Almost 50 years after the initial report, the crystal structure of Cu2GeSe3, a I2-IV-VI3 semiconductor, has been revised using modern single-crystal X-ray diffraction data. The structure of this material can be properly described in the monoclinic space group Cc (No. 9) with unit-cell parameters a = 6.7703 (4) Å, b = 11.8624 (5) Å, c = 6.7705 (4) Å, β = 108.512 (6)°, V = 515.62 (5) Å3, Z = 4, rather than in the orthorhombic space group Imm2 (No. 44) with unit-cell parameters a = 11.860 (3), b = 3.960 (1), c = 5.485 (2) Å, V = 257.61 Å3, Z = 2, as originally proposed [Parthé & Garín (1971). Monatsh. Chem. 102, 1197–1208]. Contrary to what was observed in the orthorhombic structure, the distortions of the tetrahedra in the monoclinic structure are consistent with the distortions expected from considerations derived from the bond valence model. A brief revision of the structures reported for the I2-IV-VI3 family of semiconducting compounds (I: Cu, Ag; IV: Si, Ge, Sn; and VI: S, Se, Te) is also presented.
Supporting information
CCDC reference: 2051991
Data collection: CrysAlis PRO 1.171.39.28e (Rigaku OD, 2015); cell refinement: CrysAlis PRO 1.171.39.28e (Rigaku OD, 2015); data reduction: CrysAlis PRO 1.171.39.28e (Rigaku OD, 2015); program(s) used to solve structure: ShelXT (Sheldrick, 2015); program(s) used to refine structure: SHELXL (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: Olex2 (Dolomanov et al., 2009) and enCIFer (Allen et al., 2004).
Crystal data top
Cu2GeSe3 | F(000) = 768 |
Mr = 436.55 | Dx = 5.624 Mg m−3 |
Monoclinic, Cc | Mo Kα radiation, λ = 0.71075 Å |
a = 6.7703 (4) Å | Cell parameters from 2471 reflections |
b = 11.8624 (5) Å | θ = 3.1–34.8° |
c = 6.7705 (4) Å | µ = 34.96 mm−1 |
β = 108.512 (6)° | T = 293 K |
V = 515.62 (5) Å3 | Irregular fragment, grey |
Z = 4 | 0.24 × 0.23 × 0.22 mm |
Data collection top
Rigaku XtaLab Pro diffractometer | 1824 independent reflections |
Radiation source: fine-focus sealed X-ray tube, Enhance (Mo) X-ray Source | 1605 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.021 |
Detector resolution: 5.8140 pixels mm-1 | θmax = 34.6°, θmin = 3.4° |
ω scans | h = −10→10 |
Absorption correction: multi-scan CrysAlisPro 1.171.39.28e (Rigaku Oxford Diffraction, 2015)
Empirical absorption correction using spherical harmonics,
implemented in SCALE3 ABSPACK scaling algorithm. | k = −18→18 |
Tmin = 0.505, Tmax = 1.000 | l = −10→10 |
4227 measured reflections | |
Refinement top
Refinement on F2 | w = 1/[σ2(Fo2) + (0.0266P)2 + 0.1027P] where P = (Fo2 + 2Fc2)/3 |
Least-squares matrix: full | (Δ/σ)max < 0.001 |
R[F2 > 2σ(F2)] = 0.027 | Δρmax = 1.53 e Å−3 |
wR(F2) = 0.077 | Δρmin = −1.83 e Å−3 |
S = 1.16 | Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
1824 reflections | Extinction coefficient: 0.0158 (8) |
56 parameters | Absolute structure: Flack x determined using 626 quotients [(I+)-(I-)]/[(I+)+(I-)]
(Parsons, Flack and Wagner, Acta Cryst. B69 (2013) 249-259). |
2 restraints | Absolute structure parameter: 0.043 (18) |
