inorganic compounds
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
The 2Se, 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.
of the low-temperature form of synthetic naumannite [disilver(I) selenide], AgRelated literature
The 2Se 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).
of the low-temperature form of AgExperimental
Crystal data
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Data collection: RAPID-AUTO (Rigaku, 2006); cell RAPID-AUTO; data reduction: RAPID-AUTO; 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).
Supporting information
10.1107/S1600536811028534/wm2506sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536811028534/wm2506Isup2.hkl
Single crystals of the low-temperature form of Ag2Se were isolated during attemts to prepare new mixed-metal phases of Hf/Zr
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 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 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 with TWIN and BASF instruction for the final positional parameters gave a value of 0.34 (4) for the
(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.Data collection: RAPID-AUTO (Rigaku, 2006); cell
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).Ag2Se | F(000) = 512 |
Mr = 294.7 | Dx = 8.213 Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 1738 reflections |
a = 4.3359 (8) Å | θ = 3.4–27.5° |
b = 7.070 (1) Å | µ = 31.27 mm−1 |
c = 7.774 (1) Å | T = 290 K |
V = 238.34 (7) Å3 | Needle, black |
Z = 4 | 0.30 × 0.04 × 0.02 mm |
Rigaku R-AXIS RAPID diffractometer | 447 reflections with I > 2σ(I) |
ω scans | Rint = 0.057 |
Absorption correction: multi-scan (NUMABS; Higashi, 2000) | θmax = 26.0°, θmin = 3.9° |
Tmin = 0.053, Tmax = 0.278 | h = −5→5 |
1981 measured reflections | k = −8→8 |
464 independent reflections | l = −9→9 |
Refinement on F2 | 0 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) = 0.080 | Δρmax = 1.19 e Å−3 |
S = 1.14 | Δρmin = −1.07 e Å−3 |
464 reflections | Absolute structure: Flack (1983), 167 Friedel pairs |
29 parameters | Absolute structure parameter: 0.34 (4) |
Ag2Se | V = 238.34 (7) Å3 |
Mr = 294.7 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 4.3359 (8) Å | µ = 31.27 mm−1 |
b = 7.070 (1) Å | T = 290 K |
c = 7.774 (1) Å | 0.30 × 0.04 × 0.02 mm |
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 = 0.278 | Rint = 0.057 |
1981 measured reflections |
R[F2 > 2σ(F2)] = 0.031 | 0 restraints |
wR(F2) = 0.080 | Δρmax = 1.19 e Å−3 |
S = 1.14 | Δρmin = −1.07 e Å−3 |
464 reflections | Absolute structure: Flack (1983), 167 Friedel pairs |
29 parameters | Absolute structure parameter: 0.34 (4) |
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. |
x | y | z | Uiso*/Ueq | ||
Ag1 | 0.8537 (2) | 0.11503 (14) | 0.45100 (14) | 0.0398 (3) | |
Ag2 | 0.4745 (3) | 0.77441 (14) | 0.36152 (14) | 0.0447 (4) | |
Se | 0.1124 (2) | 0.99787 (14) | 0.15274 (14) | 0.0242 (3) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Ag1 | 0.0381 (6) | 0.0378 (6) | 0.0436 (6) | −0.0010 (5) | 0.0080 (5) | 0.0060 (4) |
