Syntheses and crystal structures of the quaternary thio­germanates Cu4FeGe2S7 and Cu4CoGe2S7

Craig, A.J.; Stoyko, S.S.; Bonnoni, A.; Aitken, J.A.

doi:10.1107/S2056989020007872

research communications

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ISSN: 2056-9890

Volume 76| Part 7| July 2020| Pages 1117-1121

https://doi.org/10.1107/S2056989020007872

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Syntheses and crystal structures of the quaternary thiogermanates Cu₄FeGe₂S₇ and Cu₄CoGe₂S₇

Andrew J. Craig,^a Stanislav S. Stoyko,^a Allyson Bonnoni ^a and Jennifer A. Aitken ^a ^*

^aDepartment of Chemistry and Biochemistry, Duquesne University, 600 Forbes Ave, Pittsburgh PA 15282, USA
^*Correspondence e-mail: aitkenj@duq.edu

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 27 May 2020; accepted 10 June 2020; online 19 June 2020)

The quaternary thiogermanates Cu₄FeGe₂S₇ (tetracopper iron digermanium heptasulfide) and Cu₄CoGe₂S₇ (tetracopper cobalt digermanium heptasulfide) were prepared in evacuated fused-silica ampoules via high-temperature, solid-state synthesis using stoichiometric amounts of the elements at 1273 K. These isostructural compounds crystallize in the Cu₄NiSi₂S₇ structure type, which can be considered as a superstructure of cubic diamond or sphalerite. The monovalent (Cu⁺), divalent (Fe²⁺ or Co²⁺) and tetravalent (Ge⁴⁺) cations adopt tetrahedral geometries, each being surrounded by four S²⁻ anions. The divalent cation and one of the sulfide ions lie on crystallographic twofold axes. These tetrahedra share corners to create a three-dimensional framework structure. All of the tetrahedra align along the same crystallographic direction, rendering the structure non-centrosymmetric and polar (space group C2). Analysis of X-ray powder diffraction data revealed that the structures are the major phase of the reaction products. Thermal analysis indicated relatively high melting temperatures, near 1273 K.

Keywords: crystal structure; diamond-like; thiogermanate; quaternary sulfide.

CCDC references: 2009145; 2009144

1. Chemical context

The title compounds belong to the family of quaternary thiogermanates, which can be constructed from different [Ge_xS_y]^z- building blocks, such as [GeS₄]⁴⁻ (Aitken et al., 2001 ) and [Ge₂S₆]⁴⁻ (Choudhury et al., 2015 ). Two GeS₄ tetrahedra can share a corner to create [Ge₂S₇]⁶⁻ units, which are featured in the title compounds. Cu₄FeGe₂S₇ and Cu₄CoGe₂S₇ also belong to the family of diamond-like semiconductors (DLSs), with structures that can be derived from the cubic or hexagonal (Frondel & Marvin, 1967 ) forms of diamond. The synthesis of new diamond-like materials is guided by valence electron principles and Pauling's rules, and the resulting DLSs can be binary, ternary, or quaternary, depending on the number of elements employed in the reaction (Parthé, 1964 ; Pamplin, 1981 ; Goryunova, 1965 ). Increasing the number of elements in the formula allows for greater tunability of the material's properties; thus, quaternary DLSs are a particularly appealing class of materials. As a result of their technologically relevant properties, these materials are of interest for a number of applications, such as solar cells (Ito & Nakazawa, 1988 ; Heppke et al., 2020 ; Liu et al., 2018 ), batteries (Brant, Devlin et al., 2015 ; Kaib et al., 2013 ) and magnetic devices (Wintenberger, 1979 ; Greenwood & Whitfield, 1968 ). Furthermore, owing to their inherently non-centrosymmetric structures, DLSs are attractive candidates for infrared non-linear optical (IR–NLO) devices that make use of second-harmonic generation (SHG) crystals (Ohmer & Pandey 1998 ): only crystals that lack an inversion center can exhibit SHG.

