—S8	121.53 (3)	Ga1—S3—Ca2^xi	134.04 (4)
S7ⁱⁱⁱ—Ga4—S8	100.69 (4)	Ga1—S3—Ca2^xii	95.21 (3)
S1—Ca1—S2^iv	74.89 (3)	Ga1^ix—S3—Ca2^xi	92.90 (3)
S1—Ca1—S4^v	111.74 (3)	Ga1^ix—S3—Ca2^xii	141.19 (4)
S1—Ca1—S5^v	163.07 (4)	Ca2^xi—S3—Ca2^xii	99.38 (3)
S1—Ca1—S5ⁱⁱⁱ	89.75 (3)	Ga1—S4—Ga2	102.54 (3)
S1—Ca1—S7^vi	114.26 (3)	Ga1—S4—Ca1^xiii	121.53 (3)
S1—Ca1—S8^vii	70.50 (3)	Ga1—S4—Ca2	91.27 (3)
S2^iv—Ca1—S4^v	75.72 (3)	Ga2—S4—Ca1^xiii	87.56 (3)
S2^iv—Ca1—S5^v	92.74 (3)	Ga2—S4—Ca2	87.89 (3)
S2^iv—Ca1—S5ⁱⁱⁱ	86.54 (3)	Ca1^xiii—S4—Ca2	147.08 (3)
S2^iv—Ca1—S7^vi	160.92 (4)	Ga3—S5—Ga4	86.08 (3)
S2^iv—Ca1—S8^vii	127.19 (3)	Ga3—S5—Ca1^xiii	109.71 (4)
S4^v—Ca1—S5^v	75.27 (2)	Ga3—S5—Ca1ⁱⁱⁱ	127.11 (3)
S4^v—Ca1—S5ⁱⁱⁱ	146.76 (4)	Ga4—S5—Ca1^xiii	122.66 (3)
S4^v—Ca1—S7^vi	113.32 (3)	Ga4—S5—Ca1ⁱⁱⁱ	110.69 (4)
S4^v—Ca1—S8^vii	81.50 (3)	Ca1^xiii—S5—Ca1ⁱⁱⁱ	102.20 (3)
S5^v—Ca1—S5ⁱⁱⁱ	77.80 (3)	Ga1—S6—Ga2^ix	112.31 (4)
S5^v—Ca1—S7^vi	74.43 (3)	Ga1—S6—Ca2	91.50 (3)
S5^v—Ca1—S8^vii	126.39 (3)	Ga1—S6—Ca2ⁱ	121.80 (3)
S5ⁱⁱⁱ—Ca1—S7^vi	77.09 (3)	Ga2^ix—S6—Ca2	122.40 (3)
S5ⁱⁱⁱ—Ca1—S8^vii	130.86 (3)	Ga2^ix—S6—Ca2ⁱ	106.99 (3)
S7^vi—Ca1—S8^vii	71.73 (3)	Ca2—S6—Ca2ⁱ	101.95 (3)
S1—Ca2—S3^iv	128.30 (3)	Ga3—S7—Ga4ⁱⁱⁱ	113.74 (5)
S1—Ca2—S3^viii	97.70 (3)	Ga3—S7—Ca1^vi	148.67 (5)
S1—Ca2—S4	86.52 (3)	Ga4ⁱⁱⁱ—S7—Ca1^vi	97.39 (4)
S1—Ca2—S6	156.52 (4)	Ga2—S8—Ga4	104.91 (4)
S1—Ca2—S6^ix	88.01 (3)	Ga2—S8—Ca1ⁱⁱ	127.28 (3)
S1—Ca2—S8	77.16 (3)	Ga2—S8—Ca2	87.30 (3)
S3^iv—Ca2—S3^viii	69.21 (3)	Ga4—S8—Ca1ⁱⁱ	89.73 (3)
S3^iv—Ca2—S4	124.09 (3)	Ga4—S8—Ca2	85.67 (3)
S3^iv—Ca2—S6	74.18 (3)	Ca1ⁱⁱ—S8—Ca2	144.97 (3)

S3—Ga1—S3ⁱ—Ga1ⁱ	−153.70 (4)	S5^v—Ca1—S2^iv—Ga3^iv	−38.96 (4)
S3—Ga1—S3ⁱ—Ca2^xii	−17.36 (4)	S2^iv—Ca1—S5ⁱⁱⁱ—Ga3ⁱⁱⁱ	33.05 (5)
S3ⁱ—Ga1—S3—Ga1^ix	163.03 (4)	S2^iv—Ca1—S5ⁱⁱⁱ—Ga4ⁱⁱⁱ	134.24 (3)
