Reinvestigation of the crystal structure of lautite, CuAsS

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).

Related literature

For related literature, see: Craig & Stephenson (1965); Marumo & Nowacki (1964); Wyckoff (1963).

Experimental

Crystal data

• AsCuS

• M_r = 170.54

• Orthorhombic, P n m a

• a = 11.347 (4) Å

• b = 3.7533 (7) Å

• c = 5.453 (1) Å

• V = 232.24 (10) ų

• Z = 4

• Mo Kα radiation

• μ = 24.00 mm⁻¹

• T = 298 (2) K

• 0.12 × 0.10 × 0.08 mm

Data collection

• Bruker P4 diffractometer

• Absorption correction: ψ scan (North et al., 1968) T_min = 0.070, T_max = 0.150

• 3824 measured reflections

• 574 independent reflections

• 483 reflections with I > 2σ(I)

• R_int = 0.077

• 3 standard reflections every 150 reflections intensity decay: none

Refinement

• R[F² > 2σ(F²)] = 0.046

• wR(F²) = 0.108

• S = 1.09

• 574 reflections

• 19 parameters

• Δρ_max = 1.28 e Å⁻³

• Δρ_min = −1.07 e Å⁻³

Data collection: XSCANS (Bruker, 1997); cell refinement: XSCANS; data reduction: XSCANS; 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.

Supporting information

S1. Comment

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).

Related literature

For related literature, see: Craig & Stephenson (1965); Marumo & Nowacki (1964); Wyckoff (1963).

S2. Experimental

A crystal was selected from a natural specimen belonging to the Mineralogical Collection of the Natural History Museum of Florence (catalogue number 44202/G).

S3. Refinement

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.

Computing details

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).

Figures

	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.
	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.

copper arsenic sulfide

Crystal data

AsCuS	F(000) = 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 = 12.5–24.3°
b = 3.7533 (7) Å	µ = 24.00 mm^−1
c = 5.453 (1) Å	T = 298 K
V = 232.24 (10) Å^3	Block, black
Z = 4	0.12 × 0.10 × 0.08 mm

Data collection

Bruker P4 diffractometer	483 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.077
Graphite monochromator	θmax = 35.0°, θmin = 3.6°
ω scans	h = −18→18
Absorption correction: ψ scan (North et al., 1968)	k = −6→6
Tmin = 0.070, Tmax = 0.150	l = −8→8
3824 measured reflections	3 standard reflections every 150 reflections
574 independent reflections	intensity decay: none

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.046	Secondary atom site location: difference Fourier map
wR(F^2) = 0.108	w = 1/[σ^2(Fo^2) + (0.0856P)^2 + 1.9844P] where P = (Fo^2 + 2Fc^2)/3
S = 1.09	(Δ/σ)max < 0.001
574 reflections	Δρmax = 1.28 at 0.0736 0.2500 0.3457 (0.68 Å from As) e Å^−3
19 parameters	Δρmin = −1.07 at 0.0052 0.0883 0.4402 (0.78 Å from As) e Å^−3

Special details

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 (Ų)

	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)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
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

Geometric parameters (Å, º)

Cu—S^i	2.2908 (16)	As—As^v	2.4965 (8)
Cu—S^ii	2.2996 (10)	S—As^iv	2.2408 (16)
Cu—S^iii	2.2996 (10)	S—Cu^vi	2.2908 (16)
Cu—As	2.4114 (11)	S—Cu^vii	2.2996 (10)
As—S^iv	2.2408 (16)	S—Cu^viii	2.2996 (10)
As—As^iv	2.4965 (8)
S^i—Cu—S^ii	112.76 (3)	S^iv—As—As^v	99.01 (4)
S^i—Cu—S^iii	112.76 (3)	Cu—As—As^v	121.19 (3)
S^ii—Cu—S^iii	109.39 (7)	As^iv—As—As^v	97.48 (4)
S^i—Cu—As	101.46 (5)	As^iv—S—Cu^vi	117.64 (7)
S^ii—Cu—As	110.12 (4)	As^iv—S—Cu^vii	106.24 (5)
S^iii—Cu—As	110.12 (4)	Cu^vi—S—Cu^vii	108.56 (4)
S^iv—As—Cu	114.52 (5)	As^iv—S—Cu^viii	106.24 (5)
S^iv—As—As^iv	99.01 (4)	Cu^vi—S—Cu^viii	108.56 (4)
Cu—As—As^iv	121.19 (3)	Cu^vii—S—Cu^viii	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.