IR–NLO materials are used to shift the radiation of lasers to more suitable wavelengths for use in military (Hopkins 1998 ), medical (Stoeppler et al., 2012 ) and industrial applications (Bamford et al., 2007 ). Currently, ternary DLSs, most of which are sulfides, dominate the market of SHG crystals for use in the infrared (Ohmer & Pandey, 1998). Yet the current commercially available IR–NLO materials suffer from serious drawbacks, such as low laser-induced damage thresholds (LIDTs) and multi-photon absorption (Schunemann, 2007 ). Turning attention to the discovery of new quaternary DLSs provides a reliable route to next-generation IR–NLO materials that allows for greater control of the material's properties. Compounds such as Li₂CdGeS₄ (Brant, Clark et al., 2014 ), Li₂MnGeS₄ (Brant, Clark et al., 2015 ), and Li₄HgGe₂S₇ (Wu, Yang & Pan, 2017 ) have shown potential to outperform currently used ternary IR–NLO crystals. These DLSs have shown promising SHG capabilities, as well as resilience to high powered lasers, a necessity to broaden future usage (Hopkins, 1998). For these reasons, we were motivated to investigate the Cu–Fe–Ge–S and Cu–Co–Ge–S systems for new DLSs.

2. Structural commentary

The title compounds, Cu₄FeGe₂S₇ (I) and Cu₄CoGe₂S₇ (II), are isostructural and crystallize in the non-centrosymmetric, monoclinic space group C2 (No. 5) with the Cu₄NiSi₂S₇ structure type (Schäfer et al., 1980 ). The structure contains two crystallographically unique Cu⁺ ions, one divalent metal (Fe or Co) sited on a crystallographic twofold axis, one Ge⁴⁺ cation and four S²⁻ anions (one with site symmetry 2) (Fig. 1). The sulfide anions create a `cubic' close-packed array and the cations reside in one-half of the tetrahedral holes; these tetrahedra share corners to form a three-dimensional network. Two GeS₄ tetrahedra share corners to form (Ge₂S₇)⁶⁻ subunits that are isolated from each other (Fig. 1). These subunits are separated by isolated FeS₄ tetrahedra and surrounded by a snaking, three-dimensional network of corner-sharing CuS₄ tetrahedra that serve to link the (Ge₂S₇)⁶⁻ and FeS₄ subunits. All of the tetrahedra are aligned along one crystallographic direction, rendering the structure non-centrosymmetric (Fig. 2). All DLSs exhibit a honeycomb pattern in their crystal structure (Fig. 3); the various resulting space groups arise from the different possible cation-ordering patterns.

Figure 1
The structure of Cu₄FeGe₂S₇ with crystallographically unique ions labeled. Ellipsoids are shown at 99% probability. Cu₄CoGe₂S₇ is isostructural and has similar atomic displacement parameters.

Figure 2
Polyhedral view of Cu₄FeGe₂S₇ showing the polar nature of the structure.

Figure 3
The `honeycomb' pattern found in Cu₄FeGe₂S₇, a characteristic of DLSs. Highlighted in the bottom left corner is one of the [Ge₂S₇]⁶⁻ subunits that forms in this structure.

Selected geometrical data for (I) and (II) are given in Tables 1 and 2, respectively. The average Fe—S (I) and Co—S (II) bond distances are 2.334 (6) and 2.317 (6) Å, respectively. These values align well with other compounds containing iron or cobalt tetrahedrally coordinated by sulfur. For example, the average Fe—S distance found in Li₂FeGeS₄ is 2.34 (2) Å (Brant, dela Cruz et al., 2014 ), while the average Co—S distance found in Li₂CoGeS₄ is 2.31 (3) Å (Brant, Devlin et al., 2015). The average Ge—S distances are 2.240 (4) and 2.244 (5) Å for (I) and (II), respectively. These distances are also close to those of the lithium-containing DLSs: Li₂FeGeS₄ (Brant, Devlin et al., 2015) and Li₂CoGeS₄ (Brant, dela Cruz et al., 2014) possess values of 2.23 (2) and 2.22 (3) Å, respectively. The average tetrahedral bond angles for all cations in both title compounds is, within uncertainty, ideal. For comparison, the tetrahedral angular ranges encountered in Cu₂FeGeS₄ (Wintenberger, 1979) and Cu₂CoGeS₄ (Gulay et al., 2004 ) are 109.471–109.484° and 109.473–109.579°, respectively. The sulfur anions also exhibit tetrahedral coordination. Both S2 and S4 are coordinated by two copper, one germanium and one iron or cobalt cation. S1 is connected to two germanium and two copper cations, while S3 is surrounded by one germanium and three copper cations.

