M-type Gd2[Si2O7]

Locke, R.J.C.; Schleid, T.

doi:10.1107/S2414314623006545

inorganic compounds

IUCrDATA

ISSN: 2414-3146

Volume 8| Part 8| August 2023| x230654

https://doi.org/10.1107/S2414314623006545

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M-type Gd₂[Si₂O₇]

Ralf Jules Christian Locke ^a and Thomas Schleid ^a ^*

^aInstitut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
^*Correspondence e-mail: schleid@iac.uni-stuttgart.de

Edited by M. Weil, Vienna University of Technology, Austria (Received 14 July 2023; accepted 27 July 2023; online 1 August 2023)

The title compound, digadolinium(III) oxidodisilicate, Gd₂[Si₂O₇], was obtained in its M-type crystal structure after attempts to synthesize Gd₅Br₃[AsO₃]₄ as a by-product from fused silica ampoules. It crystallizes isotypically with M-type Eu₂[Si₂O₇]. This structure consists of layers of ecliptically arranged oxidodisilicate [Si₂O₇]⁶⁻ units separated from each other by bilayers consisting of Gd^III cations.

Keywords: crystal structure; oxidodisilicate; rare-earth metal; gadolinium; isotypism.

CCDC reference: 2279127

Structure description

M-type Gd₂[Si₂O₇] crystallizes as colourless platelets, isotypic with M-type Eu₂[Si₂O₇] (Strobel et al., 2009 ), in the monoclinic space group P2₁/n. In the crystal structure, the two crystallographically distinguishable [SiO₄]⁴⁻ tetrahedra form discrete ecliptically arranged oxidodisilicate [Si₂O₇]⁶⁻ units, which stand only on `two legs', here atoms O1 and O6, like the E- (Felsche, 1970 ) and ζ-type oxidodisilicates (Hartenbach et al., 2006 ), leading to the so-called `horseshoe' conformation, with an Si1—O4—Si2 angle of 161.3 (3)° (Fig. 1). Within the oxidosilicate tetrahedra, Si—O distances (Table 1) ranging from 1.588 (6) to 1.639 (6) Å to the terminal, as well as 1.646 (8) and 1.662 (8) Å to the bridging, oxide ligands (O4) occur, which agree well with those of the well-known dieuropium(III) oxidodisilicate, Eu₂[Si₂O₇], in its M-type structure [d(Si—O) = 1.61–1.66 Å] (Strobel et al., 2009). Six terminal and four edge-bridging Gd^III cations coordinate to each vertex-shared [Si₂O₇]⁶⁻ bitetrahedron, two of which bind one edge each of two terminal O²⁻ anions of one tetrahedral half (O1—O3 and O6—O7) and two of which bind three times each to one terminal O²⁻ anion of both tetrahedral halves of the oxosilicate doubles, as well as to the bridging O atom (O2⋯O4⋯O5 and O3⋯O4⋯O7). Both crystallographically distinct Gd^III cations are surrounded by eight O²⁻ anions, each with Gd—O distances ranging from 2.250 (8) to 2.691 (6) Å (Fig. 2). In the crystal structure of M-type Gd₂[Si₂O₇], the [Si₂O₇]⁶⁻ units are present in a layered arrangement parallel to (001) with adjacent bitetrahedra occurring mirrored along [010] at the inversion centre, whereas they are identically oriented along [100]. This structure consists of layers of [Si₂O₇]⁶⁻ units separated from each other by bilayers consisting of Gd^III cations (Fig. 3).

