inorganic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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ISSN: 2056-9890

Reinvestigation of the low-temperature form of Ag2Se (naumannite) based on single-crystal data

aDivision of Energy Systems Research and Department of Chemistry, Ajou University, Suwon 443-749, Republic of Korea
*Correspondence e-mail: hsyun@ajou.ac.kr

(Received 26 June 2011; accepted 15 July 2011; online 2 August 2011)

The crystal structure of the low-temperature form of synthetic naumannite [disilver(I) selenide], Ag2Se, has been reinvestigated based on single-crystal data. In comparison with previous powder diffraction studies, anisotropic displacement parameters are additionally reported. The structure is composed of Se layers and two crystallographically independent Ag atoms. One Ag atom lies close to the Se layer and is surrounded by four Se atoms in a distorted tetra­hedral coordination, while the second Ag atom lies between the Se layers and exhibits a [3 + 1] coordination defined by three close Se atoms, forming a trigonal plane, and one remote Se atom.

Related literature

The crystal structure of the low-temperature form of Ag2Se has been previously refined by using X-ray (Wiegers, 1971[Wiegers, G. A. (1971). Am. Mineral. 56, 1882-1888.]) and synchrotron (Billetter & Ruschewitz, 2008[Billetter, H. & Ruschewitz, U. (2008). Z. Anorg. Allg. Chem. 634, 241-246.]) powder diffraction. For the structure of the cubic high-temperature form of Ag2Se, see: Oliveria et al. (1988[Oliveria, M., McMullan, R. K. & Wuensch, B. J. (1988). Solid State Ionics, 28, 1332-1337.]). For general background, see: Frueh (1958[Frueh, A. J. (1958). Z. Kristallogr. 110, 136-144.]). For ionic radii, see: Shannon (1976[Shannon, R. D. (1976). Acta Cryst. A32, 751-767.]).

Experimental

Crystal data
  • Ag2Se

  • Mr = 294.7

  • Orthorhombic, P 21 21 21

  • a = 4.3359 (8) Å

  • b = 7.070 (1) Å

  • c = 7.774 (1) Å

  • V = 238.34 (7) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 31.27 mm−1

  • T = 290 K

  • 0.30 × 0.04 × 0.02 mm

Data collection
  • Rigaku R-AXIS RAPID diffractometer

  • Absorption correction: multi-scan (NUMABS; Higashi, 2000[Higashi, T. (2000). NUMABS. Rigaku Corporation, Tokyo, Japan.]) Tmin = 0.053, Tmax = 0.278

  • 1981 measured reflections

  • 464 independent reflections

  • 447 reflections with I > 2σ(I)

  • Rint = 0.057

Refinement
  • R[F2 > 2σ(F2)] = 0.031

  • wR(F2) = 0.080

  • S = 1.14

  • 464 reflections

  • 29 parameters

  • Δρmax = 1.19 e Å−3

  • Δρmin = −1.07 e Å−3

  • Absolute structure: Flack (1983[Flack, H. D. (1983). Acta Cryst. A39, 876-881.]), 167 Friedel pairs

  • Flack parameter: 0.34 (4)

Table 1
Selected bond lengths (Å)

Ag1—Sei 2.6800 (14)
Ag1—Seii 2.7058 (16)
Ag1—Seiii 2.8282 (14)
Ag1—Seiv 2.9076 (16)
Ag2—Seiii 2.6538 (14)
Ag2—Se 2.7560 (15)
Ag2—Sev 2.8036 (16)
Ag2—Sevi 3.2112 (16)
Symmetry codes: (i) [-x+{\script{1\over 2}}, -y+1, z+{\script{1\over 2}}]; (ii) x+1, y-1, z; (iii) [-x+1, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]; (iv) [-x+{\script{3\over 2}}, -y+1, z+{\script{1\over 2}}]; (v) [-x+{\script{1\over 2}}, -y+2, z+{\script{1\over 2}}]; (vi) [-x, y-{\script{1\over 2}}, -z+{\script{1\over 2}}].

Data collection: RAPID-AUTO (Rigaku, 2006[Rigaku (2006). RAPID-AUTO. Rigaku Corporation, Tokyo, Japan.]); cell refinement: RAPID-AUTO; data reduction: RAPID-AUTO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: locally modified version of ORTEP (Johnson, 1965[Johnson, C. K. (1965). ORTEP. Report ORNL-3794. Oak Ridge National Laboratory, Tennessee, USA.]); software used to prepare material for publication: WinGX (Farrugia, 1999[Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837-838.]).

