Ca₃ZnGeO₂[Ge₄O₁₂]: a Ca–Zn germanate related to the mineral taikanite

The title compound, Ca₃ZnGeO₂[Ge₄O₁₂] (tricalcium zinc germanium dioxide dodeca­oxido­tetra­germanate), adopts a taikanite-type structure. The tetra­hedral [Ge₄O₁₂] chain geometry is very similar to that of the silicate chain of taikanite, i.e. BaSr₂Mn³⁺₂O₂[Si₄O₁₂], while the major difference is found parallel to the c axis. In taikanite, Mn³⁺ octa­hedra form an infinite zigzag chain, whereas the title compound has a chain of distorted ZnO₆ octa­hedra, which alternates with distorted GeO₄ tetra­hedra connected to each other via two common edges. Eightfold-coordinated Ca²⁺ polyhedra and ZnO₆ octa­hedra form a slab parallel to (001) which alternates with another slab containing the tetra­hedrally coordinated Ge sites along the c axis.

S1. Introduction

Taikanite is an Mn³⁺-bearing silicate mineral with the chemical formula BaSr₂Mn³⁺₂O₂[Si₄O₁₂], whose structure was first described by Armbruster et al. (1993) [space group C2, with a = 14.600 (2), b = 7.759 (4), c = 5.142 (1) Å, β = 93.25 (2)° and Z = 2]. According to Armbruster et al., the structure of taikanite is characterized by [Si₄O₁₂] single `vierer'-chains parallel to the b axis and egde-sharing zigzag chains of Mn³⁺O₆ o­cta­hedra, running parallel to the c axis. Using the lattice parameters and the space-group symmetry found for the title compound, viz. Ca₃ZnGeO₂[Ge₄O₁₂], a close relationship to taikanite was clearly revealed by searching the Inorganic Crystal Structure Database (ICSD; Belsky et al., 2002). Armbruster et al. noticed a relationship between taikanite and the synthetic compound CMS-XI, i.e. Ca₃Mn³⁺₂O₂[Si₄O₁₂], previously described by Moore & Araki (1979). CMS-XI crystallizes in the space group I2/c, with a = 14.26 (3), b = 7.620 (12), c = 10.025 (4) Å, β = 93.27 (5)° and Z = 4. Herein the structure of the title compound is described in detail and compared to taikanite and the synthetic compound Ca₃Mn³⁺₂O₂[Si₄O₁₂].

S2. Experimental

S2.1. Synthesis and crystallization

The title compound was obtained as a by-product from sinter­ing experiments on the phase-pure synthetic pyroxene-type compound CaCu_0.95Zn_0.05Ge₂O₆ at 1283 K in open platinum tubes. The sinter­ing temperature of 1283 K was close to the melting point of the pyroxenes. Experiments were conducted in order to increase the crystal size of the pyroxenes to facilitate single-crystal X-ray diffraction studies. Needles up to 1 mm in length grew on the surface of the pyroxene sinter­ing cake, having partly an hexagonal crystal morphology. Crystals exhibit frequent twinning, with several being tested before one was found with clear and sharp spots with no obvious signs of twinning.

S2.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. Space-group determination yield two possible space groups for the title compound, viz. C2/m and C2. Intensity statistics suggested an acentric space group. Structure determination was performed first in the C2 space group using the direct methods of SHELXS2012 (Sheldrick, 2008), yielding the present structure model. No acceptable solution was found in the C2/m space group. An improvement in the refinement of teh structure could be achieved by considering inversion twinning of the crystal, as suggested by SHELXL2012 (Sheldrick, 2015). On a data set of a twinned crystal, a twin law of (-0.5 -1.5 0, 0.5 -0.5 0, 0 0 1), with a 120° rotation around the [001] axis, was determined using the program CELL_NOW (Bruker, 2012). This strategy did not improve significantly the structural refinement, yielding a twin fraction of only ca 1%.

