Acta Cryst. (2008). E64, i22 [ doi:10.1107/S1600536808004492 ]
The crystal structure of the mineral lautite (copper arsenic sulfide), CuAsS, previously described as either centrosymmetric [Pnma; Marumo & Nowacki (1964). Schweiz. Miner. Petro. Mitt. 44, 439-454] or noncentrosymmetric [Pna21; Craig & Stephenson (1965). Acta Cryst. 19, 543-547], was reinvestigated by means of single-crystal X-ray diffraction. The centrosymmetric structural model reported previously was confirmed, although with improved precision for the atomic coordinates and interatomic distances. Lautite shows a sphalerite-derivative structure with a linking of Cu[AsS3], As[CuAs2S] and S[Cu3As] tetrahedra. All atoms lie on special positions (Wyckoff position 4c, site symmetry m).
A crystal was selected from a natural specimen belonging to the Mineralogical Collection of the Natural History Museum of Florence (catalogue number 44202/G).
The crystal structure refinement was performed starting from the atomic coordinates reported by Marumo & Nowacki (1964). Convergence was rapidly obtained for an anisotropic model of the structure.
Data collection: XSCANS (Bruker, 1997); cell refinement: XSCANS (Bruker, 1997); data reduction: XSCANS (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Xtaldraw (Downs & Hall-Wallace, 2003); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).
![[Figure 1]](./fi2059fig1thm.gif)
| Fig. 1. The crystal structure of lautite down [010]. Displacement parameters are drawn at the 70% probability level. The unit-cell is outlined. Symmetry codes are: (i) -x + 1/2; -y; z + 1/2; (ii) x + 1/2; -y + 1/2; -z + 1/2; (iii) -x; y + 1/2; -z. |
![[Figure 2]](./fi2059fig2thm.gif)
| Fig. 2. The crystal structure of lautite showing the linking of Cu[AsS3], As[CuAs2S] and S[Cu3As] tetrahedra. Blu, red and yellow circles indicate Cu, As and S atoms, respectively. The unit-cell is outlined. |
| AsCuS | F000 = 312 |
| Mr = 170.54 | Dx = 4.878 Mg m−3 |
| Orthorhombic, Pnma | Mo Kα radiation λ = 0.71073 Å |
| Hall symbol: -P 2ac 2n | Cell parameters from 38 reflections |
| a = 11.347 (4) Å | θ = 12.5–24.3º |
| b = 3.7533 (7) Å | µ = 24.00 mm−1 |
| c = 5.453 (1) Å | T = 298 (2) K |
| V = 232.24 (10) Å3 | Block, black |
| Z = 4 | 0.12 × 0.10 × 0.08 mm |
| Bruker P4 diffractometer | Rint = 0.077 |
| Radiation source: fine-focus sealed tube | θmax = 35.0º |
| Monochromator: graphite | θmin = 3.6º |
| T = 298(2) K | h = −18→18 |
| ω scans | k = −6→6 |
| Absorption correction: ψ scan (North et al., 1968) | l = −8→8 |
| Tmin = 0.070, Tmax = 0.150 | 3 standard reflections |
| 3824 measured reflections | every 150 reflections |
| 574 independent reflections | intensity decay: none |
| 483 reflections with I > 2σ(I) |
| Refinement on F2 | Primary atom site location: structure-invariant direct methods |
| Least-squares matrix: full | Secondary atom site location: difference Fourier map |
| R[F2 > 2σ(F2)] = 0.046 | w = 1/[σ2(Fo2) + (0.0856P)2 + 1.9844P] where P = (Fo2 + 2Fc2)/3 |
| wR(F2) = 0.108 | (Δ/σ)max < 0.001 |
| S = 1.09 | Δρmax = 1.28at 0.0736 0.2500 0.3457 (0.68 Å from As) e Å−3 |
| 574 reflections | Δρmin = −1.07at 0.0052 0.0883 0.4402 (0.78 Å from As) e Å−3 |
| 19 parameters | Extinction correction: none |
| AsCuS | V = 232.24 (10) Å3 |
| Mr = 170.54 | Z = 4 |
| Orthorhombic, Pnma | Mo Kα |
| a = 11.347 (4) Å | µ = 24.00 mm−1 |
| b = 3.7533 (7) Å | T = 298 (2) K |
| c = 5.453 (1) Å | 0.12 × 0.10 × 0.08 mm |
| Bruker P4 diffractometer | 483 reflections with I > 2σ(I) |
| Absorption correction: ψ scan (North et al., 1968) | Rint = 0.077 |
| Tmin = 0.070, Tmax = 0.150 | 3 standard reflections |
| 3824 measured reflections | every 150 reflections |
| 574 independent reflections | intensity decay: none |
| R[F2 > 2σ(F2)] = 0.046 | 19 parameters |
| wR(F2) = 0.108 | Δρmax = 1.28at 0.0736 0.2500 0.3457 (0.68 Å from As) e Å−3 |