Supporting information


Comment top

Structural studies of the low-temperature form (transition point is 406 K) of the mineral naumannite, Ag2Se, based on powder diffraction data have been reported previously by Wiegers (1971; X-ray data) and Billetter & Ruschewitz (2008; synchrotron data). In case of the related phase Ag2S, single crystals of the high-temperature form (space group Im3m) are known to convert to polycrystalline powder of the low-temperature form on cooling (Frueh, 1958), and the same conversion has been assumed for the Se analogue (Wiegers, 1971). Consequently, structure determinations of the low-temperature form of Ag2Se have been carried out only by using powder diffraction methods. In an attempt to prepare new mixed-metal selenides using AgCl as a flux, we were able to isolate single crystals of the low-temperature form of Ag2Se and report here the results of the structure analysis. In comparison with the previous powder diffraction studies, anisotropic displacement parameters are additionally reported.

The general structural features of AgSe2 are the same as reported previously (Wiegers, 1971; Billetter & Ruschewitz, 2008). The structure of the low-temperature form of Ag2Se is closely related to the cubic high-temperature phase, where the Se atoms form a body-centered cubic packing, while the silver atoms are statistically distributed over interstitial sites (Oliveria et al., 1988). As a result, layers composed of Se atoms perpendicular to the b axis are retained in the low-temperature structure (Fig. 1). There are two crystallographically independent Ag atoms. Ag1 atoms lie close to this layer and are surrounded by four Se atoms in a distorted tetrahedral fashion (Se—Ag1—Se, 91.55 (3)–136.30 (5) °). The Ag1—Se distances range from 2.6800 (14) Å to 2.9076 (16) Å. Ag2 atoms are located between the layers and the coordination can be described as [3+1]. Three Se atoms built up a triangle that is bound to the Ag2 atom (Se—Ag2—Se, 94.00 (3)–141.46 (5) °), the coordination of which is augmented by a forth Se atom at a considerably longer distance of 3.2112 (16) Å. The observed Ag—Se distances are in agreement with the sum of the ionic radii of each element (Shannon, 1976) except for the very long Ag—Se bond. The distances and angles as calculated from single-crystal diffraction data differ slightly from those calculated previously from powder diffraction data. For example, the reported Ag1—Se distances are 2.62, 2.71, 2.79, 2.86 Å (Wiegers, 1971) and 2.658 (4), 2.668 (5), 2.861 (5), 2.937 (5) Å (Billetter & Ruschewitz, 2008) Å, and the Ag2—Se distances are 2.72, 2.74, 2.81, 3.28 Å (Wiegers, 1971) and 2.686 (5), 2.764 (5), 2.797 (4), 3.182 (5) Å (Billetter & Ruschewitz, 2008), respectively, with lattice parameters of a = 4.333 (Wiegers, 1971); 4.3373 (2) Å (Billetter & Ruschewitz, 2008), b = 7.062; 7.0702 (3) Å; c = 7.764; 7.7730 (4) Å.

Related literature top

The crystal structure of the low-temperature form of Ag2Se has been previously refined by using X-ray (Wiegers, 1971) and synchrotron (Billetter & Ruschewitz, 2008) powder diffraction. For the structure of the cubic high-temperature form of Ag2Se, see: Oliveria et al. (1988). For general background, see: Frueh (1958). For ionic radii, see: Shannon (1976).

Experimental top

Single crystals of the low-temperature form of Ag2Se were isolated during attemts to prepare new mixed-metal phases of Hf/Zr selenides. A combination of the pure elements, Zr powder, Hf powder, Se powder were mixed in a fused silica tube in a molar ratio of Zr: Hf: Se = 1:1:3 with AgCl. The mass ratio of the reactants and the halide flux was 1:2. The tube was evacuated to 0.133 Pa, sealed and heated gradually (20 K/h) to 600 K, where it was kept for 72 h. The tube was cooled to 200 K at 3 K/h and then was quenched to room temperature. The excess halide flux was removed with distilled water and black needle shaped crystals were obtained. The crystals are stable in air and water. A qualitative XRF analysis of the crystals showed only the presence of Ag and Se.

Refinement top

Refinement with TWIN and BASF instruction for the final positional parameters gave a value of 0.34 (4) for the Flack parameter (Flack, 1983). The highest peak and the deepest hole in the final Fourier map are located 1.71 Å and 0.99 Å, respectively, from atom Ag1.