S3ⁱ—Ga1—S3—Ca2^xi	−90.54 (5)	S5ⁱⁱⁱ—Ca1—S2^iv—Ga3^iv	38.63 (4)
S3ⁱ—Ga1—S3—Ca2^xii	17.88 (4)	S2^iv—Ca1—S7^vi—Ga3^vi	−17.88 (16)
S3—Ga1—S4—Ga2	−167.10 (3)	S7^vi—Ca1—S2^iv—Ga3^iv	7.90 (13)
S3—Ga1—S4—Ca2	104.78 (3)	S2^iv—Ca1—S8^vii—Ga2^vii	−64.03 (6)
S3—Ga1—S4—Ca1^xiii	−72.20 (5)	S2^iv—Ca1—S8^vii—Ga4^vii	−172.68 (3)
S4—Ga1—S3—Ga1^ix	−77.44 (4)	S2^iv—Ca1—S8^vii—Ca2^vii	105.26 (6)
S4—Ga1—S3—Ca2^xi	28.99 (5)	S8^vii—Ca1—S2^iv—Ga3^iv	179.61 (3)
S4—Ga1—S3—Ca2^xii	137.40 (3)	S4^v—Ca1—S5^v—Ga3^v	−62.52 (4)
S3—Ga1—S6—Ca2	−106.34 (3)	S4^v—Ca1—S5^v—Ga4^v	35.72 (5)
S3—Ga1—S6—Ga2^ix	19.83 (5)	S5^v—Ca1—S4^v—Ga1^v	170.74 (5)
S3—Ga1—S6—Ca2ⁱ	148.59 (4)	S5^v—Ca1—S4^v—Ga2^v	−86.03 (3)
S6—Ga1—S3—Ga1^ix	37.16 (5)	S5^v—Ca1—S4^v—Ca2^v	−3.70 (8)
S6—Ga1—S3—Ca2^xi	143.58 (4)	S4^v—Ca1—S5ⁱⁱⁱ—Ga3ⁱⁱⁱ	90.16 (7)
S6—Ga1—S3—Ca2^xii	−108.00 (3)	S4^v—Ca1—S5ⁱⁱⁱ—Ga4ⁱⁱⁱ	−168.64 (6)
S3ⁱ—Ga1—S4—Ga2	−55.34 (4)	S5ⁱⁱⁱ—Ca1—S4^v—Ga1^v	−152.37 (6)
S3ⁱ—Ga1—S4—Ca2	−143.46 (3)	S5ⁱⁱⁱ—Ca1—S4^v—Ga2^v	−49.14 (7)
S3ⁱ—Ga1—S4—Ca1^xiii	39.56 (6)	S5ⁱⁱⁱ—Ca1—S4^v—Ca2^v	33.19 (13)
S4—Ga1—S3ⁱ—Ga1ⁱ	83.93 (5)	S4^v—Ca1—S7^vi—Ga3^vi	97.24 (8)
S4—Ga1—S3ⁱ—Ca2^xii	−139.73 (3)	S7^vi—Ca1—S4^v—Ga1^v	105.29 (5)
S3ⁱ—Ga1—S6—Ca2	139.35 (4)	S7^vi—Ca1—S4^v—Ga2^v	−151.48 (3)
S3ⁱ—Ga1—S6—Ga2^ix	−94.47 (5)	S7^vi—Ca1—S4^v—Ca2^v	−69.15 (9)
S3ⁱ—Ga1—S6—Ca2ⁱ	34.28 (5)	S4^v—Ca1—S8^vii—Ga2^vii	−128.79 (4)
S6—Ga1—S3ⁱ—Ga1ⁱ	−31.56 (5)	S4^v—Ca1—S8^vii—Ga4^vii	122.55 (3)
S6—Ga1—S3ⁱ—Ca2^xii	104.78 (4)	S4^v—Ca1—S8^vii—Ca2^vii	40.50 (7)
S4—Ga1—S6—Ca2	17.50 (4)	S8^vii—Ca1—S4^v—Ga1^v	39.47 (5)
S4—Ga1—S6—Ga2^ix	143.67 (4)	S8^vii—Ca1—S4^v—Ga2^v	142.70 (3)
S4—Ga1—S6—Ca2ⁱ	−87.57 (4)	S8^vii—Ca1—S4^v—Ca2^v	−134.97 (8)
S6—Ga1—S4—Ga2	70.95 (3)	S5^v—Ca1—S5ⁱⁱⁱ—Ga3ⁱⁱⁱ	126.60 (5)
