Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270110014034/sq3242sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270110014034/sq3242Isup2.hkl |
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.
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).
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).
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) Å3 | 0.10 × 0.09 × 0.05 mm |
Z = 16 |
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 on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | w = 1/[σ2(Fo2) + (0.0287P)2] where P = (Fo2 + 2Fc2)/3 |
R[F2 > 2σ(F2)] = 0.047 | (Δ/σ)max = 0.001 |
wR(F2) = 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+0.001xFc2λ3/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) |
Cu2Se3Sn | V = 2211.7 (8) Å3 |
Mr = 482.65 | Z = 16 |
Monoclinic, Cc | Mo Kα radiation |
a = 6.9612 (14) Å | µ = 31.69 mm−1 |
b = 12.043 (2) Å | T = 295 K |
c = 26.481 (5) Å | 0.10 × 0.09 × 0.05 mm |
β = 94.97 (3)° |
Kuma KM-4 with CCD area-detector diffractometer | 4780 independent reflections |
Absorption correction: numerical (CrysAlis RED; Oxford Diffraction, 2007) | 2338 reflections with I > 2σ(I) |
Tmin = 0.038, Tmax = 0.212 | Rint = 0.095 |
12585 measured reflections |
R[F2 > 2σ(F2)] = 0.047 | 2 restraints |
wR(F2) = 0.104 | Δρmax = 1.87 e Å−3 |
S = 0.76 | Δρmin = −1.14 e Å−3 |
4780 reflections | Absolute structure: Flack (1983), with 2258 Friedel pairs |
219 parameters | Absolute structure parameter: 0.078 (15) |
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. |
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) |
U11 | U22 | U33 | U12 | U13 | U23 | |
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) |
Cu1—Se11 | 2.388 (5) | Sn1—Se11v | 2.512 (3) |
Cu1—Se12i | 2.414 (4) | Sn1—Se2 | 2.592 (3) |
Cu1—Se8 | 2.418 (4) | Sn1—Se1i | 2.615 (3) |
Cu1—Se2ii | 2.476 (5) | Sn2—Se7vii | 2.501 (3) |
Cu2—Se8iii | 2.390 (5) | Sn2—Se10v | 2.507 (3) |
Cu2—Se9iv | 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—Se7v | 2.403 (4) | Sn3—Se3 | 2.615 (3) |
Cu3—Se10vi | 2.420 (4) | Sn3—Se6 | 2.627 (3) |
Cu3—Se6 | 2.479 (4) | Sn4—Se9 | 2.488 (3) |
