Incommensurately modulated lanthanide coinage-metal diarsenides. II. GdCuAs₂, GdAu_1−δAs₂ and TbAu_1−δAs₂ – new distortion variants of the HfCuSi₂ type with irregularly stacked zigzag chains of arsenic atoms

GdCuAs₂, GdAu_1−δAs₂ and TbAu_1−δAs₂ crystallize as incommensurately modulated variants of the HfCuSi₂ type. Structure models have been developed in the monoclinic superspace group P12₁/m1(α0γ)00 (No. 11.1). The components of the modulation wavevectors q = αa* + 0b* + γc* are α = 0.04 (1) and γ = 0.48 (1) for GdCuAs₂, α = 0.03 (1) and γ = 0.48 (1) for GdAu_1−δAs₂ and α = 0.02 (1) and γ = 0.46 (1) for TbAu_1−δAs₂. The predominant effect of the positional modulation is the distortion of a square net of arsenic atoms, which results in planar zigzag chains. Rod groups and layer groups of the respective structure motifs are identified and discussed.

Computing details

For all compounds, data collection: X-AREA, STOE, 2006; cell refinement: X-AREA, STOE, 2006; data reduction: X-AREA, STOE, 2002; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: Jana2000 (Petricek, Dusek & Palatinus, 2000); molecular graphics: DIAMOND-Visuelles Informationssystem für Kristallstrukturen

(G. Bergerhoff, Bonn, 1999); software used to prepare material for publication: Jana2000 (Petricek, Dusek & Palatinus, 2000).

Figures

(I)

Crystal data

As2CuGd	F(000) = 318
Mr = 370.6	Dx = 8.153 Mg m^−3
Monoclinic, P21/m(α0γ)00†	Mo Kα radiation, λ = 0.71073 Å
q = 0.03570a* + 0.47900c*	Cell parameters from 10083 reflections
a = 3.9041 (8) Å	θ = 3.0–33.5°
b = 3.9015 (8) Å	µ = 50.25 mm^−1
c = 9.908 (2) Å	T = 293 K
β = 90.05 (3)°	Platelet, black
V = 150.92 (5) Å^3	0.26 × 0.06 × 0.02 mm
Z = 2

† Symmetry operations: (1) x₁, x₂, x₃, x₄; (2) −x₁, 1/2+x₂, −x₃, −x₄; (3) −x₁, −x₂, −x₃, −x₄; (4) x₁, 1/2−x₂, x₃, x₄.

Data collection

STOE IPDS 2 diffractometer	2043 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	751 reflections with I > 3σ(I)
Plane graphite monochromator	Rint = 0.094
Detector resolution: 6.67 pixels mm^-1	θmax = 34.2°, θmin = 3.1°
ω scans	h = −6→6
Absorption correction: numerical (Jana2000; Petricek, Dusek & Palatinus, 2000)	k = −5→6
Tmin = 0.128, Tmax = 0.460	l = −16→16
10072 measured reflections

Refinement

Refinement on F	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
R[F^2 > 2σ(F^2)] = 0.039	(Δ/σ)max = 0.022
wR(F^2) = 0.039	Δρmax = 1.64 e Å^−3
S = 1.24	Δρmin = −1.97 e Å^−3
2043 reflections	Extinction correction: B-C type 1 Gaussian isotropic (Becker & Coppens, 1974)
77 parameters	Extinction coefficient: 0.14 (1)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Gd	0.2476 (3)	0.25	0.76146 (4)	0.01281 (10)
Cu	0.7439 (13)	0.25	0.49985 (18)	0.0166 (3)
As1	0.2543 (7)	0.25	0.34179 (8)	0.0134 (2)
As2	0.7398 (11)	0.25	0.99949 (15)	0.0173 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Gd	0.00981 (17)	0.01209 (18)	0.01652 (16)	0	0.0015 (9)	0
Cu	0.0137 (7)	0.0150 (5)	0.0210 (6)	0	−0.005 (2)	0
As1	0.0095 (3)	0.0115 (3)	0.0192 (4)	0	−0.0026 (15)	0
As2	0.0154 (6)	0.0192 (5)	0.0173 (4)	0	−0.0014 (14)	0

Bond lengths (Å)