S6—Ga1—S4—Ca2	−17.17 (4)	S5^v—Ca1—S5ⁱⁱⁱ—Ga4ⁱⁱⁱ	−132.21 (4)
S6—Ga1—S4—Ca1^xiii	165.85 (4)	S5ⁱⁱⁱ—Ca1—S5^v—Ga3^v	137.15 (4)
S2ⁱⁱ—Ga2—S4—Ga1	107.72 (3)	S5ⁱⁱⁱ—Ca1—S5^v—Ga4^v	−124.60 (5)
S2ⁱⁱ—Ga2—S4—Ca2	−161.45 (3)	S5^v—Ca1—S7^vi—Ga3^vi	31.29 (8)
S2ⁱⁱ—Ga2—S4—Ca1^xiii	−14.07 (3)	S7^vi—Ca1—S5^v—Ga3^v	57.35 (4)
S4—Ga2—S2ⁱⁱ—Ga3ⁱⁱ	138.58 (3)	S7^vi—Ca1—S5^v—Ga4^v	155.60 (5)
S2ⁱⁱ—Ga2—S6ⁱ—Ga1ⁱ	−68.55 (5)	S5^v—Ca1—S8^vii—Ga2^vii	166.65 (4)
S2ⁱⁱ—Ga2—S6ⁱ—Ca2ⁱ	−175.65 (4)	S5^v—Ca1—S8^vii—Ga4^vii	58.00 (4)
S6ⁱ—Ga2—S2ⁱⁱ—Ga3ⁱⁱ	−95.60 (4)	S5^v—Ca1—S8^vii—Ca2^vii	−24.06 (9)
S2ⁱⁱ—Ga2—S8—Ga4	61.50 (6)	S8^vii—Ca1—S5^v—Ga3^v	4.92 (6)
S2ⁱⁱ—Ga2—S8—Ca2	146.29 (4)	S8^vii—Ca1—S5^v—Ga4^v	103.16 (5)
S2ⁱⁱ—Ga2—S8—Ca1ⁱⁱ	−39.84 (7)	S5ⁱⁱⁱ—Ca1—S7^vi—Ga3^vi	−49.43 (8)
S8—Ga2—S2ⁱⁱ—Ga3ⁱⁱ	27.86 (6)	S7^vi—Ca1—S5ⁱⁱⁱ—Ga3ⁱⁱⁱ	−156.82 (5)
S4—Ga2—S6ⁱ—Ga1ⁱ	48.85 (4)	S7^vi—Ca1—S5ⁱⁱⁱ—Ga4ⁱⁱⁱ	−55.63 (3)
S4—Ga2—S6ⁱ—Ca2ⁱ	−58.25 (5)	S5ⁱⁱⁱ—Ca1—S8^vii—Ga2^vii	59.76 (6)
S6ⁱ—Ga2—S4—Ga1	−10.94 (4)	S5ⁱⁱⁱ—Ca1—S8^vii—Ga4^vii	−48.89 (4)
S6ⁱ—Ga2—S4—Ca2	79.88 (3)	S5ⁱⁱⁱ—Ca1—S8^vii—Ca2^vii	−130.95 (6)
S6ⁱ—Ga2—S4—Ca1^xiii	−132.73 (3)	S8^vii—Ca1—S5ⁱⁱⁱ—Ga3ⁱⁱⁱ	−105.41 (6)
S4—Ga2—S8—Ga4	−52.39 (4)	S8^vii—Ca1—S5ⁱⁱⁱ—Ga4ⁱⁱⁱ	−4.21 (6)
S4—Ga2—S8—Ca2	32.40 (3)	S7^vi—Ca1—S8^vii—Ga2^vii	113.12 (4)
S4—Ga2—S8—Ca1ⁱⁱ	−153.73 (4)	S7^vi—Ca1—S8^vii—Ga4^vii	4.47 (2)
S8—Ga2—S4—Ga1	−123.75 (3)	S7^vi—Ca1—S8^vii—Ca2^vii	−77.59 (6)
S8—Ga2—S4—Ca2	−32.92 (3)	S8^vii—Ca1—S7^vi—Ga3^vi	169.08 (8)
S8—Ga2—S4—Ca1^xiii	114.47 (2)	S1—Ca2—S3^iv—Ga1^iv	−40.82 (6)
S6ⁱ—Ga2—S8—Ga4	−174.53 (3)	S3^iv—Ca2—S1—Ga3	155.55 (4)
S6ⁱ—Ga2—S8—Ca2	−89.74 (3)	S3^iv—Ca2—S1—Ga4	71.61 (4)
S6ⁱ—Ga2—S8—Ca1ⁱⁱ	84.13 (5)	S3^iv—Ca2—S1—Ca1	−55.44 (7)
S8—Ga2—S6ⁱ—Ga1ⁱ	157.33 (3)	S1—Ca2—S3^viii—Ga1^viii	−114.19 (4)
S8—Ga2—S6ⁱ—Ca2ⁱ	50.23 (5)	S1—Ca2—S3^viii—Ca2^ix	109.55 (4)
