Ca_7.96Cu_0.04Ge₅O₁₈: a new calcium germanate with GeO₄ and Ge₃O₁₀ units

The title compound, octa­calcium copper penta­germanium octa­deca­oxide, represents a new inter­mediate phase between CaO and GeO₂, and has not previously been reported in the literature. The structure consists of three different Ge sites, two of them on general 8d positions, site symmetry 1, one on special position 4d, site symmetry 2. Three of the five Ca sites occur on 8d positions, site symmtery 1, one Ca is on 4b with site symmetry and one Ca is on 4c with site symmetry 2. All nine O atoms have symmetry 1 (8d position). By sharing common edges, the Ca sites form infinite bands parallel to the c axis, and these bands are inter­connected by isolated GeO₄ and Ge₃O₁₀ units. These (100) layers are stacked along a in an ABAB... sequence, with the B layer being inverted and displaced along b/2.

S1. Comment

Detailed phase-equilibrium studies by Eulenberger et al. (1962) and Shirvinskaya et al. (1966) revealed the presence of six intermediate phases in the CaO–GeO₂ system. These are Ca₃GeO₅, which is meta-stable below 1593 K, Ca₂GeO₄, Ca₃Ge₂O₇, CaGeO₃, CaGe₂O₅ and CaGe₄O₉. Structure determinations have been performed on several of these compounds, including Ca₃GeO₅, which shows polymorphic forms including two-layer, nine-layer and 24-layer structures (Nishi & Takéuchi, 1984, 1985, 1986). A high-pressure polymorph of Ca₂GeO₄ was investigated by Reid & Ringwood (1970). CaGeO₃ shows a wollastonite-type structure under ambient conditions (Barbier & Levy 1997) and two high-pressure polymorphs (Prewitt & Sleigth 1969; Sasaki et al. 1983), while CaGe₂O₅ is reported to have two polymorphs (Aust et al. 1976, Nevsky, Ilyuskin & Belov, 1979). Additionally, Barbier & Levy (1997) report on the triclinic structure of Ca₅Ge₃O₁₁ and Nevsky, Ilyuskin et al. (1979) describe the orthorhombic form of a Ge-rich phase, Ca₂Ge₇O₁₆; neither of these two compounds is mentioned in the phase diagram of Shirvinskaya et al. (1966). Ca₂GeO₄ shows an olivine-type structure under ambient conditions (Eulenberger et al. 1962), although the actual atomic arrangement is undetermined, and the structure of CaGe₄O₉ is unknown.

The title compound can be regarded as an additional new phase in the CaO–GeO₂ system, being close to Ca₃Ge₂O₇ in the phase diagram of Shirvinskaya et al. (1966). It is interesting to note that Barbier & Levy (1997) were not successful in reproducing a pure phase with nominal composition of 3CaO·2GeO₂. They noted that the actual composition of the `Ca₃Ge₂O₇' compound is Ca₅Ge₃O₁₁ (Barbier & Levy 1997). The appearance of the additional Ca₈Ge₅O₁₈ phase is further evidence that the CaO–GeO₂ phase diagram is more complicated in detail than that given by Shirvinskaya et al. (1966) and probably needs additional work. It can be concluded that, instead of Ca₃Ge₂O₇ with 40 mol% GeO₂, two phases exist, having 37.5 (Ca₅Ge₃O₁₁) and 38.5 (Ca₈Ge₅O₁₈) mol% GeO₂, respectively.

Fig. 1 shows the asymmetric unit of the title compound as a displacement ellipsoid plot with the atomic numbering, while Fig. 2 is a polyhedral representation projected down the a axis. The structure contains isolated GeO₄ and Ge₃O₁₀ groups and a band of Ca polyhedra, aligned parallel to the c axis (Fig. 2). Thus, the structure of the title compound appears to be unique, as these building units are not found in other Ca–Ge–O compounds. By sharing common edges and corners of Ge and Ca sites, a layer within the (100) plane is formed. These layers are stacked along the a axis in an ABAB··· sequence. When viewing the Ge sites only, it is evident that the B layer is displaced along b/2 and inverted (Fig. 3). Here it also becomes evident that the Ca2, Ca3 and Ca5 sites reside in channels of the Ge framework, parallel to c.