Ag2 | 0.0462 (7) | 0.0338 (6) | 0.0540 (7) | 0.0131 (4) | −0.0100 (5) | −0.0057 (5) |
Se | 0.0249 (5) | 0.0190 (6) | 0.0286 (6) | 0.0001 (4) | −0.0011 (4) | −0.0006 (4) |
Ag1—Sei | 2.6800 (14) | Ag2—Seix | 3.2112 (16) |
Ag1—Seii | 2.7058 (16) | Ag2—Ag1x | 2.9979 (16) |
Ag1—Seiii | 2.8282 (14) | Ag2—Ag1xi | 3.0330 (14) |
Ag1—Seiv | 2.9076 (16) | Ag2—Ag2xii | 3.0749 (16) |
Ag1—Ag1v | 2.9872 (15) | Ag2—Ag2xiii | 3.0749 (16) |
Ag1—Ag1vi | 2.9872 (15) | Ag2—Ag1vi | 3.1591 (16) |
Ag1—Ag2vii | 2.9979 (15) | Ag2—Ag1xiv | 3.3692 (17) |
Ag1—Ag2iii | 3.0330 (14) | Se—Ag2xi | 2.6538 (14) |
Ag1—Ag2v | 3.1591 (16) | Se—Ag1xv | 2.6800 (14) |
Ag1—Ag2iv | 3.3692 (17) | Se—Ag1xvi | 2.7058 (16) |
Ag2—Seiii | 2.6538 (14) | Se—Ag2xvii | 2.8036 (16) |
Ag2—Se | 2.7560 (15) | Se—Ag1xi | 2.8282 (14) |
Ag2—Seviii | 2.8036 (16) | Se—Ag1xiv | 2.9076 (16) |
Sei—Ag1—Seii | 136.30 (5) | Seviii—Ag2—Ag1x | 54.90 (4) |
Sei—Ag1—Seiii | 119.41 (5) | Seiii—Ag2—Ag1xi | 90.54 (4) |
Seii—Ag1—Seiii | 91.55 (3) | Se—Ag2—Ag1xi | 58.26 (4) |
Sei—Ag1—Seiv | 101.71 (5) | Seviii—Ag2—Ag1xi | 142.86 (5) |
Seii—Ag1—Seiv | 92.76 (3) | Ag1x—Ag2—Ag1xi | 137.88 (5) |
Seiii—Ag1—Seiv | 112.04 (5) | Seiii—Ag2—Ag2xii | 58.04 (3) |
Seiii—Ag2—Seix | 94.87 (4) | Se—Ag2—Ag2xii | 151.45 (6) |
Se—Ag2—Seix | 82.95 (3) | Seviii—Ag2—Ag2xii | 66.03 (5) |
Seviii—Ag2—Seix | 105.72 (5) | Ag1x—Ag2—Ag2xii | 62.68 (4) |
Sei—Ag1—Ag1v | 126.05 (6) | Ag1xi—Ag2—Ag2xii | 148.22 (5) |
Seii—Ag1—Ag1v | 96.50 (4) | Seiii—Ag2—Ag2xiii | 114.98 (6) |
Seiii—Ag1—Ag1v | 54.80 (4) | Se—Ag2—Ag2xiii | 94.31 (4) |
Seiv—Ag1—Ag1v | 57.32 (3) | Seviii—Ag2—Ag2xiii | 53.43 (4) |
Sei—Ag1—Ag1vi | 59.58 (3) | Ag1x—Ag2—Ag2xiii | 108.32 (6) |
Seii—Ag1—Ag1vi | 135.65 (6) | Ag1xi—Ag2—Ag2xiii | 100.86 (4) |
Seiii—Ag1—Ag1vi | 59.92 (5) | Ag2xii—Ag2—Ag2xiii | 89.67 (6) |
Seiv—Ag1—Ag1vi | 127.99 (6) | Seiii—Ag2—Ag1vi | 59.27 (4) |
Ag1v—Ag1—Ag1vi | 93.06 (6) | Se—Ag2—Ag1vi | 132.61 (5) |
Sei—Ag1—Ag2vii | 58.86 (4) | Seviii—Ag2—Ag1vi | 96.07 (5) |
Seii—Ag1—Ag2vii | 77.44 (4) | Ag1x—Ag2—Ag1vi | 133.16 (4) |
Seiii—Ag1—Ag2vii | 136.98 (5) | Ag1xi—Ag2—Ag1vi | 88.17 (3) |
Seiv—Ag1—Ag2vii | 109.95 (4) | Ag2xii—Ag2—Ag1vi | 72.30 (4) |
Ag1v—Ag1—Ag2vii | 166.05 (5) | Ag2xiii—Ag2—Ag1vi | 57.47 (4) |
Ag1vi—Ag1—Ag2vii | 100.04 (3) | Seiii—Ag2—Ag1xiv | 88.98 (4) |
Sei—Ag1—Ag2iii | 103.04 (4) | Se—Ag2—Ag1xiv | 55.60 (4) |
Seii—Ag1—Ag2iii | 67.77 (4) | Seviii—Ag2—Ag1xiv | 131.41 (5) |
Seiii—Ag1—Ag2iii | 55.96 (3) | Ag1x—Ag2—Ag1xiv | 84.96 (4) |
Seiv—Ag1—Ag2iii | 155.18 (5) | Ag1xi—Ag2—Ag1xiv | 55.32 (3) |
Ag1v—Ag1—Ag2iii | 107.91 (5) | Ag2xii—Ag2—Ag1xiv | 122.24 (4) |
Ag1vi—Ag1—Ag2iii | 68.06 (4) | Ag2xiii—Ag2—Ag1xiv | 147.69 (4) |
Ag2vii—Ag1—Ag2iii | 81.67 (3) | Ag1vi—Ag2—Ag1xiv | 132.52 (4) |
Sei—Ag1—Ag2v | 66.13 (4) | Ag2xi—Se—Ag1xv | 134.75 (5) |
Seii—Ag1—Ag2v | 93.43 (4) | Ag2xi—Se—Ag1xvi | 95.17 (4) |
Seiii—Ag1—Ag2v | 163.17 (5) | Ag1xv—Se—Ag1xvi | 106.26 (4) |
Seiv—Ag1—Ag2v | 51.68 (3) | Ag2xi—Se—Ag2 | 93.59 (4) |
