Buy article online - an online subscription or single-article purchase is required to access this article.
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
Key indicators
- Single-crystal X-ray study
- T = 292 K
- Mean (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
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
Cs4As4Se8 | F(000) = 1248 |
Mr = 1463.00 | Dx = 4.468 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yn | Cell parameters from 24 reflections |
a = 7.1572 (13) Å | θ = 5.1–17.3° |
b = 14.862 (3) Å | µ = 26.06 mm−1 |
c = 10.515 (4) Å | T = 292 K |
β = 103.51 (2)° | Prism, red |
V = 1087.5 (5) Å3 | 0.12 × 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 tube | Rint = 0.037 |
Graphite monochromator | θmax = 25.0°, θmin = 2.4° |
ω scans | h = −1→8 |
Absorption correction: ψ scan (XPREP in SHELXTL; Sheldrick, 1995) | k = −1→17 |
Tmin = 0.054, Tmax = 0.092 | l = −12→12 |
2600 measured reflections | 3 standard reflections every 97 reflections |
1916 independent reflections | intensity decay: 0.1% |
Refinement top
Refinement on F2 | 0 restraints |
Least-squares matrix: full | Primary atom site location: structure-invariant direct methods |
R[F2 > 2σ(F2)] = 0.037 | Secondary 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 reflections | Δρmax = 1.28 e Å−3 |
73 parameters | Δρmin = −1.23 e Å−3 |
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 | x | y | z | Uiso*/Ueq | |
Cs1 | 0.85765 (9) | 0.29650 (4) | 0.54437 (6) | 0.0281 (2) | |
Cs2 | 0.27440 (9) | 0.60646 (4) | 0.06525 (6) | 0.0303 (2) | |
Se1 | 0.53222 (14) | 0.39975 (6) | 0.25300 (9) | 0.0247 (2) | |
Se21 | 0.06135 (14) | 0.32341 (6) | 0.24246 (9) | 0.0245 (2) | |
Se2 | 0.62602 (14) | 0.62158 (6) | 0.43672 (9) | 0.0230 (2) | |
Se11 | 0.81064 (14) | 0.59227 (7) | 0.14932 (10) | 0.0257 (2) | |
As1 | 0.79060 (13) | 0.51023 (6) | 0.33216 (8) | 0.0184 (2) | |
As2 | 0.25976 (13) | 0.43913 (6) | 0.34317 (9) | 0.0194 (2) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cs1 | 0.0284 (4) | 0.0241 (3) | 0.0324 (4) | −0.0005 (2) | 0.0080 (3) | 0.0027 (2) |
Cs2 | 0.0251 (3) | 0.0380 (4) | 0.0278 (4) | −0.0017 (3) | 0.0060 (3) | −0.0016 (3) |
Se1 | 0.0247 (5) | 0.0264 (5) | 0.0257 (5) | −0.0087 (4) | 0.0116 (4) | −0.0100 (4) |
Se21 | 0.0224 (5) | 0.0256 (5) | 0.0235 (5) | −0.0053 (4) | 0.0012 (4) | −0.0033 (4) |
Se2 | 0.0248 (5) | 0.0233 (5) | 0.0208 (5) | 0.0028 (4) | 0.0050 (4) | −0.0019 (4) |
Se11 | 0.0258 (5) | 0.0279 (5) | 0.0250 (5) | −0.0013 (4) | 0.0092 (4) | 0.0059 (4) |
As1 | 0.0153 (4) | 0.0209 (4) | 0.0177 (4) | −0.0003 (3) | 0.0014 (3) | 0.0000 (3) |
As2 | 0.0199 (5) | 0.0159 (4) | 0.0225 (5) | −0.0004 (4) | 0.0049 (4) | −0.0009 (3) |
Geometric parameters (Å, º) top
Cs1—Se1i | 3.6877 (13) | Cs2—Se21ix | 3.8412 (14) |
Cs1—Se11ii | 3.6966 (13) | Cs2—Se1 | 3.8778 (14) |
Cs1—Se2iii | 3.7185 (13) | Cs2—Se1vii | 3.9099 (16) |
Cs1—Se1 | 3.7192 (16) | Cs2—Se2 | 4.1289 (18) |
Cs1—Se21i | 3.7518 (14) | Se1—As2 | 2.4306 (13) |
Cs1—Se21iv | 3.8114 (16) | Se1—As1 | 2.4676 (13) |
Cs1—Se2v | 3.8516 (13) | Se21—As2 | 2.3223 (13) |
Cs1—Se11v | 3.8949 (16) | Se2—As1 | 2.4372 (13) |
Cs2—Se11vi | 3.6352 (14) | Se2—As2iii | 2.4403 (15) |
Cs2—Se11vii | 3.6801 (14) | Se11—As1 | 2.3092 (14) |
Cs2—Se21viii | 3.7009 (16) | As2—Se2iii | 2.4403 (15) |
Cs2—Se11 | 3.7377 (14) | | |
| | | |
As2—Se1—As1 | 108.33 (5) | Se2—As1—Se1 | 101.59 (5) |
As1—Se2—As2iii | 94.98 (5) | Se21—As2—Se1 | 96.01 (5) |
Se11—As1—Se2 | 98.49 (5) | Se21—As2—Se2iii | 101.09 (5) |
Se11—As1—Se1 | 104.95 (5) | Se1—As2—Se2iii | 99.18 (5) |
| | | |
As2iii—Se2—As1—Se11 | −155.96 (5) | As2—Se1—As1—Se2 | −8.79 (6) |
As2iii—Se2—As1—Se1 | 96.77 (5) | As1—Se1—As2—Se21 | 178.95 (5) |
As2—Se1—As1—Se11 | −110.96 (6) | As1—Se1—As2—Se2iii | −78.76 (6) |
Symmetry codes: (i) x+1/2, −y+1/2, z+1/2; (ii) −x+3/2, y−1/2, −z+1/2; (iii) −x+1, −y+1, −z+1; (iv) x+1, y, z; (v) −x+2, −y+1, −z+1; (vi) x−1, y, z; (vii) −x+1, −y+1, −z; (viii) −x, −y+1, −z; (ix) −x+1/2, y+1/2, −z+1/2. |
Subscribe to Acta Crystallographica Section E: Crystallographic Communications
The full text of this article is available to subscribers to the journal.
If you have already registered and are using a computer listed in your registration details, please email
support@iucr.org for assistance.