Cu4—Se7 | 2.403 (5) | Sn4—Se12ii | 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—Cu8viii | 2.455 (4) |
Cu5—Se4 | 2.397 (4) | Se1—Sn1ix | 2.615 (3) |
Cu5—Se7vii | 2.404 (4) | Se2—Cu1vii | 2.476 (5) |
Cu5—Se5iii | 2.409 (4) | Se3—Cu6vi | 2.468 (4) |
Cu5—Se3vii | 2.482 (4) | Se3—Cu5ii | 2.482 (4) |
Cu6—Se4 | 2.407 (4) | Se5—Cu6v | 2.408 (4) |
Cu6—Se5viii | 2.408 (4) | Se5—Cu5vi | 2.409 (4) |
Cu6—Se10 | 2.411 (4) | Se7—Cu3viii | 2.403 (4) |
Cu6—Se3iii | 2.468 (4) | Se7—Cu5ii | 2.404 (4) |
Cu7—Se12 | 2.392 (5) | Se7—Sn2ii | 2.501 (3) |
Cu7—Se4 | 2.403 (4) | Se8—Cu2vi | 2.390 (5) |
Cu7—Se9iii | 2.430 (4) | Se9—Cu2x | 2.410 (4) |
Cu7—Se1 | 2.475 (5) | Se9—Cu7vi | 2.430 (4) |
Cu8—Se9 | 2.398 (4) | Se10—Cu3iii | 2.420 (4) |
Cu8—Se12 | 2.420 (4) | Se10—Sn2viii | 2.507 (3) |
Cu8—Se5 | 2.430 (4) | Se11—Sn1viii | 2.512 (3) |
Cu8—Se1v | 2.455 (4) | Se12—Cu1ix | 2.414 (4) |
Sn1—Se8 | 2.502 (3) | Se12—Sn4vii | 2.502 (3) |
Se11—Cu1—Se12i | 115.91 (15) | Cu8viii—Se1—Cu7 | 114.83 (15) |
Se11—Cu1—Se8 | 108.05 (18) | Cu8viii—Se1—Sn4 | 110.10 (13) |
Se12i—Cu1—Se8 | 108.5 (2) | Cu7—Se1—Sn4 | 108.06 (12) |
Se11—Cu1—Se2ii | 109.72 (19) | Cu8viii—Se1—Sn1ix | 111.04 (14) |
Se12i—Cu1—Se2ii | 107.92 (19) | Cu7—Se1—Sn1ix | 110.12 (15) |
Se8—Cu1—Se2ii | 106.31 (15) | Sn4—Se1—Sn1ix | 101.86 (10) |
Se8iii—Cu2—Se9iv | 116.46 (15) | Cu1vii—Se2—Cu2 | 111.07 (16) |
Se8iii—Cu2—Se11 | 109.8 (2) | Cu1vii—Se2—Sn1 | 110.92 (15) |
Se9iv—Cu2—Se11 | 108.7 (2) | Cu2—Se2—Sn1 | 111.70 (15) |
Se8iii—Cu2—Se2 | 109.3 (2) | Cu1vii—Se2—Sn2 | 107.24 (11) |
Se9iv—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—Se7v | 116.21 (17) | Cu6vi—Se3—Cu5ii | 111.82 (15) |
Se8—Cu3—Se10vi | 108.92 (15) | Cu6vi—Se3—Sn4 | 107.25 (13) |
Se7v—Cu3—Se10vi | 108.70 (14) | Cu5ii—Se3—Sn4 | 111.84 (14) |
Se8—Cu3—Se6 | 108.06 (14) | Cu6vi—Se3—Sn3 | 109.89 (11) |
Se7v—Cu3—Se6 | 108.31 (16) | Cu5ii—Se3—Sn3 | 111.68 (12) |
Se10vi—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—Se7vii | 116.72 (17) | Cu6v—Se5—Cu5vi | 113.26 (17) |
Se4—Cu5—Se5iii | 109.71 (16) | Cu6v—Se5—Cu8 | 113.80 (19) |
Se7vii—Cu5—Se5iii | 108.75 (19) | Cu5vi—Se5—Cu8 | 113.24 (16) |