Table 1
Selected bond lengths (Å)

Gd1—O1ⁱ	2.291 (5)	Gd2—O3	2.565 (7)
Gd1—O7ⁱ	2.305 (8)	Gd2—O4^vii	2.655 (5)
Gd1—O3ⁱⁱ	2.376 (8)	Gd2—Si1	3.103 (3)
Gd1—O6	2.384 (5)	Gd2—Si2^vii	3.233 (3)
Gd1—O5ⁱⁱⁱ	2.441 (7)	Gd2—Si1^vi	3.269 (3)
Gd1—O2	2.533 (8)	Gd2—Gd1^viii	3.8078 (6)
Gd1—O4ⁱⁱⁱ	2.621 (5)	Si1—O2	1.588 (6)
Gd1—O7^iv	2.691 (6)	Si1—O1	1.612 (6)
Gd1—Si2^iv	3.128 (3)	Si1—O3	1.635 (6)
Gd1—Si2ⁱⁱⁱ	3.217 (3)	Si1—O4ⁱⁱⁱ	1.646 (8)
Gd1—Si1	3.277 (3)	Si1—Gd2^vi	3.269 (3)
Gd1—Gd2ⁱⁱⁱ	3.8078 (6)	Si2—O5	1.595 (6)
Gd2—O5	2.250 (8)	Si2—O6^ix	1.600 (6)
Gd2—O2^v	2.302 (7)	Si2—O7	1.639 (6)
Gd2—O6^vi	2.313 (5)	Si2—O4	1.662 (8)
Gd2—O7^vii	2.471 (8)	Si2—Gd1^ix	3.128 (3)
Gd2—O1	2.472 (5)	Si2—Gd1^viii	3.217 (3)
Gd2—O3^vi	2.522 (8)	Si2—Gd2^x	3.233 (3)
Symmetry codes: (i) ; (ii) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (iii) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (iv) ; (v) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ ; (vi) ; (vii) $[-x+{\script{1\over 2}}, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (viii) $[x-{\script{1\over 2}}, -y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ ; (ix) x, y, z+1; (x) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ .

Figure 1
The unique oxidodisilicate [Si₂O₇]⁶⁻ anion composed of two vertex-connected [SiO₄]⁴⁻ tetrahedra in M-type Gd₂[Si₂O₇], where the position of the O atoms define a horseshoe arrangement (left), and its Newman projection (right). Displacement ellipsoids are drawn at the 95% probability level. The symmetry codes are available in Table 1

Figure 2
The oxygen environment of the two crystallographically different Gd^III cations in M-type Gd₂[Si₂O₇]. Displacement ellipsoids are drawn at the 95% probability level. The symmetry codes are available in Table 1

Figure 3
View at the monoclinic crystal structure of M-type Gd₂[Si₂O₇] along [010] emphasizing the discrete [Si₂O₇]⁶⁻ anions (polyhedral representation). Displacement ellipsoids are drawn at the 95% probability level.

Synthesis and crystallization

Single crystals of M-Gd₂[Si₂O₇] were obtained as a by-product during the synthesis of Gd₅Br₃[AsO₃]₄ (Locke et al., 2023 ) by reacting Gd₂O₃ with fused silica (SiO₂) as the reaction vessel at a temperature of 1100 K, taking advantage of the presumed mineralizers As₂O₃ and GdBr₃. The transparent colourless crystals exhibit a platelet-like habit.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2.

Table 2
Experimental details

Crystal data
Chemical formula	Gd₂[Si₂O₇]
M_r	482.68
Crystal system, space group	Monoclinic, P2₁/n
Temperature (K)	293
a, b, c (Å)	7.7267 (5), 8.3859 (6), 9.6814 (7)
β (°)	113.486 (3)
V (Å³)	575.34 (7)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	23.25
Crystal size (mm)	1.0 × 0.5 × 0.1

Data collection
Diffractometer	Stoe StadiVari
Absorption correction	Numerical (LANA; Koziskova et al., 2016 )
T_min, T_max	0.031, 0.108
No. of measured, independent and observed [I > 2σ(I)] reflections	11604, 2030, 1462
R_int	0.051
(sin θ/λ)_max (Å⁻¹)	0.766

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.033, 0.068, 0.95
No. of reflections	2030
No. of parameters	102
Δρ_max, Δρ_min (e Å⁻³)	1.72, −1.87
Computer programs: X-AREA (Stoe & Cie, 2020 ), SHELXT (Sheldrick, 2015a ), SHELXL (Sheldrick, 2015b ), DIAMOND (Brandenburg & Putz, 2005 ) and publCIF (Westrip, 2010 ).

