Monoclinic Cu₂Se₃Sn

A previously unknown modification of dicopper(I) tris­elenostannate(IV), Cu₂Se₃Sn, has been obtained from the Cu₂Se-SnSe₂ quasi-binary system and investigated using X-ray single-crystal diffraction. The Se atoms are stacked in a closest-packed arrangement with the layers in the sequence ABC. The Cu atoms occupy one-third of the tetra­hedral inter­stices, whereas the Sn atoms are located in one-sixth of the tetra­hedral inter­stices. All the atoms occupy general positions. The structure possesses pseudo-inversion symmetry. The Cu₂Se₃Sn structure investigated in this paper (96 atoms per unit cell, ordered distribution of Cu and Sn over 12 cation positions) is a superstructure of the reported cubic (eight atoms per unit cell, random distribution of Cu and Sn over one cation position) and monoclinic (24 atoms per unit cell, ordered distribution of Cu and Sn over three cation positions) modifications.

S1. Comment

As a continuation of our studies of ternary chalcogenides, we have examined the Cu₂Se–SnSe₂ system because of the reported formation of several phases of composition Cu₂Se₃Sn that belong to the family of low-melting point compounds of tetrahedral lattice, which are of interest for their semiconducting and optical properties (Sharma et al., 1977; Fernandez et al., 1996). Knowledge of the crystal structure of the Cu₂SnSe₃ compounds is important for understanding their properties. Sharma et al. (1977) indicated that Cu₂SnSe₃ crystallizes in the cubic sphalerite structure (space group F43m, a = 5.6877 Å). Recently, Delgado et al. (2003) described the structure of Cu₂SnSe₃ in a monoclinic unit cell (a = 6.9670, b = 12.0493 and c = 6.9453 Å, and β = 109.19°) of the Cu₂GeS₃ structure type (space group Cc), based on X-ray powder diffraction data. Here, we present the crystal structure of a previously unknown modification of Cu₂SnSe₃ based on X-ray single-crystal diffraction analysis.

The asymmetric unit of the title compound contains eight Cu atoms, four Sn atoms and 12 Se atoms (Fig. 1). Each of the formally Cu^I and Sn^IV ions is surrounded by four Se^2- anions at distances that agree well with the sums of the respective ionic radii (Wiberg, 1995). The crystal lattice consists of corner-sharing [CuSe₄] and [SnSe₄] tetrahedra. Since the metal-centred tetrahedra are connected only by the corners, the Se-centred coordination environment is also tetrahedral. Similar values of the Cu—Se and Sn—Se interatomic distances for tetrahedral surroundings are observed in the structures of LnCuSe₂ and Eu₂SnSe₅ (Daszkiewicz et al., 2008; Evenson & Dorhout, 2001). However, from the bond-valence point of view the eight symmetry-independent Cu^I ions are overbonded, because the bond-valence sums (BVS) for these ions [based on Cu—Se distances ranging from 2.380 (5) to 2.495 (5) Å] are greater than the formal oxidation state, ~1.40 (Table 1) (Brown, 1996). Similarly, each of the Se^2- anions is overbonded. In this case, the Sn⁴⁺ ions must be underbonded, as indicated by the calculated BVS [based on Sn—Se distances in the range 2.488 (3)–2.627 (3) Å] of \sim 3.74, because the difference between the BVS for the cations and anions must be zero.

The Cu₂SnSe₃ structure described here, with 96 atoms in the unit cell, is a superstructure of the cubic (Sharma et al., 1977) (space group F43m, eight atoms per unit cell) and monoclinic (Delgado et al., 2003) (space group Cc, 24 atoms per unit cell) modifications reported earlier. The known modifications were investigated using X-ray powder diffraction, while the present monoclinic superstructure was investigated using X-ray single-crystal diffraction. The structures are similar (Fig. 2), in that the Se atoms in all modifications of Cu₂SnSe₃ are stacked in a closest-packed arrangement with the layers in the sequence ABC (cubic closest packing). In the cubic modification, a mixture of randomly distributed Cu⁺ and Sn⁴⁺ ions (2/3 Cu + 1/3 Sn) occupy half of the tetrahedral interstices. In the structures of both monoclinic modifications, the Cu⁺ ions occupy one-third of the tetrahedral interstices, whereas the Sn⁴⁺ ions are located in one-sixth of the tetrahedral interstices. The distribution of the cation positions in both monoclinic modifications is ordered. In both modifications, the Sn-centred tetrahedra create zig-zag chains along the c axis. However, the period of the chain is one-quarter as long in the previously reported structure than in the present superstructure, and this is reflected in the relation of the lattice parameters, c ≈ 4c'. Moreover, the amplitude of the chain is 1.5 times larger in the superstructure.

The presence of three structures for Cu₂SnSe₃ can be explained in two ways. The first is that the three modifications really exist. The cubic modification (random distribution of Cu⁺ and Sn⁴⁺ atoms over one position) is a high-temperature modification, while the monoclinic modifications with different ordered distributions of the positions of Cu and Sn are low-temperature modifications. The second is that only one or two modifications exist. The basic fragments of the structures for all three structures are similar. It is possible that the superstructure reflections measured in the X-ray single-crystal investigation were missed in the previous powder studies. Further work will be required on the Cu₂Se–SnSe₂ system to determine how many structural modifications actually exist.

S2. Experimental

A sample of composition Cu₂SnSe₃ was prepared by melting the high-purity (better than 99.9 wt%) elements in an evacuated silica tube. The ampoule was heated at a rate of 100 K h^-1 in a tube furnace to a temperature of 770 K, then heated at a rate of 20 K h^-1 to a maximum temperature of 1380 K and kept there for 2 h. The ampoule was then cooled slowly (10 K h^-1) to 620 K and annealed at this temperature for 500 h. After annealing, the sample was quenched in cold water. A diffraction-quality single crystal was selected from the sample.