Se4—Cu5—Se3vii | 108.77 (17) | Cu6v—Se5—Sn3 | 104.99 (12) |
Se7vii—Cu5—Se3vii | 107.39 (17) | Cu5vi—Se5—Sn3 | 107.61 (12) |
Se5iii—Cu5—Se3vii | 104.83 (15) | Cu8—Se5—Sn3 | 102.80 (16) |
Se4—Cu6—Se5viii | 107.38 (18) | Cu4—Se6—Cu3 | 114.37 (15) |
Se4—Cu6—Se10 | 109.05 (16) | Cu4—Se6—Sn2 | 110.11 (11) |
Se5viii—Cu6—Se10 | 114.83 (16) | Cu3—Se6—Sn2 | 108.69 (12) |
Se4—Cu6—Se3iii | 107.53 (15) | Cu4—Se6—Sn3 | 110.68 (11) |
Se5viii—Cu6—Se3iii | 109.34 (15) | Cu3—Se6—Sn3 | 110.69 (11) |
Se10—Cu6—Se3iii | 108.48 (18) | Sn2—Se6—Sn3 | 101.53 (10) |
Se12—Cu7—Se4 | 115.1 (2) | Cu4—Se7—Cu3viii | 109.22 (15) |
Se12—Cu7—Se9iii | 109.35 (18) | Cu4—Se7—Cu5ii | 115.86 (17) |
Se4—Cu7—Se9iii | 108.45 (15) | Cu3viii—Se7—Cu5ii | 110.17 (16) |
Se12—Cu7—Se1 | 109.13 (14) | Cu4—Se7—Sn2ii | 107.95 (13) |
Se4—Cu7—Se1 | 108.0 (2) | Cu3viii—Se7—Sn2ii | 107.63 (13) |
Se9iii—Cu7—Se1 | 106.38 (17) | Cu5ii—Se7—Sn2ii | 105.64 (14) |
Se9—Cu8—Se12 | 110.15 (17) | Cu2vi—Se8—Cu3 | 110.90 (12) |
Se9—Cu8—Se5 | 114.1 (2) | Cu2vi—Se8—Cu1 | 110.93 (18) |
Se12—Cu8—Se5 | 113.46 (16) | Cu3—Se8—Cu1 | 115.50 (15) |
Se9—Cu8—Se1v | 107.57 (15) | Cu2vi—Se8—Sn1 | 105.48 (16) |
Se12—Cu8—Se1v | 106.58 (16) | Cu3—Se8—Sn1 | 104.65 (12) |
Se5—Cu8—Se1v | 104.4 (2) | Cu1—Se8—Sn1 | 108.69 (13) |
Se8—Sn1—Se11v | 115.48 (12) | Cu8—Se9—Cu2x | 109.68 (19) |
Se8—Sn1—Se2 | 109.34 (11) | Cu8—Se9—Cu7vi | 110.53 (17) |
Se11v—Sn1—Se2 | 110.31 (12) | Cu2x—Se9—Cu7vi | 115.88 (14) |
Se8—Sn1—Se1i | 109.83 (13) | Cu8—Se9—Sn4 | 107.01 (12) |
Se11v—Sn1—Se1i | 109.34 (12) | Cu2x—Se9—Sn4 | 105.57 (18) |
Se2—Sn1—Se1i | 101.65 (11) | Cu7vi—Se9—Sn4 | 107.68 (14) |
Se7vii—Sn2—Se10v | 112.96 (11) | Cu4—Se10—Cu6 | 110.64 (16) |
Se7vii—Sn2—Se6 | 110.48 (11) | Cu4—Se10—Cu3iii | 110.74 (16) |
Se10v—Sn2—Se6 | 111.43 (10) | Cu6—Se10—Cu3iii | 115.53 (15) |
Se7vii—Sn2—Se2 | 107.08 (10) | Cu4—Se10—Sn2viii | 106.46 (14) |
Se10v—Sn2—Se2 | 110.68 (9) | Cu6—Se10—Sn2viii | 105.22 (14) |
Se6—Sn2—Se2 | 103.73 (9) | Cu3iii—Se10—Sn2viii | 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—Sn1viii | 105.01 (15) |
Se5—Sn3—Se6 | 109.44 (10) | Cu2—Se11—Sn1viii | 106.91 (14) |
Se3—Sn3—Se6 | 101.22 (10) | Cu4—Se11—Sn1viii | 103.78 (11) |