Among the three Ge sites, the isolated Ge1 site is the most regular in terms of bond length distortions (Table 1). Each corner of the Ge1O₄ tetrahedron is attached to three neighbouring Ca sites. Thus, the O1–O2–O3 face of the Ge1 tetrahedron (forming the base) fits, by edge-sharing, into a triangular cavity, formed by the Ca1, Ca2 and Ca3 sites, which themselves share three common edges with each other (cf. Fig. 2). The congener of Ca1 is located at (3/2 − x, −1/2 + y, z) [symmetry code (iii)]. Atom O4 is attached to three Ca sites [Ca1^iv, Ca2^v and Ca3^v; symmetry codes: (iv) 1/2 − x, −1/2 + y, z; (v) −1 + x, y, z] of a next-lower (100) plane via corner-sharing. The tetrahedral O—Ge1—O angles involving the basal O atoms (O1, O2, O3) are narrowed with respect to the ideal tetrahedral O—T—O angle and the angles involving O4 are opened up, with Ge1—O4 being the shortest of all four Ge1—O bonds. The distortion that gives rise to this prolate aspect of a tetrahedron is a trigonal C_3v elongation of the tetrahedron. As expected, the shared tetrahedral edges are distinctly shorter compared with the unshared ones (Table 1). Atoms Ge2, Ge3, and Ge2ⁱⁱ [symmetry code: (ii) 1 − x, y, 1/2 − z] form a trimer in which atom Ge2ⁱⁱ is rotated by 180° about the b axis with respect to Ge2. This rotation is caused by the twofold axis residing upon the Ge3 site.

The Ge2 tetrahedron shares three of its corners with three neighbouring Ca sites; the fourth is common to the Ge3, Ca4^vi and Ca5 sites [symmetry code: (vi) 1/2 − x, 1/2 + y, z]. Similar to the Ge1 polyhedron, the O5–O6–O7 triangular face of the Ge2 tetrahedron fits into a triangular cavity formed by the Ca3, Ca4 and Ca5 sites (Fig. 2). Thus, three of the six tetrahedral edges are common to the tetrahedron and to Ca polyhedra. The fourth tetrahedral corner, atom O8, is shared between the Ge2, Ca3^vii, Ca4^vii and Ca5ⁱ sites [symmetry codes: (i) 1 + x, y, z; (vii) 3/2 − x, 1/2 + y, z]. Similar to Ge1, the Ge2 tetrahedron exhibits a trigonal C_3v elongation towards this corner-shared O8 atom. The Ge2 site shows a larger polyhedral distortion which is mainly due to the long Ge2—O7 bridging bond. Average shared und unshared edge lengths are similar for the Ge1 and Ge2 sites (Table 1). The bridging angle Ge3—O7—Ge2 is 115.47 (1)°, which is low compared with other compounds such as Ca₅Ge₃O₁₁ [Ge1—O5–Ge2 = 128.03 (15)°; Barbier & Levy 1997] or CaGeO₃ [Ge—O—Ge angles between 132.1 and 149.3°; Barbier & Levy 1997]. In contrast with the Ge1 and Ge2 sites, no common edges with neighbouring polyhedra are present for the Ge3 site. Compared with the Ge1 and Ge2 sites, this results in a distinctly lower bond-angle distortion and elongation of the Ge3 site, while the bond-length distortion is still large due to the long Ge3—O7 bridging bond length (Table 1). Bond-valence sums are ideal for the Ge3 site, while the Ge1 and Ge2 sites appear to be under-bonded.

Two types of coordination polyhedra are found for the Ca sites: strongly distorted octahedral sites (Ca1–Ca4) and an eightfold coordinated site (Ca5). Connected via two common edges, the Ca2, Ca3 and Ca5 polyhedra form an infinite chain parallel to the crystallographic c axis. Thus, a Ca3–Ca2–Ca3^viii sequence [symmetry code: (viii) 2 − x, 1 − y, 1 − z] is linked by the Ca5ⁱ polyhedron (Fig. 2). Laterally attached to this chain by common edges are Ca1 and Ca4ⁱ polyhedra. This arrangement gives rise to units of three edge-sharing Ca polyhedra, namely Ca1–Ca2–Ca3 and Ca3–Ca4–Ca5, forming a triangular cavity into which the bases of the Ge1 and Ge2 tetrahedra fit, thereby interconnecting different (100) layers along the crystallographic a axis. Ca—O bond lengths are similar for the sites Ca1–Ca4 but are distinctly longer at Ca5 (Table 1). Octahedral distortion parameters (Table 1) are high, particularly for the angular distortion. This shows that the Ca sites are far from an ideal octahedral coordination. Bond-valence sums for the Ca sites are close to 2.0, except the Ca5 site.