S3. Refinement

The systematic absences were found to be consistent with the space group Cc, which was assigned for the crystal structure determination. Eight positions for Cu, four for Sn and 12 for Se were determined. All positions are fully occupied. A mixed occupation of Cu and Sn on each cation site was checked, but in all cases the refinement was unstable. The structure was checked by the PLATON program (Spek, 2003), which detected a pseudo-inversion centre. A refinement in C2/c was unsuccessful. The structure was refined as a twinned model with a twin fraction of 0.06, because the Flack parameter (Flack, 1983) initially refined to 0.041 (14).

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2007); cell refinement: CrysAlis RED (Oxford Diffraction, 2007); data reduction: CrysAlis RED (Oxford Diffraction, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2009); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. The coordination environments for the four Sn and eight Cu atoms in the asymmetric unit of Cu2SnSe3. [Symmetry codes: (i) x + 1/2, -y + 1/2, z + 1/2; (ii) x + 1/2, y + 1/2, z; (iii) x - 1, y, z; (iv) x - 1/2, -y + 1/2, z + 1/2; (v) x + 1/2, y - 1/2, z; (vi) x + 1, y, z; (vii) x - 1/2, y - 1/2, z; (viii) x - 1/2, y + 1/2, z.]
	Fig. 2. The packing of the Cu- and Sn-centred tetrahedra in (a) the cubic (space group F43m, a = 5.6877 Å; Sharma et al., 1977), (b) the monoclinic (a = 6.9670, b = 12.0493 and c = 6.9453 Å, and β = 109.19°; Delgado et al., 2003) and (c) monoclinic (a = 6.961, b = 12.043 and c = 26.481 Å, and β = 94.97°; this work) modifications of Cu2SnSe3.

dicopper(I) triselenostannate(IV)

Crystal data

Cu2Se3Sn	F(000) = 3360
Mr = 482.65	Dx = 5.798 Mg m^−3
Monoclinic, Cc	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: C -2yc	Cell parameters from 2338 reflections
a = 6.9612 (14) Å	θ = 3.4–27.5°
b = 12.043 (2) Å	µ = 31.69 mm^−1
c = 26.481 (5) Å	T = 295 K
β = 94.97 (3)°	Prism, dark red
V = 2211.7 (8) Å^3	0.10 × 0.09 × 0.05 mm
Z = 16

Data collection

Kuma KM-4 with CCD area-detector diffractometer	4780 independent reflections
Radiation source: fine-focus sealed tube	2338 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.095
Detector resolution: 1024x1024 with blocks 2x2, 33.133pixel/mm pixels mm^-1	θmax = 27.5°, θmin = 3.4°
ω scans	h = −9→9
Absorption correction: numerical (CrysAlis RED; Oxford Diffraction, 2007)	k = −15→13
Tmin = 0.038, Tmax = 0.212	l = −34→34
12585 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0287P)^2] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.047	(Δ/σ)max = 0.001
wR(F^2) = 0.104	Δρmax = 1.87 e Å^−3
S = 0.76	Δρmin = −1.14 e Å^−3
4780 reflections	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
219 parameters	Extinction coefficient: 0.000684 (14)
2 restraints	Absolute structure: Flack (1983), with 2258 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.078 (15)

