RbSn₂(PO₄)₃, a NASICON-type phosphate

Abstract

The title compound, rubidium ditin(IV) tris­(phosphate), RbSn₂(PO₄)₃, belongs to the NASICON-type family of phosphates and crystallizes in the space group R . The structure is composed of PO₄ tetra­hedra (1 symmetry) and two slightly distorted SnO₆ octa­hedra, both with 3. symmetry, which are inter­linked through corner-sharing O atoms to form a ³ _∞[Sn₂(PO₄)₃]⁻ framework. The Rb⁺ cations are located on threefold inversion axes in the voids of this framework and exhibit a coordination number of 12. The crystal studied was twinned by merohedry with a component ratio of 0.503:0.497.

Related literature

For related NASICON-type compounds, see: Boilot et al. (1987 ▶); Boujelben et al. (2007 ▶); Duhlev (1994 ▶); Zatovskii et al. (2006 ▶); Zhao et al. (2011 ▶).

Experimental

Crystal data

• RbSn₂(PO₄)₃

• M _r = 607.76

• Trigonal,

• a = 8.340 (4) Å

• c = 24.007 (8) Å

• V = 1446.1 (6) ų

• Z = 6

• Mo Kα radiation

• μ = 10.76 mm⁻¹

• T = 293 K

• 0.20 × 0.05 × 0.05 mm

Data collection

• Rigaku Mercury70 CCD diffractometer

• Absorption correction: multi-scan (ABSCOR; Higashi, 1995 ▶) T _min = 0.222, T _max = 0.615

• 3765 measured reflections

• 742 independent reflections

• 711 reflections with I > 2σ(I)

• R _int = 0.036

Refinement

• R[F ² > 2σ(F ²)] = 0.026

• wR(F ²) = 0.043

• S = 1.16

• 742 reflections

• 57 parameters

• Δρ_max = 0.65 e Å⁻³

• Δρ_min = −0.73 e Å⁻³

Data collection: CrystalClear (Rigaku, 2004 ▶); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶) and PLATON (Spek, 2009 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 2004 ▶); software used to prepare material for publication: SHELXTL (Sheldrick, 2008 ▶).

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

Sn1—O2	2.015 (4)
Sn1—O3i	2.033 (4)
P1—O2	1.523 (4)
P1—O1	1.529 (4)
P1—O3	1.533 (4)
P1—O4	1.537 (4)

Symmetry code: (i) .

supplementary crystallographic information

Comment

In recent years, the AM₂(PO₄)₃ (A = alkali metal; M = Ti, Zr, Ge, Sn) family with NASICON (Na₃Zr₂Si₂PO₁₂; Boilot et al., 1987) -type structures attracted a growing interest due to their intriguing properities, e.g. ionic conductivity of the A cations located in the voids of the three-dimensional NASICON-type framework. This framework is composed of isolated PO₄ tetrahedra sharing corners with MO₆ octahedra (Fig. 1), and is amenable to a wide variety of chemical substitutions at the various crystallographic positions, thus yielding a large number of closely related compounds, such as NaFeNb(PO₄)₃ (Zatovskii et al., 2006), Rb₂Ca₂(SO₄)₃ (Boujelben et al., 2007) or Al_0.5Nb_1.5(PO₄)₃ (Zhao et al., 2011). In order to augment this family of compounds, we prepared crystals of the compound RbSn₂(PO₄)₃ using a solid state reaction route. Unlike the analogous Ti compound RbTi₂(PO₄)₃ which crystallises in space group R3c (Duhlev, 1994), RbSn₂(PO₄)₃ crystallises in space group R3.