NB Single primes were used to denote several different symmetry codes in the original CIF, with potential for confusion. These have now been replaced with standard symmetry codes. Please check carefully that this has not introduced any errors.

S2. Experimental

The title compound was discovered by chance during attempts to synthesize melilite-related Ca₂CuGe₂O₇ from a self-flux. For this reason, a mixture of CaCO₃, CuO and GeO₂ in the stoichiometry of Ca₂CuGe₂O₇ was carefully ground in an agate mortar and placed in a small platinum tube (length 30 mm, inner diameter 5 mm, one side welded tight, the other open). This assemblage was transferred to a high-temperature furnace, slowly heated to 1623 K at a rate of 1 K min⁻¹, held at this temperature for another 12 h to homogenize the melt, and cooled down to 1323 K at a rate of 0.03 K min⁻¹. The synthesis batch mainly consisted of large colourless crystals of triclinic CaGeO₃ (Barbier & Levy 1997), some reddish brown copper oxide and several small plate-like transparent crystals of the title compound, of a very pale greenish colour. Qualitative [Please define REM] energy-dispersive X-ray diffraction (REM–EDX) analysis of the pale-green crystals yielded Ca, Ge and O as the main elements, with a very minor Cu component also being present. A semi-quantitative EDX analysis yielded the structural formula Ca_7.96Ge_4.96Cu_0.07O_17.91; the general formula can be given as Ca₈Ge₅O₁₈. In the phase diagram of Shirvinskaya et al. (1966), the title compound is very close to Ca₃Ge₂O₇ (the latter with 40 mol% GeO₂, the former with 38.5 mol%).

S3. Refinement

Structure solution using Patterson methods yielded the Ge and Ca positions. The O atoms were located from a residual electron-density analysis in a subsequent refinement cycle. After full anisotropic refinement on F², possible positions for the small Cu content were tested. While there was no evidence for occupation by Cu of the Ca1, Ca3, Ca4 and Ca5 positions, the Ca2 site refined to an occupancy of 4%. The amount of Cu, refined from the intensity data, agrees quite well with the amount found by semi-quantitative REM–EDX analysis. Five additional crystals of the same synthesis batch were tested, all giving the same unit-cell dimensions; on one of these additional crystals a full intensity data set was collected, yielding identical structural parameters within one estimated standard deviation.

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SAINT-Plus (Bruker, 2001); data reduction: SAINT-Plus (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 2005); software used to prepare material for publication: WinGX (Version 1.70.01; Farrugia 1999).

Figures

	Fig. 1. A view of (I), with 90% probability displacement ellipsoids. [Symmetry codes: (i) 1 + x, y, z; (ii) 1 − x, y, 1/2 − z.]
	Fig. 2. A polyhedral representation of the structure of (I), viewed along the crystallographic a axis. Only one (100) layer is shown.
	Fig. 3. A polyhedral representation of the structure of (I), viewed along c. Polyhedra for the Ca sites have been omitted.

(I)

Crystal data

Ca7.96Cu0.04Ge5O18	Dx = 3.669 Mg m^−3
Mr = 972.53	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbcn	Cell parameters from 17356 reflections
a = 5.2436 (2) Å	θ = 2.8–28.8°
b = 11.6079 (5) Å	µ = 10.90 mm^−1
c = 28.9238 (11) Å	T = 295 K
V = 1760.51 (12) Å^3	Cuboid, light green
Z = 4	0.12 × 0.11 × 0.08 mm
F(000) = 1857.0

Data collection

Bruker SMART APEX CCD area-detector diffractometer	1930 reflections with I > 2σ(I)
rotation, ω scans at four different ϕ positions	Rint = 0.045
Absorption correction: numerical via equivalents using X-SHAPE (Stoe & Cie 1996)	θmax = 28.8°, θmin = 2.8°
Tmin = 0.29, Tmax = 0.42	h = −7→7
19710 measured reflections	k = −15→15
2229 independent reflections	l = −37→38

Refinement

Refinement on F^2	1 restraint
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0318P)^2 + 0.7889P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.022	(Δ/σ)max = 0.001
wR(F^2) = 0.059	Δρmax = 0.93 e Å^−3
S = 1.08	Δρmin = −0.58 e Å^−3
2229 reflections	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
146 parameters	Extinction coefficient: 0.00105 (9)