Se9—Sn4—Se12ii | 113.39 (12) | Cu7—Se12—Cu1ix | 110.38 (18) |
Se9—Sn4—Se3 | 111.00 (12) | Cu7—Se12—Cu8 | 109.61 (15) |
Se12ii—Sn4—Se3 | 106.97 (12) | Cu1ix—Se12—Cu8 | 115.33 (15) |
Se9—Sn4—Se1 | 111.48 (10) | Cu7—Se12—Sn4vii | 108.24 (14) |
Se12ii—Sn4—Se1 | 109.73 (11) | Cu1ix—Se12—Sn4vii | 105.28 (17) |
Se3—Sn4—Se1 | 103.74 (11) | Cu8—Se12—Sn4vii | 107.66 (14) |
Se12—Cu7—Se1—Cu8viii | −179.39 (15) | Se7vii—Sn2—Se6—Cu4 | 53.61 (14) |
Se4—Cu7—Se1—Cu8viii | −53.5 (2) | Se10v—Sn2—Se6—Cu4 | −179.96 (13) |
Se9iii—Cu7—Se1—Cu8viii | 62.73 (18) | Se2—Sn2—Se6—Cu4 | −60.85 (12) |
Se12—Cu7—Se1—Sn4 | −56.08 (16) | Se7vii—Sn2—Se6—Cu3 | 179.60 (12) |
Se4—Cu7—Se1—Sn4 | 69.78 (18) | Se10v—Sn2—Se6—Cu3 | −53.97 (14) |
Se9iii—Cu7—Se1—Sn4 | −173.96 (12) | Se2—Sn2—Se6—Cu3 | 65.14 (12) |
Se12—Cu7—Se1—Sn1ix | 54.39 (16) | Se7vii—Sn2—Se6—Sn3 | −63.68 (12) |
Se4—Cu7—Se1—Sn1ix | −179.75 (15) | Se10v—Sn2—Se6—Sn3 | 62.75 (12) |
Se9iii—Cu7—Se1—Sn1ix | −63.49 (17) | Se2—Sn2—Se6—Sn3 | −178.14 (7) |
Se9—Sn4—Se1—Cu8viii | 179.74 (13) | Se4—Sn3—Se6—Cu4 | −51.89 (14) |
Se12ii—Sn4—Se1—Cu8viii | −53.80 (14) | Se5—Sn3—Se6—Cu4 | 179.43 (15) |
Se3—Sn4—Se1—Cu8viii | 60.22 (16) | Se3—Sn3—Se6—Cu4 | 63.00 (14) |
Se9—Sn4—Se1—Cu7 | 53.61 (14) | Se4—Sn3—Se6—Cu3 | −179.77 (13) |
Se12ii—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—Sn1ix | −62.38 (16) | Se4—Sn3—Se6—Sn2 | 64.98 (10) |
Se12ii—Sn4—Se1—Sn1ix | 64.08 (15) | Se5—Sn3—Se6—Sn2 | −63.70 (12) |
Se3—Sn4—Se1—Sn1ix | 178.10 (19) | Se3—Sn3—Se6—Sn2 | 179.87 (11) |
Se8iii—Cu2—Se2—Cu1vii | −62.34 (19) | Se10—Cu4—Se7—Cu3viii | 69.5 (2) |
Se9iv—Cu2—Se2—Cu1vii | 64.6 (2) | Se11—Cu4—Se7—Cu3viii | −59.53 (19) |
Se11—Cu2—Se2—Cu1vii | 179.99 (16) | Se6—Cu4—Se7—Cu3viii | −174.12 (13) |
Se8iii—Cu2—Se2—Sn1 | 173.25 (13) | Se10—Cu4—Se7—Cu5ii | −55.6 (2) |
Se9iv—Cu2—Se2—Sn1 | −59.8 (2) | Se11—Cu4—Se7—Cu5ii | 175.38 (15) |
Se11—Cu2—Se2—Sn1 | 55.58 (18) | Se6—Cu4—Se7—Cu5ii | 60.8 (2) |
Se8iii—Cu2—Se2—Sn2 | 57.13 (19) | Se10—Cu4—Se7—Sn2ii | −173.76 (14) |
Se9iv—Cu2—Se2—Sn2 | −175.94 (16) | Se11—Cu4—Se7—Sn2ii | 57.22 (18) |
Se11—Cu2—Se2—Sn2 | −60.53 (19) | Se6—Cu4—Se7—Sn2ii | −57.37 (16) |
