Langbeinite-type Rb₂Ca₂(SO₄)₃

Single crystals of dirubidium dicalcium tris­[sulfate­(VI)], Rb₂Ca₂(SO₄)₃, were obtained from solid-state reactions of Rb₂SO₄ and CaSO₄. The title compound crystallizes in the cubic langbeinite-type structure. It features two crystallographically independent CaO₆ octa­hedra (each with site symmetry 3), which are linked by sharing corners with SO₄ tetra­hedra to establish a framework with composition [Ca₂(SO₄)₃]^2-, where the two independent Rb⁺ cations (site symmetry 3) are located in the voids.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](S-O) = 0.010 Å
• R factor = 0.065
• wR factor = 0.128
• Data-to-parameter ratio = 18.3

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT031_ALERT_4_B Refined Extinction Parameter within Range ......       1.60 Sigma

Alert level C
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for          S
PLAT850_ALERT_2_C Check Flack Parameter Exact Value 0.00 and su ..       0.04

Alert level G
REFLT03_ALERT_1_G ALERT: Expected hkl max differ from CIF values
           From the CIF: _diffrn_reflns_theta_max           29.89
           From the CIF: _reflns_number_total               1080
           From the CIF: _diffrn_reflns_limit_ max hkl    9.   10.   14.
           From the CIF: _diffrn_reflns_limit_ min hkl   -8.  -10.  -14.
           TEST1: Expected hkl limits for theta max
           Calculated maximum hkl   14.   14.   14.
           Calculated minimum hkl  -14.  -14.  -14.
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           29.89
           From the CIF: _reflns_number_total               1080
           Count of symmetry unique reflns          654
           Completeness (_total/calc)            165.14%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured       426
           Fraction of Friedel pairs measured     0.651
           Are heavy atom types Z>Si present        yes
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
   3 ALERT level C = Check and explain
   3 ALERT level G = General alerts; check

   3 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

The double sulfate salts with formula A₂B₂(SO₄)₃ adopting the langbeinite-type structure have attracted great interest due to their ferroelastic or ferroelectric properties and first-order phase transitions (Ukeda et al., 1995; Dilanian et al., 1999 and references therein). Numerous compounds with A = NH₄, K, Rb, Tl, Cs and B = Mn, Ca, Mg, Fe, Co, Ni, Zn, Cd (e.g. Zemann & Zemann, 1957; Guelylah et al., 1996; Guelylah & Madariaga, 2003) have been characterized up to now. Gattow and Zemann (1957) mentioned the possible synthesis of 26 double sulfates, including large monovalent cations. Notable differences exist between langbeinite-type and Nasicon-type structures (Sizova et al., 1981; Dro\&s & Glaum, 2004). In the Nasicon-type structures, four interstitial vacant sites are present, while langbeinite-type structures have only two.

A projection of the crystal structure of langbeinite-type Rb₂Ca₂(SO₄)₃ is given in Fig. 1. It is characterized by the presence of alternating SO₄ tetrahedra and CaO₆ octahedra, linked by sharing corners, to establish a [Ca₂(SO₄)₃]^2- framework. The two independent Rb⁺ ions are located in the voids of this arrangement.

The SO₄ tetrahedra are quite regular, with an average S—O distance of 1.455 Å, which is virtually the same as that observed in the isotypic Rb₂Cd₂(SO₄)₂ (1.455 Å; Guelylah & Madariaga, 2003). In the title compound sulfur has a bond valence sum (BVS) of 6.69 valence units (expected 6) as calculated with the values given by Brown & Altermatt (1985). The [Ca1O₆] octahedron is quite regular, with d_av(Ca1—O) = 2.292 Å, whereas the [Ca2O₆] octahedron is considerably distorted, with d_av(Ca2—O) = 2.321 Å. Rb₁ has twelve oxygen neighbours with d_av(Rb1—O) = 3.239 Å and a BVS of 1.03 (expected 1). Rb₂ is ninefold coordinated with d_av(Rb2—O) = 3.158 Å and a BVS of 0.852 (expected 1).

Related literature

For studies of phase transitions of langbeinites, see: Ukeda et al. (1995); Dilanian et al. (1999). Double sulfates of the langbeinite-type were summarized by Gattow & Zemann (1957). For single-crystal structure analyses of selected langbeinites, see: Zemann & Zemann (1957); Guelylah et al. (1996); Guelylah & Madariaga (2003). Differences of the langbeinite and the Nasicon structure are discussed by Sizova et al. (1981) and Dro\&s & Glaum (2004). Parameters for the bond valence sum (BVS) analysis were taken from Brown & Altermatt (1985).