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.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ge1	0.56772 (5)	0.40572 (2)	0.443145 (9)	0.00880 (8)
Ge2	0.44398 (5)	0.59288 (2)	0.328864 (9)	0.00853 (8)
Ge3	0.5	0.76777 (3)	0.25	0.00863 (9)
Ca1	0.49873 (10)	0.71883 (5)	0.442698 (17)	0.00998 (12)
Ca2	1	0.5	0.5	0.01125 (19)	0.959 (3)
Cu2	1	0.5	0.5	0.01125 (19)	0.041 (3)
Ca3	0.99252 (9)	0.48754 (5)	0.37788 (2)	0.01382 (12)
Ca4	0.50723 (9)	0.28246 (4)	0.331122 (18)	0.01016 (11)
Ca5	0	0.52092 (6)	0.25	0.01266 (16)
O1	0.7136 (4)	0.54350 (16)	0.44046 (6)	0.0133 (4)
O2	0.7134 (3)	0.33463 (15)	0.39631 (6)	0.0120 (4)
O3	0.7137 (3)	0.34107 (15)	0.49146 (6)	0.0121 (4)
O4	0.2354 (4)	0.40499 (16)	0.44104 (6)	0.0129 (4)
O5	0.2872 (3)	0.65771 (15)	0.37524 (6)	0.0123 (4)
O6	0.3032 (3)	0.45886 (15)	0.32178 (6)	0.0126 (4)
O7	0.2941 (3)	0.67192 (15)	0.28106 (6)	0.0098 (4)
O8	0.7719 (3)	0.60137 (15)	0.32341 (6)	0.0107 (4)
O9	0.6768 (3)	0.85326 (15)	0.28583 (6)	0.0142 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ge1	0.00770 (15)	0.00938 (15)	0.00930 (15)	0.00019 (10)	0.00051 (9)	0.00072 (10)
Ge2	0.00749 (13)	0.00883 (14)	0.00927 (14)	−0.00013 (9)	−0.00003 (9)	0.00014 (10)
Ge3	0.00916 (17)	0.00863 (18)	0.00811 (18)	0	−0.00020 (14)	0
Ca1	0.0110 (3)	0.0094 (3)	0.0096 (3)	−0.0003 (2)	0.00051 (18)	0.00058 (18)
Ca2	0.0093 (3)	0.0130 (4)	0.0114 (4)	−0.0004 (3)	−0.0009 (3)	−0.0019 (3)
Cu2	0.0093 (3)	0.0130 (4)	0.0114 (4)	−0.0004 (3)	−0.0009 (3)	−0.0019 (3)
Ca3	0.0102 (2)	0.0164 (3)	0.0148 (3)	0.0013 (2)	0.0022 (2)	0.0061 (2)
Ca4	0.0098 (2)	0.0097 (3)	0.0109 (3)	−0.00060 (19)	0.00023 (19)	−0.00076 (19)
Ca5	0.0148 (3)	0.0097 (3)	0.0134 (4)	0	0.0002 (3)	0
O1	0.0125 (9)	0.0107 (9)	0.0167 (10)	−0.0002 (8)	0.0019 (7)	0.0010 (8)
O2	0.0106 (8)	0.0149 (10)	0.0105 (9)	0.0012 (7)	0.0011 (7)	−0.0011 (7)
O3	0.0108 (8)	0.0142 (9)	0.0112 (9)	0.0007 (7)	−0.0002 (7)	0.0026 (7)
O4	0.0085 (9)	0.0150 (10)	0.0152 (10)	−0.0010 (7)	−0.0001 (7)	0.0013 (8)
O5	0.0114 (9)	0.0153 (10)	0.0102 (9)	0.0006 (7)	0.0006 (7)	−0.0005 (7)
O6	0.0130 (9)	0.0096 (9)	0.0152 (9)	−0.0010 (7)	0.0015 (7)	−0.0014 (8)
O7	0.0084 (8)	0.0117 (9)	0.0094 (9)	−0.0011 (7)	0.0012 (7)	0.0027 (7)
O8	0.0085 (8)	0.0114 (9)	0.0123 (9)	0.0000 (7)	0.0007 (7)	0.0012 (8)
O9	0.0162 (9)	0.0104 (9)	0.0159 (10)	0.0016 (7)	−0.0067 (8)	−0.0019 (8)

Geometric parameters (Å, º)