A projection of the crystal structure of RbSn₂(PO₄)₃ is given in Fig. 2. It is characterized by the presence of isolated PO₄ tetrahedra (1 symmetry) and two different SnO₆ octahedra (both 3. symmetry), linked by sharing corner O atoms, to establish a three-dimensional ³_∞[Sn₂(PO₄)₃]^- framework. This framwork delimits two types of channels in which the twelve-coordinate Rb⁺ atoms (site symmetry 3.) are located to compensate the negative charges. The PO₄ tetrahedra are quite regular, with P–O distances ranging from 1.523 (4) to 1.537 (4) Å. The two SnO₆ octahedra exhibit Sn—O distances ranging from 2.015 (4) to 2.033 (4) Å.

Experimental

Single crystals of RbSn₂(PO₄)₃ have been prepared by a high-temperature method in air. A powder mixture of RbNO₃, SnO₂ and NH₄H₂PO₄ in the molar ratio of Rb: Sn: P = 10: 1: 15 was first ground in an agate mortar and then transferred to a platinum crucible. The sample was gradually heated in air at 1173 K for 24 h. After that, the intermediate product was slowly cooled to 673 K at the rate of 2 K h^-1. It was kept at 673 K for another 10 h and then quenched to room temperature. The obtained crystals were colorless with a prismatic shape.

Refinement

The RbSn₂(PO₄)₃ crystal studies was twinned by merohedry. For refinement the twin law (0 1 0 1 0 0 0 0 1) was used; the twin component ratio refined to 0.503: 0.497. The highest peak in the difference electron density map is at a distance of 1.38 Å from Rb2 while the deepest hole is at a distance of 1.77 Å from O2.

Figures

Fig. 1.

The expanded asymmetric unit of RbSn2(PO4)3 showing the coordination environments of the P and Sn atoms. The displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) -y, x-y, z; (ii) -x + y, -x, z; (iii) 1 - y, x-y, z; (iv) 1 - x + y, 1 - x, z; (v) 1 - x, 1 - y, -z; (vi) 1 + x-y, x, -z; (vii) y, -x + y, -z; (Viii) -1/3 + y, 1/3 - x + y, 1/3 - z; (ix) 2/3 - x, 1/3 - y, 1/3 - z; (x) -1/3 + x-y, -2/3 + x, 1/3 - z.]

Fig. 2.

View of the crystal structure of RbSn2(PO4)3 along [100]. PO4 and SnO6 units are given in the polyhedral representation.

Crystal data

RbSn2(PO4)3	Dx = 4.187 Mg m−3
Mr = 607.76	Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3	Cell parameters from 1316 reflections
Hall symbol: -R 3	θ = 2.6–27.5°
a = 8.340 (4) Å	µ = 10.76 mm−1
c = 24.007 (8) Å	T = 293 K
V = 1446.1 (6) Å3	Prism, colourless
Z = 6	0.20 × 0.05 × 0.05 mm
F(000) = 1668

Data collection

Rigaku Mercury70 CCD diffractometer	742 independent reflections
Radiation source: fine-focus sealed tube	711 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.036
Detector resolution: 14.6306 pixels mm-1	θmax = 27.5°, θmin = 2.6°
ω scans	h = −9→10
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	k = −10→10
Tmin = 0.222, Tmax = 0.615	l = −29→31
3765 measured reflections

Refinement

Refinement on F2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.026	Secondary atom site location: difference Fourier map
wR(F2) = 0.043	w = 1/[σ2(Fo2) + (0.0097P)2 + 13.5872P] where P = (Fo2 + 2Fc2)/3
S = 1.16	(Δ/σ)max < 0.001
742 reflections	Δρmax = 0.65 e Å−3
57 parameters	Δρmin = −0.73 e Å−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. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq
Sn1	0.6667	0.3333	−0.01707 (2)	0.00467 (15)
Rb1	0.3333	0.6667	0.1667	0.0164 (3)
P1	0.3780 (2)	0.3319 (3)	0.08383 (7)	0.0058 (2)
O1	0.2172 (6)	0.1463 (5)	0.10332 (14)	0.0090 (9)
Sn2	0.0000	0.0000	0.15528 (2)	0.00490 (15)
Rb2	0.0000	0.0000	0.0000	0.0227 (4)
O2	0.4497 (6)	0.2928 (6)	0.03015 (16)	0.0119 (10)
O3	0.3083 (6)	0.4664 (6)	0.07059 (16)	0.0093 (9)
O4	0.5248 (6)	0.4207 (6)	0.12987 (14)	0.0103 (10)