S2. Experimental

Single crystals of Rb₂Ca₂(SO₄)₃ were obtained by solid-state reaction of Rb₂SO₄ (Aldrich 99.999%) and CaSO₄^.H₂O (Aldrich 99.9%). Stoichiometric amounts of the starting materials were mixed thoroughly in an agate mortar. After grinding, the mixture was heated at 673 K for 4 h, then at 1173 K for 66 h and was finally allowed to cool to room temperature at a rate of 5 K/h. Transparent polycrystalline chunks were obtained from which single crystals were separated manually.

Computing details

Data collection: STADI4 (Stoe & Cie, 2000); cell refinement: STADI4; data reduction: X-RED (Stoe & Cie, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: DIAMOND (Brandenburg & Berndt, 1999); software used to prepare material for publication: CRYSTALS.

Figures

Fig. 1. Projection of the crystal structure of langbeinite-type Rb2Ca2(SO4)3 approximately along [001]. The voids are visible, where the Rb^+ cations (lavender spheres) are located. CaO6 octahedra are dark-grey and SO4 tetrahedra are light-grey.

dirubidium dicalcium tris[sulfate(VI)]

Crystal data

Rb2Ca2(SO4)3	Dx = 3.048 Mg m^−3
Mr = 539.28	Mo Kα radiation, λ = 0.71073 Å
Cubic, P213	Cell parameters from 23 reflections
Hall symbol: P 2ac 2ab 3	θ = 2.7–30.1°
a = 10.553 (3) Å	µ = 9.79 mm^−1
V = 1175.2 (6) Å^3	T = 293 K
Z = 4	Fragment, colourless
F(000) = 1032	0.22 × 0.13 × 0.05 mm

Data collection

Stoe–Siemens AED2 four-circle diffractometer	Rint = 0.08
Graphite monochromator	θmax = 29.9°, θmin = 2.7°
ω/2θ scans	h = −8→9
Absorption correction: multi-scan (MULABS in PLATON; Spek, 2003)	k = −10→10
Tmin = 0.231, Tmax = 0.644	l = −14→14
1236 measured reflections	2 standard reflections every 30 min
1080 independent reflections	intensity decay: 0.7%
658 reflections with I > 3σ(I)

Refinement

Refinement on F^2	w = 1/[σ^2(Fo^2) + (0.021P)^2 + 6.5703P] where P = (Fo^2 + 2Fc^2)/3 Method, part 1, Chebychev polynomial, (Watkin (1994). Acta Cryst. A50, 411–437. Prince (1982) Mathematical Techniques in Crystallography and Materials Science. New York: Springer-Verlag.] [weight] = 1.0/[A0*T0(x) + A1*T1(x) ··· + An-1]*Tn-1(x)] where Ai are the Chebychev coefficients listed below and x = F /Fmax Method = Robust Weighting (Prince, 1982) W = [weight] * [1-(deltaF/6*sigmaF)^2]^2 Ai are: 2.38 -2.95 2.50 -1.02 0.340
Least-squares matrix: full	(Δ/σ)max = 0.001
R[F^2 > 2σ(F^2)] = 0.065	Δρmax = 0.93 e Å^−3
wR(F^2) = 0.128	Δρmin = −1.00 e Å^−3
S = 1.12	Extinction correction: SHELXL
1080 reflections	Extinction coefficient: 0.0008 (5)
59 parameters	Absolute structure: Flack (1983), 558 Friedel pairs
0 restraints	Absolute structure parameter: 0.00 (4)
Primary atom site location: structure-invariant direct methods