Se8—Sn1—Se2—Cu1vii | −178.09 (13) | Se7v—Cu3—Se8—Cu2vi | 59.6 (2) |
Se11v—Sn1—Se2—Cu1vii | 53.88 (13) | Se10vi—Cu3—Se8—Cu2vi | −63.6 (2) |
Se1i—Sn1—Se2—Cu1vii | −62.03 (17) | Se6—Cu3—Se8—Cu2vi | −178.51 (19) |
Se8—Sn1—Se2—Cu2 | −53.59 (13) | Se7v—Cu3—Se8—Cu1 | −173.14 (14) |
Se11v—Sn1—Se2—Cu2 | 178.38 (14) | Se10vi—Cu3—Se8—Cu1 | 63.7 (2) |
Se1i—Sn1—Se2—Cu2 | 62.48 (17) | Se6—Cu3—Se8—Cu1 | −51.2 (2) |
Se8—Sn1—Se2—Sn2 | 66.80 (13) | Se7v—Cu3—Se8—Sn1 | −53.70 (17) |
Se11v—Sn1—Se2—Sn2 | −61.23 (14) | Se10vi—Cu3—Se8—Sn1 | −176.83 (14) |
Se1i—Sn1—Se2—Sn2 | −177.14 (14) | Se6—Cu3—Se8—Sn1 | 68.22 (16) |
Se7vii—Sn2—Se2—Cu1vii | 63.65 (15) | Se11—Cu1—Se8—Cu2vi | −178.10 (14) |
Se10v—Sn2—Se2—Cu1vii | −59.86 (15) | Se12i—Cu1—Se8—Cu2vi | −51.7 (2) |
Se6—Sn2—Se2—Cu1vii | −179.48 (13) | Se2ii—Cu1—Se8—Cu2vi | 64.2 (2) |
Se7vii—Sn2—Se2—Cu2 | −58.07 (17) | Se11—Cu1—Se8—Cu3 | 54.6 (2) |
Se10v—Sn2—Se2—Cu2 | 178.42 (14) | Se12i—Cu1—Se8—Cu3 | −178.94 (17) |
Se6—Sn2—Se2—Cu2 | 58.79 (16) | Se2ii—Cu1—Se8—Cu3 | −63.1 (2) |
Se7vii—Sn2—Se2—Sn1 | −178.67 (11) | Se11—Cu1—Se8—Sn1 | −62.57 (17) |
Se10v—Sn2—Se2—Sn1 | 57.81 (13) | Se12i—Cu1—Se8—Sn1 | 63.86 (19) |
Se6—Sn2—Se2—Sn1 | −61.81 (13) | Se2ii—Cu1—Se8—Sn1 | 179.71 (14) |
Se9—Sn4—Se3—Cu6vi | 59.06 (15) | Se11v—Sn1—Se8—Cu2vi | −60.75 (14) |
Se12ii—Sn4—Se3—Cu6vi | −65.12 (15) | Se2—Sn1—Se8—Cu2vi | 174.16 (13) |
Se1—Sn4—Se3—Cu6vi | 178.90 (11) | Se1i—Sn1—Se8—Cu2vi | 63.43 (17) |
Se9—Sn4—Se3—Cu5ii | −178.01 (13) | Se11v—Sn1—Se8—Cu3 | 56.31 (14) |
Se12ii—Sn4—Se3—Cu5ii | 57.82 (19) | Se2—Sn1—Se8—Cu3 | −68.78 (14) |
Se1—Sn4—Se3—Cu5ii | −58.16 (15) | Se1i—Sn1—Se8—Cu3 | −179.51 (16) |
Se9—Sn4—Se3—Sn3 | −57.34 (14) | Se11v—Sn1—Se8—Cu1 | −179.76 (15) |
Se12ii—Sn4—Se3—Sn3 | 178.49 (9) | Se2—Sn1—Se8—Cu1 | 55.15 (15) |
Se1—Sn4—Se3—Sn3 | 62.50 (12) | Se1i—Sn1—Se8—Cu1 | −55.57 (17) |
Se4—Sn3—Se3—Cu6vi | 178.63 (14) | Se12—Cu8—Se9—Cu2x | −51.2 (2) |
Se5—Sn3—Se3—Cu6vi | −52.70 (14) | Se5—Cu8—Se9—Cu2x | 179.9 (2) |
Se6—Sn3—Se3—Cu6vi | 63.09 (14) | Se1v—Cu8—Se9—Cu2x | 64.6 (2) |
Se4—Sn3—Se3—Cu5ii | 53.94 (14) | Se12—Cu8—Se9—Cu7vi | 179.86 (13) |
Se5—Sn3—Se3—Cu5ii | −177.39 (15) | Se5—Cu8—Se9—Cu7vi | 50.9 (3) |