| S = 1.09 | Δρmin = −1.07at 0.0052 0.0883 0.4402 (0.78 Å from As) e Å−3 |
| 574 reflections |
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. |
| x | y | z | Uiso*/Ueq | ||
| Cu | 0.17454 (7) | 0.2500 | 0.06264 (18) | 0.0165 (2) | |
| As | 0.01373 (5) | 0.2500 | 0.35177 (11) | 0.00894 (18) | |
| S | 0.16576 (12) | 0.7500 | 0.8196 (3) | 0.0100 (3) |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| Cu | 0.0171 (3) | 0.0168 (4) | 0.0157 (4) | 0.000 | −0.0015 (3) | 0.000 |
| As | 0.0105 (3) | 0.0084 (3) | 0.0080 (3) | 0.000 | 0.00083 (17) | 0.000 |
| S | 0.0108 (5) | 0.0114 (5) | 0.0079 (5) | 0.000 | −0.0005 (4) | 0.000 |
| Cu—Si | 2.2908 (16) | As—Asv | 2.4965 (8) |
| Cu—Sii | 2.2996 (10) | S—Asiv | 2.2408 (16) |
| Cu—Siii | 2.2996 (10) | S—Cuvi | 2.2908 (16) |
| Cu—As | 2.4114 (11) | S—Cuvii | 2.2996 (10) |
| As—Siv | 2.2408 (16) | S—Cuviii | 2.2996 (10) |
| As—Asiv | 2.4965 (8) | ||
| Si—Cu—Sii | 112.76 (3) | Siv—As—Asv | 99.01 (4) |
| Si—Cu—Siii | 112.76 (3) | Cu—As—Asv | 121.19 (3) |
| Sii—Cu—Siii | 109.39 (7) | Asiv—As—Asv | 97.48 (4) |
| Si—Cu—As | 101.46 (5) | Asiv—S—Cuvi | 117.64 (7) |
| Sii—Cu—As | 110.12 (4) | Asiv—S—Cuvii | 106.24 (5) |
| Siii—Cu—As | 110.12 (4) | Cuvi—S—Cuvii | 108.56 (4) |
| Siv—As—Cu | 114.52 (5) | Asiv—S—Cuviii | 106.24 (5) |
| Siv—As—Asiv | 99.01 (4) | Cuvi—S—Cuviii | 108.56 (4) |
| Cu—As—Asiv | 121.19 (3) | Cuvii—S—Cuviii | 109.39 (7) |
| Symmetry codes: (i) −x+1/2, −y+1, z−1/2; (ii) x, y−1, z−1; (iii) x, y, z−1; (iv) −x, −y+1, −z+1; (v) −x, −y, −z+1; (vi) −x+1/2, −y+1, z+1/2; (vii) x, y+1, z+1; (viii) x, y, z+1. |
This work was funded by CNR, Istituto di Geoscienze e Georisorse, Sezione di Firenze.
Bruker (1997). XSCANS. Bruker AXS Inc., Madison, Wisconsin, USA.
Craig, D. C. & Stephenson, N. C. (1965). Acta Cryst. 19, 543–547.
Downs, R. T. & Hall-Wallace, M. (2003). Am. Mineral. 88, 247–250.
Marumo, F. & Nowacki, W. (1964). Schweiz. Miner. Petro. Mitt. 44, 439–454.
North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351–359.
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.
Wyckoff, R. W. G. (1963). Crystal Structures, 2nd ed. New York: Interscience Publishers.
The crystal structure of lautite was solved by Marumo & Nowacki (1964) in the space group Pnma (R = 9.0%) and by Craig & Stephenson (1965) in the space group Pna21 (R = 13.7%) by means of photographic data and three-dimensional Patterson-function. The low quality of the structural data given by these authors, however, did not allow to obtain an anisotropic model of the structure. Nevertheless, the topologies and interatomic distances of both centrosymmetric and non-centrosymmetric models are very similar.
Although the structural results obtained by Craig & Stephenson (1965) indicate the acentricity of the structure of CuAsS, no clear crystal-chemical reason for the choice of a noncentrosymmetric arrangement was given. To help resolve the concerns relating to the structure of natural lautite, we present new crystal structure data for lautite from its type locality (i.e., Marienberg, Saxony, Germany).
The centrosymmetric structural model previously reported by Marumo & Nowacki (1964) was confirmed, although a higher precision of refinement was achieved (e.s.d. improved by a factor of two) and refinement with anisotropic displacement parameters could be performed (Fig. 1). All atoms lie on special positions (Wyckoff position 4c, site symmetry m). Lautite shows a sphalerite-derivative structure with a linking of Cu[AsS3], As[CuAs2S] and S[Cu3As] tetrahedra (Fig. 2). Within the framework, the As atoms form zigzag As—As chains along [010] exhibiting As—As bond distances [2.4965 (8) Å] and angles [97.48 (4)°] resembling the covalent As—As linkage observed within the sheets of the crystal structure of arsenic (Wyckoff, 1963).