Computing details top

Data collection: RAPID-AUTO (Rigaku, 2006); cell refinement: RAPID-AUTO (Rigaku, 2006); data reduction: RAPID-AUTO (Rigaku, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: locally modified version of ORTEP (Johnson, 1965); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. View of Ag2Se (50% probability displacement ellipsoids)
disilver(I) selenide top
Crystal data top
Ag2SeF(000) = 512
Mr = 294.7Dx = 8.213 Mg m3
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 1738 reflections
a = 4.3359 (8) Åθ = 3.4–27.5°
b = 7.070 (1) ŵ = 31.27 mm1
c = 7.774 (1) ÅT = 290 K
V = 238.34 (7) Å3Needle, black
Z = 40.30 × 0.04 × 0.02 mm
Data collection top
Rigaku R-AXIS RAPID
diffractometer
447 reflections with I > 2σ(I)
ω scansRint = 0.057
Absorption correction: multi-scan
(NUMABS; Higashi, 2000)
θmax = 26.0°, θmin = 3.9°
Tmin = 0.053, Tmax = 0.278h = 55
1981 measured reflectionsk = 88
464 independent reflectionsl = 99
Refinement top
Refinement on F20 restraints
Least-squares matrix: full w = 1/[σ2(Fo2) + (0.0329P)2 + 1.0072P]
where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.031(Δ/σ)max < 0.001
wR(F2) = 0.080Δρmax = 1.19 e Å3
S = 1.14Δρmin = 1.07 e Å3
464 reflectionsAbsolute structure: Flack (1983), 167 Friedel pairs
29 parametersAbsolute structure parameter: 0.34 (4)
Crystal data top
Ag2SeV = 238.34 (7) Å3
Mr = 294.7Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 4.3359 (8) ŵ = 31.27 mm1
b = 7.070 (1) ÅT = 290 K
c = 7.774 (1) Å0.30 × 0.04 × 0.02 mm
Data collection top
Rigaku R-AXIS RAPID
diffractometer
464 independent reflections
Absorption correction: multi-scan
(NUMABS; Higashi, 2000)
447 reflections with I > 2σ(I)
Tmin = 0.053, Tmax = 0.278Rint = 0.057
1981 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0310 restraints
wR(F2) = 0.080Δρmax = 1.19 e Å3
S = 1.14Δρmin = 1.07 e Å3
464 reflectionsAbsolute structure: Flack (1983), 167 Friedel pairs
29 parametersAbsolute structure parameter: 0.34 (4)
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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Ag10.8537 (2)0.11503 (14)0.45100 (14)0.0398 (3)
Ag20.4745 (3)0.77441 (14)0.36152 (14)0.0447 (4)
Se0.1124 (2)0.99787 (14)0.15274 (14)0.0242 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ag10.0381 (6)0.0378 (6)0.0436 (6)0.0010 (5)0.0080 (5)0.0060 (4)
Ag20.0462 (7)0.0338 (6)0.0540 (7)0.0131 (4)0.0100 (5)0.0057 (5)
Se0.0249 (5)0.0190 (6)0.0286 (6)0.0001 (4)0.0011 (4)0.0006 (4)
Geometric parameters (Å, º) top
Ag1—Sei2.6800 (14)Ag2—Seix3.2112 (16)
Ag1—Seii2.7058 (16)Ag2—Ag1x2.9979 (16)
Ag1—Seiii2.8282 (14)Ag2—Ag1xi3.0330 (14)
Ag1—Seiv2.9076 (16)Ag2—Ag2xii3.0749 (16)
Ag1—Ag1v2.9872 (15)Ag2—Ag2xiii3.0749 (16)
Ag1—Ag1vi2.9872 (15)Ag2—Ag1vi3.1591 (16)
Ag1—Ag2vii2.9979 (15)Ag2—Ag1xiv3.3692 (17)
Ag1—Ag2iii3.0330 (14)Se—Ag2xi2.6538 (14)
Ag1—Ag2v3.1591 (16)Se—Ag1xv2.6800 (14)
Ag1—Ag2iv3.3692 (17)Se—Ag1xvi2.7058 (16)
Ag2—Seiii2.6538 (14)Se—Ag2xvii2.8036 (16)
Ag2—Se2.7560 (15)Se—Ag1xi2.8282 (14)