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.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq
Cu1	0.7292 (7)	0.4139 (5)	0.48534 (14)	0.0214 (11)
Cu2	0.2266 (8)	0.2542 (5)	0.48543 (14)	0.0229 (11)
Cu3	0.8726 (5)	0.2443 (3)	0.36085 (12)	0.0255 (11)
Cu4	0.3566 (5)	0.4191 (3)	0.36000 (13)	0.0184 (9)
Cu5	−0.0083 (7)	0.0917 (4)	0.23564 (13)	0.0237 (10)
Cu6	−0.0020 (7)	0.4179 (4)	0.23526 (13)	0.0219 (10)
Cu7	0.1203 (5)	0.2450 (6)	0.11002 (12)	0.0211 (12)
Cu8	0.6174 (5)	0.0899 (5)	0.11018 (13)	0.0177 (10)
Sn1	0.7516 (5)	0.0824 (3)	0.48077 (10)	0.0156 (5)
Sn2	0.3575 (3)	0.07438 (15)	0.35597 (7)	0.0121 (5)
Sn3	0.4826 (5)	0.2416 (3)	0.23057 (10)	0.0151 (5)
Sn4	0.6313 (3)	0.4158 (3)	0.10611 (7)	0.0114 (5)
Se1	0.2607 (3)	0.4189 (3)	0.07970 (7)	0.0132 (6)
Se2	0.3838 (3)	0.0836 (2)	0.45495 (7)	0.0148 (6)
Se3	0.6530 (3)	0.4240 (3)	0.20480 (7)	0.0144 (6)
Se4	0.1328 (3)	0.2531 (3)	0.20093 (7)	0.0171 (6)
Se5	0.6602 (4)	0.0749 (3)	0.20198 (7)	0.0172 (6)
Se6	0.5266 (3)	0.25470 (19)	0.32993 (6)	0.0144 (6)
Se7	0.5064 (3)	0.5796 (2)	0.32649 (7)	0.0169 (6)
Se8	0.8971 (3)	0.2585 (2)	0.45159 (7)	0.0164 (6)
Se9	0.7841 (3)	0.2437 (3)	0.07649 (7)	0.0182 (7)
Se10	0.0245 (3)	0.40493 (19)	0.32643 (7)	0.0170 (6)
Se11	0.4004 (3)	0.4065 (2)	0.45131 (7)	0.0176 (6)
Se12	0.2828 (3)	0.0900 (3)	0.07663 (7)	0.0167 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.019 (2)	0.028 (2)	0.017 (2)	0.0051 (15)	0.0041 (16)	−0.0041 (15)
Cu2	0.020 (2)	0.030 (2)	0.019 (3)	−0.0023 (15)	0.0036 (17)	−0.0006 (16)
Cu3	0.033 (3)	0.0300 (18)	0.0147 (19)	−0.0018 (18)	0.0080 (17)	0.0031 (16)
Cu4	0.0200 (19)	0.0172 (19)	0.0183 (19)	−0.0017 (14)	0.0031 (15)	−0.0001 (16)
Cu5	0.025 (2)	0.028 (2)	0.0178 (18)	0.0028 (16)	0.0004 (15)	0.0002 (15)
Cu6	0.029 (2)	0.0206 (18)	0.0172 (18)	0.0062 (15)	0.0050 (15)	0.0012 (14)
Cu7	0.037 (3)	0.0162 (18)	0.0095 (17)	−0.0013 (14)	0.0011 (16)	−0.0021 (15)
Cu8	0.027 (2)	0.0121 (17)	0.0139 (19)	−0.0041 (13)	−0.0005 (15)	0.0015 (14)
Sn1	0.0196 (11)	0.0142 (11)	0.0130 (9)	−0.0001 (10)	0.0007 (8)	−0.0031 (8)
Sn2	0.0126 (10)	0.0130 (9)	0.0112 (8)	−0.0002 (7)	0.0039 (7)	−0.0005 (8)
Sn3	0.0159 (11)	0.0150 (11)	0.0147 (9)	0.0004 (10)	0.0035 (7)	0.0018 (9)
Sn4	0.0166 (12)	0.0091 (8)	0.0085 (8)	0.0004 (8)	0.0021 (7)	0.0009 (7)
Se1	0.0130 (12)	0.0112 (13)	0.0158 (12)	0.0020 (8)	0.0040 (9)	0.0025 (10)
Se2	0.0144 (15)	0.0142 (10)	0.0160 (12)	0.0016 (10)	0.0018 (10)	−0.0009 (11)
Se3	0.0163 (11)	0.0121 (14)	0.0145 (11)	−0.0001 (9)	0.0008 (9)	−0.0005 (10)
Se4	0.0153 (13)	0.0134 (11)	0.0226 (11)	0.0016 (11)	0.0029 (10)	−0.0032 (9)
Se5	0.0167 (12)	0.0144 (14)	0.0206 (11)	0.0018 (10)	0.0025 (9)	0.0003 (11)
Se6	0.0173 (12)	0.0111 (14)	0.0149 (12)	0.0010 (10)	0.0018 (9)	−0.0003 (9)
Se7	0.0133 (13)	0.0167 (13)	0.0209 (11)	−0.0001 (11)	0.0021 (10)	0.0010 (10)
Se8	0.0135 (15)	0.0127 (11)	0.0231 (12)	0.0014 (11)	0.0024 (10)	−0.0002 (11)
Se9	0.0203 (14)	0.0138 (15)	0.0204 (13)	0.0017 (11)	0.0005 (11)	0.0006 (9)
Se10	0.0148 (12)	0.0134 (13)	0.0231 (12)	0.0003 (11)	0.0028 (9)	0.0023 (11)
Se11	0.0174 (15)	0.0154 (11)	0.0204 (12)	0.0058 (11)	0.0039 (10)	−0.0001 (12)
Se12	0.0158 (14)	0.0158 (16)	0.0185 (12)	0.0018 (10)	0.0014 (10)	0.0016 (9)

Geometric parameters (Å, º)