S1—Ga3—S2—Ga2^vii	30.00 (4)	S3^viii—Ca2—S1—Ga3	−134.92 (4)
S1—Ga3—S2—Ca1^xi	126.23 (4)	S3^viii—Ca2—S1—Ga4	141.13 (3)
S2—Ga3—S1—Ga4	133.76 (3)	S3^viii—Ca2—S1—Ca1	14.08 (6)
S2—Ga3—S1—Ca1	−105.20 (4)	S1—Ca2—S4—Ga1	−154.26 (4)
S2—Ga3—S1—Ca2	47.31 (5)	S1—Ca2—S4—Ga2	103.24 (3)
S1—Ga3—S5—Ga4	−7.49 (3)	S1—Ca2—S4—Ca1^xiii	21.00 (9)
S1—Ga3—S5—Ca1^xiii	115.89 (3)	S4—Ca2—S1—Ga3	23.68 (4)
S1—Ga3—S5—Ca1ⁱⁱⁱ	−120.58 (4)	S4—Ca2—S1—Ga4	−60.26 (3)
S5—Ga3—S1—Ga4	7.41 (3)	S4—Ca2—S1—Ca1	172.69 (5)
S5—Ga3—S1—Ca1	128.44 (4)	S1—Ca2—S6—Ga1	17.08 (11)
S5—Ga3—S1—Ca2	−79.04 (4)	S1—Ca2—S6—Ga2^ix	−100.72 (10)
S1—Ga3—S7—Ga4ⁱⁱⁱ	54.29 (5)	S1—Ca2—S6—Ca2ⁱ	140.07 (9)
S1—Ga3—S7—Ca1^vi	−132.51 (7)	S6—Ca2—S1—Ga3	−5.63 (13)
S7—Ga3—S1—Ga4	−107.68 (3)	S6—Ca2—S1—Ga4	−89.57 (10)
S7—Ga3—S1—Ca1	13.35 (5)	S6—Ca2—S1—Ca1	143.38 (8)
S7—Ga3—S1—Ca2	165.87 (4)	S1—Ca2—S6^ix—Ga1^ix	136.61 (3)
S2—Ga3—S5—Ga4	−124.70 (4)	S1—Ca2—S6^ix—Ca2^ix	−124.02 (3)
S2—Ga3—S5—Ca1^xiii	−1.32 (5)	S6^ix—Ca2—S1—Ga3	−61.56 (4)
S2—Ga3—S5—Ca1ⁱⁱⁱ	122.21 (5)	S6^ix—Ca2—S1—Ga4	−145.50 (3)
S5—Ga3—S2—Ga2^vii	138.38 (3)	S6^ix—Ca2—S1—Ca1	87.45 (5)
S5—Ga3—S2—Ca1^xi	−125.39 (4)	S1—Ca2—S8—Ga2	−116.60 (3)
S2—Ga3—S7—Ga4ⁱⁱⁱ	175.67 (3)	S1—Ca2—S8—Ga4	−11.41 (2)
S2—Ga3—S7—Ca1^vi	−11.14 (9)	S1—Ca2—S8—Ca1ⁱⁱ	71.92 (6)
S7—Ga3—S2—Ga2^vii	−92.93 (4)	S8—Ca2—S1—Ga3	95.26 (4)
S7—Ga3—S2—Ca1^xi	3.30 (5)	S8—Ca2—S1—Ga4	11.32 (2)
S5—Ga3—S7—Ga4ⁱⁱⁱ	−49.58 (5)	S8—Ca2—S1—Ca1	−115.73 (5)
S5—Ga3—S7—Ca1^vi	123.62 (8)	S3^iv—Ca2—S3^viii—Ga1^viii	13.97 (3)
S7—Ga3—S5—Ga4	109.08 (3)	S3^iv—Ca2—S3^viii—Ca2^ix	−122.30 (3)
S7—Ga3—S5—Ca1^xiii	−127.55 (4)	S3^viii—Ca2—S3^iv—Ga1^iv	−124.07 (5)
S7—Ga3—S5—Ca1ⁱⁱⁱ	−4.01 (6)	S3^iv—Ca2—S4—Ga1	70.62 (5)
S1—Ga4—S5—Ga3	7.54 (3)	S3^iv—Ca2—S4—Ga2	−31.88 (4)