Structural data

CCDC reference: 2279127

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S2414314623006545/wm4193sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314623006545/wm4193Isup2.hkl

checkCIF report

Computing details top

Data collection: X-AREA (Stoe & Cie, 2020); cell refinement: X-AREA (Stoe & Cie, 2020); data reduction: X-AREA (Stoe & Cie, 2020); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg & Putz, 2005); software used to prepare material for publication: publCIF (Westrip, 2010).

igadolinium(III) oxidodisilicate top

Crystal data top

Gd₂[Si₂O₇]	F(000) = 848
M_r = 482.68	D_x = 5.572 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71069 Å
a = 7.7267 (5) Å	Cell parameters from 12003 reflections
b = 8.3859 (6) Å	θ = 2.3–33.0°
c = 9.6814 (7) Å	µ = 23.25 mm⁻¹
β = 113.486 (3)°	T = 293 K
V = 575.34 (7) Å³	Platelet, colourless
Z = 4	1.0 × 0.5 × 0.1 mm

Data collection top

Stoe StadiVari diffractometer	2030 independent reflections
Radiation source: fine-focus sealed tube	1462 reflections with I > 2σ(I)
Detector resolution: 5.81 pixels mm^-1	R_int = 0.051
rotation method, ω scans	θ_max = 33.0°, θ_min = 2.9°
Absorption correction: numerical (LANA; Koziskova et al., 2016)	h = −11→11
T_min = 0.031, T_max = 0.108	k = −12→12
11604 measured reflections	l = −14→14

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0305P)²] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.033	(Δ/σ)_max < 0.001
wR(F²) = 0.068	Δρ_max = 1.72 e Å⁻³
S = 0.95	Δρ_min = −1.86 e Å⁻³
2030 reflections	Extinction correction: SHELXL (Sheldrick, 2015b), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
102 parameters	Extinction coefficient: 0.0096 (3)

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 2-component twin.

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

	x	y	z	U_iso*/U_eq
Gd1	0.48343 (8)	0.48090 (4)	0.21037 (4)	0.00929 (12)
Gd2	0.47192 (8)	0.00947 (4)	0.70211 (4)	0.00892 (13)
Si1	0.3936 (4)	0.2763 (3)	0.4626 (3)	0.0091 (6)
Si2	0.3149 (4)	0.2212 (3)	0.9603 (3)	0.0098 (6)
O1	0.4411 (13)	0.2968 (6)	0.6396 (6)	0.0128 (12)
O2	0.2751 (11)	0.4101 (7)	0.3477 (7)	0.0126 (15)
O3	0.3205 (12)	0.0922 (7)	0.4242 (7)	0.0140 (15)
O4	0.0880 (10)	0.2262 (6)	0.9314 (6)	0.0118 (11)
O5	0.3162 (11)	0.0874 (6)	0.8436 (7)	0.0109 (14)
O6	0.4408 (13)	0.2074 (6)	0.1370 (6)	0.0125 (12)
O7	0.3525 (12)	0.4030 (6)	0.9167 (7)	0.0104 (14)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Gd1	0.0079 (2)	0.0081 (2)	0.0127 (2)	0.0003 (2)	0.0050 (2)	0.00029 (16)
Gd2	0.0078 (2)	0.0078 (2)	0.0120 (2)	−0.0004 (2)	0.0048 (2)	0.00001 (16)
Si1	0.0085 (14)	0.0073 (12)	0.0108 (12)	0.0016 (9)	0.0032 (10)	0.0000 (9)
Si2	0.0102 (14)	0.0087 (13)	0.0120 (12)	−0.0013 (9)	0.0060 (10)	0.0010 (9)
O1	0.014 (4)	0.014 (3)	0.012 (3)	−0.004 (4)	0.007 (4)	−0.001 (2)
O2	0.011 (4)	0.014 (3)	0.010 (3)	0.005 (3)	0.001 (3)	0.002 (2)
O3	0.009 (4)	0.014 (3)	0.021 (4)	−0.003 (3)	0.008 (3)	−0.003 (2)
O4	0.008 (3)	0.011 (3)	0.014 (3)	0.005 (3)	0.005 (3)	0.001 (2)
O5	0.009 (4)	0.009 (3)	0.014 (3)	0.000 (3)	0.004 (3)	−0.005 (2)
O6	0.012 (4)	0.017 (3)	0.009 (3)	0.000 (4)	0.004 (4)	−0.001 (2)
O7	0.012 (4)	0.006 (3)	0.014 (3)	−0.001 (3)	0.007 (3)	−0.001 (2)