Table 1
Selected bond lengths (Å) for (I)

Cu1—S3ⁱ	2.290 (2)	Fe—S4^v	2.331 (3)
Cu1—S3	2.302 (2)	Fe—S4	2.331 (3)
Cu1—S2ⁱⁱ	2.303 (2)	Fe—S2^iv	2.337 (3)
Cu1—S1ⁱⁱⁱ	2.353 (2)	Fe—S2^vi	2.337 (3)
Cu2—S3	2.294 (2)	Ge—S3^vii	2.196 (2)
Cu2—S2	2.309 (2)	Ge—S2	2.221 (2)
Cu2—S4^iv	2.309 (2)	Ge—S4ⁱⁱⁱ	2.233 (2)
Cu2—S4	2.319 (2)	Ge—S1ⁱⁱⁱ	2.3107 (19)
Symmetry codes: (i) $[-x+{\script{3\over 2}}, y-{\script{1\over 2}}, -z+2]$ ; (ii) x, y-1, z; (iii) $[x-{\script{1\over 2}}, y-{\script{1\over 2}}, z]$ ; (iv) $[-x+{\script{3\over 2}}, y-{\script{1\over 2}}, -z+1]$ ; (v) -x+2, y, -z+1; (vi) $[x+{\script{1\over 2}}, y-{\script{1\over 2}}, z]$ ; (vii) $[x-{\script{1\over 2}}, y+{\script{1\over 2}}, z]$ .

Table 2
Selected bond lengths (Å) for (II)

Cu1—S3ⁱ	2.292 (2)	Co—S4^v	2.308 (3)
Cu1—S2ⁱⁱ	2.295 (2)	Co—S4	2.308 (3)
Cu1—S3	2.304 (2)	Co—S2^iv	2.325 (3)
Cu1—S1ⁱⁱⁱ	2.343 (3)	Co—S2^vi	2.325 (3)
Cu2—S3	2.290 (2)	Ge—S2	2.211 (3)
Cu2—S2	2.298 (3)	Ge—S3^vii	2.211 (2)
Cu2—S4^iv	2.301 (2)	Ge—S4ⁱⁱⁱ	2.236 (2)
Cu2—S4	2.311 (2)	Ge—S1ⁱⁱⁱ	2.316 (2)
Symmetry codes: (i) $[-x+{\script{3\over 2}}, y-{\script{1\over 2}}, -z+2]$ ; (ii) x, y-1, z; (iii) $[x-{\script{1\over 2}}, y-{\script{1\over 2}}, z]$ ; (iv) $[-x+{\script{3\over 2}}, y-{\script{1\over 2}}, -z+1]$ ; (v) -x+2, y, -z+1; (vi) $[x+{\script{1\over 2}}, y-{\script{1\over 2}}, z]$ ; (vii) $[x-{\script{1\over 2}}, y+{\script{1\over 2}}, z]$ .

3. Database survey

Quaternary DLSs exist with several different formulae; examples that incorporate chalcogenides as the anion are I–II₂–III–VI₄, I₂–II–IV–VI₄, and I₄–II–IV₂–VI₇. In these formulae, the Roman numerals represent the number of valence electrons for each element. Compounds of the formula I–II₂–III–VI₄, such as CuMn₂InS₄ (Delgado & Sagredo, 2016 ) and CuFe₂InSe₄ (Delgado et al., 2008 ) include trivalent elements, while the other relevant formulae mentioned above, including the title compounds, contain tetravalent elements. Numerous DLSs of the general formula I₂–II–IV–VI₄ have been reported and crystallize in non-centrosymmetric space groups, such as I $[\overline{4}]$ 2m and Pmn2₁ with the stannite and wurtz-stannite structure types that are derived from the cubic and hexagonal diamond structures, respectively (Brunetta et al., 2013 ). The monovalent ions incorporated in these materials include Li (Wu, Zhang, et al., 2017 ; Wu & Pan, 2017 ), Cu (Parthé et al., 1969 ) or Ag (Brunetta et al., 2013) and the divalent ions include a number of metals, such as Mg (Liu et al., 2013 ), Mn (Bernert & Pfitzner, 2005 ), Fe (Wintenberger, 1979), Co (Bernert and Pfitzner 2006 ), Zn (Parasyuk et al., 2001 ), Cd (Rosmus et al., 2014 ) and Hg (Olekseyuk et al., 2005 ). The tetravalent ions found in these compounds are usually Si, Ge, or Sn, while the hexavalent atoms (i.e., the divalent anions) can be S (Lekse et al., 2009 ), Se (Gulay, Romanyuk & Parasyuk, 2002 ), or Te (Parasyuk et al., 2005 ). Some specific examples include Cu₂MgGeS₄ (Liu et al., 2013) and Ag₂MnSnS₄ (Friedrich et al., 2018 ).