Ag2—Seviii2.8036 (16)Se—Ag1xiv2.9076 (16)
Sei—Ag1—Seii136.30 (5)Seviii—Ag2—Ag1x54.90 (4)
Sei—Ag1—Seiii119.41 (5)Seiii—Ag2—Ag1xi90.54 (4)
Seii—Ag1—Seiii91.55 (3)Se—Ag2—Ag1xi58.26 (4)
Sei—Ag1—Seiv101.71 (5)Seviii—Ag2—Ag1xi142.86 (5)
Seii—Ag1—Seiv92.76 (3)Ag1x—Ag2—Ag1xi137.88 (5)
Seiii—Ag1—Seiv112.04 (5)Seiii—Ag2—Ag2xii58.04 (3)
Seiii—Ag2—Seix94.87 (4)Se—Ag2—Ag2xii151.45 (6)
Se—Ag2—Seix82.95 (3)Seviii—Ag2—Ag2xii66.03 (5)
Seviii—Ag2—Seix105.72 (5)Ag1x—Ag2—Ag2xii62.68 (4)
Sei—Ag1—Ag1v126.05 (6)Ag1xi—Ag2—Ag2xii148.22 (5)
Seii—Ag1—Ag1v96.50 (4)Seiii—Ag2—Ag2xiii114.98 (6)
Seiii—Ag1—Ag1v54.80 (4)Se—Ag2—Ag2xiii94.31 (4)
Seiv—Ag1—Ag1v57.32 (3)Seviii—Ag2—Ag2xiii53.43 (4)
Sei—Ag1—Ag1vi59.58 (3)Ag1x—Ag2—Ag2xiii108.32 (6)
Seii—Ag1—Ag1vi135.65 (6)Ag1xi—Ag2—Ag2xiii100.86 (4)
Seiii—Ag1—Ag1vi59.92 (5)Ag2xii—Ag2—Ag2xiii89.67 (6)
Seiv—Ag1—Ag1vi127.99 (6)Seiii—Ag2—Ag1vi59.27 (4)
Ag1v—Ag1—Ag1vi93.06 (6)Se—Ag2—Ag1vi132.61 (5)
Sei—Ag1—Ag2vii58.86 (4)Seviii—Ag2—Ag1vi96.07 (5)
Seii—Ag1—Ag2vii77.44 (4)Ag1x—Ag2—Ag1vi133.16 (4)
Seiii—Ag1—Ag2vii136.98 (5)Ag1xi—Ag2—Ag1vi88.17 (3)
Seiv—Ag1—Ag2vii109.95 (4)Ag2xii—Ag2—Ag1vi72.30 (4)
Ag1v—Ag1—Ag2vii166.05 (5)Ag2xiii—Ag2—Ag1vi57.47 (4)
Ag1vi—Ag1—Ag2vii100.04 (3)Seiii—Ag2—Ag1xiv88.98 (4)
Sei—Ag1—Ag2iii103.04 (4)Se—Ag2—Ag1xiv55.60 (4)
Seii—Ag1—Ag2iii67.77 (4)Seviii—Ag2—Ag1xiv131.41 (5)
Seiii—Ag1—Ag2iii55.96 (3)Ag1x—Ag2—Ag1xiv84.96 (4)
Seiv—Ag1—Ag2iii155.18 (5)Ag1xi—Ag2—Ag1xiv55.32 (3)
Ag1v—Ag1—Ag2iii107.91 (5)Ag2xii—Ag2—Ag1xiv122.24 (4)
Ag1vi—Ag1—Ag2iii68.06 (4)Ag2xiii—Ag2—Ag1xiv147.69 (4)
Ag2vii—Ag1—Ag2iii81.67 (3)Ag1vi—Ag2—Ag1xiv132.52 (4)
Sei—Ag1—Ag2v66.13 (4)Ag2xi—Se—Ag1xv134.75 (5)
Seii—Ag1—Ag2v93.43 (4)Ag2xi—Se—Ag1xvi95.17 (4)
Seiii—Ag1—Ag2v163.17 (5)Ag1xv—Se—Ag1xvi106.26 (4)
Seiv—Ag1—Ag2v51.68 (3)Ag2xi—Se—Ag293.59 (4)
Ag1v—Ag1—Ag2v108.60 (5)Ag1xv—Se—Ag2127.12 (5)
Ag1vi—Ag1—Ag2v124.02 (5)Ag1xvi—Se—Ag284.66 (5)
Ag2vii—Ag1—Ag2v59.85 (3)Ag2xi—Se—Ag2xvii68.53 (4)
Ag2iii—Ag1—Ag2v140.46 (4)Ag1xv—Se—Ag2xvii66.24 (4)
Sei—Ag1—Ag2iv71.43 (4)Ag1xvi—Se—Ag2xvii117.42 (5)
Seii—Ag1—Ag2iv142.30 (5)Ag2—Se—Ag2xvii151.82 (5)
Seiii—Ag1—Ag2iv92.10 (4)Ag2xi—Se—Ag1xi131.16 (5)
Seiv—Ag1—Ag2iv51.45 (3)Ag1xv—Se—Ag1xi65.62 (4)
Ag1v—Ag1—Ag2iv56.62 (4)Ag1xvi—Se—Ag1xi123.98 (5)
Ag1vi—Ag1—Ag2iv76.74 (5)Ag2—Se—Ag1xi65.78 (4)
Ag2vii—Ag1—Ag2iv121.83 (4)Ag2xvii—Se—Ag1xi109.05 (5)
Ag2iii—Ag1—Ag2iv140.93 (4)Ag2xi—Se—Ag1xiv69.05 (4)
Ag2v—Ag1—Ag2iv74.25 (3)Ag1xv—Se—Ag1xiv101.71 (5)
Seiii—Ag2—Se141.46 (5)Ag1xvi—Se—Ag1xiv151.20 (5)
Seiii—Ag2—Seviii123.20 (5)Ag2—Se—Ag1xiv72.95 (4)
Se—Ag2—Seviii94.00 (3)Ag2xvii—Se—Ag1xiv80.16 (4)
Seiii—Ag2—Ag1x103.38 (5)Ag1xi—Se—Ag1xiv62.75 (4)
Se—Ag2—Ag1x89.34 (4)
Symmetry codes: (i) x+1/2, y+1, z+1/2; (ii) x+1, y1, z; (iii) x+1, y1/2, z+1/2; (iv) x+3/2, y+1, z+1/2; (v) x+1/2, y+1/2, z+1; (vi) x1/2, y+1/2, z+1; (vii) x, y1, z; (viii) x+1/2, y+2, z+1/2; (ix) x, y1/2, z+1/2; (x) x, y+1, z; (xi) x+1, y+1/2, z+1/2; (xii) x+1/2, y+3/2, z+1; (xiii) x1/2, y+3/2, z+1; (xiv) x+3/2, y+1, z1/2; (xv) x+1/2, y+1, z1/2; (xvi) x1, y+1, z; (xvii) x+1/2, y+2, z1/2.