Cu1—Se11	2.388 (5)	Sn1—Se11^v	2.512 (3)
Cu1—Se12^i	2.414 (4)	Sn1—Se2	2.592 (3)
Cu1—Se8	2.418 (4)	Sn1—Se1^i	2.615 (3)
Cu1—Se2^ii	2.476 (5)	Sn2—Se7^vii	2.501 (3)
Cu2—Se8^iii	2.390 (5)	Sn2—Se10^v	2.507 (3)
Cu2—Se9^iv	2.410 (4)	Sn2—Se6	2.592 (3)
Cu2—Se11	2.415 (5)	Sn2—Se2	2.614 (3)
Cu2—Se2	2.495 (5)	Sn3—Se4	2.497 (3)
Cu3—Se8	2.400 (4)	Sn3—Se5	2.509 (3)
Cu3—Se7^v	2.403 (4)	Sn3—Se3	2.615 (3)
Cu3—Se10^vi	2.420 (4)	Sn3—Se6	2.627 (3)
Cu3—Se6	2.479 (4)	Sn4—Se9	2.488 (3)
Cu4—Se7	2.403 (5)	Sn4—Se12^ii	2.502 (3)
Cu4—Se10	2.410 (4)	Sn4—Se3	2.607 (3)
Cu4—Se11	2.416 (4)	Sn4—Se1	2.614 (3)
Cu4—Se6	2.473 (5)	Se1—Cu8^viii	2.455 (4)
Cu5—Se4	2.397 (4)	Se1—Sn1^ix	2.615 (3)
Cu5—Se7^vii	2.404 (4)	Se2—Cu1^vii	2.476 (5)
Cu5—Se5^iii	2.409 (4)	Se3—Cu6^vi	2.468 (4)
Cu5—Se3^vii	2.482 (4)	Se3—Cu5^ii	2.482 (4)
Cu6—Se4	2.407 (4)	Se5—Cu6^v	2.408 (4)
Cu6—Se5^viii	2.408 (4)	Se5—Cu5^vi	2.409 (4)
Cu6—Se10	2.411 (4)	Se7—Cu3^viii	2.403 (4)
Cu6—Se3^iii	2.468 (4)	Se7—Cu5^ii	2.404 (4)
Cu7—Se12	2.392 (5)	Se7—Sn2^ii	2.501 (3)
Cu7—Se4	2.403 (4)	Se8—Cu2^vi	2.390 (5)
Cu7—Se9^iii	2.430 (4)	Se9—Cu2^x	2.410 (4)
Cu7—Se1	2.475 (5)	Se9—Cu7^vi	2.430 (4)
Cu8—Se9	2.398 (4)	Se10—Cu3^iii	2.420 (4)
Cu8—Se12	2.420 (4)	Se10—Sn2^viii	2.507 (3)
Cu8—Se5	2.430 (4)	Se11—Sn1^viii	2.512 (3)
Cu8—Se1^v	2.455 (4)	Se12—Cu1^ix	2.414 (4)
Sn1—Se8	2.502 (3)	Se12—Sn4^vii	2.502 (3)
Se11—Cu1—Se12^i	115.91 (15)	Cu8^viii—Se1—Cu7	114.83 (15)
Se11—Cu1—Se8	108.05 (18)	Cu8^viii—Se1—Sn4	110.10 (13)
Se12^i—Cu1—Se8	108.5 (2)	Cu7—Se1—Sn4	108.06 (12)
Se11—Cu1—Se2^ii	109.72 (19)	Cu8^viii—Se1—Sn1^ix	111.04 (14)
Se12^i—Cu1—Se2^ii	107.92 (19)	Cu7—Se1—Sn1^ix	110.12 (15)
Se8—Cu1—Se2^ii	106.31 (15)	Sn4—Se1—Sn1^ix	101.86 (10)
Se8^iii—Cu2—Se9^iv	116.46 (15)	Cu1^vii—Se2—Cu2	111.07 (16)
Se8^iii—Cu2—Se11	109.8 (2)	Cu1^vii—Se2—Sn1	110.92 (15)
Se9^iv—Cu2—Se11	108.7 (2)	Cu2—Se2—Sn1	111.70 (15)
Se8^iii—Cu2—Se2	109.3 (2)	Cu1^vii—Se2—Sn2	107.24 (11)
Se9^iv—Cu2—Se2	107.0 (2)	Cu2—Se2—Sn2	111.38 (12)
Se11—Cu2—Se2	104.87 (16)	Sn1—Se2—Sn2	104.24 (9)
Se8—Cu3—Se7^v	116.21 (17)	Cu6^vi—Se3—Cu5^ii	111.82 (15)
Se8—Cu3—Se10^vi	108.92 (15)	Cu6^vi—Se3—Sn4	107.25 (13)
Se7^v—Cu3—Se10^vi	108.70 (14)	Cu5^ii—Se3—Sn4	111.84 (14)
Se8—Cu3—Se6	108.06 (14)	Cu6^vi—Se3—Sn3	109.89 (11)
Se7^v—Cu3—Se6	108.31 (16)	Cu5^ii—Se3—Sn3	111.68 (12)
Se10^vi—Cu3—Se6	106.19 (15)	Sn4—Se3—Sn3	104.00 (11)
Se7—Cu4—Se10	110.73 (17)	Cu5—Se4—Cu7	111.7 (2)
Se7—Cu4—Se11	113.50 (16)	Cu5—Se4—Cu6	109.75 (17)
Se10—Cu4—Se11	113.51 (17)	Cu7—Se4—Cu6	115.5 (2)
Se7—Cu4—Se6	106.85 (15)	Cu5—Se4—Sn3	104.77 (12)
Se10—Cu4—Se6	107.17 (17)	Cu7—Se4—Sn3	105.21 (12)
Se11—Cu4—Se6	104.45 (13)	Cu6—Se4—Sn3	109.19 (12)
Se4—Cu5—Se7^vii	116.72 (17)	Cu6^v—Se5—Cu5^vi	113.26 (17)
Se4—Cu5—Se5^iii	109.71 (16)	Cu6^v—Se5—Cu8	113.80 (19)
