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The title compound, Cs4As4Se8, contains discrete cyclic [As4Se8]4- anions consisting of corner-sharing AsSe3 pyramids. A twist-chair conformation is observed for the eight-membered As4Se4 rings, which exhibit a crystallographic inversion centre. Both of the crystallographically independent Cs+ cations contain eight Se atoms in their coordination spheres.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536806003898/wm6134sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536806003898/wm6134Isup2.hkl
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 292 K
  • Mean [sigma](e-As)= 0.002 Å
  • R factor = 0.037
  • wR factor = 0.099
  • Data-to-parameter ratio = 26.2

checkCIF/PLATON results

No syntax errors found


No errors found in this datablock

Computing details top

Data collection: R3m/V Software (Siemens, 1989); cell refinement: R3m/V Software; data reduction: XDISK (Siemens, 1989); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1995); software used to prepare material for publication: SHELXL97.

Tetracaesium octaselenidotetraarsenat(III) top
Crystal data top
Cs4As4Se8F(000) = 1248
Mr = 1463.00Dx = 4.468 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 24 reflections
a = 7.1572 (13) Åθ = 5.1–17.3°
b = 14.862 (3) ŵ = 26.06 mm1
c = 10.515 (4) ÅT = 292 K
β = 103.51 (2)°Prism, red
V = 1087.5 (5) Å30.12 × 0.11 × 0.09 mm
Z = 2
Data collection top
Siemens P4 four-circle
diffractometer
1594 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.037
Graphite monochromatorθmax = 25.0°, θmin = 2.4°
ω scansh = 18
Absorption correction: ψ scan
(XPREP in SHELXTL; Sheldrick, 1995)
k = 117
Tmin = 0.054, Tmax = 0.092l = 1212
2600 measured reflections3 standard reflections every 97 reflections
1916 independent reflections intensity decay: 0.1%
Refinement top
Refinement on F20 restraints
Least-squares matrix: fullPrimary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.037Secondary atom site location: difference Fourier map
wR(F2) = 0.099 w = 1/[σ2(Fo2) + (0.0697P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.02(Δ/σ)max < 0.001
1916 reflectionsΔρmax = 1.28 e Å3
73 parametersΔρmin = 1.23 e Å3
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 (Å2) top
xyzUiso*/Ueq
Cs10.85765 (9)0.29650 (4)0.54437 (6)0.0281 (2)
Cs20.27440 (9)0.60646 (4)0.06525 (6)0.0303 (2)
Se10.53222 (14)0.39975 (6)0.25300 (9)0.0247 (2)
Se210.06135 (14)0.32341 (6)0.24246 (9)0.0245 (2)
Se20.62602 (14)0.62158 (6)0.43672 (9)0.0230 (2)
Se110.81064 (14)0.59227 (7)0.14932 (10)0.0257 (2)
As10.79060 (13)0.51023 (6)0.33216 (8)0.0184 (2)
As20.25976 (13)0.43913 (6)0.34317 (9)0.0194 (2)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cs10.0284 (4)0.0241 (3)0.0324 (4)0.0005 (2)0.0080 (3)0.0027 (2)
Cs20.0251 (3)0.0380 (4)0.0278 (4)0.0017 (3)0.0060 (3)0.0016 (3)
Se10.0247 (5)0.0264 (5)0.0257 (5)0.0087 (4)0.0116 (4)0.0100 (4)
Se210.0224 (5)0.0256 (5)0.0235 (5)0.0053 (4)0.0012 (4)0.0033 (4)
Se20.0248 (5)0.0233 (5)0.0208 (5)0.0028 (4)0.0050 (4)0.0019 (4)
Se110.0258 (5)0.0279 (5)0.0250 (5)0.0013 (4)0.0092 (4)0.0059 (4)
As10.0153 (4)0.0209 (4)0.0177 (4)0.0003 (3)0.0014 (3)0.0000 (3)
As20.0199 (5)0.0159 (4)0.0225 (5)0.0004 (4)0.0049 (4)0.0009 (3)
Geometric parameters (Å, º) top
Cs1—Se1i3.6877 (13)Cs2—Se21ix3.8412 (14)
Cs1—Se11ii3.6966 (13)Cs2—Se13.8778 (14)
Cs1—Se2iii3.7185 (13)Cs2—Se1vii3.9099 (16)
Cs1—Se13.7192 (16)Cs2—Se24.1289 (18)
Cs1—Se21i3.7518 (14)Se1—As22.4306 (13)
Cs1—Se21iv3.8114 (16)Se1—As12.4676 (13)
Cs1—Se2v3.8516 (13)Se21—As22.3223 (13)
Cs1—Se11v3.8949 (16)Se2—As12.4372 (13)
Cs2—Se11vi3.6352 (14)Se2—As2iii2.4403 (15)
Cs2—Se11vii3.6801 (14)Se11—As12.3092 (14)
Cs2—Se21viii3.7009 (16)As2—Se2iii2.4403 (15)
Cs2—Se113.7377 (14)
As2—Se1—As1108.33 (5)Se2—As1—Se1101.59 (5)
As1—Se2—As2iii94.98 (5)Se21—As2—Se196.01 (5)
Se11—As1—Se298.49 (5)Se21—As2—Se2iii101.09 (5)
Se11—As1—Se1104.95 (5)Se1—As2—Se2iii99.18 (5)
As2iii—Se2—As1—Se11155.96 (5)As2—Se1—As1—Se28.79 (6)
As2iii—Se2—As1—Se196.77 (5)As1—Se1—As2—Se21178.95 (5)
As2—Se1—As1—Se11110.96 (6)As1—Se1—As2—Se2iii78.76 (6)
Symmetry codes: (i) x+1/2, y+1/2, z+1/2; (ii) x+3/2, y1/2, z+1/2; (iii) x+1, y+1, z+1; (iv) x+1, y, z; (v) x+2, y+1, z+1; (vi) x1, y, z; (vii) x+1, y+1, z; (viii) x, y+1, z; (ix) x+1/2, y+1/2, z+1/2.
 

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