Geometric parameters (Å, º) top

Gd1—O1ⁱ	2.291 (5)	Si1—O1	1.612 (6)
Gd1—O7ⁱ	2.305 (8)	Si1—O3	1.635 (6)
Gd1—O3ⁱⁱ	2.376 (8)	Si1—O4ⁱⁱⁱ	1.646 (8)
Gd1—O6	2.384 (5)	Si1—Gd2^vi	3.269 (3)
Gd1—O5ⁱⁱⁱ	2.441 (7)	Si2—O5	1.595 (6)
Gd1—O2	2.533 (8)	Si2—O6^ix	1.600 (6)
Gd1—O4ⁱⁱⁱ	2.621 (5)	Si2—O7	1.639 (6)
Gd1—O7^iv	2.691 (6)	Si2—O4	1.662 (8)
Gd1—Si2^iv	3.128 (3)	Si2—Gd1^ix	3.128 (3)
Gd1—Si2ⁱⁱⁱ	3.217 (3)	Si2—Gd1^viii	3.217 (3)
Gd1—Si1	3.277 (3)	Si2—Gd2^x	3.233 (3)
Gd1—Gd2ⁱⁱⁱ	3.8078 (6)	O1—Gd1ⁱ	2.291 (5)
Gd2—O5	2.250 (8)	O2—Gd2^xi	2.302 (7)
Gd2—O2^v	2.302 (7)	O3—Gd1^xii	2.376 (8)
Gd2—O6^vi	2.313 (5)	O3—Gd2^vi	2.522 (8)
Gd2—O7^vii	2.471 (8)	O4—Si1^viii	1.646 (8)
Gd2—O1	2.472 (5)	O4—Gd1^viii	2.621 (5)
Gd2—O3^vi	2.522 (8)	O4—Gd2^x	2.655 (5)
Gd2—O3	2.565 (7)	O5—Gd1^viii	2.441 (7)
Gd2—O4^vii	2.655 (5)	O6—Si2^iv	1.600 (6)
Gd2—Si1	3.103 (3)	O6—Gd2^vi	2.313 (5)
Gd2—Si2^vii	3.233 (3)	O7—Gd1ⁱ	2.305 (8)
Gd2—Si1^vi	3.269 (3)	O7—Gd2^x	2.471 (8)
Gd2—Gd1^viii	3.8078 (6)	O7—Gd1^ix	2.691 (6)
Si1—O2	1.588 (6)

