Crystal structure, XANES and charge distribution investigation of krennerite and sylvanite: analysis of Au—Te and Te—Te bonds in Au_1–xAg_xTe₂ group minerals

The structure refinement and XANES study of two gold–silver–tellurides [Au_1+xAg_xTe₂, krennerite (x = 0.11–0.13) and sylvanite (x = 0.29–0.31)] are presented and the structures are compared with the prototype structure of calaverite (x = 0.08–0.10). Whereas the latter is well known for being incommensurately modulated at ambient conditions, neither krennerite nor sylvanite present any modulation. This is attributed to the presence of relatively strong Te—Te bonds (bond distances < 2.9 Å) in the two minerals, which are absent in calaverite (bond distances > 3.2 Å). In both tellurides, trivalent gold occurs in slightly distorted square planar coordination, whereas monovalent gold, partly substituted by monovalent silver, presents a 2+2+2 coordination, corresponding to distorted rhombic bipyramids. The differentiation between bonding and non-bonding contacts is obtained by computation of the Effective Coordination Number (ECoN). The CHARge DIstribution (CHARDI) analysis is satisfactory for both tellurides but suggests that the Te—Te bond in the [Te₃]²⁻ anion is not entirely homopolar. Both tellurides can therefore be described as Madelung-type compounds, despite the presence of Te–Te in both structures.

Computing details

(global)

Crystal data

Ag0.1245Au0.8755Te2	F(000) = 1432
Mr = 441.5	Dx = 8.936 Mg m^−3
Orthorhombic, Pma2	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2 -2a	Cell parameters from 4231 reflections
a = 16.5937 (3) Å	θ = 3.4–40.6°
b = 8.8310 (1) Å	µ = 57.31 mm^−1
c = 4.4786 (1) Å	T = 293 K
V = 656.29 (2) Å^3	Prism, yellow
Z = 8	0.06 × 0.04 × 0.04 mm

Data collection

Rigaku XtaLAB Synergy-S diffractometer	4231 independent reflections
Radiation source: X-ray tube	3779 reflections with I > 3σ(I)
Graphite monochromator	Rint = 0.040
Detector resolution: 10 pixels mm^-1	θmax = 40.6°, θmin = 3.4°
ω scans	h = −30→30
Absorption correction: integration Busing, W.R. and Levy, H.A. 1957. High-Speed Computation of the Absorption Correction for Single Crystal Diffraction Measurements. Acta Cryst. 10, 180-182.	k = −15→16
Tmin = 0.110, Tmax = 0.253	l = −8→8
48587 measured reflections

Refinement

Refinement on F^2	14 constraints
R[F^2 > 2σ(F^2)] = 0.018	Weighting scheme based on measured s.u.'s w = 1/(σ^2(I) + 0.0004I^2)
wR(F^2) = 0.039	(Δ/σ)max = 0.007
S = 0.97	Δρmax = 1.38 e Å^−3
4231 reflections	Δρmin = −4.03 e Å^−3
63 parameters	Absolute structure: 1906 of Friedel pairs used in the refinement
0 restraints	Absolute structure parameter: −0.005 (2)