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Sn1	0.0051 (2)	0.0051 (2)	0.0039 (3)	0.00253 (11)	0.000	0.000
Rb1	0.0221 (5)	0.0221 (5)	0.0051 (5)	0.0111 (2)	0.000	0.000
P1	0.0046 (8)	0.0068 (6)	0.0050 (6)	0.0022 (7)	0.0000 (6)	0.0008 (5)
O1	0.008 (2)	0.008 (2)	0.0097 (17)	0.0028 (17)	0.0044 (15)	0.0025 (14)
Sn2	0.0055 (2)	0.0055 (2)	0.0037 (3)	0.00275 (11)	0.000	0.000
Rb2	0.0304 (6)	0.0304 (6)	0.0073 (6)	0.0152 (3)	0.000	0.000
O2	0.009 (2)	0.018 (2)	0.009 (2)	0.008 (2)	0.0020 (17)	−0.0029 (17)
O3	0.014 (2)	0.010 (2)	0.0064 (17)	0.0077 (19)	−0.0023 (16)	0.0001 (16)
O4	0.011 (2)	0.008 (2)	0.0100 (17)	0.003 (2)	−0.0050 (17)	−0.0005 (16)

Geometric parameters (Å, °)

Sn1—O2i	2.015 (4)	P1—Rb2	3.595 (2)
Sn1—O2ii	2.015 (4)	O1—Sn2	2.029 (4)
Sn1—O2	2.015 (4)	O1—Rb2	2.952 (4)
Sn1—O3iii	2.033 (4)	Sn2—O1xii	2.029 (4)
Sn1—O3iv	2.033 (4)	Sn2—O1xiii	2.029 (4)
Sn1—O3v	2.033 (4)	Sn2—O4xiv	2.033 (4)
Sn1—Rb1vi	3.5915 (13)	Sn2—O4xv	2.033 (4)
Rb1—O3vii	2.794 (4)	Sn2—O4viii	2.033 (4)
Rb1—O3viii	2.794 (4)	Sn2—Rb2	3.7278 (13)
Rb1—O3ix	2.794 (4)	Rb2—O1xvi	2.952 (4)
Rb1—O3	2.793 (4)	Rb2—O1xii	2.952 (4)
Rb1—O3x	2.794 (4)	Rb2—O1xvii	2.952 (4)
Rb1—O3xi	2.794 (4)	Rb2—O1iv	2.952 (4)
Rb1—O4vii	3.289 (5)	Rb2—O1xiii	2.952 (4)
Rb1—O4x	3.288 (5)	Rb2—O2xvii	3.375 (5)
Rb1—O4ix	3.288 (5)	Rb2—O2xvi	3.375 (5)
Rb1—O4viii	3.288 (5)	Rb2—O2xii	3.375 (5)
Rb1—O4xi	3.288 (5)	Rb2—O2iv	3.375 (5)
Rb1—O4	3.288 (5)	Rb2—O2xiii	3.375 (5)
P1—O2	1.523 (4)	Rb2—O2	3.376 (5)
P1—O1	1.529 (4)	O3—Sn1v	2.034 (4)
P1—O3	1.533 (4)	O4—Sn2xiv	2.033 (4)
P1—O4	1.537 (4)
O2i—Sn1—O2ii	91.47 (17)	Rb2—P1—Rb1	121.07 (4)
O2i—Sn1—O2	91.47 (17)	P1—O1—Sn2	149.8 (3)
O2ii—Sn1—O2	91.47 (17)	P1—O1—Rb2	101.98 (17)
O2i—Sn1—O3iii	83.62 (17)	Sn2—O1—Rb2	95.11 (15)
