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The title compound, tricalcium monogermanate dichloride, is ortho­rhom­bic and consists of one distinct Ge site on special position 4c, site symmetry m, and two different Ca sites, Ca1 and Ca2, one on general position 8d, site symmetry 1, and the other on special position 4c. Two of the O atoms occupy the 4c position (symmetry m); the third O atom is situated on the general 8d position, symmetry 1, as is the one distinct Cl position. By sharing common edges, the distorted Ca1 octa­hedra form infinite crankshaft-like chains parallel to the b direction. Along a and c, these chains are connected to one another via common corners, thereby forming a three-dimensional framework of edge- and corner-sharing Ca1O4Cl2 octa­hedra. Triangular prisms of Ca2O4Cl2 polyhedra and GeO4 tetra­hedra fill the inter­stitial space within the Ca1 polyhedral framework. Relationships between the structures of the title compound and the humite-type materials norbergite (Mg3SiO4F2) and Mn3SiO4F2 are discussed.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270107030478/em3006sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270107030478/em3006Isup2.hkl
Contains datablock I

Comment top

As part of our investigations of Ca germanates with clinopyroxene and olivine-type structures, the title compound was obtained during attempts to synthesize CaFeGeO4 from a CaCl2 flux. Ca3GeO4Cl2 is, to our best knowledge, the first calcium–germanate–chloride compound so far; no corresponding entries were found in the Inorganic Crystal Structure Database (ICSD, 2006) or in the Powder Diffraction File (ICDD, 1999). Czaya & Bissert (1971) reported the crystal structure of Ca3SiO4Cl2, representing the silicate analogue of the title compound in the chemical sense. The silicate compound, however, is monoclinic, P21/c, and forms a structure distinctly different to that found for the germanate reported here. The structure of Ca3SiO4Cl2 can be described in terms of two different sheet systems (Czaya & Bissert, 1971), the first containing a two-dimensional network of corner- and edge-sharing, irregularly shaped, sixfold-coordinated Ca1O2Cl4 polyhedra within the bc plane. The second sheet system is built up by infinite chains of edge-sharing triangular Ca3O6 prisms, which are parallel to the b axis and which are connected laterally to each other via common corners by isolated SiO4 tetrahedra. Perpendicular to the Ca3 polyhedral chain, the sevenfold-coordinated Ca2O4Cl3 polyhedra form a second chain via corner sharing; this is also part of the second sheet system within the bc plane and interconnects the two systems along a. The sheet-like structure of Ca3SiO4Cl2 is fundamentally different from that of the title compound, described below. The topology of the title compound is, however, related to the structure of the humite-type mineral norbergite, Mg3SiO4F2 (Gibbs & Ribbe, 1969; Camara 1997), and synthetic Mn3SiO4F2 (Zenser et al., 2000). This is further reflected by similar lattice parameters and the same space-group symmetry. Some basic structural parameters are included in Table 1.

The crystal structure of the title compound contains one distinct Ge site, two distinct Ca sites, three O-atom positions and one Cl position. An anisotropic displacement plot, containing the atomic nomenclature, is given in Fig. 1, while Figs. 2 and 3 are polyhedral representations. The structure can be described in terms of infinite crankshaft-like chains of edge-sharing Ca1 octahedra (Fig. 2). Along a, these chains are connected to each other via isolated GeO4 tetrahedra and the isolated sixfold-coordinated Ca2 sites. Within the crankshaft-like chain, two different Ca1···Ca1 distances can be identified; the shorter is aligned parallel to b with Ca1···Ca1i = 3.513 (1) Å; the longer forms an angle of ~120° with b and has Ca1···Ca1vi = 4.385 (1) Å [symmetry codes: (i) x, -y + 1/2, z; (vi) -x + 1, -y, -z + 1]. The next nearest Ca1-octahedral chains are displaced along the <101> directions by a/2 and c/2, the symmetry equivalents of Ca1 being Ca1v and Ca1vii and the congeners of Ca1i being Ca1iv and Ca1viii, respectively [symmetry codes: (iv) x + 1/2, y, -z + 3/2; (v) -x + 1/2, -y, z - 1/2; (vii) -x + 1/2, -y, z = 1/2; x + 1/2, y, -z + 1/2]. Thus one central Ca1 chain has four nearest chains, which are connected to each other via common corners, thereby forming a dense framework of Ca1-polyhedra (Fig. 3a). The shortest interchain interatomic distance between neighboring Ca1 atoms of different chains (e.g. Ca1···Ca1iv or Ca1···Ca1v) is 3.871 (1) Å. The interstitial space is filled by GeO4 tetrahedra and sixfold-coordinated Ca2 sites. Viewed on their own, these two polyhedra form a chain parallel to the a direction and thus perpendicular to the Ca1-octahedral chain (Fig. 3b). Within this chain, the GeO4 tetrahedra alternate with the Ca2 polyhedra; the connection of these polyhedra also alternates between edge and corner sharing.