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Au1	0	0	0.00370 (5)	0.01733 (6)	0.826 (2)
Ag1	0	0	0.00370 (5)	0.01733 (6)	0.174 (2)
Au2	0.75	0.68062 (3)	1.01425 (6)	0.01917 (7)	0.676 (2)
Ag2	0.75	0.68062 (3)	1.01425 (6)	0.01917 (7)	0.324 (2)
Au3	0.873367 (9)	0.335341 (16)	0.51797 (4)	0.01359 (3)
Te1	0.75	0.98428 (4)	0.05676 (8)	0.01388 (8)
Te2	0.75	0.38115 (3)	0.13380 (8)	0.01273 (7)
Te3	−0.007587 (13)	0.30143 (2)	0.92478 (7)	0.01296 (5)
Te4	0.873352 (14)	0.63863 (3)	0.54224 (7)	0.01417 (6)
Te5	0.878789 (13)	0.03379 (3)	0.47508 (6)	0.01394 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Au1	0.02020 (11)	0.01162 (9)	0.02017 (12)	0.00117 (6)	0	0
Ag1	0.02020 (11)	0.01162 (9)	0.02017 (12)	0.00117 (6)	0	0
Au2	0.02106 (12)	0.01115 (10)	0.02529 (13)	0	0	−0.00022 (8)
Ag2	0.02106 (12)	0.01115 (10)	0.02529 (13)	0	0	−0.00022 (8)
Au3	0.01360 (5)	0.01049 (5)	0.01668 (5)	0.00052 (3)	−0.00257 (4)	−0.00081 (4)
Te1	0.01378 (12)	0.01146 (12)	0.01639 (16)	0	0	−0.00231 (10)
Te2	0.01223 (12)	0.01132 (12)	0.01463 (13)	0	0	0.00009 (10)
Te3	0.01301 (8)	0.01121 (9)	0.01467 (9)	−0.00017 (6)	−0.00025 (8)	0.00075 (8)
Te4	0.01436 (9)	0.01074 (9)	0.01741 (11)	−0.00044 (7)	0.00103 (7)	−0.00063 (8)
Te5	0.01398 (9)	0.01056 (8)	0.01727 (12)	−0.00013 (6)	0.00157 (7)	−0.00011 (7)

Geometric parameters (Å, º)

Au1—Ag1	0	Au2—Te2^v	2.6983 (4)
Au1—Te3^i	2.6882 (2)	Ag2—Te1^v	2.6884 (4)
Au1—Te3^ii	2.6882 (2)	Ag2—Te2^v	2.6983 (4)
Au1—Te5^iii	2.9311 (3)	Au3—Te2	2.7046 (3)
Au1—Te5^iv	2.9311 (3)	Au3—Te3^vi	2.7039 (3)
Ag1—Te3^i	2.6882 (2)	Au3—Te4	2.6805 (3)
Ag1—Te3^ii	2.6882 (2)	Au3—Te5	2.6714 (3)
Ag1—Te5^iii	2.9311 (3)	Te1—Te5^vii	2.8755 (4)
Ag1—Te5^iv	2.9311 (3)	Te1—Te5^viii	2.8755 (4)
Au2—Ag2	0	Te3—Te4^ix	2.8595 (4)
Au2—Te1^v	2.6884 (4)
Ag1—Au1—Te3^i	0	Te3^vi—Au3—Te4	94.785 (9)
Ag1—Au1—Te3^ii	0	Te3^vi—Au3—Te5	85.034 (8)
Ag1—Au1—Te5^iii	0	Te4—Au3—Te5	177.364 (11)
Ag1—Au1—Te5^iv	0	Au2^i—Te1—Ag2^i	0
Te3^i—Au1—Te3^ii	164.890 (13)	Au2^i—Te1—Te5^vii	101.409 (11)
Te3^i—Au1—Te5^iii	87.808 (8)	Au2^i—Te1—Te5^viii	101.409 (11)
Te3^i—Au1—Te5^iv	103.158 (8)	Ag2^i—Te1—Te5^vii	101.409 (11)
Te3^ii—Au1—Te5^iii	103.158 (8)	Ag2^i—Te1—Te5^viii	101.409 (11)
Te3^ii—Au1—Te5^iv	87.808 (8)	Te5^vii—Te1—Te5^viii	96.011 (13)
Te5^iii—Au1—Te5^iv	87.849 (9)	Au2^i—Te2—Ag2^i	0
Au1—Ag1—Te3^i	0	Au2^i—Te2—Au3	105.834 (9)
Au1—Ag1—Te3^ii	0	Au2^i—Te2—Au3^x	105.834 (9)
Au1—Ag1—Te5^iii	0	Ag2^i—Te2—Au3	105.834 (9)
Au1—Ag1—Te5^iv	0	Ag2^i—Te2—Au3^x	105.834 (9)
Te3^i—Ag1—Te3^ii	164.890 (13)	Au3—Te2—Au3^x	98.385 (12)
Te3^i—Ag1—Te5^iii	87.808 (8)	Au1^v—Te3—Ag1^v	0
Te3^i—Ag1—Te5^iv	103.158 (8)	Au1^v—Te3—Au3^iii	103.443 (9)
Te3^ii—Ag1—Te5^iii	103.158 (8)	Au1^v—Te3—Te4^ix	103.039 (9)
Te3^ii—Ag1—Te5^iv	87.808 (8)	Ag1^v—Te3—Au3^iii	103.443 (9)
Te5^iii—Ag1—Te5^iv	87.849 (9)	Ag1^v—Te3—Te4^ix	103.039 (9)
Ag2—Au2—Te1^v	0	Au3^iii—Te3—Te4^ix	98.330 (12)
Ag2—Au2—Te2^v	0	Au3—Te4—Te3^ix	102.075 (10)
Te1^v—Au2—Te2^v	164.494 (15)	Au1^vi—Te5—Ag1^vi	0
Au2—Ag2—Te1^v	0	Au1^vi—Te5—Au3	100.159 (9)
Au2—Ag2—Te2^v	0	Au1^vi—Te5—Te1^xi	91.446 (10)
Te1^v—Ag2—Te2^v	164.494 (15)	Ag1^vi—Te5—Au3	100.159 (9)
Te2—Au3—Te3^vi	176.554 (11)	Ag1^vi—Te5—Te1^xi	91.446 (10)
Te2—Au3—Te4	82.892 (9)	Au3—Te5—Te1^xi	99.985 (11)
Te2—Au3—Te5	97.404 (10)