O2ii—Sn1—O3iii	102.00 (17)	O1—Sn2—O1xii	86.16 (16)
O2—Sn1—O3iii	165.74 (17)	O1—Sn2—O1xiii	86.16 (16)
O2i—Sn1—O3iv	102.00 (17)	O1xii—Sn2—O1xiii	86.16 (16)
O2ii—Sn1—O3iv	165.74 (17)	O1—Sn2—O4xiv	93.48 (16)
O2—Sn1—O3iv	83.62 (17)	O1xii—Sn2—O4xiv	89.54 (16)
O3iii—Sn1—O3iv	84.32 (17)	O1xiii—Sn2—O4xiv	175.70 (16)
O2i—Sn1—O3v	165.74 (17)	O1—Sn2—O4xv	175.70 (16)
O2ii—Sn1—O3v	83.62 (17)	O1xii—Sn2—O4xv	93.48 (16)
O2—Sn1—O3v	102.00 (17)	O1xiii—Sn2—O4xv	89.54 (16)
O3iii—Sn1—O3v	84.32 (17)	O4xiv—Sn2—O4xv	90.80 (16)
O3iv—Sn1—O3v	84.32 (17)	O1—Sn2—O4viii	89.54 (16)
O2i—Sn1—Rb1vi	124.22 (12)	O1xii—Sn2—O4viii	175.70 (16)
O2ii—Sn1—Rb1vi	124.22 (12)	O1xiii—Sn2—O4viii	93.48 (16)
O2—Sn1—Rb1vi	124.22 (12)	O4xiv—Sn2—O4viii	90.80 (16)
O3iii—Sn1—Rb1vi	50.81 (11)	O4xv—Sn2—O4viii	90.80 (16)
O3iv—Sn1—Rb1vi	50.81 (11)	O1—Sn2—Rb2	52.06 (11)
O3v—Sn1—Rb1vi	50.81 (11)	O1xii—Sn2—Rb2	52.06 (11)
O3vii—Rb1—O3viii	58.49 (13)	O1xiii—Sn2—Rb2	52.06 (11)
O3vii—Rb1—O3ix	58.49 (13)	O4xiv—Sn2—Rb2	124.70 (11)
O3viii—Rb1—O3ix	58.49 (13)	O4xv—Sn2—Rb2	124.69 (11)
O3vii—Rb1—O3	180.0	O4viii—Sn2—Rb2	124.69 (11)
O3viii—Rb1—O3	121.51 (13)	O1xvi—Rb2—O1xii	180.0 (3)
O3ix—Rb1—O3	121.51 (13)	O1xvi—Rb2—O1xvii	56.00 (13)
O3vii—Rb1—O3x	121.51 (13)	O1xii—Rb2—O1xvii	124.00 (13)
O3viii—Rb1—O3x	121.51 (13)	O1xvi—Rb2—O1iv	56.00 (13)
O3ix—Rb1—O3x	180.0	O1xii—Rb2—O1iv	124.00 (13)
O3—Rb1—O3x	58.49 (13)	O1xvii—Rb2—O1iv	56.00 (13)
O3vii—Rb1—O3xi	121.51 (13)	O1xvi—Rb2—O1xiii	124.00 (13)
O3viii—Rb1—O3xi	180.0	O1xii—Rb2—O1xiii	56.00 (13)
O3ix—Rb1—O3xi	121.51 (13)	O1xvii—Rb2—O1xiii	124.00 (13)
O3—Rb1—O3xi	58.49 (13)	O1iv—Rb2—O1xiii	180.00 (17)
O3x—Rb1—O3xi	58.49 (13)	O1xvi—Rb2—O1	124.00 (13)
O3vii—Rb1—O4vii	47.14 (10)	O1xii—Rb2—O1	56.00 (13)
O3viii—Rb1—O4vii	75.80 (10)	O1xvii—Rb2—O1	180.0