Se6—Sn3—Se3—Cu5ii | −61.60 (14) | Se1v—Cu8—Se9—Cu7vi | −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) | Se1v—Cu8—Se9—Sn4 | 178.66 (14) |
Se7vii—Cu5—Se4—Cu7 | 176.7 (2) | Se12ii—Sn4—Se9—Cu8 | 179.35 (15) |
Se5iii—Cu5—Se4—Cu7 | −59.1 (2) | Se3—Sn4—Se9—Cu8 | 58.91 (14) |
Se3vii—Cu5—Se4—Cu7 | 55.06 (19) | Se1—Sn4—Se9—Cu8 | −56.21 (14) |
Se7vii—Cu5—Se4—Cu6 | −53.8 (3) | Se12ii—Sn4—Se9—Cu2x | −63.85 (14) |
Se5iii—Cu5—Se4—Cu6 | 70.40 (19) | Se3—Sn4—Se9—Cu2x | 175.70 (16) |
Se3vii—Cu5—Se4—Cu6 | −175.47 (13) | Se1—Sn4—Se9—Cu2x | 60.58 (16) |
Se7vii—Cu5—Se4—Sn3 | 63.3 (2) | Se12ii—Sn4—Se9—Cu7vi | 60.51 (14) |
Se5iii—Cu5—Se4—Sn3 | −172.49 (14) | Se3—Sn4—Se9—Cu7vi | −59.93 (16) |
Se3vii—Cu5—Se4—Sn3 | −58.35 (16) | Se1—Sn4—Se9—Cu7vi | −175.06 (12) |
Se12—Cu7—Se4—Cu5 | −59.6 (2) | Se7—Cu4—Se10—Cu6 | 51.2 (2) |
Se9iii—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—Cu3iii | −179.41 (15) |
Se9iii—Cu7—Se4—Cu6 | −63.1 (2) | Se11—Cu4—Se10—Cu3iii | −50.4 (2) |
Se1—Cu7—Se4—Cu6 | 51.8 (2) | Se6—Cu4—Se10—Cu3iii | 64.39 (19) |
Se12—Cu7—Se4—Sn3 | 53.6 (2) | Se7—Cu4—Se10—Sn2viii | −62.65 (16) |
Se9iii—Cu7—Se4—Sn3 | 176.44 (14) | Se11—Cu4—Se10—Sn2viii | 66.37 (18) |
Se1—Cu7—Se4—Sn3 | −68.65 (19) | Se6—Cu4—Se10—Sn2viii | −178.84 (13) |
Se5viii—Cu6—Se4—Cu5 | 176.92 (13) | Se4—Cu6—Se10—Cu4 | 69.5 (2) |
Se10—Cu6—Se4—Cu5 | 51.9 (2) | Se5viii—Cu6—Se10—Cu4 | −51.1 (2) |
Se3iii—Cu6—Se4—Cu5 | −65.52 (18) | Se3iii—Cu6—Se10—Cu4 | −173.70 (17) |
Se5viii—Cu6—Se4—Cu7 | −55.7 (2) | Se4—Cu6—Se10—Cu3iii | −57.3 (2) |
Se10—Cu6—Se4—Cu7 | 179.31 (19) | Se5viii—Cu6—Se10—Cu3iii | −177.87 (19) |
Se3iii—Cu6—Se4—Cu7 | 61.9 (2) | Se3iii—Cu6—Se10—Cu3iii | 59.49 (18) |
Se5viii—Cu6—Se4—Sn3 | 62.60 (16) | Se4—Cu6—Se10—Sn2viii | −175.94 (16) |
Se10—Cu6—Se4—Sn3 | −62.40 (19) | Se5viii—Cu6—Se10—Sn2viii | 63.53 (19) |
Se3iii—Cu6—Se4—Sn3 | −179.84 (12) | Se3iii—Cu6—Se10—Sn2viii | −59.11 (15) |
Se5—Sn3—Se4—Cu5 | 61.25 (15) | Se12i—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) | Se2ii—Cu1—Se11—Cu2 | −174.04 (14) |
Se5—Sn3—Se4—Cu7 | −56.7 (2) | Se12i—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) | Se2ii—Cu1—Se11—Cu4 | 54.9 (2) |