Symmetry codes: (i) x, y, z−1; (ii) −x, −y, z−1; (iii) x−1, y, z; (iv) −x+1, −y, z; (v) x, y, z+1; (vi) x+1, y, z; (vii) x, y+1, z; (viii) −x+3/2, y+1, z; (ix) −x+1, −y+1, z; (x) −x+3/2, y, z; (xi) x, y−1, z.

(sylvanite)

Crystal data

Ag0.32Au0.68Te2	F(000) = 1383
Mr = 423.7	Dx = 8.457 Mg m^−3
Monoclinic, B2/e	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yc	Cell parameters from 2105 reflections
a = 10.136 (6) Å	θ = 4.0–40.6°
b = 4.4835 (1) Å	µ = 48.88 mm^−1
c = 14.6444 (15) Å	T = 293 K
β = 90.21 (3)°	Prism, yellow
V = 665.5 (4) Å^3	0.06 × 0.05 × 0.04 mm
Z = 8

Data collection

Rigaku XtaLAB Synergy-S diffractometer	2105 independent reflections
Radiation source: X-ray tube	1844 reflections with I > 3σ(I)
Graphite monochromator	Rint = 0.045
Detector resolution: 10 pixels mm^-1	θmax = 40.6°, θmin = 4.0°
ω scans	h = −18→18
Absorption correction: integration Busing, W.R. and Levy, H.A. 1957. High-Speed Computation of the Absorption Correction for Single Crystal Diffraction Measurements. Acta Cryst. 10, 180-182.	k = −8→8
Tmin = 0.161, Tmax = 0.262	l = −26→26
22154 measured reflections

Refinement

Refinement on F^2	0 restraints
R[F^2 > 2σ(F^2)] = 0.019	6 constraints
wR(F^2) = 0.043	Weighting scheme based on measured s.u.'s w = 1/(σ^2(I) + 0.0004I^2)
S = 1.10	(Δ/σ)max = 0.024
2105 reflections	Δρmax = 1.55 e Å^−3
31 parameters	Δρmin = −3.34 e Å^−3