O3ix—Rb1—O4vii	105.07 (10)	O1iv—Rb2—O1	124.00 (13)
O3—Rb1—O4vii	132.87 (10)	O1xiii—Rb2—O1	56.00 (13)
O3x—Rb1—O4vii	74.93 (10)	O1xvi—Rb2—O2xvii	94.20 (11)
O3xi—Rb1—O4vii	104.20 (10)	O1xii—Rb2—O2xvii	85.80 (11)
O3vii—Rb1—O4x	104.20 (11)	O1xvii—Rb2—O2xvii	44.81 (10)
O3viii—Rb1—O4x	74.93 (10)	O1iv—Rb2—O2xvii	95.50 (10)
O3ix—Rb1—O4x	132.86 (10)	O1xiii—Rb2—O2xvii	84.50 (10)
O3—Rb1—O4x	75.80 (11)	O1—Rb2—O2xvii	135.19 (10)
O3x—Rb1—O4x	47.14 (10)	O1xvi—Rb2—O2xvi	44.81 (10)
O3xi—Rb1—O4x	105.07 (10)	O1xii—Rb2—O2xvi	135.19 (10)
O4vii—Rb1—O4x	66.94 (5)	O1xvii—Rb2—O2xvi	95.50 (10)
O3vii—Rb1—O4ix	75.80 (11)	O1iv—Rb2—O2xvi	94.20 (11)
O3viii—Rb1—O4ix	105.07 (10)	O1xiii—Rb2—O2xvi	85.80 (11)
O3ix—Rb1—O4ix	47.14 (10)	O1—Rb2—O2xvi	84.50 (10)
O3—Rb1—O4ix	104.20 (11)	O2xvii—Rb2—O2xvi	115.54 (5)
O3x—Rb1—O4ix	132.87 (10)	O1xvi—Rb2—O2xii	135.19 (10)
O3xi—Rb1—O4ix	74.93 (10)	O1xii—Rb2—O2xii	44.81 (10)
O4vii—Rb1—O4ix	113.06 (5)	O1xvii—Rb2—O2xii	84.50 (10)
O4x—Rb1—O4ix	180.0	O1iv—Rb2—O2xii	85.80 (11)
O3vii—Rb1—O4viii	105.07 (10)	O1xiii—Rb2—O2xii	94.20 (11)
O3viii—Rb1—O4viii	47.14 (10)	O1—Rb2—O2xii	95.50 (10)
O3ix—Rb1—O4viii	75.80 (11)	O2xvii—Rb2—O2xii	64.46 (5)
O3—Rb1—O4viii	74.93 (10)	O2xvi—Rb2—O2xii	180.00 (19)
O3x—Rb1—O4viii	104.20 (11)	O1xvi—Rb2—O2iv	95.50 (10)
O3xi—Rb1—O4viii	132.87 (10)	O1xii—Rb2—O2iv	84.50 (10)
O4vii—Rb1—O4viii	113.06 (5)	O1xvii—Rb2—O2iv	94.20 (11)
O4x—Rb1—O4viii	66.94 (5)	O1iv—Rb2—O2iv	44.81 (10)
O4ix—Rb1—O4viii	113.06 (5)	O1xiii—Rb2—O2iv	135.19 (10)
O3vii—Rb1—O4xi	74.93 (10)	O1—Rb2—O2iv	85.80 (11)
O3viii—Rb1—O4xi	132.86 (10)	O2xvii—Rb2—O2iv	115.54 (5)
O3ix—Rb1—O4xi	104.20 (11)	O2xvi—Rb2—O2iv	115.54 (5)
O3—Rb1—O4xi	105.08 (10)	O2xii—Rb2—O2iv	64.46 (5)
O3x—Rb1—O4xi	75.80 (11)	O1xvi—Rb2—O2xiii	84.50 (10)