Based on the C2 space group and the lattice parameters, the title compound was identified to be similar to the taikanite structure. To test if the structures were indeed isotypical, the fractional atomic coordinates reported by Armbruster et al. (1993) were used as the starting model and produced identical results to those herein reported. Data presented here follows the atomic nomenclature of Armbruster et al. (1993).

S3. Results and discussion

The title compound, viz. Ca₃ZnGeO₂[Ge₄O₁₂], displays monoclinic symmetry (space group C2), with the asymmetric unit being composed of Ca1 on special position 2a (site symmetry 2) and Ca2 on general position 4c; three different Ge sites, of which Ge1 and Ge2 are on general positions 4c, and Ge3 is on special position 2b; one Zn atom found at special position 2a; seven different O atoms, all located on 4c positions. In the atomic model for BaSr₂Mn³⁺₂O₂[Si₄O₁₂], the Ca1 site is occupied by Ba²⁺, while the Ca2 site hosts the smaller Sr atom; the Zn1 and Ge3 sites are filled by Mn³⁺, and Ge1 and Ge2 are equivalent to the Si2 and Si2 positions of taikanite (Armbruster et al., 1993). Fig. 1 depicts the asymmetric unit of the title compound and some symmetry-equivalent atoms, including the atomic nomenclature.

Figs. 2 and 3 show polyhedral representations of the tetra­hedral–o­cta­hedral and Ca-site framework in different orientations. The main building unit of the title compound is a `vierer'-single [Ge₄O₁₂] chain running parallel to the b axis (Fig. 2a). It consists of the Ge1 and Ge2 sites, being tetra­edrally coordinated by O atoms. Tetra­hedra are corner-shared to form a chain with a crankshaft-like topology (Figs. 1 and 2a). There is a close similarity to the [Si₄O₁₂] chains in taikanite. The Ge1^vii—Ge2—Ge1 angle is 118.9 (7)° and the Ge2—Ge1—Ge2^viii angle is 95.4 (6)°, with both values comparing well to the analogous angles in taikanite (120.40 and 96.77°, respectively) and CMS-XI (122.67 and 95.36°, respectively) (Moore & Araki, 1979) [symmetry codes: (vii) -x+1/2, y+1/2, -z+1; (viii) -x+1/2, y-1/2, -z+1]. The Ge2^viii—O2—Ge1 [120.2 (4)°] and Ge2—O7—Ge1 [120.2 (3)°] angles in the title compound are, however, distinctly smaller when compared to the corresponding Si—O—Si angles in CMS-XI (125.3 and 126.3°, respectively) and taikanite (127 and 128°, respectively). This shows that the chain of tetra­hedra in taikanite is more stretched because of the presence of larger Sr²⁺ and Ba²⁺ cations at the inter­stitial sites. Thus, Ca₃ZnGeO₂[Ge₄O₁₂] has the most compressed chains of the three compounds under discussion. Within the chain of tetra­hedra, the angle around the Ge1 site is larger both with respect to <Ge—O> and the tetra­hedral volume. This tetra­hedron also displays higher polyhedral distortion, with a tetra­hedral quadratic elongation (TQE) of 1.0352 and a large tetra­hedral bond angle variance (TAV) of 162.7°². The tetra­hedron around the Ge2 site is somewhat more regular, with TQE = 1.0160 and TAV = 73.62°2, but is still far away from the values of a regular GeO₄ tetra­hedron, such as found in Ge–pyroxenes with zweier-single chains; in CaZnGe₂O₆, a TQE value of 1.0111 and a TAV value of 47.44°2 were reported by Redhammer & Roth (2005). While the Ge1 tetra­hedron shares only corners with neighbouring polyhedra, two edges of the base plane of the Ge2 tetra­hedron are common with two neighbouring Ca2O₈, and the third edge common to the neighbooring Ca1O₈ polyhedra. The O5 apex atom of the Ge2 site shares corners with two Ca2 and one Ca1 site, inter­connecting the slab of tetra­hedral sites with the sheet of ZnO₆ and CaO₈ polyhedra. The average Ge—O distances are 1.777 (7) and 1.754 (7) Å for Ge1 and Ge2, respectively, which are values typically found in germanate compounds with chain structures (Redhammer & Roth 2005). In taikanite and CMS-XI, the tetra­hedral sites are distinctly more regular when compared to those in the title compound. Bond-valence-sum calculations (Brese & O'Keeffe, 1991) show that the Ge1 site is slightly under-bonded [bond-valence-sum S = 3.74 valence units (v.u.)], while the Ge2site has a nearly ideal S value of 3.94 v.u.