S1—Ga4—S5—Ca1^xiii	−103.42 (4)	S3^iv—Ca2—S4—Ca1^xiii	−114.12 (8)
S1—Ga4—S5—Ca1ⁱⁱⁱ	135.89 (3)	S4—Ca2—S3^iv—Ga1^iv	75.36 (6)
S5—Ga4—S1—Ga3	−7.48 (3)	S3^iv—Ca2—S6—Ga1	−147.66 (3)
S5—Ga4—S1—Ca1	−120.76 (4)	S3^iv—Ca2—S6—Ga2^ix	94.54 (4)
S5—Ga4—S1—Ca2	109.31 (3)	S3^iv—Ca2—S6—Ca2ⁱ	−24.67 (3)
S1—Ga4—S7ⁱⁱⁱ—Ga3ⁱⁱⁱ	−55.77 (5)	S6—Ca2—S3^iv—Ga1^iv	131.51 (4)
S7ⁱⁱⁱ—Ga4—S1—Ga3	115.90 (4)	S3^iv—Ca2—S6^ix—Ga1^ix	−81.77 (5)
S7ⁱⁱⁱ—Ga4—S1—Ca1	2.62 (6)	S3^iv—Ca2—S6^ix—Ca2^ix	17.60 (5)
S7ⁱⁱⁱ—Ga4—S1—Ca2	−127.31 (4)	S6^ix—Ca2—S3^iv—Ga1^iv	−168.56 (4)
S1—Ga4—S8—Ga2	100.35 (4)	S3^iv—Ca2—S8—Ga2	108.02 (3)
S1—Ga4—S8—Ca2	14.31 (3)	S3^iv—Ca2—S8—Ga4	−146.80 (3)
S1—Ga4—S8—Ca1ⁱⁱ	−130.93 (3)	S3^iv—Ca2—S8—Ca1ⁱⁱ	−63.47 (6)
S8—Ga4—S1—Ga3	−131.83 (3)	S8—Ca2—S3^iv—Ga1^iv	19.95 (4)
S8—Ga4—S1—Ca1	114.88 (4)	S3^viii—Ca2—S4—Ga1	−52.14 (11)
S8—Ga4—S1—Ca2	−15.04 (3)	S3^viii—Ca2—S4—Ga2	−154.64 (10)
S5—Ga4—S7ⁱⁱⁱ—Ga3ⁱⁱⁱ	56.51 (5)	S3^viii—Ca2—S4—Ca1^xiii	123.12 (10)
S7ⁱⁱⁱ—Ga4—S5—Ga3	−119.03 (3)	S4—Ca2—S3^viii—Ga1^viii	145.80 (9)
S7ⁱⁱⁱ—Ga4—S5—Ca1^xiii	130.02 (4)	S4—Ca2—S3^viii—Ca2^ix	9.54 (12)
S7ⁱⁱⁱ—Ga4—S5—Ca1ⁱⁱⁱ	9.33 (5)	S3^viii—Ca2—S6—Ga1	146.44 (3)
S5—Ga4—S8—Ga2	−4.69 (5)	S3^viii—Ca2—S6—Ga2^ix	28.64 (5)
S5—Ga4—S8—Ca2	−90.73 (4)	S3^viii—Ca2—S6—Ca2ⁱ	−90.57 (3)
S5—Ga4—S8—Ca1ⁱⁱ	124.03 (3)	S6—Ca2—S3^viii—Ga1^viii	83.93 (4)
S8—Ga4—S5—Ga3	118.33 (3)	S6—Ca2—S3^viii—Ca2^ix	−52.34 (4)
S8—Ga4—S5—Ca1^xiii	7.37 (6)	S3^viii—Ca2—S6^ix—Ga1^ix	−124.78 (4)
S8—Ga4—S5—Ca1ⁱⁱⁱ	−113.32 (4)	S3^viii—Ca2—S6^ix—Ca2^ix	−25.41 (3)
S7ⁱⁱⁱ—Ga4—S8—Ga2	−134.25 (3)	S6^ix—Ca2—S3^viii—Ga1^viii	160.16 (3)
S7ⁱⁱⁱ—Ga4—S8—Ca2	139.71 (3)	S6^ix—Ca2—S3^viii—Ca2^ix	23.89 (3)
S7ⁱⁱⁱ—Ga4—S8—Ca1ⁱⁱ	−5.53 (3)	S3^viii—Ca2—S8—Ga2	154.19 (4)
S8—Ga4—S7ⁱⁱⁱ—Ga3ⁱⁱⁱ	−170.40 (3)	S3^viii—Ca2—S8—Ga4	−100.62 (4)