Experimental details

Crystal data
Chemical formulaAg2Se
Mr294.7
Crystal system, space groupOrthorhombic, P212121
Temperature (K)290
a, b, c (Å)4.3359 (8), 7.070 (1), 7.774 (1)
V3)238.34 (7)
Z4
Radiation typeMo Kα
µ (mm1)31.27
Crystal size (mm)0.30 × 0.04 × 0.02
Data collection
DiffractometerRigaku R-AXIS RAPID
diffractometer
Absorption correctionMulti-scan
(NUMABS; Higashi, 2000)
Tmin, Tmax0.053, 0.278
No. of measured, independent and
observed [I > 2σ(I)] reflections
1981, 464, 447
Rint0.057
(sin θ/λ)max1)0.617
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.031, 0.080, 1.14
No. of reflections464
No. of parameters29
Δρmax, Δρmin (e Å3)1.19, 1.07
Absolute structureFlack (1983), 167 Friedel pairs
Absolute structure parameter0.34 (4)

Computer programs: RAPID-AUTO (Rigaku, 2006), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), locally modified version of ORTEP (Johnson, 1965), WinGX (Farrugia, 1999).

Selected bond lengths (Å) top
Ag1—Sei2.6800 (14)Ag2—Seiii2.6538 (14)
Ag1—Seii2.7058 (16)Ag2—Se2.7560 (15)
Ag1—Seiii2.8282 (14)Ag2—Sev2.8036 (16)
Ag1—Seiv2.9076 (16)Ag2—Sevi3.2112 (16)
Symmetry codes: (i) x+1/2, y+1, z+1/2; (ii) x+1, y1, z; (iii) x+1, y1/2, z+1/2; (iv) x+3/2, y+1, z+1/2; (v) x+1/2, y+2, z+1/2; (vi) x, y1/2, z+1/2.
 

Acknowledgements

This work was supported by the Ajou University Research Fellowship (2010). Use was made of the X-ray facilities supported by Ajou University.

References

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First citationHigashi, T. (2000). NUMABS. Rigaku Corporation, Tokyo, Japan.  Google Scholar
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First citationRigaku (2006). RAPID-AUTO. Rigaku Corporation, Tokyo, Japan.  Google Scholar
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First citationWiegers, G. A. (1971). Am. Mineral. 56, 1882–1888.  CAS Google Scholar

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