O1ⁱ—Gd1—O7ⁱ	86.5 (3)	O5—Gd2—Si2^vii	94.83 (17)
O1ⁱ—Gd1—O3ⁱⁱ	88.5 (3)	O2^v—Gd2—Si2^vii	148.23 (16)
O7ⁱ—Gd1—O3ⁱⁱ	100.09 (19)	O6^vi—Gd2—Si2^vii	72.48 (17)
O1ⁱ—Gd1—O6	160.3 (2)	O7^vii—Gd2—Si2^vii	29.74 (15)
O7ⁱ—Gd1—O6	106.7 (3)	O1—Gd2—Si2^vii	128.99 (19)
O3ⁱⁱ—Gd1—O6	103.0 (3)	O3^vi—Gd2—Si2^vii	87.49 (15)
O1ⁱ—Gd1—O5ⁱⁱⁱ	84.7 (3)	O3—Gd2—Si2^vii	75.78 (15)
O7ⁱ—Gd1—O5ⁱⁱⁱ	72.1 (2)	O4^vii—Gd2—Si2^vii	30.84 (16)
O3ⁱⁱ—Gd1—O5ⁱⁱⁱ	170.0 (2)	Si1—Gd2—Si2^vii	106.49 (7)
O6—Gd1—O5ⁱⁱⁱ	85.6 (3)	O5—Gd2—Si1^vi	149.41 (16)
O1ⁱ—Gd1—O2	85.0 (3)	O2^v—Gd2—Si1^vi	94.01 (18)
O7ⁱ—Gd1—O2	168.21 (19)	O6^vi—Gd2—Si1^vi	71.81 (19)
O3ⁱⁱ—Gd1—O2	71.6 (2)	O7^vii—Gd2—Si1^vi	88.20 (16)
O6—Gd1—O2	83.7 (3)	O1—Gd2—Si1^vi	127.82 (19)
O5ⁱⁱⁱ—Gd1—O2	115.06 (16)	O3^vi—Gd2—Si1^vi	29.34 (15)
O1ⁱ—Gd1—O4ⁱⁱⁱ	95.96 (18)	O3—Gd2—Si1^vi	77.72 (16)
O7ⁱ—Gd1—O4ⁱⁱⁱ	131.3 (2)	O4^vii—Gd2—Si1^vi	30.05 (17)
O3ⁱⁱ—Gd1—O4ⁱⁱⁱ	128.6 (2)	Si1—Gd2—Si1^vi	99.74 (6)
O6—Gd1—O4ⁱⁱⁱ	64.33 (18)	Si2^vii—Gd2—Si1^vi	60.26 (5)
O5ⁱⁱⁱ—Gd1—O4ⁱⁱⁱ	59.7 (2)	O5—Gd2—Gd1^viii	37.46 (17)
O2—Gd1—O4ⁱⁱⁱ	58.0 (2)	O2^v—Gd2—Gd1^viii	139.14 (19)
O1ⁱ—Gd1—O7^iv	139.54 (18)	O6^vi—Gd2—Gd1^viii	91.6 (3)
O7ⁱ—Gd1—O7^iv	66.0 (3)	O7^vii—Gd2—Gd1^viii	35.64 (16)
O3ⁱⁱ—Gd1—O7^iv	69.1 (3)	O1—Gd2—Gd1^viii	89.1 (2)
O6—Gd1—O7^iv	60.18 (17)	O3^vi—Gd2—Gd1^viii	147.64 (15)
O5ⁱⁱⁱ—Gd1—O7^iv	112.0 (2)	O3—Gd2—Gd1^viii	88.6 (2)
O2—Gd1—O7^iv	116.6 (2)	O4^vii—Gd2—Gd1^viii	92.70 (16)
O4ⁱⁱⁱ—Gd1—O7^iv	124.43 (16)	Si1—Gd2—Gd1^viii	95.78 (5)
O1ⁱ—Gd1—Si2^iv	168.31 (19)	Si2^vii—Gd2—Gd1^viii	62.16 (5)
O7ⁱ—Gd1—Si2^iv	91.68 (16)	Si1^vi—Gd2—Gd1^viii	122.43 (5)
O3ⁱⁱ—Gd1—Si2^iv	80.41 (16)	O2—Si1—O1	119.5 (4)
O6—Gd1—Si2^iv	30.06 (14)	O2—Si1—O3	117.2 (4)
O5ⁱⁱⁱ—Gd1—Si2^iv	105.74 (15)	O1—Si1—O3	104.7 (3)
O2—Gd1—Si2^iv	95.01 (15)	O2—Si1—O4ⁱⁱⁱ	101.2 (4)