S1—Ca1—S2^iv—Ga3^iv	129.31 (4)	S3^viii—Ca2—S8—Ca1ⁱⁱ	−17.29 (9)
S2^iv—Ca1—S1—Ga3	−148.00 (4)	S8—Ca2—S3^viii—Ga1^viii	−34.53 (5)
S2^iv—Ca1—S1—Ga4	−50.23 (4)	S8—Ca2—S3^viii—Ca2^ix	−170.80 (4)
S2^iv—Ca1—S1—Ca2	61.91 (5)	S4—Ca2—S6—Ga1	−13.63 (3)
S1—Ca1—S4^v—Ga1^v	−25.51 (7)	S4—Ca2—S6—Ga2^ix	−131.43 (5)
S1—Ca1—S4^v—Ga2^v	77.72 (4)	S4—Ca2—S6—Ca2ⁱ	109.36 (3)
S1—Ca1—S4^v—Ca2^v	160.05 (7)	S6—Ca2—S4—Ga1	13.98 (3)
S4^v—Ca1—S1—Ga3	144.50 (4)	S6—Ca2—S4—Ga2	−88.53 (3)
S4^v—Ca1—S1—Ga4	−117.73 (4)	S6—Ca2—S4—Ca1^xiii	−170.76 (8)
S4^v—Ca1—S1—Ca2	−5.59 (7)	S4—Ca2—S6^ix—Ga1^ix	49.94 (4)
S1—Ca1—S5^v—Ga3^v	−179.34 (12)	S4—Ca2—S6^ix—Ca2^ix	149.31 (3)
S1—Ca1—S5^v—Ga4^v	−81.09 (14)	S6^ix—Ca2—S4—Ga1	−65.96 (3)
S5^v—Ca1—S1—Ga3	−103.81 (14)	S6^ix—Ca2—S4—Ga2	−168.46 (3)
S5^v—Ca1—S1—Ga4	−6.04 (16)	S6^ix—Ca2—S4—Ca1^xiii	109.30 (8)
S5^v—Ca1—S1—Ca2	106.10 (13)	S4—Ca2—S8—Ga2	−25.94 (2)
S1—Ca1—S5ⁱⁱⁱ—Ga3ⁱⁱⁱ	−41.83 (5)	S4—Ca2—S8—Ga4	79.25 (3)
S1—Ca1—S5ⁱⁱⁱ—Ga4ⁱⁱⁱ	59.36 (4)	S4—Ca2—S8—Ca1ⁱⁱ	162.58 (6)
S5ⁱⁱⁱ—Ca1—S1—Ga3	−61.51 (4)	S8—Ca2—S4—Ga1	128.13 (3)
S5ⁱⁱⁱ—Ca1—S1—Ga4	36.26 (5)	S8—Ca2—S4—Ga2	25.63 (2)
S5ⁱⁱⁱ—Ca1—S1—Ca2	148.40 (5)	S8—Ca2—S4—Ca1^xiii	−56.61 (8)
S1—Ca1—S7^vi—Ga3^vi	−133.22 (7)	S6—Ca2—S6^ix—Ga1^ix	−23.74 (4)
S7^vi—Ca1—S1—Ga3	14.18 (5)	S6—Ca2—S6^ix—Ca2^ix	75.63 (3)
S7^vi—Ca1—S1—Ga4	111.95 (5)	S6^ix—Ca2—S6—Ga1	74.59 (3)
S7^vi—Ca1—S1—Ca2	−135.91 (5)	S6^ix—Ca2—S6—Ga2^ix	−43.21 (4)
S1—Ca1—S8^vii—Ga2^vii	−12.04 (4)	S6^ix—Ca2—S6—Ca2ⁱ	−162.43 (3)
S1—Ca1—S8^vii—Ga4^vii	−120.69 (3)	S6—Ca2—S8—Ga2	39.37 (3)
S1—Ca1—S8^vii—Ca2^vii	157.25 (6)	S6—Ca2—S8—Ga4	144.56 (3)
S8^vii—Ca1—S1—Ga3	72.56 (4)	S6—Ca2—S8—Ca1ⁱⁱ	−132.12 (6)
S8^vii—Ca1—S1—Ga4	170.33 (4)	S8—Ca2—S6—Ga1	−77.71 (4)
S8^vii—Ca1—S1—Ca2	−77.53 (5)	S8—Ca2—S6—Ga2^ix	164.48 (4)
S2^iv—Ca1—S4^v—Ga1^v	−92.49 (5)	S8—Ca2—S6—Ca2ⁱ	45.27 (3)