The major difference between taikanite and the title compound occurs parallel to the c axis. In taikanite, the Mn1 and Mn2 sites form zigzag chains of edge-sharing Mn³⁺O₆ o­cta­hedra with a cis–cis arrangement. The O-atom distribution around the Mn2 site resembles an elongated o­cta­hedron, with four short and two long bonds. This site is occupied by Zn²⁺ in the title compound, also having four short [1.991 (7)–2.007 (8) Å] and two long [2.101 (8) Å] bonds. The coordination o­cta­hedron deviates, however, from an ideal o­cta­hedron, with an o­cta­hedral quadratic elongation (OQE) of 1.0282 and a quadratic o­cta­hedral angle variance (OAV) of 91.55. The corresponding distortion parameters in taikanite for the Mn³⁺O₆ o­cta­hedron are OQE = 1.0248 and OAV = 36.74°2. For comparison, the regular ZnO₆ o­cta­hedron in the pyroxene-type compound CaZnGe₂O₆ has OQE = 1.0106 and OAV = 34.22°2, with bond lengths ranging from 2.096 (3) to 2.176 (3) Å (Redhammer & Roth, 2005). The Mn1 site of taikanite, which represents a compressed Mn³⁺O₆ o­cta­hedron with four medium and two short distances between 1.88 and 2.15 Å, is occupied by Ge⁴⁺ in the title compound. The coordination number is fourfold, with bond lengths ranging from 1.749 (6) to 1.852 (6) Å, giving rise to a strongly distorted tetra­hedron (TAV = 257.6°2 and TQE = 1.0558). The <Ge3—O> bond length is 1.800 (7) Å, which is still in the range of typical Ge—O bonds in tetra­hedral coordination. Thus, no edge-sharing zigzag chain, such as in taikanite, is present in the title compound along the b axis, but the O-atom coordination polyhedron around the Ge3 site only shares two common corners via the O4 atoms. Two more distant Ge3—O1 bonds are found at 2.476 (6) Å. These are, however, untypically long Ge—O distances, even for Ge in an o­cta­hedral coordination. The latter are commonly between 1.8 and 1.9 Å, e.g. as observed in Ca₂Ge₇O₁₆ (Redhammer et al., 2007) or in A₂Ge₄O₉ (A = Na, K, Rb) compounds (Redhammer & Tippelt, 2013). Nevertheless, including these long Ge—O3 distances, an edge-sharing GeO₆–ZnO₆ zigzag chain with a cis–cis arrangement is formed. The GeO₆ `o­cta­hedron' shows an average <Ge—O> bond length of 2.033 (6) Å and a larger OQE value of 1.0921, while the bond-angle variance is reduced to 159.46°². Using bond-valence-sum calculations, the two long Ge—O3 bonds contribute 0.14 v.u. to the valence of Ge⁴⁺, giving S = 3.78 v.u., still showing an under-bonding at the Ge3 site.