Se5—Sn3—Se4—Cu6 | 178.76 (15) | Se12i—Cu1—Se11—Sn1viii | 64.4 (3) |
Se3—Sn3—Se4—Cu6 | −55.99 (15) | Se8—Cu1—Se11—Sn1viii | −173.65 (13) |
Se6—Sn3—Se4—Cu6 | 53.93 (15) | Se2ii—Cu1—Se11—Sn1viii | −58.14 (14) |
Se9—Cu8—Se5—Cu6v | −178.72 (15) | Se8iii—Cu2—Se11—Cu1 | 177.74 (13) |
Se12—Cu8—Se5—Cu6v | 54.0 (2) | Se9iv—Cu2—Se11—Cu1 | 49.3 (2) |
Se1v—Cu8—Se5—Cu6v | −61.6 (2) | Se2—Cu2—Se11—Cu1 | −65.0 (2) |
Se9—Cu8—Se5—Cu5vi | −47.5 (2) | Se8iii—Cu2—Se11—Cu4 | −50.8 (2) |
Se12—Cu8—Se5—Cu5vi | −174.74 (17) | Se9iv—Cu2—Se11—Cu4 | −179.27 (16) |
Se1v—Cu8—Se5—Cu5vi | 69.6 (2) | Se2—Cu2—Se11—Cu4 | 66.5 (2) |
Se9—Cu8—Se5—Sn3 | 68.3 (2) | Se8iii—Cu2—Se11—Sn1viii | 62.99 (17) |
Se12—Cu8—Se5—Sn3 | −58.9 (2) | Se9iv—Cu2—Se11—Sn1viii | −65.5 (2) |
Se1v—Cu8—Se5—Sn3 | −174.56 (13) | Se2—Cu2—Se11—Sn1viii | −179.70 (15) |
Se4—Sn3—Se5—Cu6v | −60.15 (14) | Se7—Cu4—Se11—Cu1 | −54.5 (2) |
Se3—Sn3—Se5—Cu6v | 175.34 (14) | Se10—Cu4—Se11—Cu1 | 177.96 (17) |
Se6—Sn3—Se5—Cu6v | 64.81 (14) | Se6—Cu4—Se11—Cu1 | 61.6 (2) |
Se4—Sn3—Se5—Cu5vi | 178.91 (16) | Se7—Cu4—Se11—Cu2 | 174.93 (16) |
Se3—Sn3—Se5—Cu5vi | 54.40 (14) | Se10—Cu4—Se11—Cu2 | 47.3 (3) |
Se6—Sn3—Se5—Cu5vi | −56.12 (15) | Se6—Cu4—Se11—Cu2 | −69.1 (2) |
Se4—Sn3—Se5—Cu8 | 59.14 (17) | Se7—Cu4—Se11—Sn1viii | 59.28 (17) |
Se3—Sn3—Se5—Cu8 | −65.37 (16) | Se10—Cu4—Se11—Sn1viii | −68.31 (19) |
Se6—Sn3—Se5—Cu8 | −175.89 (17) | Se6—Cu4—Se11—Sn1viii | 175.29 (15) |
Se7—Cu4—Se6—Cu3 | 62.89 (19) | Se4—Cu7—Se12—Cu1ix | 174.6 (2) |
Se10—Cu4—Se6—Cu3 | −178.38 (14) | Se9iii—Cu7—Se12—Cu1ix | 52.2 (2) |
Se11—Cu4—Se6—Cu3 | −57.67 (19) | Se1—Cu7—Se12—Cu1ix | −63.8 (2) |
Se7—Cu4—Se6—Sn2 | −174.40 (13) | Se4—Cu7—Se12—Cu8 | −57.3 (2) |
Se10—Cu4—Se6—Sn2 | −55.67 (17) | Se9iii—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—Sn4vii | 59.9 (2) |
Se10—Cu4—Se6—Sn3 | 55.77 (18) | Se9iii—Cu7—Se12—Sn4vii | −62.51 (16) |
Se11—Cu4—Se6—Sn3 | 176.49 (11) | Se1—Cu7—Se12—Sn4vii | −178.50 (13) |
Se8—Cu3—Se6—Cu4 | 53.69 (19) | Se9—Cu8—Se12—Cu7 | −68.70 (19) |
Se7v—Cu3—Se6—Cu4 | −179.64 (14) | Se5—Cu8—Se12—Cu7 | 60.6 (3) |
Se10vi—Cu3—Se6—Cu4 | −63.04 (19) | Se1v—Cu8—Se12—Cu7 | 174.89 (13) |
Se8—Cu3—Se6—Sn2 | −69.79 (15) | Se9—Cu8—Se12—Cu1ix | 56.6 (3) |