In contrast, considerably fewer compounds of the general formula I₄–II–IV₂–VI₇ have been discovered: only seven of these, which crystallize in either space group C2 or Cc with structures derived from cubic or hexagonal diamond, respectively, have been published to date: Li₄MnGe₂S₇ (Cc) (Kaib et al., 2013), Li₄MnSn₂Se₇ (Cc) (Kaib et al., 2013), Li₄HgGe₂S₇ (Cc) (Wu, Yang, Pan 2017), Ag₄HgGe₂S₇ (Cc) (Gulay, Olekseyuk & Parasyuk 2002 ), Ag₄CdGe₂S₇ (Cc) (Gulay, Olekseyuk & Parasyuk 2002), Cu₄NiSi₂S₇ (C2) (Schäfer et al., 1980), and Cu₄NiGe₂S₇ (C2) (Schäfer et al., 1980).

4. X-ray powder diffraction and thermal analysis

The calculated and observed X-ray powder diffraction patterns match well (Fig. 4), indicating that the title compounds are the major phases of the respective reactions. An optimization of the synthetic protocol is needed to isolate the desired phases in phase-pure form.

Figure 4
Comparison of experimental X-ray powder diffraction patterns before and after DTA with those calculated using the single-crystal structures for Cu₄FeGe₂S₇ (left) and Cu₄CoGe₂S₇ (right).

Differential thermal analysis (DTA) reveals that Cu₄FeGe₂S₇ and Cu₄CoGe₂S₇ show relatively high thermal stability and melting and recrystallization events with appropriate hysteresis around 1000°C (Fig. 5). Multiple heating-cooling cycles for each sample were consistent, suggesting that the thermal events are reversible. X-ray powder diffraction of the DTA residues indicated that the samples were not changed by the thermal analyses, implying that they melt congruently. DTA also suggests that neither compound is a single phase, as there are some small shoulders on the peaks indicative of the thermal events.

Figure 5
Differential thermal analysis diagrams obtained for the title compounds showing the melting and recrystallization events.

5. Materials and methods

All powdered elements were acquired from commercial suppliers and used as obtained with the exception of germanium metal, which was purchased as chunks and ground to a fine powder using a Diamonite™ mortar and pestle prior to use. Powder X-ray diffraction data were recorded from 10–100° 2θ using a PANalytical X'Pert Pro MPD powder X-ray diffractometer operating with Cu K_α radiation (λ = 1.541871 Å), a tube power of 45 kV and 40 mA and a step size of 0.017°. DTA data were obtained using a Shimadzu DTA50 thermal analyzer. Each sample was vacuum-sealed in a fused-silica ampoule, placed alongside an ampoule containing an Al₂O₃ reference of comparable mass, heated from room temperature to 1050°C at a rate of 10°C min⁻¹ and subsequently cooled to room temperature at the same rate. A second heating–cooling cycle was conducted in order to determine the reproducibility of the thermal events.

6. Synthesis and crystallization

Cu₄FeGe₂S₇ and Cu₄CoGe₂S₇ were synthesized by combining stoichiometric amounts of Cu (99.999%), Fe (99.99%) or Co (99.99%), Ge (99.999%) and S (99.5%, sublimed) powders. The powders were mixed and placed into 12 mm o.d. fused-silica tubes that were subsequently attached to a vacuum line, evacuated and flame sealed. The reaction vessels were placed upright into ceramic containers inside programmable furnaces, where they were heated to 1000°C in 24 h, held there for 48 h, cooled to 900°C over the course of 50 h, and held there for 96 h, before being allowed to cool to room temperature over a 24 h period. Subsequently, the reaction vessels were cut open and the contents were examined under a light microscope. The products consisted of loose silvery gray microcrystalline powders from which small single crystals were selected for single-crystal X-ray diffraction.

7. Refinement

Crystal data, data collection parameters, and structure refinement details are summarized in Table 3. Extinction parameters were refined for each compound. After the final refinement, the Flack parameter for both structures refined to 0.06 (3), indicating that the absolute structure is correct. In Cu₄FeGe₂S₇, the largest difference peak is located 1.15 Å from Cu2 while the deepest difference hole is 1.50 Å from S3. For Cu₄CoGe₂S₇, the largest difference peak is 0.67 Å from Co while the deepest difference hole is 0.83 Å from Ge.