The coordination polyhedron around the Ca1 site can be described as a distinctly distorted octahedron, having four short Ca—O and two long Ca—Cl bonds (Table 1). The next nearest Cl atom is 3.207 (2) Å away from Ca1 (dashed line in Fig. 1). The two long bonds to Cl atoms are responsible for the distinct deviation from octahedral geometry, both the octahedral angle variance, OAV, and the quadratic octahedral elongation, OQE (Robinson et al., 1971), being large (Table 2). Similar large values can be found in for the ScO6 octahedra in the compound Cu2Sc2Ge4O13 [OAV 211° and OQE 1.056; Redhammer & Roth, 2004). The noteworthy point here is the remarkable topological similarity of the infinite Ca1 chain of the title compound and the ScO6 chain in Cu2Sc2Ge4O13; both chains exhibit the identical crankshaft-like appearance with a cistrans connection of individual edge-sharing octahedra, and four octahedra are needed to reach the next symmetry-equivalent octahedron along b (equal to the unit-cell dimension). When taking into account the size difference between Ca2+ (ionic radius r = 1.00 Å for sixfold coordination (Shannon & Prewitt, 1969) and Sc3+ (r = 0.73 Å for sixfold coordination) the b axes in both compounds are comparable. However, it should be noted that the inter-chain connection is distinctly different in the two compounds, especially along c. While the title compound can be understood as a framework of Ca1 octahedra, Cu2Sc2Ge4O13 displays a sheet-like structure with Cu– and Sc–oxygen polyhedral sheets separated from each other by Ge4O13 units along c.

In Mg3SiO4F2, the M1 site is also sixfold coordinated, forming a zigzag chain of edge-sharing MgO4F2 octahedra similar to that in the title compound but with polyhedral distortion parameters of approximately on-third of those found in Ca3GeO4Cl2 (Table 1). This is due to the close similarity between Mg—O and Mg—F bonds, while Ca—O and Ca—Cl bonds differ distinctly. In Mn3SiO4F2 (Zenser et al., 2000), the M1 octahedra are also regular (Table 1), forming the same wavelike chains passing through the structure along b; differences in average bond lengths cleary reflect the cationic size differences between Mg2+, Mn2+ and Ca2+. A comparison of the title compound with the olivine-type material Ca2GeO4 is also worthy of discussion. This germanate olivine contains a realisation of a somewhat more regular octahedral coordination of Ca2+ (Redhammer & Roth 2007). Here, Ca2+ on the smaller M1 site has Ca—O bond lengths between 2.330 (1) and 2.407 (2) Å, while the larger M2 site has Ca—O values between 2.295 (2) and 2.458 (2) Å (Redhammer & Roth, 2007), and the polyhedral distortion parameters are distinctly smaller than those of the title compound (Table 2). It is evident that the Ca—O bonds in the title compound are similar to those in Ca2GeO4, while the Ca—Cl bonds are quite different from these values (owing to the larger size of Cl-) and cause the large polyhedral distortion.