Se7^vii—Cu5—Se5^iii	108.75 (19)	Cu5^vi—Se5—Cu8	113.24 (16)
Se4—Cu5—Se3^vii	108.77 (17)	Cu6^v—Se5—Sn3	104.99 (12)
Se7^vii—Cu5—Se3^vii	107.39 (17)	Cu5^vi—Se5—Sn3	107.61 (12)
Se5^iii—Cu5—Se3^vii	104.83 (15)	Cu8—Se5—Sn3	102.80 (16)
Se4—Cu6—Se5^viii	107.38 (18)	Cu4—Se6—Cu3	114.37 (15)
Se4—Cu6—Se10	109.05 (16)	Cu4—Se6—Sn2	110.11 (11)
Se5^viii—Cu6—Se10	114.83 (16)	Cu3—Se6—Sn2	108.69 (12)
Se4—Cu6—Se3^iii	107.53 (15)	Cu4—Se6—Sn3	110.68 (11)
Se5^viii—Cu6—Se3^iii	109.34 (15)	Cu3—Se6—Sn3	110.69 (11)
Se10—Cu6—Se3^iii	108.48 (18)	Sn2—Se6—Sn3	101.53 (10)
Se12—Cu7—Se4	115.1 (2)	Cu4—Se7—Cu3^viii	109.22 (15)
Se12—Cu7—Se9^iii	109.35 (18)	Cu4—Se7—Cu5^ii	115.86 (17)
Se4—Cu7—Se9^iii	108.45 (15)	Cu3^viii—Se7—Cu5^ii	110.17 (16)
Se12—Cu7—Se1	109.13 (14)	Cu4—Se7—Sn2^ii	107.95 (13)
Se4—Cu7—Se1	108.0 (2)	Cu3^viii—Se7—Sn2^ii	107.63 (13)
Se9^iii—Cu7—Se1	106.38 (17)	Cu5^ii—Se7—Sn2^ii	105.64 (14)
Se9—Cu8—Se12	110.15 (17)	Cu2^vi—Se8—Cu3	110.90 (12)
Se9—Cu8—Se5	114.1 (2)	Cu2^vi—Se8—Cu1	110.93 (18)
Se12—Cu8—Se5	113.46 (16)	Cu3—Se8—Cu1	115.50 (15)
Se9—Cu8—Se1^v	107.57 (15)	Cu2^vi—Se8—Sn1	105.48 (16)
Se12—Cu8—Se1^v	106.58 (16)	Cu3—Se8—Sn1	104.65 (12)
Se5—Cu8—Se1^v	104.4 (2)	Cu1—Se8—Sn1	108.69 (13)
Se8—Sn1—Se11^v	115.48 (12)	Cu8—Se9—Cu2^x	109.68 (19)
Se8—Sn1—Se2	109.34 (11)	Cu8—Se9—Cu7^vi	110.53 (17)
Se11^v—Sn1—Se2	110.31 (12)	Cu2^x—Se9—Cu7^vi	115.88 (14)
Se8—Sn1—Se1^i	109.83 (13)	Cu8—Se9—Sn4	107.01 (12)
Se11^v—Sn1—Se1^i	109.34 (12)	Cu2^x—Se9—Sn4	105.57 (18)
Se2—Sn1—Se1^i	101.65 (11)	Cu7^vi—Se9—Sn4	107.68 (14)
Se7^vii—Sn2—Se10^v	112.96 (11)	Cu4—Se10—Cu6	110.64 (16)
Se7^vii—Sn2—Se6	110.48 (11)	Cu4—Se10—Cu3^iii	110.74 (16)
Se10^v—Sn2—Se6	111.43 (10)	Cu6—Se10—Cu3^iii	115.53 (15)
Se7^vii—Sn2—Se2	107.08 (10)	Cu4—Se10—Sn2^viii	106.46 (14)
Se10^v—Sn2—Se2	110.68 (9)	Cu6—Se10—Sn2^viii	105.22 (14)
Se6—Sn2—Se2	103.73 (9)	Cu3^iii—Se10—Sn2^viii	107.67 (12)
Se4—Sn3—Se5	116.26 (10)	Cu1—Se11—Cu2	112.46 (18)
Se4—Sn3—Se3	108.84 (9)	Cu1—Se11—Cu4	114.17 (14)
Se5—Sn3—Se3	110.30 (10)	Cu2—Se11—Cu4	113.45 (15)
Se4—Sn3—Se6	109.72 (11)	Cu1—Se11—Sn1^viii	105.01 (15)
Se5—Sn3—Se6	109.44 (10)	Cu2—Se11—Sn1^viii	106.91 (14)
Se3—Sn3—Se6	101.22 (10)	Cu4—Se11—Sn1^viii	103.78 (11)
Se9—Sn4—Se12^ii	113.39 (12)	Cu7—Se12—Cu1^ix	110.38 (18)
Se9—Sn4—Se3	111.00 (12)	Cu7—Se12—Cu8	109.61 (15)
Se12^ii—Sn4—Se3	106.97 (12)	Cu1^ix—Se12—Cu8	115.33 (15)
Se9—Sn4—Se1	111.48 (10)	Cu7—Se12—Sn4^vii	108.24 (14)
Se12^ii—Sn4—Se1	109.73 (11)	Cu1^ix—Se12—Sn4^vii	105.28 (17)
Se3—Sn4—Se1	103.74 (11)	Cu8—Se12—Sn4^vii	107.66 (14)
Se12—Cu7—Se1—Cu8^viii	−179.39 (15)	Se7^vii—Sn2—Se6—Cu4	53.61 (14)
Se4—Cu7—Se1—Cu8^viii	−53.5 (2)	Se10^v—Sn2—Se6—Cu4	−179.96 (13)
Se9^iii—Cu7—Se1—Cu8^viii	62.73 (18)	Se2—Sn2—Se6—Cu4	−60.85 (12)