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

	x	y	z	Uiso*/Ueq
Ca1	0.3314 (2)	0.3314 (2)	0.3314 (2)	0.0170 (9)
Ca2	0.5920 (2)	0.5920 (2)	0.5920 (2)	0.0170 (9)
Rb1	0.81628 (13)	0.81628 (13)	0.81628 (13)	0.0270 (5)
Rb2	0.04991 (13)	0.04991 (13)	0.04991 (13)	0.0291 (6)
S	0.2243 (3)	0.3749 (3)	0.0108 (3)	0.0136 (6)
O1	0.3089 (9)	0.2795 (8)	0.9600 (9)	0.032 (2)
O2	0.0954 (8)	0.3285 (10)	0.0046 (10)	0.039 (3)
O3	0.2364 (10)	0.4880 (10)	0.9326 (11)	0.043 (3)
O4	0.2580 (10)	0.4059 (11)	0.1420 (9)	0.044 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ca1	0.0170 (9)	0.0170 (9)	0.0170 (9)	−0.0002 (10)	−0.0002 (10)	−0.0002 (10)
Ca2	0.0170 (9)	0.0170 (9)	0.0170 (9)	−0.0004 (10)	−0.0004 (10)	−0.0004 (10)
Rb1	0.0270 (5)	0.0270 (5)	0.0270 (5)	−0.0023 (6)	−0.0023 (6)	−0.0023 (6)
Rb2	0.0291 (6)	0.0291 (6)	0.0291 (6)	0.0012 (6)	0.0012 (6)	0.0012 (6)
S	0.0156 (15)	0.0120 (13)	0.0131 (15)	0.0031 (11)	0.0003 (11)	0.0015 (10)
O1	0.034 (5)	0.023 (5)	0.039 (6)	0.011 (4)	0.012 (5)	−0.006 (4)
O2	0.015 (5)	0.037 (6)	0.064 (7)	−0.007 (4)	0.011 (5)	−0.016 (6)
O3	0.059 (7)	0.030 (6)	0.041 (6)	0.015 (5)	0.008 (5)	0.023 (5)
O4	0.060 (8)	0.047 (7)	0.026 (6)	−0.003 (6)	−0.009 (5)	−0.011 (5)

Geometric parameters (Å, º)