Ge1—O4	1.744 (2)	Ca2—O3	2.3912 (18)
Ge1—O2	1.7604 (17)	Ca3—O6^iv	2.3235 (19)
Ge1—O3	1.7613 (17)	Ca3—O8	2.3592 (18)
Ge1—O1	1.7746 (19)	Ca3—O2	2.3616 (18)
Ge2—O8	1.7296 (18)	Ca3—O1	2.4161 (19)
Ge2—O6	1.7341 (18)	Ca3—O4^iv	2.4244 (19)
Ge2—O5	1.7440 (17)	Ca3—O5^iv	2.5090 (18)
Ge2—O7	1.8362 (17)	Ca4—O2	2.2562 (18)
Ge3—O9	1.7082 (18)	Ca4—O9^v	2.2664 (18)
Ge3—O7	1.7919 (17)	Ca4—O6	2.3259 (18)
Ca1—O3^i	2.3132 (18)	Ca4—O8^v	2.4103 (18)
Ca1—O1	2.3272 (19)	Ca4—O5^vi	2.4716 (18)
Ca1—O5	2.3539 (18)	Ca4—O7^vi	2.4979 (18)
Ca1—O2^ii	2.4261 (19)	Ca5—O9^vii	2.3918 (19)
Ca1—O4^iii	2.486 (2)	Ca5—O7	2.5014 (18)
Ca1—O3^ii	2.5052 (19)	Ca5—O8^viii	2.6098 (18)
Ca2—O1	2.3399 (18)	Ca5—O6	2.7124 (18)
Ca2—O4^iv	2.3764 (19)
O4—Ge1—O2	113.86 (8)	O9^vii—Ca5—O9^vi	71.09 (9)
O4—Ge1—O3	117.39 (8)	O9^vii—Ca5—O7	119.13 (6)
O2—Ge1—O3	102.84 (9)	O9^vi—Ca5—O7	130.81 (6)
O4—Ge1—O1	115.70 (9)	O7—Ca5—O7^xi	91.03 (8)
O2—Ge1—O1	101.64 (8)	O9^vii—Ca5—O8^viii	145.21 (6)
O3—Ge1—O1	103.37 (8)	O9^vi—Ca5—O8^viii	76.18 (6)
O8—Ge2—O6	117.61 (9)	O7—Ca5—O8^viii	74.90 (6)
O8—Ge2—O5	120.95 (8)	O7^xi—Ca5—O8^viii	76.05 (6)
O6—Ge2—O5	106.11 (8)	O8^viii—Ca5—O8^ix	138.06 (8)
O8—Ge2—O7	109.18 (8)	O9^vii—Ca5—O6^xi	71.31 (6)
O6—Ge2—O7	100.20 (8)	O9^vi—Ca5—O6^xi	83.58 (6)
O5—Ge2—O7	99.31 (8)	O7—Ca5—O6^xi	145.32 (6)
O9—Ge3—O9^ix	108.97 (12)	O8^viii—Ca5—O6^xi	116.69 (6)
O9—Ge3—O7	112.56 (8)	O8^ix—Ca5—O6^xi	74.99 (5)
O9^ix—Ge3—O7	109.74 (8)	O7—Ca5—O6	63.25 (5)
O7—Ge3—O7^ix	103.23 (11)	O6^xi—Ca5—O6	149.20 (8)
O3^i—Ca1—O1	89.61 (6)	Ge1—O1—Ca1	125.32 (10)
O3^i—Ca1—O5	111.40 (7)	Ge1—O1—Ca2	92.87 (8)
O1—Ca1—O5	86.65 (6)	Ca1—O1—Ca2	118.62 (8)
O3^i—Ca1—O2^ii	157.14 (6)	Ge1—O1—Ca3	92.95 (8)
O1—Ca1—O2^ii	99.67 (7)	Ca1—O1—Ca3	123.30 (8)
O5—Ca1—O2^ii	90.10 (6)	Ca2—O1—Ca3	96.02 (7)
O3^i—Ca1—O4^iii	92.25 (6)	Ge1—O2—Ca4	124.13 (9)
O1—Ca1—O4^iii	177.23 (7)	Ge1—O2—Ca3	95.18 (8)
O5—Ca1—O4^iii	90.77 (6)	Ca4—O2—Ca3	108.06 (7)
O2^ii—Ca1—O4^iii	79.34 (6)	Ge1—O2—Ca1^v	95.98 (8)
O3^i—Ca1—O3^ii	89.80 (4)	Ca4—O2—Ca1^v	127.70 (8)
O1—Ca1—O3^ii	102.68 (7)	Ca3—O2—Ca1^v	98.95 (6)