Table 3
Experimental details

	(I)	(II)
Crystal data
Chemical formula	Cu₄FeGe₂S₇	Cu₄CoGe₂S₇
M_r	679.61	682.69
Crystal system, space group	Monoclinic, C2	Monoclinic, C2
Temperature (K)	296	296
a, b, c (Å)	11.7405 (6), 5.3589 (2), 8.3420 (4)	11.7280 (2), 5.33987 (10), 8.33133 (14)
β (°)	98.661 (3)	98.6680 (12)
V (Å³)	518.86 (4)	515.80 (2)
Z	2	2
Radiation type	Mo Kα	Mo Kα
μ (mm⁻¹)	16.46	16.76
Crystal size (mm)	0.08 × 0.08 × 0.03	0.08 × 0.07 × 0.06

Data collection
Diffractometer	Bruker SMART APEXII	Bruker SMART APEXII
Absorption correction	Multi-scan (SADABS; Sheldrick, 2002 )	Multi-scan (SADABS; Sheldrick, 2002)
T_min, T_max	0.246, 0.435	0.356, 0.435
No. of measured, independent and observed [I > 2σ(I)] reflections	2258, 1187, 994	2239, 1177, 1039
R_int	0.021	0.017
(sin θ/λ)_max (Å⁻¹)	0.649	0.649

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.034, 0.094, 1.06	0.030, 0.075, 1.11
No. of reflections	1187	1177
No. of parameters	67	67
No. of restraints	1	1
Δρ_max, Δρ_min (e Å⁻³)	0.75, −0.89	0.88, −0.49
Absolute structure	Flack (1983 )	Flack (1983)
Absolute structure parameter	0.06 (3)	0.06 (3)
Computer programs: SMART and SAINT (Bruker, 1998 ), SHELXS97 (Sheldrick, 2008 ), SHELXL2018/3 (Sheldrick, 2015 ) and CrystalMaker (Palmer, 2014 ).

Supporting information

CCDC references: 2009145; 2009144

Crystal structure: contains datablocks I, II, global. DOI: https://doi.org/10.1107/S2056989020007872/hb7920sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989020007872/hb7920Isup2.hkl

Structure factors: contains datablock II. DOI: https://doi.org/10.1107/S2056989020007872/hb7920IIsup3.hkl

checkCIF report

Computing details top

For both structures, data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015); molecular graphics: CrystalMaker (Palmer, 2014); software used to prepare material for publication: SHELXL2018/3 (Sheldrick, 2015).

Tetracopper iron digermanium heptasulfide (I) top

Crystal data top

Cu₄FeGe₂S₇	F(000) = 636
M_r = 679.61	D_x = 4.350 Mg m⁻³
Monoclinic, C2	Mo Kα radiation, λ = 0.71073 Å
a = 11.7405 (6) Å	Cell parameters from 4891 reflections
b = 5.3589 (2) Å	θ = 4.2–31.4°
c = 8.3420 (4) Å	µ = 16.46 mm⁻¹
β = 98.661 (3)°	T = 296 K
V = 518.86 (4) Å³	Irregular, grey
Z = 2	0.08 × 0.08 × 0.03 mm

Data collection top

Bruker SMART APEXII diffractometer	994 reflections with I > 2σ(I)
φ and ω Scans scans	R_int = 0.021
Absorption correction: multi-scan (SADABS; Sheldrick, 2002)	θ_max = 27.5°, θ_min = 2.5°
T_min = 0.246, T_max = 0.435	h = −15→15
2258 measured reflections	k = −6→6
1187 independent reflections	l = −10→10

Refinement top

Refinement on F²	w = 1/[σ²(F_o²) + (0.0315P)²] where P = (F_o² + 2F_c²)/3
Least-squares matrix: full	(Δ/σ)_max < 0.001
R[F² > 2σ(F²)] = 0.034	Δρ_max = 0.75 e Å⁻³
wR(F²) = 0.094	Δρ_min = −0.89 e Å⁻³
S = 1.06	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
1187 reflections	Extinction coefficient: 0.0123 (9)
67 parameters	Absolute structure: Flack (1983)
1 restraint	Absolute structure parameter: 0.06 (3)
Primary atom site location: structure-invariant direct methods

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.