O4ⁱⁱⁱ—Gd1—Si2^iv	93.91 (12)	O1—Si1—O4ⁱⁱⁱ	111.0 (4)
O7^iv—Gd1—Si2^iv	31.58 (13)	O3—Si1—O4ⁱⁱⁱ	101.8 (4)
O1ⁱ—Gd1—Si2ⁱⁱⁱ	91.52 (18)	O2—Si1—Gd2	156.8 (3)
O7ⁱ—Gd1—Si2ⁱⁱⁱ	100.47 (18)	O1—Si1—Gd2	52.31 (19)
O3ⁱⁱ—Gd1—Si2ⁱⁱⁱ	159.41 (19)	O3—Si1—Gd2	55.7 (2)
O6—Gd1—Si2ⁱⁱⁱ	72.03 (17)	O4ⁱⁱⁱ—Si1—Gd2	102.0 (2)
O5ⁱⁱⁱ—Gd1—Si2ⁱⁱⁱ	28.81 (16)	O2—Si1—Gd2^vi	112.5 (3)
O2—Gd1—Si2ⁱⁱⁱ	87.91 (15)	O1—Si1—Gd2^vi	127.9 (3)
O4ⁱⁱⁱ—Gd1—Si2ⁱⁱⁱ	30.98 (17)	O3—Si1—Gd2^vi	49.1 (3)
O7^iv—Gd1—Si2ⁱⁱⁱ	121.22 (15)	O4ⁱⁱⁱ—Si1—Gd2^vi	53.89 (19)
Si2^iv—Gd1—Si2ⁱⁱⁱ	100.16 (3)	Gd2—Si1—Gd2^vi	80.26 (6)
O1ⁱ—Gd1—Si1	91.69 (18)	O2—Si1—Gd1	48.9 (3)
O7ⁱ—Gd1—Si1	160.70 (18)	O1—Si1—Gd1	135.2 (3)
O3ⁱⁱ—Gd1—Si1	99.08 (19)	O3—Si1—Gd1	118.8 (3)
O6—Gd1—Si1	70.92 (19)	O4ⁱⁱⁱ—Si1—Gd1	52.41 (19)
O5ⁱⁱⁱ—Gd1—Si1	88.55 (16)	Gd2—Si1—Gd1	153.91 (9)
O2—Gd1—Si1	28.19 (15)	Gd2^vi—Si1—Gd1	79.48 (6)
O4ⁱⁱⁱ—Gd1—Si1	29.85 (17)	O5—Si2—O6^ix	122.3 (4)
O7^iv—Gd1—Si1	123.92 (15)	O5—Si2—O7	114.8 (4)
Si2^iv—Gd1—Si1	93.76 (7)	O6^ix—Si2—O7	104.4 (3)
Si2ⁱⁱⁱ—Gd1—Si1	60.34 (5)	O5—Si2—O4	101.7 (4)
O1ⁱ—Gd1—Gd2ⁱⁱⁱ	89.6 (3)	O6^ix—Si2—O4	109.5 (4)
O7ⁱ—Gd1—Gd2ⁱⁱⁱ	38.66 (17)	O7—Si2—O4	102.5 (4)
O3ⁱⁱ—Gd1—Gd2ⁱⁱⁱ	138.72 (18)	O5—Si2—Gd1^ix	156.8 (3)
O6—Gd1—Gd2ⁱⁱⁱ	92.0 (2)	O6^ix—Si2—Gd1^ix	48.29 (18)
O5ⁱⁱⁱ—Gd1—Gd2ⁱⁱⁱ	34.10 (16)	O7—Si2—Gd1^ix	59.3 (2)
O2—Gd1—Gd2ⁱⁱⁱ	149.15 (15)	O4—Si2—Gd1^ix	101.5 (2)
O4ⁱⁱⁱ—Gd1—Gd2ⁱⁱⁱ	92.60 (17)	O5—Si2—Gd1^viii	47.5 (3)
O7^iv—Gd1—Gd2ⁱⁱⁱ	86.64 (19)	O6^ix—Si2—Gd1^viii	136.8 (3)
Si2^iv—Gd1—Gd2ⁱⁱⁱ	96.26 (5)	O7—Si2—Gd1^viii	117.8 (3)
Si2ⁱⁱⁱ—Gd1—Gd2ⁱⁱⁱ	61.86 (5)	O4—Si2—Gd1^viii	54.3 (2)
Si1—Gd1—Gd2ⁱⁱⁱ	122.19 (5)	Gd1^ix—Si2—Gd1^viii	155.51 (9)
O5—Gd2—O2^v	101.69 (19)	O5—Si2—Gd2^x	112.2 (3)
O5—Gd2—O6^vi	84.4 (3)	O6^ix—Si2—Gd2^x	125.5 (3)
O2^v—Gd2—O6^vi	82.3 (3)	O7—Si2—Gd2^x	48.4 (3)
O5—Gd2—O7^vii	72.5 (2)	O4—Si2—Gd2^x	55.0 (2)