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Au1	0	0	0	0.01388 (3)
Au2	0	0.51632 (6)	0.25	0.02237 (7)	0.3609 (19)
Ag2	0	0.51632 (6)	0.25	0.02237 (7)	0.6391 (19)
Te1	0.149428 (18)	0.02793 (4)	−0.149336 (13)	0.01469 (4)
Te2	0.140673 (16)	0.40559 (4)	0.095699 (12)	0.01390 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Au1	0.01228 (6)	0.01609 (6)	0.01326 (6)	−0.00270 (4)	0.00000 (4)	−0.00025 (4)
Au2	0.02203 (12)	0.02976 (14)	0.01535 (11)	0	0.00381 (8)	0
Ag2	0.02203 (12)	0.02976 (14)	0.01535 (11)	0	0.00381 (8)	0
Te1	0.01250 (7)	0.01718 (7)	0.01440 (8)	0.00046 (5)	0.00073 (6)	0.00043 (5)
Te2	0.01205 (6)	0.01505 (7)	0.01460 (7)	−0.00012 (5)	−0.00031 (5)	−0.00115 (5)

Geometric parameters (Å, º)

Au1—Te1	2.6677 (14)	Au2—Te2	2.7220 (13)
Au1—Te1^i	2.6677 (14)	Au2—Te2^iv	2.7220 (13)
Au1—Te2	2.6999 (10)	Ag2—Te1^ii	2.9370 (11)
Au1—Te2^i	2.6999 (10)	Ag2—Te1^iii	2.9370 (11)
Au2—Ag2	0	Ag2—Te2	2.7220 (13)
Au2—Te1^ii	2.9370 (11)	Ag2—Te2^iv	2.7220 (13)
Au2—Te1^iii	2.9370 (11)	Te1—Te2^v	2.8281 (19)
Te1—Au1—Te1^i	180	Au2—Ag2—Te2^iv	0
Te1—Au1—Te2	95.37 (3)	Te1^ii—Ag2—Te1^iii	91.83 (2)
Te1—Au1—Te2^i	84.63 (3)	Te1^ii—Ag2—Te2	88.91 (2)
Te1^i—Au1—Te2	84.63 (3)	Te1^ii—Ag2—Te2^iv	105.83 (3)
Te1^i—Au1—Te2^i	95.37 (3)	Te1^iii—Ag2—Te2	105.83 (3)
Te2—Au1—Te2^i	180	Te1^iii—Ag2—Te2^iv	88.91 (2)
Ag2—Au2—Te1^ii	0	Te2—Ag2—Te2^iv	158.983 (13)
Ag2—Au2—Te1^iii	0	Au1—Te1—Au2^ii	98.68 (3)
Ag2—Au2—Te2	0	Au1—Te1—Ag2^ii	98.68 (3)
Ag2—Au2—Te2^iv	0	Au1—Te1—Te2^v	103.25 (3)
Te1^ii—Au2—Te1^iii	91.83 (2)	Au2^ii—Te1—Ag2^ii	0
Te1^ii—Au2—Te2	88.91 (2)	Au2^ii—Te1—Te2^v	96.25 (3)
Te1^ii—Au2—Te2^iv	105.83 (3)	Ag2^ii—Te1—Te2^v	96.25 (3)
Te1^iii—Au2—Te2	105.83 (3)	Au1—Te2—Au2	106.05 (3)
Te1^iii—Au2—Te2^iv	88.91 (2)	Au1—Te2—Ag2	106.05 (3)
Te2—Au2—Te2^iv	158.983 (13)	Au1—Te2—Te1^v	97.83 (3)
Au2—Ag2—Te1^ii	0	Au2—Te2—Ag2	0
Au2—Ag2—Te1^iii	0	Au2—Te2—Te1^v	105.93 (3)
Au2—Ag2—Te2	0	Ag2—Te2—Te1^v	105.93 (3)

Symmetry codes: (i) −x, −y, −z; (ii) −x, −y+1, −z; (iii) x, −y+1, z+1/2; (iv) −x, y, −z+1/2; (v) −x+1/2, y, −z.