	Average	Minimum	Maximum
Gd—Cu^i	3.253 (6)	3.239 (6)	3.268 (6)
Gd—Cu	3.236 (6)	3.213 (6)	3.260 (6)
Gd—Cu^ii	3.242 (5)	3.228 (5)	3.255 (5)
Gd—Cu^iii	3.242 (5)	3.228 (5)	3.255 (5)
Gd—As1^iv	2.948 (3)	2.945 (3)	2.951 (3)
Gd—As1^v	2.948 (3)	2.945 (3)	2.951 (3)
Gd—As1^ii	2.938 (3)	2.934 (3)	2.943 (3)
Gd—As1^iii	2.938 (3)	2.934 (3)	2.943 (3)
Gd—As2^i	3.082 (5)	3.017 (5)	3.145 (5)
Gd—As2	3.042 (5)	3.026 (5)	3.059 (5)
Gd—As2^vi	3.070 (4)	3.037 (4)	3.107 (4)
Gd—As2^vii	3.070 (4)	3.037 (4)	3.107 (4)
Cu—Cu^ii	2.726 (5)	2.724 (5)	2.728 (5)
Cu—Cu^iii	2.726 (5)	2.724 (5)	2.728 (5)
Cu—Cu^viii	2.794 (5)	2.787 (5)	2.801 (5)
Cu—Cu^ix	2.794 (5)	2.787 (5)	2.801 (5)
Cu—As1	2.471 (7)	2.464 (7)	2.478 (7)
Cu—As1^x	2.535 (7)	2.521 (7)	2.548 (7)
Cu—As1^ii	2.503 (5)	2.492 (5)	2.515 (5)
Cu—As1^iii	2.503 (5)	2.492 (5)	2.515 (5)
As2—As2^vi	2.705 (5)	2.568 (4)	2.850 (5)
As2—As2^vii	2.705 (5)	2.568 (4)	2.850 (5)
As2—As2^xi	2.820 (5)	2.675 (5)	2.967 (5)
As2—As2^xii	2.820 (5)	2.675 (5)	2.967 (5)

Symmetry codes: (i) x₁−1, x₂, x₃, x₄; (ii) −x₁+1, −x₂, −x₃+1, −x₄; (iii) −x₁+1, −x₂+1, −x₃+1, −x₄; (iv) −x₁, −x₂, −x₃+1, −x₄; (v) −x₁, −x₂+1, −x₃+1, −x₄; (vi) −x₁+1, −x₂, −x₃+2, −x₄; (vii) −x₁+1, −x₂+1, −x₃+2, −x₄; (viii) −x₁+2, −x₂, −x₃+1, −x₄; (ix) −x₁+2, −x₂+1, −x₃+1, −x₄; (x) x₁+1, x₂, x₃, x₄; (xi) −x₁+2, −x₂, −x₃+2, −x₄; (xii) −x₁+2, −x₂+1, −x₃+2, −x₄.

(II)

Crystal data

As2Au0.973Gd	F(000) = 414
Mr = 498.7	Dx = 10.174 Mg m^−3
Monoclinic, P21/m(α0γ)00†	Mo Kα radiation, λ = 0.71073 Å
q = 0.03000a* + 0.48000c*	Cell parameters from 6594 reflections
a = 3.9570 (8) Å	θ = 3.0–33.5°
b = 4.060 (2) Å	µ = 83.84 mm^−1
c = 10.135 (2) Å	T = 293 K
β = 90.01 (3)°	Platelet, black
V = 162.82 (9) Å^3	0.31 × 0.06 × 0.0025 mm
Z = 2

† Symmetry operations: (1) x₁, x₂, x₃, x₄; (2) −x₁, 1/2+x₂, −x₃, −x₄; (3) −x₁, −x₂, −x₃, −x₄; (4) x₁, 1/2−x₂, x₃, x₄.

Data collection

STOE IPDS 2 diffractometer	2428 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	1634 reflections with I > 3σ(I)
Plane graphite monochromator	Rint = 0.077
Detector resolution: 6.67 pixels mm^-1	θmax = 33.8°, θmin = 3.0°
ω scans	h = −6→5
Absorption correction: numerical (Jana2000; Petricek, Dusek & Palatinus, 2000)	k = −6→6
Tmin = 0.064, Tmax = 0.807	l = −16→13
9508 measured reflections

Refinement

Refinement on F	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
R[F^2 > 2σ(F^2)] = 0.046	(Δ/σ)max = 0.042
wR(F^2) = 0.050	Δρmax = 3.04 e Å^−3
S = 2.37	Δρmin = −2.62 e Å^−3
2428 reflections	Extinction correction: B-C type 1 Gaussian isotropic (Becker & Coppens, 1974)
78 parameters	Extinction coefficient: 0.19 (5)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Gd	0.2519 (4)	0.25	0.76613 (5)	0.0129 (3)
Au	0.7492 (4)	0.25	0.5006 (3)	0.0197 (3)	0.973 (3)
As1	0.2590 (10)	0.25	0.31231 (13)	0.0137 (6)
As2	0.7511 (12)	0.25	0.9981 (6)	0.0188 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Gd	0.0189 (7)	0.0075 (5)	0.0122 (2)	0	−0.0056 (8)	0
Au	0.0250 (6)	0.0154 (5)	0.0186 (2)	0	−0.0049 (8)	0
As1	0.0165 (13)	0.0090 (12)	0.0157 (5)	0	−0.0073 (13)	0
As2	0.0248 (14)	0.0225 (13)	0.0090 (6)	0	−0.0028 (17)	0