Ca1—O4^i	2.284 (10)	Rb1—O3^xxiii	3.464 (13)
Ca1—O4^ii	2.284 (10)	Rb1—O3^xxiv	3.464 (13)
Ca1—O4	2.284 (10)	Rb2—O2^i	3.018 (10)
Ca1—O3^iii	2.299 (10)	Rb2—O2	3.018 (10)
Ca1—O3^iv	2.299 (10)	Rb2—O2^ii	3.018 (10)
Ca1—O3^v	2.299 (10)	Rb2—O1^xxv	3.118 (10)
Ca1—Rb1^vi	4.0344 (18)	Rb2—O1^xxvi	3.118 (10)
Ca1—Rb1^vii	4.0344 (18)	Rb2—O1^xxvii	3.118 (10)
Ca1—Rb1^viii	4.0344 (18)	Rb2—O3^xxvi	3.338 (11)
Ca1—Rb2^ix	4.804 (2)	Rb2—O3^xxvii	3.338 (11)
Ca1—Rb2^x	4.804 (2)	Rb2—O3^xxv	3.338 (11)
Ca1—Rb2^xi	4.804 (2)	Rb2—S^xxviii	3.584 (3)
Ca2—O1^xii	2.304 (9)	Rb2—S^xxix	3.584 (3)
Ca2—O1^xiii	2.304 (9)	Rb2—S^xxx	3.584 (3)
Ca2—O1^xiv	2.304 (9)	S—O1^xxxi	1.449 (9)
Ca2—O2^xv	2.338 (9)	S—O2	1.447 (9)
Ca2—O2^xvi	2.338 (9)	S—O3^xxxi	1.456 (10)
Ca2—O2^xvii	2.338 (9)	S—O4	1.466 (10)
Ca2—S^xv	3.464 (4)	S—Ca2^xxvii	3.464 (4)
Ca2—S^xvi	3.464 (4)	S—Rb1^v	3.533 (3)
Ca2—S^xvii	3.464 (4)	S—Rb2^xi	3.584 (3)
Ca2—Rb2^xv	4.0891 (19)	S—Rb1^viii	3.859 (3)
Ca2—Rb2^xviii	4.0891 (19)	O1—S^xxxii	1.449 (9)
Ca2—Rb2^xvii	4.0891 (19)	O1—Ca2^vii	2.304 (9)
Rb1—O4^xix	3.028 (11)	O1—Rb2^xv	3.118 (10)
Rb1—O4^xx	3.028 (11)	O1—Rb1^vii	3.224 (9)
Rb1—O4^xxi	3.028 (11)	O2—Ca2^xxvii	2.338 (9)
Rb1—O1^xii	3.224 (9)	O2—Rb1^v	3.515 (10)
Rb1—O1^xiii	3.224 (9)	O3—S^xxxii	1.456 (10)
Rb1—O1^xiv	3.224 (10)	O3—Ca1^xviii	2.299 (10)
Rb1—O3^xiv	3.239 (12)	O3—Rb1^vii	3.239 (12)
Rb1—O3^xii	3.239 (12)	O3—Rb2^xv	3.338 (11)
Rb1—O3^xiii	3.239 (12)	O3—Rb1^xxxiii	3.464 (13)
Rb1—O3^xxii	3.464 (13)	O4—Rb1^viii	3.028 (11)
O4^i—Ca1—O4^ii	96.9 (4)	O3^xii—Rb1—O3^xxiii	138.68 (19)
O4^i—Ca1—O4	96.9 (4)	O3^xiii—Rb1—O3^xxiii	58.5 (4)
O4^ii—Ca1—O4	96.9 (4)	O3^xxii—Rb1—O3^xxiii	82.8 (3)
O4^i—Ca1—O3^iii	90.9 (4)	O4^xix—Rb1—O3^xxiv	107.7 (3)
O4^ii—Ca1—O3^iii	81.3 (4)	O4^xx—Rb1—O3^xxiv	54.3 (3)
O4—Ca1—O3^iii	172.1 (4)	O4^xxi—Rb1—O3^xxiv	42.4 (2)
O4^i—Ca1—O3^iv	81.3 (4)	O1^xii—Rb1—O3^xxiv	96.7 (2)
O4^ii—Ca1—O3^iv	172.1 (4)	O1^xiii—Rb1—O3^xxiv	131.6 (2)
O4—Ca1—O3^iv	90.9 (4)	O1^xiv—Rb1—O3^xxiv	145.4 (2)
O3^iii—Ca1—O3^iv	91.0 (4)	O3^xiv—Rb1—O3^xxiv	138.68 (19)
O4^i—Ca1—O3^v	172.1 (4)	O3^xii—Rb1—O3^xxiv	58.5 (4)
O4^ii—Ca1—O3^v	90.9 (4)	O3^xiii—Rb1—O3^xxiv	104.18 (3)
O4—Ca1—O3^v	81.3 (4)	O3^xxii—Rb1—O3^xxiv	82.8 (3)
O3^iii—Ca1—O3^v	91.0 (4)	O3^xxiii—Rb1—O3^xxiv	82.8 (3)
O3^iv—Ca1—O3^v	91.0 (4)	O2^i—Rb2—O2	91.4 (3)
O1^xii—Ca2—O1^xiii	85.6 (4)	O2^i—Rb2—O2^ii	91.4 (3)
O1^xii—Ca2—O1^xiv	85.6 (4)	O2—Rb2—O2^ii	91.4 (3)
O1^xiii—Ca2—O1^xiv	85.6 (4)	O2^i—Rb2—O1^xxv	64.0 (2)
O1^xii—Ca2—O2^xv	172.2 (4)	O2—Rb2—O1^xxv	153.1 (3)
O1^xiii—Ca2—O2^xv	88.5 (3)	O2^ii—Rb2—O1^xxv	79.1 (2)
O1^xiv—Ca2—O2^xv	89.0 (3)	O2^i—Rb2—O1^xxvi	79.1 (2)
O1^xii—Ca2—O2^xvi	89.0 (3)	O2—Rb2—O1^xxvi	64.0 (2)
O1^xiii—Ca2—O2^xvi	172.2 (4)	O2^ii—Rb2—O1^xxvi	153.1 (3)
O1^xiv—Ca2—O2^xvi	88.5 (3)	O1^xxv—Rb2—O1^xxvi	117.59 (9)
O2^xv—Ca2—O2^xvi	96.4 (3)	O2^i—Rb2—O1^xxvii	153.1 (3)
O1^xii—Ca2—O2^xvii	88.5 (3)	O2—Rb2—O1^xxvii	79.1 (2)
O1^xiii—Ca2—O2^xvii	89.0 (3)	O2^ii—Rb2—O1^xxvii	64.0 (2)
O1^xiv—Ca2—O2^xvii	172.2 (4)	O1^xxv—Rb2—O1^xxvii	117.59 (9)