Two types of cavities can be identified along the c axis, both occupied by the Ca²⁺ ions showing eightfold coordination. While these are different in size in taikanite, mainly because of the larger Ba²⁺ cation found at the equivalent Ca1 site of the title compound, the average <Ca—O> bond length and the polyhedral volume of the two Ca sites are similar, with <Ca1—O> and <Ca2—O> values of 2.568 (6) and 2.546 (6) Å, respectively. These are similar to those found in CMS-XI, i.e. 2.663 (5) and 2.539 (4) Å (Moore & Araki, 1979). The larger <Ca1—O> bond length in CMS-XI is due to a rather long Ca1—O7 distance of 3.160 (5) Å, as compared to the value of 2.937 (6) Å in the title compound. The difference is related to the larger size requirements of the [Ge₄O₁₂] chain, thereby reducing the inter­atomic distances of the bonding O atoms to the Ca²⁺ atom.

The Ca2 site forms an eightfold-coordinated polyhedron, adopting the shape of a distorted square anti­prism. It shares two common edges with neighbouring Ca2 sites, building up infinite chains parallel to the b axis. Bond lengths vary between 2.322 (7) and 2.849 (7) Å. The Ca1 site is also eightfold coordinated, with Ca—O bond lengths ranging between 2.319 (7) and 2.937 (6) Å. The Ca1 O-atom coordination polyhedron shares four edges with four different Ca2 polyhedra, thereby connecting two different Ca2O₈ chains in a trans–trans arrangement to each other along the a axis (Fig. 3). Additionally, the Ca1 polyhedron shares one edge with the Ge2O₄ tetra­hedron and the ZnO₆ o­cta­hedron. Together with the latter, the Ca polyhedra form a slab parallel to (001) which alternates along the c axis with a slab containing the [Ge₄O₁₂] tetra­hedral chains and the Ge3 tetra­hedral site (Fig. 2b). The O5 atom is at the triple connection point of two Ge2 and one Ge1 sites, and it is simultaneously the apex O atom of the Ge2O₄ tetra­hedron. Above atom O5, a triangular cavity is formed (marked in Fig. 3), into which the base plane of the Ge2O₄ tetra­hedron fits, thus inter­connecting the [Ge₄O₁₂] chains with the Ge–Zn slab. The Ge1O₄ tetra­hedron lies above and below the approximately quadratic cavities of the Ca/Zn slab.

Computing details

Data collection: APEX2 (Bruker, 2012); cell refinement: APEX2 (Bruker, 2012); data reduction: APEX2 (Bruker, 2012); program(s) used to solve structure: SHELXS2012 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2012 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg,2006); software used to prepare material for publication: WinGX (Farrugia, 2012).

Figures

	Fig. 1. The asymmetric unit and symmetry related atoms of Ca3ZnGeO2[Ge4O12], shown with 95% probability displacement ellipsoids. Colour code: orange and yellow = Ca^2+ on Ca1 and Ca2 sites, respectively; cyan and blue = Ge^4+ on Ge1 and Ge2 sites forming the [Ge4O12] chain and the Ge3 site, respectively; green = Zn^2+; red = oxygen atoms. [Symmetry codes: (i) x+1/2, y+1/2, z; (ii) -x+1/2, y+1/2, -z; (iii) -x+1, y, -z; (iv) x, y, z-1; (v) -x+1, y, -z+1; (vi) x+1/2, y+1/2, z-1; (vii) -x+1/2, y+1/2, -z+1; (viii) -x+1/2, y-1/2, -z+1; (ix) -x+1/2, y-1/2, -z; (x) x+1/2, y-1/2, z; (xi) x+1/2, y-1/2, z-1.] [Please provide an unlabelled version of this figure and we will label it]
	Fig. 2. Polyhedral representation of the structure of Ca3ZnGeO2[Ge4O12], viewed along (a) the [001] and (b) the [010] direction. Ca sites are not represented as polyhedra for clarity (see Fig. 3). Colour codes are as in Fig. 1.
	Fig. 3. Polyhedral representation of a slab of Ca1–Ca2–Zn sites of Ca3ZnGeO2[Ge4O12], viewed along [001], drawn at a height of z = 1.0. The triangular faces formed by one Ca1 and two Ca2 polyhedra are highlighted. Colour codes are as in Fig. 1.