Ag1v—Ag1—Ag2v | 108.60 (5) | Ag1xv—Se—Ag2 | 127.12 (5) |
Ag1vi—Ag1—Ag2v | 124.02 (5) | Ag1xvi—Se—Ag2 | 84.66 (5) |
Ag2vii—Ag1—Ag2v | 59.85 (3) | Ag2xi—Se—Ag2xvii | 68.53 (4) |
Ag2iii—Ag1—Ag2v | 140.46 (4) | Ag1xv—Se—Ag2xvii | 66.24 (4) |
Sei—Ag1—Ag2iv | 71.43 (4) | Ag1xvi—Se—Ag2xvii | 117.42 (5) |
Seii—Ag1—Ag2iv | 142.30 (5) | Ag2—Se—Ag2xvii | 151.82 (5) |
Seiii—Ag1—Ag2iv | 92.10 (4) | Ag2xi—Se—Ag1xi | 131.16 (5) |
Seiv—Ag1—Ag2iv | 51.45 (3) | Ag1xv—Se—Ag1xi | 65.62 (4) |
Ag1v—Ag1—Ag2iv | 56.62 (4) | Ag1xvi—Se—Ag1xi | 123.98 (5) |
Ag1vi—Ag1—Ag2iv | 76.74 (5) | Ag2—Se—Ag1xi | 65.78 (4) |
Ag2vii—Ag1—Ag2iv | 121.83 (4) | Ag2xvii—Se—Ag1xi | 109.05 (5) |
Ag2iii—Ag1—Ag2iv | 140.93 (4) | Ag2xi—Se—Ag1xiv | 69.05 (4) |
Ag2v—Ag1—Ag2iv | 74.25 (3) | Ag1xv—Se—Ag1xiv | 101.71 (5) |
Seiii—Ag2—Se | 141.46 (5) | Ag1xvi—Se—Ag1xiv | 151.20 (5) |
Seiii—Ag2—Seviii | 123.20 (5) | Ag2—Se—Ag1xiv | 72.95 (4) |
Se—Ag2—Seviii | 94.00 (3) | Ag2xvii—Se—Ag1xiv | 80.16 (4) |
Seiii—Ag2—Ag1x | 103.38 (5) | Ag1xi—Se—Ag1xiv | 62.75 (4) |
Se—Ag2—Ag1x | 89.34 (4) |
Symmetry codes: (i) −x+1/2, −y+1, z+1/2; (ii) x+1, y−1, z; (iii) −x+1, y−1/2, −z+1/2; (iv) −x+3/2, −y+1, z+1/2; (v) x+1/2, −y+1/2, −z+1; (vi) x−1/2, −y+1/2, −z+1; (vii) x, y−1, z; (viii) −x+1/2, −y+2, z+1/2; (ix) −x, y−1/2, −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) x−1/2, −y+3/2, −z+1; (xiv) −x+3/2, −y+1, z−1/2; (xv) −x+1/2, −y+1, z−1/2; (xvi) x−1, y+1, z; (xvii) −x+1/2, −y+2, z−1/2. |
Experimental details
Crystal data | |
Chemical formula | Ag2Se |
Mr | 294.7 |
Crystal system, space group | Orthorhombic, P212121 |
Temperature (K) | 290 |
a, b, c (Å) | 4.3359 (8), 7.070 (1), 7.774 (1) |
V (Å3) | 238.34 (7) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 31.27 |
Crystal size (mm) | 0.30 × 0.04 × 0.02 |
Data collection | |
Diffractometer | Rigaku R-AXIS RAPID diffractometer |
Absorption correction | Multi-scan (NUMABS; Higashi, 2000) |
Tmin, Tmax | 0.053, 0.278 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 1981, 464, 447 |
Rint | 0.057 |
(sin θ/λ)max (Å−1) | 0.617 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.031, 0.080, 1.14 |
No. of reflections | 464 |
No. of parameters | 29 |
Δρmax, Δρmin (e Å−3) | 1.19, −1.07 |
Absolute structure | Flack (1983), 167 Friedel pairs |
Absolute structure parameter | 0.34 (4) |
Computer programs: RAPID-AUTO (Rigaku, 2006), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), locally modified version of ORTEP (Johnson, 1965), WinGX (Farrugia, 1999).
Ag1—Sei | 2.6800 (14) | Ag2—Seiii | 2.6538 (14) |
Ag1—Seii | 2.7058 (16) | Ag2—Se | 2.7560 (15) |
Ag1—Seiii | 2.8282 (14) | Ag2—Sev | 2.8036 (16) |
Ag1—Seiv | 2.9076 (16) | Ag2—Sevi | 3.2112 (16) |
Symmetry codes: (i) −x+1/2, −y+1, z+1/2; (ii) x+1, y−1, z; (iii) −x+1, y−1/2, −z+1/2; (iv) −x+3/2, −y+1, z+1/2; (v) −x+1/2, −y+2, z+1/2; (vi) −x, y−1/2, −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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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.