O2^xv—Ca2—O2^xvii	96.4 (3)	O1^xxvi—Rb2—O1^xxvii	117.59 (9)
O2^xvi—Ca2—O2^xvii	96.4 (3)	O2^i—Rb2—O3^xxvi	78.9 (3)
O4^xix—Rb1—O4^xx	94.9 (3)	O2—Rb2—O3^xxvi	106.5 (2)
O4^xix—Rb1—O4^xxi	94.9 (3)	O2^ii—Rb2—O3^xxvi	159.8 (2)
O4^xx—Rb1—O4^xxi	94.9 (3)	O1^xxv—Rb2—O3^xxvi	80.6 (2)
O4^xix—Rb1—O1^xii	155.6 (3)	O1^xxvi—Rb2—O3^xxvi	42.5 (2)
O4^xx—Rb1—O1^xii	99.5 (2)	O1^xxvii—Rb2—O3^xxvi	127.9 (3)
O4^xxi—Rb1—O1^xii	103.3 (3)	O2^i—Rb2—O3^xxvii	159.8 (2)
O4^xix—Rb1—O1^xiii	103.3 (3)	O2—Rb2—O3^xxvii	78.9 (3)
O4^xx—Rb1—O1^xiii	155.6 (3)	O2^ii—Rb2—O3^xxvii	106.5 (2)
O4^xxi—Rb1—O1^xiii	99.5 (2)	O1^xxv—Rb2—O3^xxvii	127.9 (3)
O1^xii—Rb1—O1^xiii	58.1 (3)	O1^xxvi—Rb2—O3^xxvii	80.6 (2)
O4^xix—Rb1—O1^xiv	99.5 (2)	O1^xxvii—Rb2—O3^xxvii	42.5 (2)
O4^xx—Rb1—O1^xiv	103.3 (3)	O3^xxvi—Rb2—O3^xxvii	86.7 (3)
O4^xxi—Rb1—O1^xiv	155.6 (3)	O2^i—Rb2—O3^xxv	106.5 (2)
O1^xii—Rb1—O1^xiv	58.1 (3)	O2—Rb2—O3^xxv	159.8 (2)
O1^xiii—Rb1—O1^xiv	58.1 (3)	O2^ii—Rb2—O3^xxv	78.9 (3)
O4^xix—Rb1—O3^xiv	62.7 (3)	O1^xxv—Rb2—O3^xxv	42.5 (2)
O4^xx—Rb1—O3^xiv	85.4 (3)	O1^xxvi—Rb2—O3^xxv	127.9 (3)
O4^xxi—Rb1—O3^xiv	157.5 (3)	O1^xxvii—Rb2—O3^xxv	80.6 (2)
O1^xii—Rb1—O3^xiv	98.8 (3)	O3^xxvi—Rb2—O3^xxv	86.7 (3)
O1^xiii—Rb1—O3^xiv	88.6 (2)	O3^xxvii—Rb2—O3^xxv	86.7 (3)
O1^xiv—Rb1—O3^xiv	42.6 (2)	O1^xxxi—S—O2	109.1 (6)
O4^xix—Rb1—O3^xii	157.5 (3)	O1^xxxi—S—O3^xxxi	107.8 (6)
O4^xx—Rb1—O3^xii	62.7 (3)	O2—S—O3^xxxi	109.5 (7)
O4^xxi—Rb1—O3^xii	85.4 (3)	O1^xxxi—S—O4	110.8 (6)
O1^xii—Rb1—O3^xii	42.6 (2)	O2—S—O4	110.2 (6)
O1^xiii—Rb1—O3^xii	98.8 (2)	O3^xxxi—S—O4	109.3 (7)
O1^xiv—Rb1—O3^xii	88.6 (2)	S^xxxii—O1—Ca2^vii	164.7 (6)
O3^xiv—Rb1—O3^xii	114.23 (15)	S^xxxii—O1—Rb2^xv	96.5 (4)
O4^xix—Rb1—O3^xiii	85.4 (3)	Ca2^vii—O1—Rb2^xv	96.8 (3)
O4^xx—Rb1—O3^xiii	157.5 (3)	S^xxxii—O1—Rb1^vii	89.9 (4)
O4^xxi—Rb1—O3^xiii	62.7 (3)	Ca2^vii—O1—Rb1^vii	94.3 (3)
O1^xii—Rb1—O3^xiii	88.6 (2)	Rb2^xv—O1—Rb1^vii	103.6 (3)
O1^xiii—Rb1—O3^xiii	42.6 (2)	S—O2—Ca2^xxvii	131.0 (6)
O1^xiv—Rb1—O3^xiii	98.8 (3)	S—O2—Rb2	118.2 (5)
O3^xiv—Rb1—O3^xiii	114.23 (15)	Ca2^xxvii—O2—Rb2	98.8 (3)
O3^xii—Rb1—O3^xiii	114.23 (14)	S—O2—Rb1^v	78.8 (4)
O4^xix—Rb1—O3^xxii	54.3 (3)	Ca2^xxvii—O2—Rb1^v	128.1 (4)
O4^xx—Rb1—O3^xxii	42.4 (2)	Rb2—O2—Rb1^v	99.1 (3)
O4^xxi—Rb1—O3^xxii	107.7 (3)	S^xxxii—O3—Ca1^xviii	156.2 (7)
O1^xii—Rb1—O3^xxii	131.6 (2)	S^xxxii—O3—Rb1^vii	89.2 (5)
O1^xiii—Rb1—O3^xxii	145.4 (2)	Ca1^xviii—O3—Rb1^vii	91.9 (4)
O1^xiv—Rb1—O3^xxii	96.7 (2)	S^xxxii—O3—Rb2^xv	87.6 (5)
O3^xiv—Rb1—O3^xxii	58.5 (4)	Ca1^xviii—O3—Rb2^xv	115.7 (4)
O3^xii—Rb1—O3^xxii	104.18 (3)	Rb1^vii—O3—Rb2^xv	98.5 (3)
O3^xiii—Rb1—O3^xxii	138.68 (19)	S^xxxii—O3—Rb1^xxxiii	94.4 (5)
O4^xix—Rb1—O3^xxiii	42.4 (2)	Ca1^xviii—O3—Rb1^xxxiii	86.4 (3)
O4^xx—Rb1—O3^xxiii	107.7 (3)	Rb1^vii—O3—Rb1^xxxiii	174.7 (3)
O4^xxi—Rb1—O3^xxiii	54.3 (3)	Rb2^xv—O3—Rb1^xxxiii	77.7 (3)
O1^xii—Rb1—O3^xxiii	145.4 (2)	S—O4—Ca1	146.3 (7)
O1^xiii—Rb1—O3^xxiii	96.7 (2)	S—O4—Rb1^viii	113.7 (6)
O1^xiv—Rb1—O3^xxiii	131.6 (2)	Ca1—O4—Rb1^viii	97.9 (3)
O3^xiv—Rb1—O3^xxiii	104.18 (3)