Tricalcium zinc germanium dioxide dodecaoxidotetragermanate

Crystal data

Ca3ZnGeO2[Ge4O12]	F(000) = 724
Mr = 772.56	Dx = 4.585 Mg m^−3
Monoclinic, C2	Mo Kα radiation, λ = 0.71073 Å
a = 13.938 (5) Å	Cell parameters from 3487 reflections
b = 7.941 (3) Å	θ = 2.9–29.2°
c = 5.0560 (17) Å	µ = 16.83 mm^−1
β = 90.817 (4)°	T = 293 K
V = 559.5 (3) Å^3	Prismatic, colourless
Z = 2	0.17 × 0.09 × 0.08 mm

Data collection

Bruker SMART APEX diffractometer	1455 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.038
rotation, ω–scans at 4 different ϕ positions	θmax = 29.8°, θmin = 2.9°
Absorption correction: multi-scan (APEX2; Bruker, 2012)	h = −19→19
Tmin = 0.359, Tmax = 0.746	k = −11→10
3487 measured reflections	l = −6→7
1481 independent reflections

Refinement

Refinement on F^2	1 restraint
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0395P)^2 + 0.5647P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.030	(Δ/σ)max < 0.001
wR(F^2) = 0.076	Δρmax = 1.57 e Å^−3
S = 1.09	Δρmin = −1.05 e Å^−3
1481 reflections	Absolute structure: Refined as an inversion twin.
107 parameters	Absolute structure parameter: 0.16 (3)

Special details

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.

Refinement. Refined as a 2-component inversion twin.

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

	x	y	z	Uiso*/Ueq
Ca1	0.5	0.7639 (3)	0	0.0166 (5)
Ca2	0.29262 (13)	0.3939 (2)	−0.0011 (3)	0.0160 (3)
Ge1	0.12017 (6)	0.56994 (12)	0.49129 (17)	0.0158 (2)
Ge2	0.33374 (6)	0.68607 (12)	0.47432 (15)	0.01253 (19)
Ge3	0.5	0.41679 (16)	0.5	0.0169 (3)
Zn2	0.5	0.1812 (2)	0	0.0182 (3)
O1	0.1114 (6)	0.7217 (10)	0.7317 (18)	0.039 (2)
O2	0.1600 (5)	0.3856 (8)	0.6801 (12)	0.0194 (13)
O3	0.4272 (4)	0.5753 (9)	0.3185 (12)	0.0193 (12)
O4	0.4296 (5)	0.3399 (11)	0.7568 (16)	0.034 (2)
O5	0.3325 (4)	0.6851 (10)	0.8130 (10)	0.0174 (11)
O6	0.0415 (5)	0.4994 (8)	0.2476 (15)	0.0260 (15)
O7	0.2317 (4)	0.6012 (8)	0.3112 (12)	0.0183 (13)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ca1	0.0182 (11)	0.0173 (11)	0.0140 (10)	0	−0.0038 (8)	0
Ca2	0.0157 (7)	0.0187 (8)	0.0134 (7)	0.0013 (6)	−0.0023 (6)	0.0008 (6)
Ge1	0.0145 (4)	0.0178 (4)	0.0150 (4)	0.0003 (3)	−0.0050 (3)	−0.0041 (3)
Ge2	0.0112 (3)	0.0144 (4)	0.0119 (3)	−0.0004 (3)	−0.0027 (3)	−0.0003 (3)
Ge3	0.0189 (6)	0.0166 (6)	0.0155 (6)	0	0.0032 (4)	0
Zn2	0.0194 (6)	0.0214 (6)	0.0136 (6)	0	−0.0030 (5)	0
O1	0.020 (3)	0.034 (5)	0.063 (5)	−0.005 (3)	0.004 (4)	−0.034 (4)
O2	0.023 (3)	0.020 (3)	0.015 (3)	0.003 (2)	−0.005 (2)	−0.006 (3)
O3	0.018 (3)	0.020 (3)	0.020 (3)	0.010 (3)	0.004 (2)	0.004 (3)
O4	0.022 (3)	0.035 (4)	0.044 (5)	0.008 (3)	0.020 (3)	0.022 (4)
O5	0.020 (3)	0.019 (3)	0.013 (2)	−0.001 (3)	0.001 (2)	0.003 (3)
O6	0.026 (4)	0.018 (3)	0.034 (4)	−0.001 (3)	−0.017 (3)	−0.003 (3)
O7	0.014 (3)	0.023 (3)	0.018 (3)	−0.004 (2)	−0.001 (2)	−0.006 (2)