Se7v—Cu3—Se6—Sn2 | 56.88 (15) | Se5—Cu8—Se12—Cu1ix | −174.1 (3) |
Se10vi—Cu3—Se6—Sn2 | 173.48 (12) | Se1v—Cu8—Se12—Cu1ix | −59.8 (2) |
Se8—Cu3—Se6—Sn3 | 179.53 (9) | Se9—Cu8—Se12—Sn4vii | 173.76 (13) |
Se7v—Cu3—Se6—Sn3 | −53.80 (18) | Se5—Cu8—Se12—Sn4vii | −57.0 (2) |
Se10vi—Cu3—Se6—Sn3 | 62.80 (18) | Se1v—Cu8—Se12—Sn4vii | 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. |
Experimental details
Crystal data | |
Chemical formula | Cu2Se3Sn |
Mr | 482.65 |
Crystal system, space group | Monoclinic, Cc |
Temperature (K) | 295 |
a, b, c (Å) | 6.9612 (14), 12.043 (2), 26.481 (5) |
β (°) | 94.97 (3) |
V (Å3) | 2211.7 (8) |
Z | 16 |
Radiation type | Mo Kα |
µ (mm−1) | 31.69 |
Crystal size (mm) | 0.10 × 0.09 × 0.05 |
Data collection | |
Diffractometer | Kuma KM-4 with CCD area-detector diffractometer |
Absorption correction | Numerical (CrysAlis RED; Oxford Diffraction, 2007) |
Tmin, Tmax | 0.038, 0.212 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 12585, 4780, 2338 |
Rint | 0.095 |
(sin θ/λ)max (Å−1) | 0.649 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.047, 0.104, 0.76 |
No. of reflections | 4780 |
No. of parameters | 219 |
No. of restraints | 2 |
Δρmax, Δρmin (e Å−3) | 1.87, −1.14 |
Absolute structure | Flack (1983), with 2258 Friedel pairs |
Absolute structure parameter | 0.078 (15) |
Computer programs: CrysAlis CCD (Oxford Diffraction, 2007), CrysAlis RED (Oxford Diffraction, 2007), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2009), publCIF (Westrip, 2010).
Cu1 | 1.401 | Sn1 | 3.742 | Se5 | 2.122 |
Cu2 | 1.390 | Sn2 | 3.762 | Se6 | 2.210 |
Cu3 | 1.395 | Sn3 | 3.690 | Se7 | 2.181 |
Cu4 | 1.394 | Sn4 | 3.781 | Se8 | 2.180 |
Cu5 | 1.405 | Se1 | 2.205 | Se9 | 2.192 |
Cu6 | 1.401 | Se2 | 2.222 | Se10 | 2.133 |
Cu7 | 1.397 | Se3 | 2.203 | Se11 | 2.141 |
Cu8 | 1.391 | Se4 | 2.195 | Se12 | 2.162 |
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 CuI and SnIV ions is surrounded by four Se2- 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 CuI 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 Se2- 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.