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The crystal structure of the third polymorph of the Cu7PSe6 argyrodite compound, α-Cu7PSe6, heptacopper phosphorus hexaselenide, is determined by means of single-crystal diffraction from twinned crystals and X-ray powder diffraction, with the help of extensive NMR measurements. In the low-temperature form, i.e. below the last phase transition, α-Cu7PSe6 crystallizes in orthorhombic symmetry, space group Pna21, with a = 14.3179 (4), b = 7.1112 (2), c = 10.1023 (3) Å, V = 1028.590 (9) Å3 (deduced from powder data, T = 173 K) and Z  = 4. Taking into account a twinning by reticular merohedry, the refinement of the α-Cu7PSe6 structure leads to the residual factors R = 0.0466 and wR = 0.0486 for 127 parameters and 3714 observed, independent reflections (single-crystal data, T = 173 K). A full localization of the Cu+d10 element is reached with one twofold-, one threefold- and five fourfold-coordinated Cu atoms. The observation of two phase transitions for Cu7PSe6, to be compared with only one for Ag7PSe6, is attributed to the d10 element stability in a low coordination environment, copper being less prone to lower coordination sites than silver, especially at low temperature.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768100010260/lc0028sup1.cif
Contains datablock alpha_Cu7PSe6

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108768100010260/lc0028sup2.hkl
Supplementary material

Computing details top

(alpha_Cu7PSe6) top
Crystal data top
Cu7PSe6V = 1028.59 (5) Å3
Mr = 949.6Z = 4
Orthorhombic, Pna21F(000) = 1688
Hall symbol: P 2c -2nDx = 6.117 Mg m3
a = 14.3179 (4) ÅMo Kα radiation, λ = 0.71073 Å
b = 7.1112 (2) ŵ = 352.9 mm1
c = 10.1023 (3) Å × × mm
Data collection top
STOE IPDS
diffractometer
3714 reflections with 3
Absorption correction: spherical
?
h = ??
Tmin = 0.053, Tmax = 0.145k = ??
29369 independent reflectionsl = ??
Refinement top
Refinement on FWeighting scheme based on measured s.u.'s w = 1/(σ2(F) + 0.0004F2)
R[F2 > 2σ(F2)] = 0.047(Δ/σ)max = 0.004
wR(F2) = 0.080Δρmax = 2.30 e Å3
S = 1.06Δρmin = 2.02 e Å3
29369 reflectionsExtinction correction: B-C type 1 Lorentzian isotropic
127 parametersExtinction coefficient: 0.018565
Crystal data top
Cu7PSe6V = 1028.59 (5) Å3
Mr = 949.6Z = 4
Orthorhombic, Pna21Mo Kα radiation
a = 14.3179 (4) ŵ = 352.9 mm1
b = 7.1112 (2) Å × × mm
c = 10.1023 (3) Å
Data collection top
STOE IPDS
diffractometer
29369 independent reflections
Absorption correction: spherical
?
3714 reflections with 3
Tmin = 0.053, Tmax = 0.145
Refinement top
R[F2 > 2σ(F2)] = 0.047127 parameters
wR(F2) = 0.080Δρmax = 2.30 e Å3
S = 1.06Δρmin = 2.02 e Å3
29369 reflections
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
P0.1239 (3)0.7531 (6)0.2500 (5)0.0027 (4)
Se1a0.0023 (2)0.7567 (3)0.1179 (5)0.0059 (6)
Se1b0.2511 (2)0.2514 (2)0.6242 (5)0.0060 (6)
Se1c0.3787 (1)0.5038 (3)0.8764 (5)0.0067 (6)
Se1d0.1194 (1)0.5047 (3)0.8734 (5)0.0058 (6)
Se20.1253 (1)0.7180 (3)0.7351 (5)0.0075 (6)
Se30.3847 (1)0.7398 (3)0.5057 (5)0.0089 (7)
Cu1a0.2375 (2)0.4640 (4)0.9976 (6)0.0224 (9)
Cu1b0.7709 (2)0.4158 (4)0.0472 (5)0.0173 (8)
Cu20.2936 (2)0.7675 (4)0.7451 (6)0.0237 (8)
Cu3a0.9671 (2)0.0921 (4)0.0879 (6)0.0240 (9)
Cu3b0.5513 (2)0.9364 (4)0.9281 (5)0.0191 (9)
Cu4a0.8575 (3)0.0214 (6)0.3652 (7)0.0523 (14)
Cu4b0.3765 (2)0.8298 (5)0.2702 (5)0.0308 (10)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Se1a0.0065 (9)0.007 (1)0.004 (1)0.0010 (7)0.0010 (7)0.0001 (8)
Se1b0.0061 (9)0.007 (1)0.005 (1)0.0010 (8)0.0041 (7)0.0009 (9)
Se1c0.0085 (9)0.006 (1)0.006 (1)0.0014 (9)0.0015 (9)0.0024 (7)
Se1d0.0069 (9)0.006 (1)0.005 (1)0.0022 (9)0.0002 (9)0.0030 (7)
Se20.0074 (9)0.0057 (9)0.009 (1)0.0009 (8)0.001 (1)0.0016 (7)
Se30.00610.012 (1)0.009 (1)0.0008 (8)0.0012 (8)0.0000 (9)
Cu1a0.017 (1)0.016 (1)0.034 (2)0.008 (1)0.012 (1)0.010 (1)
Cu1b0.016 (1)0.020 (1)0.016 (1)0.003 (1)0.008 (1)0.004 (1)
Cu20.013 (1)0.024 (2)0.034 (2)0.006 (1)0.010 (1)0.004 (2)
Cu3a0.025 (2)0.019 (2)0.028 (2)0.003 (1)0.000 (1)0.004 (1)
Cu3b0.021 (1)0.024 (2)0.013 (1)0.000 (1)0.004 (1)0.001 (1)
Cu4a0.048 (2)0.044 (2)0.065 (3)0.004 (2)0.004 (2)0.040 (2)
Cu4b0.007 (1)0.072 (2)0.013 (1)0.002 (2)0.002 (1)0.011 (1)
Bond lengths (Å) top
P—Se1a2.194 (5)Cu2—Se32.755 (7)
P—Se1ci2.195 (5)Cu3a—Se2vi2.405 (6)
P—Se1bi2.193 (5)Cu3a—Se1aviii2.457 (4)
P—Se1dii2.218 (5)Cu3a—Se3ix2.509 (4)
Cu1a—Se3iii2.369 (3)Cu3a—Se1cx2.575 (7)
Cu1a—Se1c2.380 (5)Cu3b—Se1axi2.461 (6)
Cu1a—Se1biv2.417 (5)Cu3b—Se2vii2.476 (6)
Cu1b—Se1dv2.439 (6)Cu3b—Se1dvii2.541 (4)
Cu1b—Se1bvi2.511 (4)Cu3b—Se3xii2.599 (4)
Cu1b—Se3vi2.523 (3)Cu4a—Se2vi2.285 (6)
Cu1b—Se2vi2.592 (6)Cu4a—Se3xiii2.370 (7)
Cu2—Se1dvii2.420 (5)Cu4b—Se1bi2.413 (5)
Cu2—Se22.437 (3)Cu4b—Se1avii2.447 (6)
Cu2—Se1c2.600 (5)Cu4b—Se32.467 (7)
Symmetry codes: (i) x+1/2, y+1/2, z1/2; (ii) x, y+1, z1/2; (iii) x+1/2, y1/2, z+1/2; (iv) x+1/2, y+1/2, z+1/2; (v) x+1, y, z1; (vi) x+1, y+1, z1/2; (vii) x+1/2, y+3/2, z; (viii) x+1, y1, z; (ix) x+3/2, y1/2, z1/2; (x) x+1/2, y+1/2, z1; (xi) x+1/2, y+3/2, z+1; (xii) x+1, y+2, z+1/2; (xiii) x+1/2, y+1/2, z.