Refinement. Refined as a two-component inversion twin

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Cu1	0.64298 (8)	0.2054 (3)	0.93484 (11)	0.0174 (7)
Cu2	0.71147 (8)	0.7098 (2)	0.64229 (10)	0.0165 (6)
Fe	1.000000	0.7200 (6)	0.500000	0.0112 (6)
Ge	0.42524 (6)	0.7285 (3)	0.78371 (7)	0.0092 (3)
S1	1.000000	0.9789 (6)	1.000000	0.0091 (6)
S2	0.56834 (15)	0.9593 (5)	0.71791 (18)	0.0111 (6)
S3	0.78390 (14)	0.4527 (4)	0.85310 (17)	0.0091 (6)
S4	0.85688 (15)	0.9704 (5)	0.58180 (19)	0.0101 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cu1	0.0171 (6)	0.0169 (15)	0.0184 (6)	−0.0019 (5)	0.0032 (4)	0.0025 (5)
Cu2	0.0171 (6)	0.0142 (13)	0.0185 (6)	0.0005 (8)	0.0037 (4)	0.0017 (4)
Fe	0.0115 (8)	0.0137 (17)	0.0093 (7)	0.000	0.0041 (6)	0.000
Ge	0.0080 (5)	0.0100 (8)	0.0096 (5)	−0.0009 (8)	0.0018 (3)	−0.0007 (4)
S1	0.0095 (13)	0.0093 (16)	0.0087 (11)	0.000	0.0014 (9)	0.000
S2	0.0089 (11)	0.0128 (15)	0.0120 (9)	−0.0029 (10)	0.0030 (7)	0.0009 (9)
S3	0.0081 (11)	0.0076 (14)	0.0122 (9)	0.0004 (8)	0.0033 (8)	−0.0003 (8)
S4	0.0101 (10)	0.0094 (13)	0.0107 (9)	−0.0012 (7)	0.0010 (7)	−0.0004 (10)

Geometric parameters (Å, º) top

Cu1—S3ⁱ	2.290 (2)	Fe—S4^v	2.331 (3)
Cu1—S3	2.302 (2)	Fe—S4	2.331 (3)
Cu1—S2ⁱⁱ	2.303 (2)	Fe—S2^iv	2.337 (3)
Cu1—S1ⁱⁱⁱ	2.353 (2)	Fe—S2^vi	2.337 (3)
Cu2—S3	2.294 (2)	Ge—S3^vii	2.196 (2)
Cu2—S2	2.309 (2)	Ge—S2	2.221 (2)
Cu2—S4^iv	2.309 (2)	Ge—S4ⁱⁱⁱ	2.233 (2)
Cu2—S4	2.319 (2)	Ge—S1ⁱⁱⁱ	2.3107 (19)

S3ⁱ—Cu1—S3	111.52 (5)	Ge^viii—S1—Ge^ix	109.23 (13)
S3ⁱ—Cu1—S2ⁱⁱ	108.81 (12)	Ge^viii—S1—Cu1^viii	112.37 (4)
S3—Cu1—S2ⁱⁱ	107.60 (6)	Ge^ix—S1—Cu1^viii	109.92 (4)
S3ⁱ—Cu1—S1ⁱⁱⁱ	112.79 (6)	Ge^viii—S1—Cu1^ix	109.92 (4)
S3—Cu1—S1ⁱⁱⁱ	106.23 (13)	Ge^ix—S1—Cu1^ix	112.37 (4)
S2ⁱⁱ—Cu1—S1ⁱⁱⁱ	109.75 (6)	Cu1^viii—S1—Cu1^ix	102.96 (15)
S3—Cu2—S2	109.84 (6)	Ge—S2—Cu1^x	109.71 (8)
S3—Cu2—S4^iv	109.30 (11)	Ge—S2—Cu2	110.72 (12)
S2—Cu2—S4^iv	111.38 (6)	Cu1^x—S2—Cu2	109.87 (7)
S3—Cu2—S4	109.17 (7)	Ge—S2—Fe^vii	109.96 (9)
S2—Cu2—S4	107.49 (11)	Cu1^x—S2—Fe^vii	108.33 (14)
S4^iv—Cu2—S4	109.62 (5)	Cu2—S2—Fe^vii	108.21 (7)
S4^v—Fe—S4	109.72 (19)	Ge^vi—S3—Cu1^viii	108.48 (7)
S4^v—Fe—S2^iv	107.13 (6)	Ge^vi—S3—Cu2	109.52 (7)
S4—Fe—S2^iv	113.18 (6)	Cu1^viii—S3—Cu2	106.84 (11)
S4^v—Fe—S2^vi	113.18 (6)	Ge^vi—S3—Cu1	111.62 (11)
S4—Fe—S2^vi	107.13 (6)	Cu1^viii—S3—Cu1	108.31 (7)
S2^iv—Fe—S2^vi	106.58 (17)	Cu2—S3—Cu1	111.89 (8)
S3^vii—Ge—S2	112.97 (13)	Ge^ix—S4—Cu2^xi	107.94 (11)
S3^vii—Ge—S4ⁱⁱⁱ	109.74 (6)	Ge^ix—S4—Cu2	113.68 (8)
S2—Ge—S4ⁱⁱⁱ	110.97 (6)	Cu2^xi—S4—Cu2	109.46 (7)
S3^vii—Ge—S1ⁱⁱⁱ	108.92 (5)	Ge^ix—S4—Fe	112.60 (9)
S2—Ge—S1ⁱⁱⁱ	107.64 (6)	Cu2^xi—S4—Fe	105.12 (7)
S4ⁱⁱⁱ—Ge—S1ⁱⁱⁱ	106.34 (12)	Cu2—S4—Fe	107.68 (14)