In Ca3GeO4Cl2, the Ca1 octahedron is characterized by a high degree of edge- and corner-sharing with neighboring polyhedra. It shares two of its edges with two neighboring Ca1 sites (thus forming the Ca1 chain along b), while two out of the four O-atom corners are common to two Ca1 octahedra from two different chains. One edge is common to the Ca1 and Ca2 polyhedra, while four corners of Ca1O6 are also corners of four neighboring Ca2O6 polyhedra. Finally, one edge is common to the Ca1 octahedron and the GeO4 tetrahedron. This common O1···O3 edge is the shortest among the octahedral edges [2.755 (1) Å], while the longest edge is the Cl1iv···Cl1v edge [3.565 (1) Å]. The bond valence sums, S (Brese & O'Keeffe, 1991), are ideal for the Ca1 site (S = 2.00 valence units).

The Ca2 site is also sixfold coordinated, the coordination polyhedron being close to a triangular prism. Three short bonds connect atom Ca2 to O atoms of the O1/O1i/O3ii triangular face [symmetry codes: (i) x, -y + 1/2, z; (ii) x - 1/2, -y + 1/2, -z + 1/2], which defines the lower base of the triangular prism, having common corners with octahedra of one and the same crankshaft-like Ca1 chain. However this lower base shares one of its edges with a neighboring GeO4 tetrahedron. The upper triangular face of the Ca2 prism is formed by Cl1/Cl1i/O2ii and shows distinctly longer bond lengths to Ca2 (Table 1). This upper triangular face fits into a triangular area between two edge-sharing Ca1 octahedra of the next higher crankshaft-like Ca1 chain along the c direction. Thus the upper triangular face of the Ca2 prism shares two edges with two neighboring Ca1-polyhedra. The Ca2-triangular prisms are isolated from each other but connect individual crankshaft-like Ca1 chains along the a axis to each other. The bond valence sum for Ca2 is lower than expected (S = 1.85).

For the Ca2 (M2) site some more evident differences do exist between the structure of the title compound and the norbergite-type structures of Mg3SiO4F2 and Mn3SiO4F2. Here the M2 site is in a true octahedral coordination. Similar to the olivine-type structure, M2 in norbergite is somewhat larger in size and polyhedral distortion (Table 1), but clearly less distorted than the M2 site in the title compound and also in the olivine Ca2GeO4 (Redhammer & Roth, 2007). The M2 site in Mg3SiO4F2 is laterally attached to the zigzag chain of M1 via three common edges, while in the title compound the Ca2 site is attached to the Ca1 chain only via two common corners (Fig. 2). It should also be noted that the M2 octahedron in norbergite only shares common corners with the next higher and lower zigzag chains along c, while the title compound shares common edges through the upper triangular face Cl1/Cl1i/O2ii of the Ca2 prism. Additionally, no common edge, but only one common corner with the neighboring tetrahedral site, is found in the norbergite structure, while the title compound shares a common edge with the GeO4 tetrahedron. All these differences are due to the distinct distortion of the structure as a consequence of the Cl- incorporation.

The GeO4 tetrahedra in Ca3GeO4Cl2 are not connected to each other. Two of their edges are common to the tetrahedron and neighboring Ca1 polyhedra (O1···O1i and O1···O3), and two are common to neighboring Ca2 sites (O1···O2). Bond angles opposite to the common edges are smaller than the ideal O—T—O values (Table 1), while those to the non-common edges are larger. As a consequence, the tetrahedron suffers a trigonal C3v distortion and is stretched towards atom O2. Thus, the tetrahedral distortion parameters are quite large (Table 2). In olivine-type Ca2GeO4 the basal plane edges of the isolated GeO4 tetrahedra also are common to two M1 and one M2 sites and the tetrahedron exhibits the same prolate aspect of basal plane O—T—O bond angles with a trigonal C3v distortion and an elongation towards the apex oxygen. As the amount of common edges is lower in the olivine-type compound, tetrahedral distortion parameters for the Ge site in that compound are lower (Table 2). For comparison, regular GeO4 tetrahedra are realised in the compound Ca7.96Cu0.04Ge5O18. There, the isolated Ge3 site has no common edges with neighboring polyhedra, and thus exhibits low TAV and TQE values of 11.7° and 1.0034, respectively (Redhammer et al., 2006).