Se12—Cu7—Se1—Sn4	−56.08 (16)	Se7^vii—Sn2—Se6—Cu3	179.60 (12)
Se4—Cu7—Se1—Sn4	69.78 (18)	Se10^v—Sn2—Se6—Cu3	−53.97 (14)
Se9^iii—Cu7—Se1—Sn4	−173.96 (12)	Se2—Sn2—Se6—Cu3	65.14 (12)
Se12—Cu7—Se1—Sn1^ix	54.39 (16)	Se7^vii—Sn2—Se6—Sn3	−63.68 (12)
Se4—Cu7—Se1—Sn1^ix	−179.75 (15)	Se10^v—Sn2—Se6—Sn3	62.75 (12)
Se9^iii—Cu7—Se1—Sn1^ix	−63.49 (17)	Se2—Sn2—Se6—Sn3	−178.14 (7)
Se9—Sn4—Se1—Cu8^viii	179.74 (13)	Se4—Sn3—Se6—Cu4	−51.89 (14)
Se12^ii—Sn4—Se1—Cu8^viii	−53.80 (14)	Se5—Sn3—Se6—Cu4	179.43 (15)
Se3—Sn4—Se1—Cu8^viii	60.22 (16)	Se3—Sn3—Se6—Cu4	63.00 (14)
Se9—Sn4—Se1—Cu7	53.61 (14)	Se4—Sn3—Se6—Cu3	−179.77 (13)
Se12^ii—Sn4—Se1—Cu7	−179.93 (13)	Se5—Sn3—Se6—Cu3	51.55 (16)
Se3—Sn4—Se1—Cu7	−65.91 (16)	Se3—Sn3—Se6—Cu3	−64.88 (16)
Se9—Sn4—Se1—Sn1^ix	−62.38 (16)	Se4—Sn3—Se6—Sn2	64.98 (10)
Se12^ii—Sn4—Se1—Sn1^ix	64.08 (15)	Se5—Sn3—Se6—Sn2	−63.70 (12)
Se3—Sn4—Se1—Sn1^ix	178.10 (19)	Se3—Sn3—Se6—Sn2	179.87 (11)
Se8^iii—Cu2—Se2—Cu1^vii	−62.34 (19)	Se10—Cu4—Se7—Cu3^viii	69.5 (2)
Se9^iv—Cu2—Se2—Cu1^vii	64.6 (2)	Se11—Cu4—Se7—Cu3^viii	−59.53 (19)
Se11—Cu2—Se2—Cu1^vii	179.99 (16)	Se6—Cu4—Se7—Cu3^viii	−174.12 (13)
Se8^iii—Cu2—Se2—Sn1	173.25 (13)	Se10—Cu4—Se7—Cu5^ii	−55.6 (2)
Se9^iv—Cu2—Se2—Sn1	−59.8 (2)	Se11—Cu4—Se7—Cu5^ii	175.38 (15)
Se11—Cu2—Se2—Sn1	55.58 (18)	Se6—Cu4—Se7—Cu5^ii	60.8 (2)
Se8^iii—Cu2—Se2—Sn2	57.13 (19)	Se10—Cu4—Se7—Sn2^ii	−173.76 (14)
Se9^iv—Cu2—Se2—Sn2	−175.94 (16)	Se11—Cu4—Se7—Sn2^ii	57.22 (18)
Se11—Cu2—Se2—Sn2	−60.53 (19)	Se6—Cu4—Se7—Sn2^ii	−57.37 (16)
Se8—Sn1—Se2—Cu1^vii	−178.09 (13)	Se7^v—Cu3—Se8—Cu2^vi	59.6 (2)
Se11^v—Sn1—Se2—Cu1^vii	53.88 (13)	Se10^vi—Cu3—Se8—Cu2^vi	−63.6 (2)
Se1^i—Sn1—Se2—Cu1^vii	−62.03 (17)	Se6—Cu3—Se8—Cu2^vi	−178.51 (19)
Se8—Sn1—Se2—Cu2	−53.59 (13)	Se7^v—Cu3—Se8—Cu1	−173.14 (14)
Se11^v—Sn1—Se2—Cu2	178.38 (14)	Se10^vi—Cu3—Se8—Cu1	63.7 (2)
Se1^i—Sn1—Se2—Cu2	62.48 (17)	Se6—Cu3—Se8—Cu1	−51.2 (2)
Se8—Sn1—Se2—Sn2	66.80 (13)	Se7^v—Cu3—Se8—Sn1	−53.70 (17)
Se11^v—Sn1—Se2—Sn2	−61.23 (14)	Se10^vi—Cu3—Se8—Sn1	−176.83 (14)
Se1^i—Sn1—Se2—Sn2	−177.14 (14)	Se6—Cu3—Se8—Sn1	68.22 (16)
Se7^vii—Sn2—Se2—Cu1^vii	63.65 (15)	Se11—Cu1—Se8—Cu2^vi	−178.10 (14)
Se10^v—Sn2—Se2—Cu1^vii	−59.86 (15)	Se12^i—Cu1—Se8—Cu2^vi	−51.7 (2)
Se6—Sn2—Se2—Cu1^vii	−179.48 (13)	Se2^ii—Cu1—Se8—Cu2^vi	64.2 (2)
Se7^vii—Sn2—Se2—Cu2	−58.07 (17)	Se11—Cu1—Se8—Cu3	54.6 (2)
Se10^v—Sn2—Se2—Cu2	178.42 (14)	Se12^i—Cu1—Se8—Cu3	−178.94 (17)
Se6—Sn2—Se2—Cu2	58.79 (16)	Se2^ii—Cu1—Se8—Cu3	−63.1 (2)
Se7^vii—Sn2—Se2—Sn1	−178.67 (11)	Se11—Cu1—Se8—Sn1	−62.57 (17)
Se10^v—Sn2—Se2—Sn1	57.81 (13)	Se12^i—Cu1—Se8—Sn1	63.86 (19)
Se6—Sn2—Se2—Sn1	−61.81 (13)	Se2^ii—Cu1—Se8—Sn1	179.71 (14)
Se9—Sn4—Se3—Cu6^vi	59.06 (15)	Se11^v—Sn1—Se8—Cu2^vi	−60.75 (14)
Se12^ii—Sn4—Se3—Cu6^vi	−65.12 (15)	Se2—Sn1—Se8—Cu2^vi	174.16 (13)