O5—Ca1—O3^ii	157.07 (6)	Ge1—O3—Ca1^i	124.88 (9)
O2^ii—Ca1—O3^ii	67.85 (6)	Ge1—O3—Ca2	91.49 (7)
O4^iii—Ca1—O3^ii	79.38 (6)	Ca1^i—O3—Ca2	116.69 (7)
O1^x—Ca2—O4^i	84.57 (6)	Ge1—O3—Ca1^v	93.22 (7)
O1—Ca2—O4^i	95.43 (6)	Ca1^i—O3—Ca1^v	125.67 (7)
O1—Ca2—O3^x	108.20 (6)	Ca2—O3—Ca1^v	96.74 (6)
O4^i—Ca2—O3^x	83.91 (6)	Ge1—O4—Ca2^viii	119.46 (9)
O4^iv—Ca2—O3^x	96.09 (6)	Ge1—O4—Ca3^viii	123.32 (9)
O1—Ca2—O3	71.80 (6)	Ca2^viii—O4—Ca3^viii	94.85 (7)
O4^i—Ca2—O3	96.09 (6)	Ge1—O4—Ca1^vi	119.81 (10)
O6^iv—Ca3—O8	87.58 (7)	Ca2^viii—O4—Ca1^vi	97.65 (7)
O6^iv—Ca3—O2	118.99 (7)	Ca3^viii—O4—Ca1^vi	95.67 (7)
O8—Ca3—O2	105.53 (6)	Ge2—O5—Ca1	123.06 (9)
O6^iv—Ca3—O1	170.48 (6)	Ge2—O5—Ca4^iii	98.64 (8)
O8—Ca3—O1	93.03 (6)	Ca1—O5—Ca4^iii	123.07 (8)
O2—Ca3—O1	69.98 (6)	Ge2—O5—Ca3^viii	88.51 (7)
O6^iv—Ca3—O4^iv	95.82 (7)	Ca1—O5—Ca3^viii	120.15 (7)
O8—Ca3—O4^iv	169.15 (6)	Ca4^iii—O5—Ca3^viii	95.30 (6)
O2—Ca3—O4^iv	81.86 (6)	Ge2—O6—Ca3^viii	95.01 (8)
O1—Ca3—O4^iv	81.93 (7)	Ge2—O6—Ca4	125.48 (9)
O6^iv—Ca3—O5^iv	70.11 (6)	Ca3^viii—O6—Ca4	111.56 (8)
O8—Ca3—O5^iv	80.83 (6)	Ge2—O6—Ca5	95.84 (8)
O2—Ca3—O5^iv	168.60 (6)	Ca3^viii—O6—Ca5	94.90 (6)
O1—Ca3—O5^iv	100.60 (6)	Ca4—O6—Ca5	126.32 (7)
O4^iv—Ca3—O5^iv	90.61 (6)	Ge3—O7—Ge2	115.45 (9)
O2—Ca4—O9^v	92.04 (7)	Ge3—O7—Ca4^iii	110.66 (8)
O2—Ca4—O6	94.65 (7)	Ge2—O7—Ca4^iii	95.22 (7)
O9^v—Ca4—O6	87.12 (7)	Ge3—O7—Ca5	128.79 (8)
O2—Ca4—O8^v	94.66 (6)	Ge2—O7—Ca5	100.62 (7)
O9^v—Ca4—O8^v	84.92 (6)	Ca4^iii—O7—Ca5	100.27 (6)
O6—Ca4—O8^v	167.95 (7)	Ge2—O8—Ca3	113.25 (9)
O2—Ca4—O5^vi	91.44 (6)	Ge2—O8—Ca4^ii	121.26 (9)
O9^v—Ca4—O5^vi	165.35 (7)	Ca3—O8—Ca4^ii	101.02 (7)
O6—Ca4—O5^vi	106.77 (6)	Ge2—O8—Ca5^iv	120.62 (9)
O8^v—Ca4—O5^vi	80.61 (6)	Ca3—O8—Ca5^iv	96.79 (6)
O2—Ca4—O7^vi	157.73 (6)	Ca4^ii—O8—Ca5^iv	99.62 (6)
O9^v—Ca4—O7^vi	108.27 (6)	Ge3—O9—Ca4^ii	122.46 (9)
O6—Ca4—O7^vi	95.39 (6)	Ge3—O9—Ca5^xii	89.97 (7)
O8^v—Ca4—O7^vi	78.59 (6)	Ca4^ii—O9—Ca5^xii	145.98 (8)
O5^vi—Ca4—O7^vi	66.62 (6)

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