As noted above, the structure of the title compound bares some remote similarities to the orthorhombic olivine-type structure of Ca2GeO4, which also shows Pnma symmetry at room temperature (Redhammer & Roth, 2007). The olivine M1 polyhedra (Ca1) form infinite stretched [extended?] chains of edge-sharing CaO6 octahedra parallel to the b axis. They are located at the center of the unit cell and at its corners, in close relation to the title compound, except that in Ca3GeO4Cl2 these chains display a crankshaft character. The kinking of the Ca1 chain is presumably responsible for the differences in b lattice parameters to Ca2GeO4, where b is smaller by about one-third, while a and c are of similar size (Redhammer & Roth, 2007). Owing to the elongation of the Ca1 polyhedra towards the Cl atoms in the title compound, individual Ca1 chains are connected to a framework while the more regular Ca1 polyhedra in Ca2GeO4 form isolated chains. The incorporation of Cl atoms to the structure of the title compound also causes the Ca2 polyhedron to become a triangular prism without any connections to next nearest Ca2 polyedra, while the Ca2 sites in the olivine form a framework of corner-sharing Ca2O6 octahedra. However, the spatial distribution of Ca2 sites within the unit cell is similar in both compounds, as is the distribution of GeO4 tetrahedra.

Related literature top

For related literature, see: Brese & O'Keeffe (1991); Camara (1997); Czaya & Bissert (1971); Gibbs & Ribbe (1969); ICDD (1999); ICSD (2006); Redhammer & Roth (2004, 2007); Redhammer et al. (2006); Redhammer, Tippelt, Roth & Amthauer (2004); Robinson et al. (1971); Shannon & Prewitt (1969); Zenser et al. (2000).

Experimental top

The title compound was obtained during synthesis of olivine-type CaFeGeO4. For this synthesis, a homogeneous mixture (1 g) of CaCO3, Fe, Fe2O3 and GeO2, weighted in the molar ratio of CaFe2+GeO4, was put into a platinum crucible together with CaCl2 (2.5 g), serving as the high-temperature solution. This assemblage was transferred to a chamber furnace, heated to 1273 K at a rate of 100 K h-1, held at this temperature for 12 h to ensure complete melting and decomposition of CaCO3, and then cooled slowly to 1073 K at a rate of 6 K h-1. After dissolving the flux with hot water, the experimental yield consisted of hematite flakes up to 3 mm in diameter, colorless crystals of the title compound, bordeaux-red crystals of an as yet unidentified phase, black idiomorphic cubes up to 150 µm, which transpired to be Ge and Pt containing brown millerite-type Ca2Fe2O5 (Redhammer et al., 2004), and fine-grained powder of Ge andradite, Ca3Fe2Ge3O12.

Refinement top

Structure solution using Patterson methods yielded the Ge and Ca positions, as well as an initially unidentified peak, which was identified as chlorine during the later refinement procedure. O-atom positions were located in a residual electron density analysis. After full anisotropic refinement on F2, the occupation factors of the cations were released (while fixing the anisotropic atomic displacement parameters to avoid infinite correlations) and refined to values corresponding to full occupation within one standard deviation. Thus, in the final refinement cycles, site occupation factors were again fixed to ideal values.

Computing details top

Data collection: SMART (Bruker, 2001) [or APEX2?]; cell refinement: SAINT-Plus (Bruker, 2001); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX (Version 1.70.01; Farrugia 1999).