Se1—Sn4—Se3—Cu6^vi	178.90 (11)	Se1^i—Sn1—Se8—Cu2^vi	63.43 (17)
Se9—Sn4—Se3—Cu5^ii	−178.01 (13)	Se11^v—Sn1—Se8—Cu3	56.31 (14)
Se12^ii—Sn4—Se3—Cu5^ii	57.82 (19)	Se2—Sn1—Se8—Cu3	−68.78 (14)
Se1—Sn4—Se3—Cu5^ii	−58.16 (15)	Se1^i—Sn1—Se8—Cu3	−179.51 (16)
Se9—Sn4—Se3—Sn3	−57.34 (14)	Se11^v—Sn1—Se8—Cu1	−179.76 (15)
Se12^ii—Sn4—Se3—Sn3	178.49 (9)	Se2—Sn1—Se8—Cu1	55.15 (15)
Se1—Sn4—Se3—Sn3	62.50 (12)	Se1^i—Sn1—Se8—Cu1	−55.57 (17)
Se4—Sn3—Se3—Cu6^vi	178.63 (14)	Se12—Cu8—Se9—Cu2^x	−51.2 (2)
Se5—Sn3—Se3—Cu6^vi	−52.70 (14)	Se5—Cu8—Se9—Cu2^x	179.9 (2)
Se6—Sn3—Se3—Cu6^vi	63.09 (14)	Se1^v—Cu8—Se9—Cu2^x	64.6 (2)
Se4—Sn3—Se3—Cu5^ii	53.94 (14)	Se12—Cu8—Se9—Cu7^vi	179.86 (13)
Se5—Sn3—Se3—Cu5^ii	−177.39 (15)	Se5—Cu8—Se9—Cu7^vi	50.9 (3)
Se6—Sn3—Se3—Cu5^ii	−61.60 (14)	Se1^v—Cu8—Se9—Cu7^vi	−64.36 (18)
Se4—Sn3—Se3—Sn4	−66.83 (13)	Se12—Cu8—Se9—Sn4	62.87 (16)
Se5—Sn3—Se3—Sn4	61.83 (13)	Se5—Cu8—Se9—Sn4	−66.1 (2)
Se6—Sn3—Se3—Sn4	177.63 (12)	Se1^v—Cu8—Se9—Sn4	178.66 (14)
Se7^vii—Cu5—Se4—Cu7	176.7 (2)	Se12^ii—Sn4—Se9—Cu8	179.35 (15)
Se5^iii—Cu5—Se4—Cu7	−59.1 (2)	Se3—Sn4—Se9—Cu8	58.91 (14)
Se3^vii—Cu5—Se4—Cu7	55.06 (19)	Se1—Sn4—Se9—Cu8	−56.21 (14)
Se7^vii—Cu5—Se4—Cu6	−53.8 (3)	Se12^ii—Sn4—Se9—Cu2^x	−63.85 (14)
Se5^iii—Cu5—Se4—Cu6	70.40 (19)	Se3—Sn4—Se9—Cu2^x	175.70 (16)
Se3^vii—Cu5—Se4—Cu6	−175.47 (13)	Se1—Sn4—Se9—Cu2^x	60.58 (16)
Se7^vii—Cu5—Se4—Sn3	63.3 (2)	Se12^ii—Sn4—Se9—Cu7^vi	60.51 (14)
Se5^iii—Cu5—Se4—Sn3	−172.49 (14)	Se3—Sn4—Se9—Cu7^vi	−59.93 (16)
Se3^vii—Cu5—Se4—Sn3	−58.35 (16)	Se1—Sn4—Se9—Cu7^vi	−175.06 (12)
Se12—Cu7—Se4—Cu5	−59.6 (2)	Se7—Cu4—Se10—Cu6	51.2 (2)
Se9^iii—Cu7—Se4—Cu5	63.3 (2)	Se11—Cu4—Se10—Cu6	−179.82 (15)
Se1—Cu7—Se4—Cu5	178.21 (15)	Se6—Cu4—Se10—Cu6	−65.03 (18)
Se12—Cu7—Se4—Cu6	174.05 (17)	Se7—Cu4—Se10—Cu3^iii	−179.41 (15)
Se9^iii—Cu7—Se4—Cu6	−63.1 (2)	Se11—Cu4—Se10—Cu3^iii	−50.4 (2)
Se1—Cu7—Se4—Cu6	51.8 (2)	Se6—Cu4—Se10—Cu3^iii	64.39 (19)
Se12—Cu7—Se4—Sn3	53.6 (2)	Se7—Cu4—Se10—Sn2^viii	−62.65 (16)
Se9^iii—Cu7—Se4—Sn3	176.44 (14)	Se11—Cu4—Se10—Sn2^viii	66.37 (18)
Se1—Cu7—Se4—Sn3	−68.65 (19)	Se6—Cu4—Se10—Sn2^viii	−178.84 (13)
Se5^viii—Cu6—Se4—Cu5	176.92 (13)	Se4—Cu6—Se10—Cu4	69.5 (2)
Se10—Cu6—Se4—Cu5	51.9 (2)	Se5^viii—Cu6—Se10—Cu4	−51.1 (2)
Se3^iii—Cu6—Se4—Cu5	−65.52 (18)	Se3^iii—Cu6—Se10—Cu4	−173.70 (17)
Se5^viii—Cu6—Se4—Cu7	−55.7 (2)	Se4—Cu6—Se10—Cu3^iii	−57.3 (2)
Se10—Cu6—Se4—Cu7	179.31 (19)	Se5^viii—Cu6—Se10—Cu3^iii	−177.87 (19)
Se3^iii—Cu6—Se4—Cu7	61.9 (2)	Se3^iii—Cu6—Se10—Cu3^iii	59.49 (18)
Se5^viii—Cu6—Se4—Sn3	62.60 (16)	Se4—Cu6—Se10—Sn2^viii	−175.94 (16)
Se10—Cu6—Se4—Sn3	−62.40 (19)	Se5^viii—Cu6—Se10—Sn2^viii	63.53 (19)
Se3^iii—Cu6—Se4—Sn3	−179.84 (12)	Se3^iii—Cu6—Se10—Sn2^viii	−59.11 (15)
Se5—Sn3—Se4—Cu5	61.25 (15)	Se12^i—Cu1—Se11—Cu2	−51.5 (3)