Primary atom site location: dual | |
Special details top
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell esds are taken
into account individually in the estimation of esds in distances, angles
and torsion angles; correlations between esds in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell esds is used for estimating esds involving l.s. planes. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Cu1 | −0.0001 (2) | −0.08657 (5) | 0.49994 (18) | 0.0163 (3) | |
Cu2 | 0.51489 (16) | −0.24677 (5) | 0.50463 (15) | 0.0152 (3) | |
Ge | 0.52816 (19) | 0.08587 (3) | 0.52302 (18) | 0.00457 (14) | |
Se1 | 0.38650 (10) | −0.08110 (3) | 0.64001 (9) | 0.00524 (19) | |
Se2 | 0.38880 (11) | 0.24558 (4) | 0.63172 (10) | 0.00721 (16) | |
Se3 | 0.89215 (10) | 0.08425 (3) | 0.62468 (10) | 0.0066 (2) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cu1 | 0.0197 (9) | 0.0157 (3) | 0.0137 (6) | 0.0019 (3) | 0.0058 (6) | 0.0006 (3) |
Cu2 | 0.0146 (4) | 0.0176 (3) | 0.0126 (7) | −0.0014 (3) | 0.0034 (4) | 0.0013 (3) |
Ge | 0.0041 (3) | 0.0067 (2) | 0.0023 (3) | −0.0005 (3) | 0.0001 (2) | −0.0003 (2) |
Se1 | 0.0054 (3) | 0.0071 (2) | 0.0021 (3) | −0.00096 (16) | −0.0005 (2) | 0.00054 (15) |
Se2 | 0.0072 (3) | 0.0082 (2) | 0.0059 (3) | 0.0019 (2) | 0.00160 (19) | −0.0005 (2) |
Se3 | 0.0041 (3) | 0.0090 (2) | 0.0061 (4) | 0.00028 (14) | 0.0006 (2) | 0.00026 (15) |
Geometric parameters (Å, º) top
Cu1—Se1 | 2.4855 (18) | Cu2—Se2v | 2.3947 (15) |
Cu1—Se2i | 2.3985 (10) | Cu2—Se3i | 2.4080 (10) |
Cu1—Se3ii | 2.3964 (10) | Ge—Se1 | 2.4398 (9) |
Cu1—Se3iii | 2.4106 (16) | Ge—Se1v | 2.4634 (15) |
Cu2—Se1 | 2.4420 (10) | Ge—Se2 | 2.3371 (10) |
Cu2—Se2iv | 2.4028 (16) | Ge—Se3 | 2.3388 (17) |
| | | |
Se2i—Cu1—Se1 | 107.24 (5) | Cu2—Se1—Cu1 | 107.04 (4) |
Se2i—Cu1—Se3iii | 112.08 (5) | Cu2—Se1—Gevi | 108.10 (4) |
Se3ii—Cu1—Se1 | 104.18 (5) | Gevi—Se1—Cu1 | 114.32 (5) |
Se3iii—Cu1—Se1 | 109.36 (6) | Ge—Se1—Cu1 | 111.85 (5) |
Se3ii—Cu1—Se2i | 113.85 (6) | Ge—Se1—Cu2 | 107.94 (5) |
Se3ii—Cu1—Se3iii | 109.73 (5) | Ge—Se1—Gevi | 107.37 (5) |
Se2iv—Cu2—Se1 | 110.86 (5) | Cu1vii—Se2—Cu2viii | 104.75 (5) |
Se2v—Cu2—Se1 | 109.92 (5) | Cu2vi—Se2—Cu1vii | 109.78 (5) |
Se2v—Cu2—Se2iv | 111.11 (6) | Cu2vi—Se2—Cu2viii | 111.08 (6) |
Se2iv—Cu2—Se3i | 106.56 (5) | Ge—Se2—Cu1vii | 110.50 (5) |
Se2v—Cu2—Se3i | 108.36 (4) | Ge—Se2—Cu2viii | 113.74 (6) |
Se3i—Cu2—Se1 | 109.94 (5) | Ge—Se2—Cu2vi | 107.00 (5) |
Se1—Ge—Se1v | 105.15 (5) | Cu1ix—Se3—Cu1x | 110.92 (5) |
Se2—Ge—Se1 | 108.44 (6) | Cu1ix—Se3—Cu2vii | 114.12 (6) |
Se2—Ge—Se1v | 106.79 (5) | Cu2vii—Se3—Cu1x | 108.96 (4) |
Se2—Ge—Se3 | 114.02 (6) | Ge—Se3—Cu1ix | 108.27 (5) |
Se3—Ge—Se1 | 112.57 (5) | Ge—Se3—Cu1x | 104.37 (6) |
Se3—Ge—Se1v | 109.35 (5) | Ge—Se3—Cu2vii | 109.76 (4) |
Symmetry codes: (i) x−1/2, y−1/2, z; (ii) x−1, y, z; (iii) x−1, −y, z−1/2; (iv) x+1/2, y−1/2, z; (v) x, −y, z−1/2; (vi) x, −y, z+1/2; (vii) x+1/2, y+1/2, z; (viii) x−1/2, y+1/2, z; (ix) x+1, y, z; (x) x+1, −y, z+1/2. |