Figures top
[Figure 1] Fig. 1. A view of the title compound, with 95% probability displacement ellipsoids. [Symmetry codes: (i) x, -y + 1/2, z; (ii) x - 1/2, -y + 1/2, -z + 1/2; (iii) x, y, z + 1; (iv) x + 1/2, y, -z + 3/2; (v)-x + 1/2, -y, z - 1/2.]
[Figure 2] Fig. 2. A polyhedral representation of the structure of the title compound, viewed along c. Polyhedra for the Ca2 site are not shown to highlight the crankshaft-like chains of Ca1 polyhedra.
[Figure 3] Fig. 3. Polyhedral representations of the structure of the title compound, viewed along b. In (a), Ca2 polyhdra are not shown, while in (b), Ca1 polyhedra are omitted to highlight chains of Ca2 polyhedra and GeO4 tetrahedra along the a direction.
tricalcium monogermanate dichloride top
Crystal data top
Ca3GeO4Cl2Dx = 3.15 Mg m3
Mr = 327.73Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, PnmaCell parameters from 7524 reflections
a = 11.7045 (8) Åθ = 2.8–28.8°
b = 10.3432 (7) ŵ = 7.37 mm1
c = 5.7082 (4) ÅT = 295 K
V = 691.05 (8) Å3Cuboid, colourless
Z = 40.19 × 0.17 × 0.11 mm
F(000) = 632
Data collection top
Bruker SMART APEX
diffractometer
880 reflections with I > 2σ(I)
rotation, ω scans at 4 different ϕ positionsRint = 0.047
Absorption correction: numerical
(via equivalents using X-SHAPE; Stoe & Cie, 1996)
θmax = 28.7°, θmin = 3.5°
Tmin = 0.27, Tmax = 0.44h = 1515
7796 measured reflectionsk = 1313
908 independent reflectionsl = 77
Refinement top
Refinement on F20 restraints
Least-squares matrix: full w = 1/[σ2(Fo2) + (0.0302P)2 + 0.5214P]
where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.025(Δ/σ)max < 0.001
wR(F2) = 0.057Δρmax = 1.05 e Å3
S = 1.15Δρmin = 0.51 e Å3
908 reflectionsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
53 parametersExtinction coefficient: 0.0324 (16)
Crystal data top
Ca3GeO4Cl2V = 691.05 (8) Å3
Mr = 327.73Z = 4
Orthorhombic, PnmaMo Kα radiation
a = 11.7045 (8) ŵ = 7.37 mm1
b = 10.3432 (7) ÅT = 295 K
c = 5.7082 (4) Å0.19 × 0.17 × 0.11 mm
Data collection top
Bruker SMART APEX
diffractometer
908 independent reflections
Absorption correction: numerical
(via equivalents using X-SHAPE; Stoe & Cie, 1996)
880 reflections with I > 2σ(I)
Tmin = 0.27, Tmax = 0.44Rint = 0.047
7796 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.02553 parameters
wR(F2) = 0.0570 restraints
S = 1.15Δρmax = 1.05 e Å3
908 reflectionsΔρmin = 0.51 e Å3
Special details top