Bond lengths (Å)

	Average	Minimum	Maximum
Gd—Au^i	3.347 (4)	3.342 (4)	3.352 (4)
Gd—Au	3.335 (4)	3.310 (4)	3.359 (4)
Gd—Au^ii	3.381 (4)	3.366 (4)	3.395 (4)
Gd—Au^iii	3.381 (4)	3.366 (4)	3.395 (4)
Gd—As1^iv	2.973 (4)	2.970 (4)	2.977 (4)
Gd—As1^v	2.973 (4)	2.970 (4)	2.977 (4)
Gd—As1^ii	2.915 (4)	2.908 (4)	2.922 (4)
Gd—As1^iii	2.915 (4)	2.908 (4)	2.922 (4)
Gd—As2^i	3.074 (8)	3.003 (9)	3.148 (9)
Gd—As2	3.071 (8)	3.038 (9)	3.104 (9)
Gd—As2^vi	3.140 (8)	3.112 (8)	3.174 (8)
Gd—As2^vii	3.140 (8)	3.112 (8)	3.174 (8)
Au—Au^ii	2.8304 (19)	2.8244 (19)	2.8364 (19)
Au—Au^iii	2.8304 (19)	2.8244 (19)	2.8364 (19)
Au—Au^viii	2.8391 (19)	2.8337 (19)	2.8444 (19)
Au—Au^ix	2.8391 (19)	2.8337 (19)	2.8444 (19)
Au—As1	2.720 (6)	2.716 (6)	2.725 (6)
Au—As1^x	2.777 (6)	2.750 (6)	2.804 (6)
Au—As1^ii	2.779 (5)	2.763 (5)	2.794 (5)
Au—As1^iii	2.779 (5)	2.763 (5)	2.794 (5)
As1—As2^xi	3.769 (10)	3.686 (11)	3.856 (11)
As1—As2^xii	3.734 (10)	3.593 (11)	3.881 (11)
As2—As2^vi	2.848 (5)	2.641 (5)	3.058 (6)
As2—As2^vii	2.848 (5)	2.641 (5)	3.058 (6)
As2—As2^xiii	2.831 (5)	2.632 (5)	3.044 (6)
As2—As2^xiv	2.831 (5)	2.632 (5)	3.044 (6)

Symmetry codes: (i) x₁−1, x₂, x₃, x₄; (ii) −x₁+1, −x₂, −x₃+1, −x₄; (iii) −x₁+1, −x₂+1, −x₃+1, −x₄; (iv) −x₁, −x₂, −x₃+1, −x₄; (v) −x₁, −x₂+1, −x₃+1, −x₄; (vi) −x₁+1, −x₂, −x₃+2, −x₄; (vii) −x₁+1, −x₂+1, −x₃+2, −x₄; (viii) −x₁+2, −x₂, −x₃+1, −x₄; (ix) −x₁+2, −x₂+1, −x₃+1, −x₄; (x) x₁+1, x₂, x₃, x₄; (xi) x₁−1, x₂, x₃−1, x₄; (xii) x₁, x₂, x₃−1, x₄; (xiii) −x₁+2, −x₂, −x₃+2, −x₄; (xiv) −x₁+2, −x₂+1, −x₃+2, −x₄.

(III)

Crystal data

As2Au0.966Tb	F(000) = 415
Mr = 499.0	Dx = 10.166 Mg m^−3
Monoclinic, P21/m(α0γ)00†	Mo Kα radiation, λ = 0.71073 Å
q = 0.02000a* + 0.46000c*	Cell parameters from 7354 reflections
a = 3.933 (2) Å	θ = 3.0–33.4°
b = 4.0891 (15) Å	µ = 84.78 mm^−1
c = 10.1350 (14) Å	T = 293 K
β = 90.0 (3)°	Platelet, black
V = 163.01 (12) Å^3	0.13 × 0.12 × 0.01 mm
Z = 2

† Symmetry operations: (1) x₁, x₂, x₃, x₄; (2) −x₁, 1/2+x₂, −x₃, −x₄; (3) −x₁, −x₂, −x₃, −x₄; (4) x₁, 1/2−x₂, x₃, x₄.