O2^v—Gd2—O7^vii	170.8 (2)	Gd1^ix—Si2—Gd2^x	81.32 (6)
O6^vi—Gd2—O7^vii	89.9 (3)	Gd1^viii—Si2—Gd2^x	80.91 (6)
O5—Gd2—O1	81.0 (3)	Si1—O1—Gd1ⁱ	130.8 (3)
O2^v—Gd2—O1	80.8 (2)	Si1—O1—Gd2	96.6 (2)
O6^vi—Gd2—O1	154.8 (2)	Gd1ⁱ—O1—Gd2	131.5 (3)
O7^vii—Gd2—O1	104.9 (3)	Si1—O2—Gd2^xi	142.9 (5)
O5—Gd2—O3^vi	172.35 (19)	Si1—O2—Gd1	102.9 (4)
O2^v—Gd2—O3^vi	73.0 (2)	Gd2^xi—O2—Gd1	108.3 (2)
O6^vi—Gd2—O3^vi	89.4 (3)	Si1—O3—Gd1^xii	132.2 (4)
O7^vii—Gd2—O3^vi	112.04 (17)	Si1—O3—Gd2^vi	101.6 (4)
O1—Gd2—O3^vi	103.2 (3)	Gd1^xii—O3—Gd2^vi	106.4 (2)
O5—Gd2—O3	115.4 (3)	Si1—O3—Gd2	92.6 (3)
O2^v—Gd2—O3	119.4 (2)	Gd1^xii—O3—Gd2	114.0 (3)
O6^vi—Gd2—O3	143.85 (18)	Gd2^vi—O3—Gd2	107.8 (3)
O7^vii—Gd2—O3	69.9 (3)	Si1^viii—O4—Si2	161.3 (3)
O1—Gd2—O3	61.35 (18)	Si1^viii—O4—Gd1^viii	97.7 (3)
O3^vi—Gd2—O3	72.2 (3)	Si2—O4—Gd1^viii	94.7 (3)
O5—Gd2—O4^vii	121.6 (2)	Si1^viii—O4—Gd2^x	96.1 (3)
O2^v—Gd2—O4^vii	119.9 (2)	Si2—O4—Gd2^x	94.2 (3)
O6^vi—Gd2—O4^vii	64.64 (16)	Gd1^viii—O4—Gd2^x	104.97 (18)
O7^vii—Gd2—O4^vii	60.2 (2)	Si2—O5—Gd2	142.3 (4)
O1—Gd2—O4^vii	140.50 (18)	Si2—O5—Gd1^viii	103.7 (4)
O3^vi—Gd2—O4^vii	58.9 (2)	Gd2—O5—Gd1^viii	108.4 (2)
O3—Gd2—O4^vii	79.25 (17)	Si2^iv—O6—Gd2^vi	131.8 (3)
O5—Gd2—Si1	104.65 (16)	Si2^iv—O6—Gd1	101.7 (3)
O2^v—Gd2—Si1	95.40 (16)	Gd2^vi—O6—Gd1	126.0 (2)
O6^vi—Gd2—Si1	171.0 (2)	Si2—O7—Gd1ⁱ	136.3 (4)
O7^vii—Gd2—Si1	93.06 (15)	Si2—O7—Gd2^x	101.8 (4)
O1—Gd2—Si1	31.07 (14)	Gd1ⁱ—O7—Gd2^x	105.7 (2)
O3^vi—Gd2—Si1	81.58 (15)	Si2—O7—Gd1^ix	89.1 (3)
O3—Gd2—Si1	31.75 (14)	Gd1ⁱ—O7—Gd1^ix	114.0 (3)
O4^vii—Gd2—Si1	109.70 (12)	Gd2^x—O7—Gd1^ix	106.8 (3)

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

Acknowledgements

We thank Dr Falk Lissner for the single-crystal X-ray diffraction measurements.

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