Symmetry codes: (i) z, x, y; (ii) y, z, x; (iii) z−1/2, −x+1/2, −y+1; (iv) −x+1/2, −y+1, z−1/2; (v) −y+1, z−1/2, −x+1/2; (vi) −y+3/2, −z+1, x−1/2; (vii) −y+1, z−1/2, −x+3/2; (viii) z−1/2, −x+3/2, −y+1; (ix) −y, z+1/2, −x+1/2; (x) −y+1/2, −z, x+1/2; (xi) z+1/2, −x+1/2, −y; (xii) −x+1, y+1/2, −z+3/2; (xiii) y+1/2, −z+3/2, −x+1; (xiv) −z+3/2, −x+1, y+1/2; (xv) z+1/2, −x+1/2, −y+1; (xvi) −x+1/2, −y+1, z+1/2; (xvii) −y+1, z+1/2, −x+1/2; (xviii) −y+1/2, −z+1, x+1/2; (xix) −z+1, x+1/2, −y+3/2; (xx) x+1/2, −y+3/2, −z+1; (xxi) −y+3/2, −z+1, x+1/2; (xxii) x+1/2, −y+3/2, −z+2; (xxiii) −z+2, x+1/2, −y+3/2; (xxiv) −y+3/2, −z+2, x+1/2; (xxv) −z+1, x−1/2, −y+1/2; (xxvi) x−1/2, −y+1/2, −z+1; (xxvii) −y+1/2, −z+1, x−1/2; (xxviii) −z, x−1/2, −y+1/2; (xxix) x−1/2, −y+1/2, −z; (xxx) −y+1/2, −z, x−1/2; (xxxi) x, y, z−1; (xxxii) x, y, z+1; (xxxiii) z−1/2, −x+3/2, −y+2.