Data collection

STOE IPDS 2 diffractometer	2101 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	1092 reflections with I > 3σ(I)
Plane graphite monochromator	Rint = 0.059
Detector resolution: 6.67 pixels mm^-1	θmax = 33.4°, θmin = 3.0°
ω scans	h = −5→6
Absorption correction: numerical (Jana2000; Petricek, Dusek & Palatinus, 2000)	k = −5→6
Tmin = 0.066, Tmax = 0.892	l = −16→16
9845 measured reflections

Refinement

Refinement on F	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
R[F^2 > 2σ(F^2)] = 0.056	(Δ/σ)max = 0.034
wR(F^2) = 0.066	Δρmax = 3.84 e Å^−3
S = 2.96	Δρmin = −3.65 e Å^−3
2101 reflections	Extinction correction: B-C type 1 Lorentzian isotropic (Becker & Coppens, 1974)
78 parameters	Extinction coefficient: 0.26 (3)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Au1	0.7484 (10)	0.25	0.50072 (17)	0.0259 (3)	0.968 (4)
As1	0.2667 (16)	0.25	0.31004 (18)	0.0174 (6)
As2	0.751 (3)	0.25	0.9982 (4)	0.0246 (8)
Tb1	0.2494 (8)	0.25	0.76696 (6)	0.0179 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Au1	0.0256 (6)	0.0250 (6)	0.0271 (3)	0	−0.001 (2)	0
As1	0.0138 (13)	0.0155 (11)	0.0229 (5)	0	−0.0045 (19)	0
As2	0.0315 (18)	0.0253 (15)	0.0170 (5)	0	−0.002 (4)	0
Tb1	0.0173 (6)	0.0167 (6)	0.0198 (2)	0	0.0004 (19)	0

Bond lengths (Å)

	Average	Minimum	Maximum
Au1—Au1^i	2.829 (4)	2.826 (4)	2.831 (4)
Au1—Au1^ii	2.829 (4)	2.826 (4)	2.831 (4)
Au1—Au1^iii	2.845 (4)	2.843 (4)	2.848 (4)
Au1—Au1^iv	2.845 (4)	2.843 (4)	2.848 (4)
Au1—As1	2.707 (8)	2.684 (8)	2.729 (8)
Au1—As1^v	2.809 (8)	2.779 (8)	2.839 (8)
Au1—As1^i	2.804 (5)	2.778 (5)	2.830 (5)
Au1—As1^ii	2.804 (5)	2.778 (5)	2.830 (5)
Au1—Tb1	3.337 (5)	3.319 (5)	3.354 (5)
Au1—Tb1^v	3.341 (5)	3.333 (5)	3.349 (5)
Au1—Tb1^i	3.397 (4)	3.385 (4)	3.409 (4)
Au1—Tb1^ii	3.397 (4)	3.385 (4)	3.409 (4)
As1—As2^vi	3.757 (11)	3.666 (12)	3.848 (12)
As1—As2^vii	3.690 (11)	3.648 (12)	3.735 (12)
As1—Tb1^viii	2.985 (6)	2.974 (6)	2.996 (6)
As1—Tb1^ix	2.985 (6)	2.974 (6)	2.996 (6)
As1—Tb1^i	2.901 (6)	2.897 (6)	2.904 (6)
As1—Tb1^ii	2.901 (6)	2.897 (6)	2.904 (6)
As2—As2^x	2.844 (12)	2.725 (11)	2.962 (13)
As2—As2^xi	2.844 (12)	2.725 (11)	2.962 (13)
As2—As2^xii	2.833 (12)	2.717 (11)	2.954 (12)
As2—As2^xiii	2.833 (12)	2.717 (11)	2.954 (12)
As2—Tb1	3.063 (10)	3.026 (11)	3.100 (11)
As2—Tb1^v	3.056 (10)	3.029 (11)	3.085 (11)
As2—Tb1^x	3.139 (6)	3.135 (6)	3.141 (7)
As2—Tb1^xi	3.139 (6)	3.135 (6)	3.141 (7)

Symmetry codes: (i) −x₁+1, −x₂, −x₃+1, −x₄; (ii) −x₁+1, −x₂+1, −x₃+1, −x₄; (iii) −x₁+2, −x₂, −x₃+1, −x₄; (iv) −x₁+2, −x₂+1, −x₃+1, −x₄; (v) x₁+1, x₂, x₃, x₄; (vi) x₁−1, x₂, x₃−1, x₄; (vii) x₁, x₂, x₃−1, x₄; (viii) −x₁, −x₂, −x₃+1, −x₄; (ix) −x₁, −x₂+1, −x₃+1, −x₄; (x) −x₁+1, −x₂, −x₃+2, −x₄; (xi) −x₁+1, −x₂+1, −x₃+2, −x₄; (xii) −x₁+2, −x₂, −x₃+2, −x₄; (xiii) −x₁+2, −x₂+1, −x₃+2, −x₄.