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 (Å2) top
xyzUiso*/Ueq
Ge10.27873 (3)0.250.17883 (6)0.00980 (15)
Ca10.33637 (4)0.08012 (4)0.61786 (8)0.01406 (16)
Ca20.03976 (6)0.250.39747 (12)0.01485 (18)
Cl10.07046 (6)0.06716 (7)0.75132 (13)0.0294 (2)
O10.19748 (15)0.11792 (16)0.2774 (3)0.0143 (3)
O20.3352 (2)0.250.1034 (4)0.0147 (5)
O30.3966 (2)0.250.3725 (4)0.0129 (5)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ge10.0098 (2)0.0103 (2)0.0094 (2)00.00101 (12)0
Ca10.0189 (3)0.0108 (2)0.0124 (3)0.00092 (17)0.00031 (18)0.00070 (16)
Ca20.0103 (3)0.0200 (4)0.0142 (3)00.0004 (2)0
Cl10.0243 (4)0.0374 (4)0.0264 (4)0.0121 (3)0.0068 (3)0.0170 (3)
O10.0140 (8)0.0122 (8)0.0166 (8)0.0031 (6)0.0036 (7)0.0003 (7)
O20.0179 (12)0.0150 (11)0.0112 (11)00.0037 (9)0
O30.0120 (11)0.0154 (12)0.0113 (11)00.0021 (9)0
Geometric parameters (Å, º) top
Ge1—O21.742 (2)Ca1—Cl1iv2.8084 (8)
Ge1—O1i1.7570 (17)Ca1—Cl1v2.8429 (9)
Ge1—O11.7570 (17)Ca2—O3vi2.277 (2)
Ge1—O31.767 (2)Ca2—O1i2.3967 (18)
Ca1—O1ii2.2764 (18)Ca2—O12.3967 (18)
Ca1—O32.3549 (16)Ca2—O2vi2.667 (3)
Ca1—O2iii2.3703 (16)Ca2—Cl1i2.7903 (8)
Ca1—O12.5638 (19)Ca2—Cl12.7903 (8)
O2—Ge1—O1120.11 (7)O1—Ca1—Cl1v144.83 (4)
O1i—Ge1—O1102.07 (11)Cl1iv—Ca1—Cl1v78.22 (3)
O2—Ge1—O3106.40 (11)O3vi—Ca2—O1i111.93 (7)
O1—Ge1—O3102.83 (7)O3vi—Ca2—O1111.93 (7)
O1ii—Ca1—O3164.03 (7)O1i—Ca2—O169.50 (8)
O1ii—Ca1—O2iii113.43 (6)O3vi—Ca2—O2vi68.74 (8)
O3—Ca1—O2iii81.25 (6)O1i—Ca2—O2vi144.83 (4)
O1ii—Ca1—O1109.27 (4)O1—Ca2—O2vi144.83 (4)
O3—Ca1—O167.97 (7)O3vi—Ca2—Cl1i125.78 (4)
O2iii—Ca1—O1113.08 (7)O1i—Ca2—Cl1i73.83 (5)
O1ii—Ca1—Cl1iv82.96 (5)O1—Ca2—Cl1i119.62 (5)
O3—Ca1—Cl1iv81.11 (5)O2vi—Ca2—Cl1i78.26 (4)
O2iii—Ca1—Cl1iv154.73 (6)O3vi—Ca2—Cl1125.78 (4)
O1—Ca1—Cl1iv76.36 (4)O1i—Ca2—Cl1119.62 (5)
O1ii—Ca1—Cl1v91.16 (5)O1—Ca2—Cl173.83 (5)
O3—Ca1—Cl1v84.44 (6)O2vi—Ca2—Cl178.26 (4)
O2iii—Ca1—Cl1v82.20 (6)Cl1i—Ca2—Cl185.34 (4)
Symmetry codes: (i) x, y+1/2, z; (ii) x+1/2, y, z+1/2; (iii) x, y, z+1; (iv) x+1/2, y, z1/2; (v) x+1/2, y, z+3/2; (vi) x1/2, y, z+1/2.

Experimental details

Crystal data
Chemical formulaCa3GeO4Cl2
Mr327.73
Crystal system, space groupOrthorhombic, Pnma
Temperature (K)295
a, b, c (Å)11.7045 (8), 10.3432 (7), 5.7082 (4)
V3)691.05 (8)
Z4
Radiation typeMo Kα
µ (mm1)7.37
Crystal size (mm)0.19 × 0.17 × 0.11
Data collection
DiffractometerBruker SMART APEX
diffractometer
Absorption correctionNumerical
(via equivalents using X-SHAPE; Stoe & Cie, 1996)
Tmin, Tmax0.27, 0.44
No. of measured, independent and
observed [I > 2σ(I)] reflections
7796, 908, 880
Rint0.047
(sin θ/λ)max1)0.676
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.025, 0.057, 1.15
No. of reflections908
No. of parameters53
Δρmax, Δρmin (e Å3)1.05, 0.51

Computer programs: SMART (Bruker, 2001) [or APEX2?], SAINT-Plus (Bruker, 2001), SAINT-Plus, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), DIAMOND (Brandenburg, 1999), WinGX (Version 1.70.01; Farrugia 1999).