Experimental details

Crystal data
Chemical formulaCu7PSe6
Mr949.6
Crystal system, space groupOrthorhombic, Pna21
Temperature (K)?
a, b, c (Å)14.3179 (4), 7.1112 (2), 10.1023 (3)
V3)1028.59 (5)
Z4
Radiation typeMo Kα
µ (mm1)352.9
Crystal size (mm) × ×
Data collection
DiffractometerSTOE IPDS
diffractometer
Absorption correctionSpherical
Tmin, Tmax0.053, 0.145
No. of measured, independent and
observed (3) reflections
?, 29369, 3714
Rint?
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.047, 0.080, 1.06
No. of reflections29369
No. of parameters127
No. of restraints?
Δρmax, Δρmin (e Å3)2.30, 2.02

Selected bond lengths (Å) top
P—Se1a2.194 (5)Cu2—Se32.755 (7)
P—Se1ci2.195 (5)Cu3a—Se2vi2.405 (6)
P—Se1bi2.193 (5)Cu3a—Se1aviii2.457 (4)
P—Se1dii2.218 (5)Cu3a—Se3ix2.509 (4)
Cu1a—Se3iii2.369 (3)Cu3a—Se1cx2.575 (7)
Cu1a—Se1c2.380 (5)Cu3b—Se1axi2.461 (6)
Cu1a—Se1biv2.417 (5)Cu3b—Se2vii2.476 (6)
Cu1b—Se1dv2.439 (6)Cu3b—Se1dvii2.541 (4)
Cu1b—Se1bvi2.511 (4)Cu3b—Se3xii2.599 (4)
Cu1b—Se3vi2.523 (3)Cu4a—Se2vi2.285 (6)
Cu1b—Se2vi2.592 (6)Cu4a—Se3xiii2.370 (7)
Cu2—Se1dvii2.420 (5)Cu4b—Se1bi2.413 (5)
Cu2—Se22.437 (3)Cu4b—Se1avii2.447 (6)
Cu2—Se1c2.600 (5)Cu4b—Se32.467 (7)
Symmetry codes: (i) x+1/2, y+1/2, z1/2; (ii) x, y+1, z1/2; (iii) x+1/2, y1/2, z+1/2; (iv) x+1/2, y+1/2, z+1/2; (v) x+1, y, z1; (vi) x+1, y+1, z1/2; (vii) x+1/2, y+3/2, z; (viii) x+1, y1, z; (ix) x+3/2, y1/2, z1/2; (x) x+1/2, y+1/2, z1; (xi) x+1/2, y+3/2, z+1; (xii) x+1, y+2, z+1/2; (xiii) x+1/2, y+1/2, z.
 

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