S2^iv—Ca1—S4^v—Ga2^v	10.73 (2)	S6^ix—Ca2—S8—Ga2	−57.78 (7)
S2^iv—Ca1—S4^v—Ca2^v	93.07 (8)	S6^ix—Ca2—S8—Ga4	47.41 (7)
S4^v—Ca1—S2^iv—Ga3^iv	−113.01 (4)	S6^ix—Ca2—S8—Ca1ⁱⁱ	130.74 (7)
S2^iv—Ca1—S5^v—Ga3^v	−136.98 (3)	S8—Ca2—S6^ix—Ga1^ix	80.03 (8)
S2^iv—Ca1—S5^v—Ga4^v	−38.74 (5)	S8—Ca2—S6^ix—Ca2^ix	179.40 (6)

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

Experimental details

Crystal data
Chemical formula	CaGa₂S₄
M_r	307.76
Crystal system, space group	Monoclinic, P2₁/a
Temperature (K)	270
a, b, c (Å)	6.841 (3), 27.069 (9), 7.231 (3)
β (°)	109.413 (5)
V (Å³)	1262.9 (8)
Z	8
Radiation type	Mo Kα
µ (mm⁻¹)	10.52
Crystal size (mm)	0.10 × 0.10 × 0.05

Data collection
Diffractometer	Rigaku Saturn724+ diffractometer
Absorption correction	Multi-scan (REQABS; Jacobson, 1998)
T_min, T_max	0.417, 0.591
No. of measured, independent and observed [F² > 2σ(F²)] reflections	8869, 2869, 256
R_int	0.047
(sin θ/λ)_max (Å⁻¹)	0.649

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.038, 0.050, 1.21
No. of reflections	2869
No. of parameters	127
No. of restraints	?
Δρ_max, Δρ_min (e Å⁻³)	2.64, −3.10

Computer programs: CrystalClear (Rigaku/MSC and Rigaku, 2006), CrystalStructure (Rigaku/MSC and Rigaku, 2006), SIR92 (Altomare et al., 1994), CRYSTALS (Betteridge et al., 2003), VESTA 3 (Momma & Izumi, 2011).

Acknowledgements

The authors would like to express their sincere thanks to Professor A. Kobayashi and Dr B. Zhou for their help with single-crystal X-ray diffraction measurements. This work was partly supported by the grant for private universities for 2009–2013 from the Ministry of Education, Sports, Science, Culture and Technology, Japan.

References

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