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

Tetracopper cobalt digermanium heptasulfide (II) top

Crystal data top

Cu₄CoGe₂S₇	F(000) = 638
M_r = 682.69	D_x = 4.396 Mg m⁻³
Monoclinic, C2	Mo Kα radiation, λ = 0.71073 Å
a = 11.7280 (2) Å	Cell parameters from 4827 reflections
b = 5.33987 (10) Å	θ = 4.2–32.6°
c = 8.33133 (14) Å	µ = 16.76 mm⁻¹
β = 98.6680 (12)°	T = 296 K
V = 515.80 (2) Å³	Irregular, grey
Z = 2	0.08 × 0.07 × 0.06 mm

Data collection top

Bruker SMART APEXII diffractometer	1039 reflections with I > 2σ(I)
φ and ω Scans scans	R_int = 0.017
Absorption correction: multi-scan (SADABS; Sheldrick, 2002)	θ_max = 27.5°, θ_min = 2.5°
T_min = 0.356, T_max = 0.435	h = −15→15
2239 measured reflections	k = −6→6
1177 independent reflections	l = −10→10

Refinement top

Refinement on F²	w = 1/[σ²(F_o²) + 3.9921P] where P = (F_o² + 2F_c²)/3
Least-squares matrix: full	(Δ/σ)_max < 0.001
R[F² > 2σ(F²)] = 0.030	Δρ_max = 0.88 e Å⁻³
wR(F²) = 0.075	Δρ_min = −0.49 e Å⁻³
S = 1.11	Extinction correction: SHELXL2018/3 (Sheldrick 2015), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
1177 reflections	Extinction coefficient: 0.060 (3)
67 parameters	Absolute structure: Flack (1983)
1 restraint	Absolute structure parameter: 0.06 (3)
Primary atom site location: structure-invariant direct methods

Special details top

Refinement. Refined as a two-component inversion twin

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Cu1	0.64303 (9)	0.2051 (4)	0.93412 (12)	0.0177 (7)
Cu2	0.71154 (9)	0.7108 (2)	0.64143 (12)	0.0158 (6)
Co	1.000000	0.7206 (7)	0.500000	0.0141 (8)
Ge	0.42703 (6)	0.7276 (4)	0.78209 (9)	0.0092 (4)
S1	1.000000	0.9762 (6)	1.000000	0.0090 (6)
S2	0.56898 (15)	0.9604 (5)	0.7167 (2)	0.0118 (6)
S3	0.78425 (15)	0.4533 (4)	0.8520 (2)	0.0092 (6)
S4	0.85742 (15)	0.9682 (5)	0.5803 (2)	0.0094 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cu1	0.0181 (6)	0.0182 (18)	0.0167 (6)	−0.0026 (5)	0.0023 (4)	0.0018 (6)
Cu2	0.0168 (6)	0.0131 (14)	0.0175 (6)	0.0004 (8)	0.0029 (4)	0.0014 (6)
Co	0.0118 (7)	0.021 (2)	0.0096 (7)	0.000	0.0028 (5)	0.000
Ge	0.0090 (5)	0.0100 (9)	0.0086 (5)	−0.0011 (7)	0.0012 (3)	−0.0019 (6)
S1	0.0102 (12)	0.0092 (18)	0.0072 (11)	0.000	−0.0001 (9)	0.000
S2	0.0101 (9)	0.0160 (15)	0.0097 (9)	−0.0022 (11)	0.0028 (7)	−0.0007 (9)
S3	0.0095 (9)	0.0076 (16)	0.0109 (9)	0.0012 (8)	0.0025 (7)	0.0017 (9)
S4	0.0113 (9)	0.0090 (13)	0.0076 (8)	−0.0008 (7)	0.0008 (7)	−0.0012 (10)