O3xi—Rb1—O4xi	47.14 (10)	O1xii—Rb2—O2xiii	95.50 (10)
O4vii—Rb1—O4xi	66.94 (5)	O1xvii—Rb2—O2xiii	85.80 (11)
O4x—Rb1—O4xi	113.06 (5)	O1iv—Rb2—O2xiii	135.19 (10)
O4ix—Rb1—O4xi	66.94 (5)	O1xiii—Rb2—O2xiii	44.81 (10)
O4viii—Rb1—O4xi	180.0	O1—Rb2—O2xiii	94.20 (11)
O3vii—Rb1—O4	132.86 (10)	O2xvii—Rb2—O2xiii	64.46 (5)
O3viii—Rb1—O4	104.20 (10)	O2xvi—Rb2—O2xiii	64.46 (5)
O3ix—Rb1—O4	74.92 (10)	O2xii—Rb2—O2xiii	115.54 (5)
O3—Rb1—O4	47.14 (10)	O2iv—Rb2—O2xiii	180.0 (2)
O3x—Rb1—O4	105.08 (10)	O1xvi—Rb2—O2	85.80 (11)
O3xi—Rb1—O4	75.80 (10)	O1xii—Rb2—O2	94.20 (11)
O4vii—Rb1—O4	180.0	O1xvii—Rb2—O2	135.19 (10)
O4x—Rb1—O4	113.06 (5)	O1iv—Rb2—O2	84.50 (10)
O4ix—Rb1—O4	66.94 (5)	O1xiii—Rb2—O2	95.50 (10)
O4viii—Rb1—O4	66.94 (5)	O1—Rb2—O2	44.81 (10)
O4xi—Rb1—O4	113.06 (5)	O2xvii—Rb2—O2	180.0
O2—P1—O1	106.4 (3)	O2xvi—Rb2—O2	64.47 (5)
O2—P1—O3	108.3 (2)	O2xii—Rb2—O2	115.53 (5)
O1—P1—O3	110.1 (3)	O2iv—Rb2—O2	64.46 (5)
O2—P1—O4	114.1 (2)	O2xiii—Rb2—O2	115.54 (5)
O1—P1—O4	110.6 (2)	P1—O2—Sn1	148.8 (3)
O3—P1—O4	107.4 (2)	P1—O2—Rb2	85.6 (2)
O2—P1—Rb2	69.43 (19)	Sn1—O2—Rb2	125.48 (17)
O1—P1—Rb2	53.44 (15)	P1—O3—Sn1v	144.2 (3)
O3—P1—Rb2	86.57 (16)	P1—O3—Rb1	108.91 (19)
O4—P1—Rb2	162.60 (19)	Sn1v—O3—Rb1	94.85 (15)
O2—P1—Rb1	147.0 (2)	P1—O4—Sn2xiv	134.6 (3)
O1—P1—Rb1	103.79 (16)	P1—O4—Rb1	88.59 (19)
O3—P1—Rb1	47.30 (15)	Sn2xiv—O4—Rb1	128.46 (15)
O4—P1—Rb1	66.10 (17)

Symmetry codes: (i) −y+1, x−y, z; (ii) −x+y+1, −x+1, z; (iii) x−y+1, x, −z; (iv) y, −x+y, −z; (v) −x+1, −y+1, −z; (vi) x+1/3, y−1/3, z−1/3; (vii) −x+2/3, −y+4/3, −z+1/3; (viii) y−1/3, −x+y+1/3, −z+1/3; (ix) x−y+2/3, x+1/3, −z+1/3; (x) −x+y, −x+1, z; (xi) −y+1, x−y+1, z; (xii) −x+y, −x, z; (xiii) −y, x−y, z; (xiv) −x+2/3, −y+1/3, −z+1/3; (xv) x−y−1/3, x−2/3, −z+1/3; (xvi) x−y, x, −z; (xvii) −x, −y, −z.