Se3—Sn3—Se4—Cu5	−173.49 (14)	Se8—Cu1—Se11—Cu2	70.46 (17)
Se6—Sn3—Se4—Cu5	−63.57 (14)	Se2^ii—Cu1—Se11—Cu2	−174.04 (14)
Se5—Sn3—Se4—Cu7	−56.7 (2)	Se12^i—Cu1—Se11—Cu4	177.37 (19)
Se3—Sn3—Se4—Cu7	68.6 (2)	Se8—Cu1—Se11—Cu4	−60.6 (2)
Se6—Sn3—Se4—Cu7	178.5 (2)	Se2^ii—Cu1—Se11—Cu4	54.9 (2)
Se5—Sn3—Se4—Cu6	178.76 (15)	Se12^i—Cu1—Se11—Sn1^viii	64.4 (3)
Se3—Sn3—Se4—Cu6	−55.99 (15)	Se8—Cu1—Se11—Sn1^viii	−173.65 (13)
Se6—Sn3—Se4—Cu6	53.93 (15)	Se2^ii—Cu1—Se11—Sn1^viii	−58.14 (14)
Se9—Cu8—Se5—Cu6^v	−178.72 (15)	Se8^iii—Cu2—Se11—Cu1	177.74 (13)
Se12—Cu8—Se5—Cu6^v	54.0 (2)	Se9^iv—Cu2—Se11—Cu1	49.3 (2)
Se1^v—Cu8—Se5—Cu6^v	−61.6 (2)	Se2—Cu2—Se11—Cu1	−65.0 (2)
Se9—Cu8—Se5—Cu5^vi	−47.5 (2)	Se8^iii—Cu2—Se11—Cu4	−50.8 (2)
Se12—Cu8—Se5—Cu5^vi	−174.74 (17)	Se9^iv—Cu2—Se11—Cu4	−179.27 (16)
Se1^v—Cu8—Se5—Cu5^vi	69.6 (2)	Se2—Cu2—Se11—Cu4	66.5 (2)
Se9—Cu8—Se5—Sn3	68.3 (2)	Se8^iii—Cu2—Se11—Sn1^viii	62.99 (17)
Se12—Cu8—Se5—Sn3	−58.9 (2)	Se9^iv—Cu2—Se11—Sn1^viii	−65.5 (2)
Se1^v—Cu8—Se5—Sn3	−174.56 (13)	Se2—Cu2—Se11—Sn1^viii	−179.70 (15)
Se4—Sn3—Se5—Cu6^v	−60.15 (14)	Se7—Cu4—Se11—Cu1	−54.5 (2)
Se3—Sn3—Se5—Cu6^v	175.34 (14)	Se10—Cu4—Se11—Cu1	177.96 (17)
Se6—Sn3—Se5—Cu6^v	64.81 (14)	Se6—Cu4—Se11—Cu1	61.6 (2)
Se4—Sn3—Se5—Cu5^vi	178.91 (16)	Se7—Cu4—Se11—Cu2	174.93 (16)
Se3—Sn3—Se5—Cu5^vi	54.40 (14)	Se10—Cu4—Se11—Cu2	47.3 (3)
Se6—Sn3—Se5—Cu5^vi	−56.12 (15)	Se6—Cu4—Se11—Cu2	−69.1 (2)
Se4—Sn3—Se5—Cu8	59.14 (17)	Se7—Cu4—Se11—Sn1^viii	59.28 (17)
Se3—Sn3—Se5—Cu8	−65.37 (16)	Se10—Cu4—Se11—Sn1^viii	−68.31 (19)
Se6—Sn3—Se5—Cu8	−175.89 (17)	Se6—Cu4—Se11—Sn1^viii	175.29 (15)
Se7—Cu4—Se6—Cu3	62.89 (19)	Se4—Cu7—Se12—Cu1^ix	174.6 (2)
Se10—Cu4—Se6—Cu3	−178.38 (14)	Se9^iii—Cu7—Se12—Cu1^ix	52.2 (2)
Se11—Cu4—Se6—Cu3	−57.67 (19)	Se1—Cu7—Se12—Cu1^ix	−63.8 (2)
Se7—Cu4—Se6—Sn2	−174.40 (13)	Se4—Cu7—Se12—Cu8	−57.3 (2)
Se10—Cu4—Se6—Sn2	−55.67 (17)	Se9^iii—Cu7—Se12—Cu8	−179.68 (13)
Se11—Cu4—Se6—Sn2	65.04 (15)	Se1—Cu7—Se12—Cu8	64.34 (18)
Se7—Cu4—Se6—Sn3	−62.96 (16)	Se4—Cu7—Se12—Sn4^vii	59.9 (2)
Se10—Cu4—Se6—Sn3	55.77 (18)	Se9^iii—Cu7—Se12—Sn4^vii	−62.51 (16)
Se11—Cu4—Se6—Sn3	176.49 (11)	Se1—Cu7—Se12—Sn4^vii	−178.50 (13)
Se8—Cu3—Se6—Cu4	53.69 (19)	Se9—Cu8—Se12—Cu7	−68.70 (19)
Se7^v—Cu3—Se6—Cu4	−179.64 (14)	Se5—Cu8—Se12—Cu7	60.6 (3)
Se10^vi—Cu3—Se6—Cu4	−63.04 (19)	Se1^v—Cu8—Se12—Cu7	174.89 (13)
Se8—Cu3—Se6—Sn2	−69.79 (15)	Se9—Cu8—Se12—Cu1^ix	56.6 (3)
Se7^v—Cu3—Se6—Sn2	56.88 (15)	Se5—Cu8—Se12—Cu1^ix	−174.1 (3)
Se10^vi—Cu3—Se6—Sn2	173.48 (12)	Se1^v—Cu8—Se12—Cu1^ix	−59.8 (2)
Se8—Cu3—Se6—Sn3	179.53 (9)	Se9—Cu8—Se12—Sn4^vii	173.76 (13)
Se7^v—Cu3—Se6—Sn3	−53.80 (18)	Se5—Cu8—Se12—Sn4^vii	−57.0 (2)
Se10^vi—Cu3—Se6—Sn3	62.80 (18)	Se1^v—Cu8—Se12—Sn4^vii	57.35 (15)

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