Geometric parameters (Å, º)

Ca1—O6^i	2.319 (7)	Ge1—O6	1.731 (7)
Ca1—O6^ii	2.319 (7)	Ge1—O2	1.830 (7)
Ca1—O3	2.432 (7)	Ge1—O7	1.830 (6)
Ca1—O3^iii	2.432 (7)	Ge2—O5	1.713 (5)
Ca1—O5^iv	2.583 (6)	Ge2—O3	1.767 (6)
Ca1—O5^v	2.583 (6)	Ge2—O7	1.767 (6)
Ca1—O2^vi	2.937 (7)	Ge2—O2^vii	1.769 (6)
Ca1—O2^vii	2.937 (6)	Ge3—O4	1.749 (6)
Ca2—O4^iv	2.322 (7)	Ge3—O4^v	1.749 (6)
Ca2—O1^viii	2.337 (8)	Ge3—O3	1.852 (6)
Ca2—O2^iv	2.436 (7)	Ge3—O3^v	1.852 (6)
Ca2—O7	2.441 (6)	Zn2—O6^ix	1.991 (7)
Ca2—O5^iv	2.560 (8)	Zn2—O6^x	1.991 (7)
Ca2—O5^viii	2.597 (7)	Zn2—O4^v	2.007 (8)
Ca2—O7^ix	2.822 (7)	Zn2—O4^iv	2.007 (8)
Ca2—O3	2.849 (7)	Zn2—O1^xi	2.101 (8)
Ge1—O1	1.717 (7)	Zn2—O1^viii	2.101 (8)
O6^i—Ca1—O6^ii	72.5 (4)	O7—Ca2—O7^ix	150.99 (12)
O6^i—Ca1—O3	104.0 (3)	O5^iv—Ca2—O7^ix	124.40 (19)
O6^ii—Ca1—O3	138.7 (2)	O5^viii—Ca2—O7^ix	66.50 (19)
O6^i—Ca1—O3^iii	138.7 (2)	O4^iv—Ca2—O3	81.5 (3)
O6^ii—Ca1—O3^iii	104.0 (3)	O1^viii—Ca2—O3	66.3 (3)
O3—Ca1—O3^iii	104.0 (3)	O2^iv—Ca2—O3	151.2 (2)
O6^i—Ca1—O5^iv	127.6 (3)	O7—Ca2—O3	61.61 (18)
O6^ii—Ca1—O5^iv	77.3 (2)	O5^iv—Ca2—O3	66.87 (19)
O3—Ca1—O5^iv	73.1 (2)	O5^viii—Ca2—O3	123.73 (18)
O3^iii—Ca1—O5^iv	89.5 (2)	O7^ix—Ca2—O3	143.57 (18)
O6^i—Ca1—O5^v	77.3 (2)	O1—Ge1—O6	132.8 (4)
O6^ii—Ca1—O5^v	127.6 (3)	O1—Ge1—O2	102.5 (4)
O3—Ca1—O5^v	89.5 (2)	O6—Ge1—O2	107.3 (3)
O3^iii—Ca1—O5^v	73.1 (2)	O1—Ge1—O7	109.1 (3)
O5^iv—Ca1—O5^v	152.0 (4)	O6—Ge1—O7	102.9 (3)
O6^i—Ca1—O2^vi	81.2 (2)	O2—Ge1—O7	96.6 (3)
O6^ii—Ca1—O2^vi	67.8 (2)	O5—Ge2—O3	117.5 (3)