Selected geometric parameters (Å, º) top
Ge1—O21.742 (2)Ca1—Cl1iii2.8084 (8)
Ge1—O11.7570 (17)Ca1—Cl1iv2.8429 (9)
Ge1—O31.767 (2)Ca2—O3v2.277 (2)
Ca1—O1i2.2764 (18)Ca2—O12.3967 (18)
Ca1—O32.3549 (16)Ca2—O2v2.667 (3)
Ca1—O2ii2.3703 (16)Ca2—Cl1vi2.7903 (8)
Ca1—O12.5638 (19)
O2—Ge1—O1120.11 (7)O2—Ge1—O3106.40 (11)
O1vi—Ge1—O1102.07 (11)O1—Ge1—O3102.83 (7)
Symmetry codes: (i) x+1/2, y, z+1/2; (ii) x, y, z+1; (iii) x+1/2, y, z1/2; (iv) x+1/2, y, z+3/2; (v) x1/2, y, z+1/2; (vi) x, y+1/2, z.
Selected structural parameters of Ca3GeO4Cl2 in comparison to Ca2GeO4 (Redhammer &amp; Roth, 2007), norbergite Mg3SiO4F2 (Gibbs &amp; Ribbe, 1969) and Mn3SiO4F2 (Zenser et al., 2000). top
Ca3GeO4Cl2Ca2GeO4Mg3SiO4F2Mn3SiO4F2
T-site
<T—O> (Å)1.7561.7651.6301.630
<O–O> (Å)2.8532.8732.6542.654
BLDa (%)0.400.570.560.72
Vol. (Å3)2.7052.7792.1932.196
TAVb (°)75.7247.7441.3235.55
TQEc1.01791.01081.00931.0079
Sd (v.u.)3.923.834.013.95
M1-site
<M1—X> (Å)2.5352.3622.0682.170
<X—X> (Å)3.5063.3242.9153.055
BLDa (%)7.971.253.032.67
Vol. (Å3)19.34816.52911.51513.169
OAVe (°)232.84149.5756.5079.77
OQEf1.08941.04221.01741.0240
Sd (v.u.)2.012.072.002.00
M2-site
<M2—X> (Å)2.5532.3972.1042.203
<X—X> (Å)3.3583.3682.9583.091
BLDa (%)7.692.344.315.17
Vol. (Å3)16.82517.41312.02913.628
OAVe (°)129.7675.64106.13
OQEf1.03681.02361.0324
Sd (v.u.)1.851.901.891.89
(a) Bond length distortion, BLD = (100/n)Σi=1n[{(X-O)i-(<x-O>)}/(<X-O>)], with n = number of bonds, (X-O)i = central cation to oxygen length and <X-O> = average cation-oxygen bond length (Renner & Lehmann, 1986). b) tetrahedral angle variance TAV=Σi=1n(Θi-109.47)2/5 (Robinson et al., 1971). c) Tetrahedral quadratic elongation TQE = Σi=14(li/lt)2/4 with lt = centre to vertex distance for a regular tetrahedron whose volume is equal to that of the undistorted tetrahedron with bond length li (Robinson et al., 1971). d) bond valence sum S (Brese & O'Keeffe, 1991) e) octahedral angle variance OAV=Σi=1n(Θi-90)2/11 (Robinson et al., 1971). f) octahedral quadratic elongation OQE = Σi=16(li/lo)2/6 with lo = centre to vertex distance for a regular octahedron whose volume is equal to that of the undistorted octahedron with bond length li. (Robinson et al., 1971)
 

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