Geometric parameters (Å, º) top

Cu1—S3ⁱ	2.292 (2)	Co—S4^v	2.308 (3)
Cu1—S2ⁱⁱ	2.295 (2)	Co—S4	2.308 (3)
Cu1—S3	2.304 (2)	Co—S2^iv	2.325 (3)
Cu1—S1ⁱⁱⁱ	2.343 (3)	Co—S2^vi	2.325 (3)
Cu2—S3	2.290 (2)	Ge—S2	2.211 (3)
Cu2—S2	2.298 (3)	Ge—S3^vii	2.211 (2)
Cu2—S4^iv	2.301 (2)	Ge—S4ⁱⁱⁱ	2.236 (2)
Cu2—S4	2.311 (2)	Ge—S1ⁱⁱⁱ	2.316 (2)

S3ⁱ—Cu1—S2ⁱⁱ	109.37 (12)	Ge^viii—S1—Ge^ix	109.14 (15)
S3ⁱ—Cu1—S3	111.62 (6)	Ge^viii—S1—Cu1^viii	111.56 (4)
S2ⁱⁱ—Cu1—S3	107.25 (7)	Ge^ix—S1—Cu1^viii	110.41 (4)
S3ⁱ—Cu1—S1ⁱⁱⁱ	112.08 (6)	Ge^viii—S1—Cu1^ix	110.41 (4)
S2ⁱⁱ—Cu1—S1ⁱⁱⁱ	109.73 (7)	Ge^ix—S1—Cu1^ix	111.56 (4)
S3—Cu1—S1ⁱⁱⁱ	106.65 (13)	Cu1^viii—S1—Cu1^ix	103.68 (17)
S3—Cu2—S2	109.96 (7)	Ge—S2—Cu1^x	109.59 (8)
S3—Cu2—S4^iv	108.79 (11)	Ge—S2—Cu2	110.30 (13)
S2—Cu2—S4^iv	111.31 (7)	Cu1^x—S2—Cu2	109.95 (8)
S3—Cu2—S4	108.88 (8)	Ge—S2—Co^vii	109.91 (9)
S2—Cu2—S4	107.97 (11)	Cu1^x—S2—Co^vii	108.57 (14)
S4^iv—Cu2—S4	109.90 (5)	Cu2—S2—Co^vii	108.48 (8)
S4^v—Co—S4	110.11 (19)	Ge^vi—S3—Cu2	109.57 (8)
S4^v—Co—S2^iv	107.45 (6)	Ge^vi—S3—Cu1^viii	108.46 (8)
S4—Co—S2^iv	112.63 (7)	Cu2—S3—Cu1^viii	107.17 (11)
S4^v—Co—S2^vi	112.63 (7)	Ge^vi—S3—Cu1	111.81 (11)
S4—Co—S2^vi	107.45 (6)	Cu2—S3—Cu1	111.81 (8)
S2^iv—Co—S2^vi	106.59 (18)	Cu1^viii—S3—Cu1	107.84 (7)
S2—Ge—S3^vii	112.75 (14)	Ge^ix—S4—Cu2^xi	107.42 (11)
S2—Ge—S4ⁱⁱⁱ	111.49 (7)	Ge^ix—S4—Co	111.98 (10)
S3^vii—Ge—S4ⁱⁱⁱ	109.30 (7)	Cu2^xi—S4—Co	105.80 (7)
S2—Ge—S1ⁱⁱⁱ	108.43 (7)	Ge^ix—S4—Cu2	113.66 (9)
S3^vii—Ge—S1ⁱⁱⁱ	108.34 (6)	Cu2^xi—S4—Cu2	109.24 (7)
S4ⁱⁱⁱ—Ge—S1ⁱⁱⁱ	106.29 (12)	Co—S4—Cu2	108.42 (14)

Acknowledgements

We gratefully acknowledge Mr Daniel J. Bodnar, instrument maintenance manager of the Bayer School of Natural and Environmental Sciences at Duquesne University, for keeping the diffractometers running.

Funding information

This research was supported by the National Science Foundation, Division of Materials Research under grant No. DMR-1611198. The single-crystal and powder X-ray diffractometers were purchased with funds from the National Science Foundation under grant Nos. CHE-0234872 and DUE-0511444, respectively.

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