O3—Ca1—O2^vi	153.5 (2)	O5—Ge2—O7	116.4 (3)
O3^iii—Ca1—O2^vi	60.70 (18)	O3—Ge2—O7	101.3 (3)
O5^iv—Ca1—O2^vi	124.57 (18)	O5—Ge2—O2^vii	116.5 (4)
O5^v—Ca1—O2^vi	65.92 (19)	O3—Ge2—O2^vii	102.0 (3)
O6^i—Ca1—O2^vii	67.8 (2)	O7—Ge2—O2^vii	100.4 (3)
O6^ii—Ca1—O2^vii	81.2 (2)	O4—Ge3—O4^v	139.2 (6)
O3—Ca1—O2^vii	60.70 (18)	O4—Ge3—O3	107.2 (3)
O3^iii—Ca1—O2^vii	153.5 (2)	O4^v—Ge3—O3	100.3 (4)
O5^iv—Ca1—O2^vii	65.92 (19)	O4—Ge3—O3^v	100.3 (4)
O5^v—Ca1—O2^vii	124.57 (18)	O4^v—Ge3—O3^v	107.2 (3)
O2^vi—Ca1—O2^vii	141.6 (3)	O3—Ge3—O3^v	94.4 (4)
O4^iv—Ca2—O1^viii	74.4 (3)	O6^ix—Zn2—O6^x	87.0 (4)
O4^iv—Ca2—O2^iv	105.5 (3)	O6^ix—Zn2—O4^v	167.3 (3)
O1^viii—Ca2—O2^iv	142.4 (3)	O6^x—Zn2—O4^v	86.3 (3)
O4^iv—Ca2—O7	139.6 (3)	O6^ix—Zn2—O4^iv	86.3 (3)
O1^viii—Ca2—O7	102.7 (3)	O6^x—Zn2—O4^iv	167.3 (3)
O2^iv—Ca2—O7	100.3 (2)	O4^v—Zn2—O4^iv	102.2 (6)
O4^iv—Ca2—O5^iv	77.8 (2)	O6^ix—Zn2—O1^xi	85.2 (3)
O1^viii—Ca2—O5^iv	128.1 (2)	O6^x—Zn2—O1^xi	107.8 (3)
O2^iv—Ca2—O5^iv	87.0 (2)	O4^v—Zn2—O1^xi	86.6 (3)
O7—Ca2—O5^iv	73.0 (2)	O4^iv—Zn2—O1^xi	82.4 (3)
O4^iv—Ca2—O5^viii	129.5 (3)	O6^ix—Zn2—O1^viii	107.8 (3)
O1^viii—Ca2—O5^viii	78.2 (2)	O6^x—Zn2—O1^viii	85.2 (3)
O2^iv—Ca2—O5^viii	73.6 (2)	O4^v—Zn2—O1^viii	82.4 (3)
O7—Ca2—O5^viii	87.3 (2)	O4^iv—Zn2—O1^viii	86.6 (3)
O5^iv—Ca2—O5^viii	149.5 (2)	O1^xi—Zn2—O1^viii	162.4 (4)
O4^iv—Ca2—O7^ix	69.4 (3)	Ge2^viii—O2—Ge1	120.2 (4)
O1^viii—Ca2—O7^ix	84.5 (3)	Ge2—O3—Ge3	121.3 (3)
O2^iv—Ca2—O7^ix	61.68 (19)	Ge2—O7—Ge1	120.2 (3)

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